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Visual orienting in responseto attentional cues: Spatialcorrespondence is critical,conscious awareness is notMyoung-Ju Shin a , Narisa Marrett a & Anthony J.Lambert aa Research Centre for Cognitive Neuroscience,Department of Psychology , University of Auckland ,Auckland, New ZealandPublished online: 07 Jul 2011.

To cite this article: Myoung-Ju Shin , Narisa Marrett & Anthony J. Lambert (2011) Visualorienting in response to attentional cues: Spatial correspondence is critical, consciousawareness is not, Visual Cognition, 19:6, 730-761, DOI: 10.1080/13506285.2011.582053

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Visual orienting in response to attentional cues: Spatial

correspondence is critical, conscious awareness is not

Myoung-Ju Shin, Narisa Marrett, andAnthony J. Lambert

Research Centre for Cognitive Neuroscience, Department of

Psychology, University of Auckland, Auckland, New Zealand

Three experiments examined visual orienting in response to spatial precues. InExperiments 1 and 2, attentional effects of central letters were stimulus driven:Orienting was dependent on the spatial layout of the cue display. When there wereno correspondences between spatial features of the cue display and target location,attentional effects were absent, despite a conscious intention to orient in response tothe symbolic information carried by the cue letters. In Experiment 3 clear orientingeffects were observed when target location corresponded with spatial features of thecue display, but the magnitude of these effects was unaffected by whetherparticipants were aware or unaware of the cue�target relationship. These findingsare consistent with the view that (1) spatial correspondences between cues andtargets are a critical factor driving visual orienting in cueing paradigms, and(2) attentional effects of spatial precues are largely independent of participants’conscious awareness of the cue�target relationship.

Keywords: Attention; Endogenous; Orienting; Spatial correspondence; Spatial

cues.

The idea that movements of spatial attention are under the control of two

distinct mechanisms has been strongly influential in theories of attention for

several decades. One form of attentional control has been characterized as

automatic, direct, reflexive, stimulus-driven, and exogenous; a second

control mechanism has been characterized as voluntary, symbolic, goal-

driven, and endogenous (Corbetta & Shulman, 2002; Jonides, 1981; Klein,

2004; Wright & Ward, 1998, 2008). Critical features of attention movements

Please address all correspondence to Anthony J. Lambert, Research Centre for Cognitive

Neuroscience, Department of Psychology, University of Auckland, Private Bag 92019, Auckland,

New Zealand. E-mail: a.lambert@auckland.ac.nz

VISUAL COGNITION, 2011, 19 (6), 730�761

# 2011 Psychology Press, an imprint of the Taylor & Francis Group, an Informa business

http://www.psypress.com/viscog DOI: 10.1080/13506285.2011.582053

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performed via the first mechanism, under exogenous, stimulus-driven control

are that they occur rapidly, via a nonconscious, bottom-up process that is

relatively independent of participants’ conscious goals. Attention move-

ments made under endogenous control, on the other hand, are thought to

occur via a distinct neurocognitive mechanism (Corbetta & Shulman, 2002),which has a slower time course, and involves top-down influences from

consciously held goals. In this paper we report findings from three

experiments which are problematic for this two-process model, but

consistent with a simpler and more parsimonious single process model of

attentional control.

Endogenous orienting has typically been studied by presenting partici-

pants with a centrally presented cue such as an arrow, which indicates the

likely location of the next target (e.g., see Doallo et al., 2004; Peelen,Heslenfeld, & Theeuwes, 2004) Typically, exogenous orienting has been

studied by presenting participants with peripheral cues that comprise a

peripheral visual change (e.g., see Hopfinger & Mangun, 2001; Olk,

Hildebrandt, & Kingstone, 2010; Peelen et al., 2004) or an abrupt onset

(e.g., see Tipples, 2008). In this case the cued location is marked directly,

without any need for detailed encoding of the information carried by the cue.

Although the theoretical dichotomy between endogenous and exogenous

orienting continues to play a prominent role in contemporary theories ofattentional control (e.g., see Corbetta & Shulman, 2002; Klein, 2004;

Santangelo & Spence, 2008), in recent years a variety of empirical findings

have been reported that are problematic for the dichotomy. For example, it

has been found that the orienting elicited by certain kinds of central cues,

namely directional words (Hommel, Pratt, Colzato, & Godijn, 2001), arrows

(Hommel et al., 2001; Tipples, 2002, 2008), and faces that gaze to left or

right (Friesen, Moore, & Kingstone, 2005; Friesen, Ristic, & Kingstone,

2004), is relatively automatic. In addition, some of our own work has shownthat orienting in response to both centrally presented and peripherally

presented cues can be rapid, endogenous and goal-directed (Lambert &

Duddy, 2002).

As already indicated, goal-driven orienting has often been studied using a

cueing paradigm in which participants are presented with a central cue, such

as an arrow-head, which indicates the likely location of a target object. The

notion of endogenous orienting implies that the visual form of the central

cue is immaterial in this situation, and central cues of this kind are oftendescribed as ’’symbolic cues’’ (e.g., see Greene, Mooshagian, Kaplan, Zaidel,

& Iacoboni, 2009; Nummenmaa & Hietanen, 2009; Pratt, Radulescu, Guo,

& Hommel, 2010). If central cues play a purely symbolic role in indicating

the likely location of the next target to participants, the visual form of the

cue should not matter. Contrary to this prediction, Lambert, Roser, Wells,

and Heffer (2006) found that the visual form of centrally presented cue

SPATIAL CUES AND ATTENTION 731

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stimuli was critically important. In two experiments the attentional effects of

visually asymmetric cues (b, d) were compared with effects of visually

symmetric cues (X, T, v, o; Lambert et al., 2006, Exps. 2A and 2B). In both

experiments response times for valid trials, where the target appeared at the

location indicated by the cue were compared with invalid trials where the

target appeared at the noncued location. In addition, the time course of

orienting, indexed by the difference between valid and invalid trials, was

assessed by varying the stimulus�onset asynchrony (SOA) between cue onset

and target onset. Consistent with earlier studies of central cueing (Wright &

Ward, 1998), when the central cues were visually asymmetric letters (d, b)

response times were reliably faster on valid compared to invalid trials at long

SOAs between cue and target, but not at short SOAs (less than 150 ms). To

our surprise, visually symmetric cues (X, T, v, o) failed to produce any

orienting effects at all: Response times on valid and invalid trials did not

differ, regardless of whether the delay between cue and target was brief (150

ms or less) or long (400�500 ms). These were important results because they

suggested that in a key sense covert visual orienting in response to central

cues might be stimulus driven. That is, covert orienting in response to central

cues may depend critically upon a stimulus feature*visual asymmetry.1

However, data from an earlier study (Lambert & Duddy, 2002) suggested

that asymmetry of the cue display may not be the only factor at work here.

Lambert and Duddy (2002) describe a series of experiments that investigated

the attentional effects of bilateral cues, which could be either visually

symmetric or visually asymmetric. In the latter condition, the cues

comprised two different letters (X and T) presented on the left or right

side of a visual display. Participants were informed that the target would

probably appear on the same side as one of the letters (X or T). This

condition embodied a feature that the authors termed ‘‘spatial

correspondence’’*the location of the target usually corresponded with the

location of one of the letters. In the former condition bilateral letters again

served as spatial cues, but in this case the cue display was symmetric, and

comprised either two Ts or two Xs, presented to the left and right of fixation.

Participants were informed that one of the letters indicated that a target

would probably appear on the left, whereas the other indicated that a target

1 It is important to recognize that we make this proposal solely in relation to covert

orienting. We take it as self-evident that participants would be able to initiate overt orienting, by

moving their eyes or head, in response to any arbitrary symbolic stimulus, such as ‘‘Look left’’.

The simple detection task employed in this study and previously (Lambert & Duddy, 2002;

Lambert et al., 2006) may represent an ideal method for studying covert orienting. In this very

simple task situation participants have little incentive to move their eyes, and early work by

Posner showed, first, that they rarely do so, and second, that patterns of behavioural

performance were unaffected by eye movements (Posner, 1978; Posner, Snyder, & Davidson,

1980).

732 SHIN, MARRETT, LAMBERT

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would probably appear on the right. This was termed the spatial translation

condition, because participants were required to translate the information

carried by the cue letters (X or T) into spatial terms (‘‘next target likely on

the left’’ vs. ‘‘next target likely on the right’’). In a series of five experiments it

was found that visual orienting effects were stronger overall, and occurred at

briefer cue�target SOAs in the visually asymmetric spatial correspondence

conditions, compared to the visually symmetric spatial translation condi-

tions. This pattern obtained regardless of whether the two letter cues were

presented centrally (immediately to the left and right of a central fixation

marker) or peripherally (7o from fixation). However, although orienting

effects were weaker and had a slower time course in the symmetric, spatial

translation conditions, reliable differences between response times on valid

and invalid trials were nevertheless observed at cue�target SOAs of 150 ms

or longer.

Thus, there is an empirical discrepancy between findings reported by

Lambert and Duddy (2002) and those reported by Lambert et al. (2006),

with regard to effects of visually symmetric cue displays. In the former case,

orienting effects, though weak, were reliable at longer cue�target SOAs. In

the latter case, orienting effects were absent at both short and long cue�target SOAs. The critical difference between the two studies appears to be

that in Lambert and Duddy participants were presented with a bilateral pair

of cue letters, whereas in the experiments of Lambert et al. participants were

presented with a single, centrally located letter. However, it is difficult to

assert this generalization with confidence because the two experimental

conditions were part of separate studies. It is possible that ostensibly minor,

but uncontrolled differences between the two studies (e.g., levels of ambient

illumination in the testing environment, cue luminance contrast [see Lambert

& Shin, 2010], and target luminance contrast) may confound comparisons

between the symmetric double letter condition of Lambert and Duddy and

the symmetric single letter condition of Lambert et al. Therefore, an

important aim of Experiment 1 was to test this interpretation of our earlier

findings, by undertaking a direct, within experiment comparison of the

effects of symmetric double cues and symmetric single cues on visual

attention.

The empirical pattern observed across the studies reported by Lambert

and Duddy (2002) and by Lambert et al. (2006) was that visual orienting

effects were: (1) Strong and rapid in response to asymmetric (bilateral)

spatial correspondence cues; (2) weak and slow, but reliable in response to

symmetric (bilateral) spatial translation cues; and (3) completely absent in

response to symmetric central cues comprising a single letter. Lambert et al.

proposed a theoretical interpretation of this pattern in terms of spatial

SPATIAL CUES AND ATTENTION 733

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correspondence learning. According to this interpretation, attention move-

ments in response to spatial cues are driven by a simple form of associative

learning in which participants learn statistical associations between spatial

features of the cue display and spatial features of the target display. That is,

the covert orienting response (attend left or attend right) is driven by simple

associative learning of spatial correspondences between the cue display and

the target display*the target usually appears on the same side as one of the

cue stimuli. They referred to this as spatial correspondence learning. The

bilateral spatial correspondence conditions investigated by Lambert and

Duddy afforded optimal conditions for this kind of learning to occur*the

location of the target usually corresponded with the location of one of the

cue letters. There is less opportunity for spatial correspondence learning in

central cueing designs where participants are presented with a single, visually

asymmetric cue such as an arrow. Nevertheless, spatial correspondences

between elements of the cue stimulus (e.g., left or right pointing arrow-

heads B�, or features of asymmetric letters such as d and b) are still

available to participants, and can drive visual orienting in this situation. In

the bilateral spatial translation conditions of Lambert and Duddy, cue

displays comprised two Xs, to left and right of fixation, or two Ts.

Participants were informed that one letter pair indicated that the target

would probably appear on the right of the display, whereas the other

indicated that the target would probably appear on the left of the display. A

weak form of spatial correspondence learning can still occur in this situation,

because a target on the left was associated with presentation of the cue for a

left target (e.g., X) on the left side of the display, accompanied by another X

on the right; and a target on the right was associated with presentation of the

cue for a right target (e.g., T) on the right side of the display, accompanied by

another T on the left. In the final type of design, where participants are

presented with a central cue comprising a single symmetric letter, there is

little or no opportunity for spatial correspondence learning to occur.

Because the cue object is always central, its location never corresponds

with that of the target; and because the cues are symmetric, the location of

stimulus elements within the cue never correspond with the location of the

target. In this situation, the absence of any opportunity from spatial

correspondence learning appears to be associated with the absence of covert

orienting effects, even with long cue�target delays of about half a second

which should provide ample opportunity for participants to prepare for the

target under endogenous control.

Hence, the aim of Experiment 1 was both empirical and theoretical. At an

empirical level we wished to ascertain whether the different results obtained

by Lambert and Duddy (2002) and by Lambert et al. (2006) regarding

734 SHIN, MARRETT, LAMBERT

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orienting in response to visually symmetric cue displays were driven by the

fact that in the former study two cues were presented bilaterally, whereas in

the latter a single cue was presented centrally. Direct, within experiment

manipulation of the cueing procedure (single cues vs. double cues) enabled us

to answer this question. At a theoretical level this manipulation was of

interest because spatial correspondence learning between features of the cue

display and features of the target display is possible with cue displays

comprising two bilateral letters, but difficult or impossible when the cue

comprises a single, visually symmetric central letter. Thus, the comparison

between visual orienting effects in response to bilateral double cues and

single central cues is important theoretically. Work reported by Lambert and

Duddy showed that spatial correspondence is a critical factor driving visual

orienting in response to peripheral cues; results described by Lambert et al.

showed that spatial correspondence is a critical factor driving visual

orienting in response to central cues. If it is also the case that eliminating

the potential for spatial correspondence learning to occur, by using single,

visually symmetric central cues, eliminates covert orienting effects altogether,

then the need for a two-process (goal-driven, endogenous vs. stimulus-

driven, exogenous) explanation of covert visual orienting effects is called into

question. Instead, a more parsimonious, single process explanation in terms

of spatial correspondence learning would be favoured.

EXPERIMENT 1

As explained earlier, the aim of this experiment was to undertake a direct

comparison of the attentional effects of single cues that were visually

symmetric and bilateral double cues that were also visually symmetric. In the

central condition, single, symmetric central letters (X, T) and symmetric

letter pairs (X�X, T�T) presented bilaterally were used as spatial precues.

As in the central conditions of Lambert and Duddy (2002), the bilateral

letters were presented immediately to the left and right of a central fixation

cross. In the peripheral condition, single, symmetric central letters and

symmetric letter pairs presented bilaterally were again used as spatial

precues, but in this case the bilateral letters were presented at a peripheral

location, as in the peripheral conditions of Lambert and Duddy. Two

predictions were made. First, in the symmetric bilateral cue conditions visual

orienting effects (i.e., faster response times on valid compared to invalid

trials) will be manifest at long, but not at short cue�target SOAs (see

Lambert & Duddy, 2002). Second, participants will be unable to orient

attention in the symmetric single cue conditions, regardless of whether the

delay between cue and target is brief or long (Lambert et al., 2006).

SPATIAL CUES AND ATTENTION 735

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Methods

Participants. Twenty-five and eighteen volunteers aged 18�30 years were

recruited for the ‘‘central’’ and ‘‘peripheral’’ conditions respectively in the

experiment.

Apparatus. The experiment was conducted on a Generic PnP Monitor

controlled by an Intel Core 2 Duo CPU. The screen resolution was

640�480. E-Prime was used to write the software to control the presenta-tion and timing of visual stimuli. A chinrest was used to prevent any

unnecessary head movements and to maintain the head at a distance of

approximately 57 cm from the monitor.

Display and stimuli. All stimuli were presented in black against a white

background (see Figure 1). A fixation cross subtending 0.68�0.68 was

Figure 1. The upper two panels show the sequence of events on typical trials with single central and

bilateral central cues, in the central condition. The lower two panels show the sequence of events on

typical trials with single central and bilateral peripheral cues, in the peripheral condition.

736 SHIN, MARRETT, LAMBERT

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presented in the centre of the screen. Cue stimuli were the letters X or T

subtending 18 (width)�1.78 (height). The centre of the single central cues

was 1.48 above the fixation. This ensured that the letters were presented as

centrally as possible, and did not overlap with the central fixation cross.

Bilateral cues, in both central and peripheral conditions, were presented on

the same horizontal meridian as the central cues, but the centre of each letter

was 0.98 from the centre of the screen in central condition and 68 from the

centre of the screen in peripheral condition. The target stimulus was a black

filled square subtending 0.48�0.48 presented either to the left or to the right

of the fixation cross. The centre of each target was approximately 68 from the

fixation cross.

Procedure. The sequence of each trial was explained to participants as to

be the presentation of a fixation cross and cues (either central or peripheral)

followed by a target, presented on either the left or right of the screen.

Participants were instructed to press the spacebar as soon as they detected the

target on the left or right of the screen. They were instructed to fixate their

eyes on the fixation cross and not to move their heads or eyes throughout the

experiment. For every trial, the fixation cross disappeared for 100 ms one

second before the cues were presented in order to draw the participants’

attention to it (i.e., the fixation cross blinked at the beginning of every trial).

Then, the cue letter(s), X or T, were presented for 66 ms. The cue letters were

followed by a target on 83% of the trials. For half of the participants, the

targets usually appeared on the left if X appeared, and on the right if T

appeared. For the other half of the participants, this contingency was

reversed. Participants were told to use the cue letters, X and T, in order to

predict the probable location of the target. On trials with a target, the SOA

between cue and target varied randomly, and could take the following values:

0 ms, 150 ms, or 500 ms.2 The target stimulus disappeared when participants

responded to it. After an interval that varied randomly from 500 ms to 1000

ms, the fixation cross blinked again to signal the beginning of the next trial.

Seventeen per cent of the trials were catch trials on which cue letters were

presented without a target. There was an interval of 0.5�1 s between the

offset of the letter cues and the ‘‘blink’’ of the fixation cross. Participants

were instructed to press the spacebar only when a target was presented and

to refrain from pressing the spacebar when there was no target. A warning

message was presented for 1 s when any catch trial or anticipation errors

occurred. There were 16 practice trials so that participants could familiarize

2 Even though we predicted that a clear validity effect would be observed only at the SOA of

500 ms, and only in the double cue conditions, the two brief SOAs (0 ms and 150 ms) were

included in the experimental design in order to maintain comparability and consistency with a

longer series of experiments (see Lambert & Shin, 2010).

SPATIAL CUES AND ATTENTION 737

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themselves with the task. The task comprised of four blocks of 72 trials. At

the beginning of each block, there was a message that emphasized the

importance of central fixation during the experiment.

Design. On 83% of the trials in each block the cue letters were followed

by a target. Of these, 75% were valid trials where the cue letters (X or T)

correctly indicated the location of the target, and 25% were invalid trials

where the cue letter indicated the location opposite to that where the targetappeared. The location of the target (left or right), the three different SOA

values, and the type of the cues (single or double) varied randomly from trial

to trial.

Results

Response times that were less than 100 ms or more than 1000 ms were

excluded from the analyses. The average rates of anticipation errors and

catch trial errors were 2.7% and 0%, respectively.

Results from Experiment 1 are illustrated in Figure 2. The prediction that

bilateral double cues would elicit significant covert orienting with a long

cue�target SOA (500 ms), but not when the cue�target SOA was brief was

tested by comparing response times on valid and invalid trials at each SOA.On bilateral trials with a cue�target SOA of 500 ms, response times were

faster on valid trials (339 ms) compared to invalid trials (355 ms),

F(1, 41) �7.60, p B .01, and this effect did not vary as a function of

whether the bilateral cues were presented centrally or peripherally, F B1. On

bilateral trials with brief cue�target SOAs (0 ms and 150 ms) response times

on valid and invalid trials did not differ, F B1 in both cases, and validity did

not interact with whether the cues were central or peripheral, F B1 in both

cases.When participants were presented with single, centrally located, visually

symmetric cues no reliable orienting effects were observed. Response times

on valid and invalid trials did not differ with a cue�target SOA of 500 ms,

F(1, 42) �1.03, ns, nor with a cue�target SOA of 150 ms, F(1, 42) �1.62, ns,

nor with a cue�target SOA of 0 ms (FB1). Furthermore, in an omnibus

analysis, evaluating validity effects in response to single cues at all three

SOAs, the main effect of validity failed to approach significance, F(1,

42) �1.38, ns, and there was no interaction between validity and SOA, F(1,42) �1.00, ns.

The prediction that validity effects would be observed at the long cue�target SOA with bilateral cues, but not with single, central cues was further

tested by comparing validity effects elicited by single and double cues at the

long SOA. This confirmed that at the long SOA validity effects were reliably

stronger with bilateral cues, compared to single cues, F(1, 42) �4.68,

738 SHIN, MARRETT, LAMBERT

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p �.036 (see Figure 2). However, in an overall analysis, examining

performance across all three SOAs, the three-way interaction between

validity, SOA, and cue type (bilateral or single, central) did not attain

significance, F(2, 82) �1.89, p�.157.As in our earlier studies (Lambert & Duddy, 2002; Lambert & Shin 2010),

when was no delay between cue and target (SOA �0 ms) response times

were reliably greater when there when there were longer delays between cue

and target (SOA �150 ms, SOA �500 ms*see Figure 2). This was true of

both the single central, F(2, 84) �107.81, p B.001, and bilateral, F(2,

82) �116.72, p B .001, conditions.

Discussion

Results from the experiment showed that, as predicted, symmetric bilateral

cues elicited visual orienting at the long cue�target SOA (500 ms), but not at

brief (0 ms or 150 ms) SOAs, and that symmetric single cues failed to elicit

any orienting effects at all, regardless of SOA. A within-participants

Figure 2. Mean response times in the bilateral peripheral condition (a), bilateral central condition

(b), and single central (c) conditions of Experiment 1. Error bars represent the standard error of the

difference between valid and invalid trials at each SOA.

SPATIAL CUES AND ATTENTION 739

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comparison confirmed that visual orienting effects were reliably larger with

bilateral than with single symmetric cues at the long SOA. These findings are

in agreement with our theoretical proposal that visual orienting effects are

driven by spatial correspondence learning. Symmetric bilateral cues enable

spatial correspondence learning of cue�target relationships to occur (albeit

much less effectively than in the case of asymmetric bilateral cues), because a

target on the right is associated with the appearance of the cue letter for a

right target (e.g., X) on the right of the cue display; and a target on the left is

associated with the appearance of the cue letter for a left target (e.g., T) on

the left of the cue display. In the case of single symmetric cues, the overall

location of the cue never corresponds with that of the target, and the

location of stimulus elements within the cue never correspond with that of

the target (Lambert et al., 2006). In agreement with the spatial correspon-

dence hypothesis, visual orienting effects were observed in the former

condition, but not in the latter. In empirical terms, the results confirm that

the critical factor responsible for the different findings obtained with

symmetric cue displays in Lambert and Duddy (2002) and in Lambert

et al. (2006) was the spatial layout of the cue stimuli*single central cue

or bilateral cue pair.

Before examining the theoretical implications of these findings in detail, a

further experiment will be described which tested an alternative explanation

for the results obtained in Experiment 1. According to the spatial

correspondence framework outlined previously, the critical difference

between the bilateral and single cue conditions is that in the former case

the cues are lateralized (i.e., the two objects in the cue display are located in

the left and right visual fields), whereas in the latter case neither the cue

object itself, nor any of its constituent elements, are lateralized. However, an

alternative interpretation is that the critical difference lies with the spatial

extent of the cues on the cue display, which is clearly larger in the case of

bilateral displays. This interpretation, of course, fails to explain why the

single cues used in Experiment 1 failed to elicit orienting, whereas scores of

published studies using central arrow cues with a similar or smaller spatial

extent have elicited clear orienting effects (Wright & Ward, 2008). The spatial

correspondence learning framework outlined in the introduction provides a

clear answer to this conundrum, in terms of learning spatial correspondences

between the location of the target and spatial features of asymmetric cue

objects. Nevertheless, we felt that it would be worthwhile to test this

alternative interpretation experimentally. In Experiment 2 the effects of

symmetric single cues that were identical with those employed in Experiment

1 were compared with symmetric single cues that were larger, and which

covered the same spatial extent as the bilateral cues used in Experiment 1. If

spatial extent, rather than lateralization of the cue objects, is the critical

740 SHIN, MARRETT, LAMBERT

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factor mediating orienting effects in Experiment 1, then in this experiment,

large cues should elicit a reliable orienting effect at the long SOA.

EXPERIMENT 2

Methods

Participants. Twenty-four volunteers aged 18�30 years took part. They

did not participate in Experiment 1.

Apparatus. This was the same as in Experiment 1.

Display and stimuli. This was the same as in Experiment 1, except that

cue letters could either be large or small. In the big cue condition the cue

letters subtended 2.68 (horizontal)�1.518 (vertical), and in the small cue

condition letters subtended 0.968�1.518. Cue size varied randomly from

trial to trial.

Procedure. This was the same as in Experiment 1.

Results

Any reaction time that were less than 100 ms or more than 1000 ms were

excluded from the analyses. The average rates of anticipation and catch

errors were 0.8% and 2.1%, respectively.

Response time results from Experiment 2 are summarized in Figure 3. If

the visual orienting effects of bilateral cues in Experiment 1 were mediatedby their greater spatial extent, then a reliable difference between valid and

invalid trials should be observed in the big cue condition at the long cue�target SOA. Contrary to this hypothesis, response times on valid (343 ms)

Figure 3. Mean response times in the small cue (a) and big cue (b) conditions of Experiment 2. Error

bars represent the standard error of the difference between valid and invalid trials at each SOA.

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and invalid (355 ms) trials in the big cue condition did not differ, F(1,

23) �2.37, ns. Furthermore, As Figure 3 illustrates, the mean difference

between valid and invalid response times at the long cue�target SOA was

slightly smaller in the big cue condition, in comparison with the small cue

condition. Response times on valid and invalid trials in the big cue conditionat the two short SOAs (0 ms, 150 ms) did not differ, F(1, 23) �1.16 and

FB1, respectively (see Figure 3).

In the small cue condition response times on valid and invalid trials did

not differ at the long cue�target SOA, F(1, 23) �2.36, ns, nor did they differ

at the two briefer (0 ms, 150 ms) SOAs (F B1 in both cases). In an omnibus

analysis that included data from all three SOAs, and from both the big cue

and small cue conditions, the main effect of cue validity failed to approach

significance, F(1, 23) �2.13, ns, as did the interaction of validity with SOA,F(1, 23) �1.69, ns.

Although no reliable effects of cue validity were observed in Experiment

2, visual inspection of Figure 3 suggests that there may be some risk of

making a Type 2 error in concluding that response times on valid and invalid

trials do not differ in this study. With an SOA of 500 ms in both the small

cue and big cue conditions, the mean response time on valid trials was 10�15

ms quicker than the mean response time on invalid trials. In order to

perform a more powerful test of the hypothesis that single symmetric cue caninfluence covert attention at long cue�target SOAs, a further analysis was

performed which combined data from Experiment 1 with Experiment 2. This

analysis compared the mean response time at the long cue�target SOA, on

valid and invalid trials with single symmetric cues for the 43 participants who

participated in Experiment 1 together with the 24 who participated in

Experiment 2, making a total of 67 participants. In this combined analysis

the difference in response time between valid trials (337 ms) and invalid trials

(345 ms) failed to attain the conventional standard of statistical reliability,F(1, 66) �3.62, p �.062.

Discussion

If the stronger orienting effects observed with bilateral compared to single

cues in Experiment 1 were due to the greater spatial extent of the bilateral

cues, then orienting effects in the big cue condition of Experiment 2 should

have been greater than in the small cue condition. This was not the case*there were no reliable orienting effects at any SOA in either the big cue or

small cue condition. Indeed, the mean difference in response time between

valid and invalid trials at the long SOA was slightly smaller in the big cue

condition. This is consistent with our proposal that the critical difference

between the bilateral and single central cue conditions in Experiment 1, and

in our earlier work (Lambert & Duddy, 2002; Lambert et al., 2006) is the

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lateral positioning of the cue stimuli in the bilateral cue conditions. That is,

the critical factor at work here is the fact that the cue displays, like the target

displays, contain objects located to the left and right of centre.A surprising aspect of the results obtained from both Experiment 2 and

Experiment 1, as well as those found in Experiments 2A and 2B of Lambert

et al. (2006) is that highly discriminable, centrally located cues failed to elicit

reliable orienting effects. It is of course impossible to prove the null

hypothesis*that response times on valid and invalid trials do not differ in

the symmetric, single cue conditions. However, in an attempt to provide a

powerful test of the hypothesis that symmetric central cues can affect spatial

attention, data from Experiments 1 and 2 were combined. In this combined

analysis, using data from nearly 70 participants, the response time difference

between valid and invalid trials at the long SOA still failed to attain the

conventional (p B.05) level of statistical reliability. At brief SOAs (150 ms or

less) there is no hint of a difference between valid and invalid trials, either in

the present study, or in our earlier work (Lambert et al., 2006). It seems safe

to conclude that visually symmetric central cues have no effect on spatial

attention at brief SOAs, and that at long SOAs any effect of these cues is

weak at best.

EXPERIMENT 3

Findings from Experiments 1 and 2 show that in the absence of any

correspondences between spatial features of the precue stimulus and the

target location, conscious volition had no influence on visual orienting*in

the sense that participants were unable to comply with experimental

instructions and shift attention under conscious, voluntary control, in

response to the symbolic information carried by the cue. While these data

pose a clear challenge to the notion of voluntary orienting in response to

symbolic cues, the conclusion that covert visual orienting, in response to

spatial cues, is independent of conscious control processes would of course be

unwarranted. It is entirely conceivable that in a situation where clear

orienting effects are observed, these orienting effects may be modulated by

conscious awareness and control. Experiment 3 addressed this issue by

studying a situation where clear visual orienting effects were predicted to

occur, and by assessing effects on performance of conscious awareness of cue

utility, in terms of predicting target location. This was done by examining

visual orienting in response to spatial correspondence cues of the kind

employed previously (Lambert & Duddy, 2002), which are known to elicit

rapid and clear orienting effects. Participants made a simple detection

response to target objects that were preceded by a pair of peripheral letter

cues. A critical new feature in the design of Experiment 3 was that two pairs of

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letter cues were used. For both letter pairs, the target object usually appeared

on the same side as one letter, and opposite to the other. For each participant,

one letter pair was designated to act as an ‘‘explicit cue’’ while the other acted

as an ‘‘implicit cue’’. That is, participants were informed of the predictive

relationship between cues and targets for one letter pair, and were instructedto attempt to make use of this information to prepare for a target at the

expected location (explicit cue condition). Participants were not informed of

the predictive information carried by the second letter pair, which acted as an

implicit cue. Thus, on some trials participants were explicitly aware of the

predictive utility of the letter cues, whereas on other trials participants had

not been informed of the predictive information carried by the letters. By

comparing performance in the explicit and implicit cue condition,s we were

able to perform a relatively sensitive, within-participants assessment of theextent to which attentional effects were dependent upon, or were modulated

by, consciously held knowledge of the predictive information carried by the

cues. In order to explore this issue comprehensively, the extent to which

participants gained conscious knowledge of the predictive utility of the

implicit cues in the course of the experiment was assessed by administering a

postexperiment questionnaire. The performance of participants who gained

some awareness of the predictive utility of the implicit cues was then

compared with that of participants who remained unaware of the cue�targetcontingency.

In a recent report, Risko and Stolz (2010) assessed the relationship

between conscious awareness of the predictive utility of spatial cues and the

attentional effects of those cues. In two experiments the predictive relation-

ship between the location of a target object and the location of a peripheral

cue (Experiment 1) and between target location and the direction indicated

by a central arrow cue (Experiment 2) was either strong (target appeared at

the cued location on 75% of trials) or weak (target appeared at the cuedlocation on 50% of trials). Consistent with earlier work a ‘‘proportion valid

effect’’ was observed in both experiments. That is, the performance

difference between valid trials, where targets appeared at the cued location,

and invalid trials, where targets appeared at the uncued location, was greater

when the predictive utility of the cue was stronger. Interestingly, although

participants’ response time performance was closely coupled with the

predictive utility of cues, validity effects failed to show any relationship

with participants’ awareness, assessed via postexperiment questionnaire, ofhow well the cues predicted target location. Thus, the data of Risko and

Stolz suggest that conscious awareness of the cue�target relationship may be

independent of the covert orienting effects elicited by spatial precues.

However, Chica and Bartolomeo (2010) noted that the cues used by Risko

and Stolz (onset of a peripheral object and centrally presented arrows) both

elicit shifts of attention that occur in a relatively automatic manner (Hommel

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et al., 2001; Muller & Rabbitt, 1989; Tipples, 2002). Thus, while agreeing that

the data of Risko and Stolz demonstrate that orienting in response to spatial

cues can be independent of conscious awareness, Chica and Bartolomeo

noted that their data do not exclude the possibility that conscious, strategic

processes may nevertheless contribute and play an important role in thecontrol of visual orienting, when attention is directed in response to cues that

do not elicit automatic shifts of attention. In Experiment 3 this issue was

addressed by using letter cues (X, T, M, O) that were related to target location

in a way that was nonautomatic, arbitrary, and counterbalanced across

participants. As noted previously, the design enabled us to compare

performance in an explicit cue condition, where participants were encouraged

to adopt a conscious strategy by directly informing them of the predictive

utility of the cues, with performance in an implicit cue condition, whereparticipants were given no information about the predictive utility of the cue

letters.

Method

Participants. The participants consisted of 16 individuals (10 females, 12

right-handed) between the ages of 20 and 28 years (mean age �21.94 years,

SD�2.21 years).

Apparatus. The experiments were run using an IBM-compatible laptop

computer connected to an LCD monitor, with a graphics resolution of

1280�1024 pixels. The testing programme was written using E-Prime

software. A chinrest was used to maintain viewing distance at approximately

57 cm.

Display and stimuli. The stimuli were presented in black against a white

background. The fixation display was a central cross subtending approxi-mately 0.68�0.68. The target stimulus was an asterisk that subtended

0.58�0.58 and appeared either to the left or right of the central cross. The

inner edge of the target asterisk was approximately 88 from the central cross.

The lower edge of each letter was presented 0.38 above the horizontal

meridian. All letters were presented in upper case in the font style Arial for

all participants. Each participant was randomly allocated two ‘‘informed

(explicit) cue’’ stimuli and two ‘‘uninformed (implicit) cue’’ stimuli out of a

letter pool (X, T, M, O) and these subtended approximately 0.68 (height) and0.58 (width).

Procedure. For half of the participants ‘‘X’’ and ‘‘T’’ were the informed

(explicit) cues, and ‘‘M’’ and ‘‘O’’ were the uninformed (implicit) cues. This

was reversed for the other participants. Half of the participants received a

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version where the target usually (p �.8) appeared on the same side as the

letter ‘‘X’’; and half of the participants received a version where the target

usually (p �.8) appeared on the same side as the letter ‘‘T’’. Thus, ‘‘X’’

marked the valid location and ‘‘T’’ marked the invalid location for half the

participants, and this arrangement was reversed for the other participants.Similarly, half of the participants received a version where the target usually

(p �.8) appeared on the same side as the letter ‘‘M’’; and half of the

participants received a version where the target usually (p �.8) appeared on

the same side as the letter ‘‘O’’. Trials randomly alternated between an SOA

of 150 ms and 500 ms. Participants were informed that the asterisk would

appear on the same side as the valid, explicit cue 80% of the time, and that

they should try to use the letter cue to prepare for the target asterisk

occurring on the same side as the valid letter, and opposite to the invalidletter. They were instructed to pay attention covertly, by directing attention

to the expected location of the target, whilst their eyes remained fixated on

the central cross. Participants were also informed that on random trials

‘‘other letter stimuli’’ would appear that were different from the informed

(explicit) letter cues. Participants were informed that these letters were

control stimuli and that they should merely respond to the asterisk as fast as

possible on these trials and not attend to the letters.

Participants performed a block of eight practice trials followed by fourblocks of 40 trials that were identical to the practice block. Within each

block there were 32 valid trials and eight invalid trials; there were 20 trials at

each of the two SOAs; there were 20 trials with the target in the right visual

field and 20 trials with the target on the left. There were 20 trials with explicit

letter cues and 20 trials with implicit letter cues. After the final block was

completed, participants were given a questionnaire to probe their conscious

awareness of the cue�target relationship.

Postexperiment questionnaire. After completion of the experiment

participants were issued with the questionnaire.

1. While you were carrying out the experiment, were you aware of any

relationship between the letters M and O and the location of the target?

Please explain your answer.

Note: In this example ‘‘M’’ and ‘‘O’’ were the implicit cues. For half the

participants ‘‘X’’ and ‘‘T’’ were used as the implicit cues.

Upon answering, participants were instructed to turn over the page, to revealthe next questionnaire items.

2. Please estimate the percentage of trials where the target asterisk (*)

came up on the same side as the letter M and opposite to the letter O.

Write a number (1�100%) on the scale below to indicate your estimate.

3. Please circle a number to indicate your level of confidence in your above

estimate:

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1 Pure guess

2 Mainly guesswork

3 Possibly the correct choice

4 Probably the correct choice

5 Very likely the correct choice

6 Certainly the correct choice

4. Please indicate the percentage of trials where the target asterisk (*) came

up on the same side as the letter X and opposite to the letter T.

Write a number (1�100%) on the scale below to indicate your estimate.

Note: In this example ‘‘X’’ and ‘‘T’’ were the explicit cues. For half the

participants ‘‘M’’ and ‘‘O’’ were used as the explicit cues.

5. Please circle a number to indicate your level of confidence in your above

estimate:

1 Pure guess

2 Mainly guesswork

3 Possibly the correct choice

4 Probably the correct choice

5 Very likely the correct choice

6 Certainly the correct choice

Note: For Items 1 and 2 half the participants received the version that

mentioned their uninformed, valid letter first; the other half received the version

that mentioned their uninformed invalid letter first. Scales were anchored at

0%, 50%, and 100%.

Results

Trials with a response time (RT) of less than 100 ms were categorized as

anticipatory responses and were discarded. Trials with delayed responses,

where RT exceeded 1000 ms, were also discarded. These constituted 3.51%

and .195% of the data set respectively. Response time results based on the

remaining data are summarized in Figure 4. Participants were classified as

having gained awareness of the predictive relationship between target

location and the implicit cue letters, or as remaining unaware of this

relationship. The aware group comprised five participants who were able to

describe the cue�target relationship in response to the first item of the

postexperiment questionnaire; the unaware group comprised 11 participants

who were unable to describe the cue�target relationship in response to the

first item of the postexperiment questionnaire. Mean response times were

calculated for each participant in each condition, and these data were then

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entered into analysis of variance with strategic condition (explicit, implicit),

cue validity (valid, invalid), and SOA (150 ms, 500 ms) as within-participant

factors. In addition, whether participants had gained awareness of the

predictive relationship between implicit cues and targets was entered as a

between-participants factor. This analysis revealed that response times were

faster on valid (289 ms) compared to invalid (307 ms) trials, F(1, 14) �7.54,

p �.016. As Figure 4 illustrates, this effect did not vary as a function of

strategic instructions, F B1, or as a function of SOA, F B1, or as a conjoint

function of strategic instructions and SOA, F B1. As in our earlier work

(Lambert & Duddy, 2002; Lambert et al., 2006) response times were faster

when the delay between cue and target onset was 500 ms (279 ms) compared

to trials where the cue�target SOA was 150 ms (317 ms), F(1, 14) �39.82,

p B.001.

Awareness and validity effects. The data shown in Figure 4 show that cue

validity effects were unaffected by strategic instructions. However, to test the

hypotheses described in the introduction to this experiment comprehensively,

it was also necessary to evaluate whether conscious awareness of the

relationship between target location and the implicit cue letters had any

impact on visual orienting in response to those cues. This was achieved by

performing a further analysis which focused specifically on performance in

the implicit cue condition. Response time results in the implicit cue condition

for ‘‘aware’’ and ‘‘unaware’’ participants are shown in Figure 5. Analysis of

variance of these data showed that the contrast between valid (mean

RT �297 ms) and invalid trials (mean RT �314 ms) remained significant

when implicit trials were analysed separately, F(1, 15) �6.96, p�.019.

Furthermore, this effect did not vary as a function of awareness group,

Figure 4. Mean response times in the implicit and explicit conditions of Experiment 3.

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F B1, as a function of SOA, F B1, or as a conjoint function of awareness

and SOA, F B1.It might be objected that dividing our participants into ‘‘aware’’ and

‘‘unaware’’ groups on the basis of their response to the first item of the

postexperiment questionnaire fails to provide a fully comprehensive assess-

ment of whether orienting effects might be related to, or dependent upon,

conscious awareness of cue predictiveness. For example, it is conceivable that

participants may be able to demonstrate some awareness of the cue�target

relationship, but be unable to describe it. Thus, participants who were

unable to describe the relationship in response to the first item of the

questionnaire (which asked whether they were aware of any relationship

between the implicit letters and target location), could still show evidence of

awareness, via their responses to the second item of the questionnaire, which

asked for a direct estimate of the percentage of occasions where the target

appeared on the same side as the valid letter and opposite the invalid letter.

Participants’ estimates of this value ranged from 20% to 85%, with a mean

of 56.9%. The correct answer was 80%. In agreement with Risko and Stolz’s

(2010) findings, there was no relationship between participants’ estimates of

the percentage of occasions where the target appeared at the valid location

and their validity effects, indexed by the response time difference between

valid and invalid trials, at either the short SOA, r �.268, df�15, ns, or the

long SOA, r�.263, df�15, ns.

Discussion

Results from the experiment were clear. As Figure 4 shows, participants

capitalized upon the predictive relationship between peripheral cue letters

Figure 5. Mean response times in the implicit condition of Experiment 3 for participants who

remained unaware of the cue�target relationship (N � 11, left-hand panel) and for those who gained

some awareness of the relationship between implicit cues and target location (N � 5, right-hand

panel).

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and target location, regardless of whether they were informed of this

relationship and instructed explicitly to make use of it to allocate attention

appropriately (explicit condition), or were given no information regarding

the cue�target relationship (implicit condition). Furthermore, as Figure 5

shows, in the implicit condition there was no evidence that participants who

gained awareness of the cue�target relation performed any differently, or

used the cues more effectively than participants who remained unaware of

the cue�target relationship. These findings add to a growing body of

evidence that covert visual orienting in response to spatial cues is a mental

operation that occurs independently of conscious awareness (Bartolomeo,

Decaix, & Sieroff, 2007; Lambert, Naikar, McLachlan, & Aitken, 1999;

Risko & Stolz, 2010). However, all of these earlier studies involved showing

that participants who were given no information about cue�target con-

tingencies, and who gained no awareness of the cue�target relationship,

nevertheless oriented attention appropriately in response to the cues. As

Chica and Bartolomeo (2010) have noted, such findings do not exclude the

possibility that conscious, strategic processes may also influence covert

orienting behaviour in the spatial cueing paradigm. Addressing this issue

requires a design in which performance in the absence of awareness of cue�target contingencies is compared with a condition where participants are

given explicit, strategic instructions. Thus, the current findings provide

valuable new information, in showing not only that participants who lack

conscious knowledge of cue�target contingencies display appropriate

orienting, but also that orienting behaviour in response to spatial cues was

unaffected by the provision of explicit instructions.

GENERAL DISCUSSION

The findings described here have important implications for the widely

invoked distinction between endogenous and exogenous orienting. For

example, as Santangelo and Spence (2008) wrote, ‘‘Ever since Michael

Posner published his classic paper in 1980, the covert (i.e., without eye

movements) focusing of a person’s attentional resources on a particular

source of interest in the environment has been seen as the result of the

operation of two qualitatively different attentional orienting mechanisms,

one voluntary and the other reflexive’’ (pp. 989�990; Posner, 1980). They go

on to note that the two mechanisms are often labelled as endogenous and

exogenous, respectively. Two critical assumptions are often made in studies

that purport to examine the endogenous orienting process: That participants

encode centrally presented (endogenous) cues as symbols, and that orienting

in response to such cues is under voluntary control. Both these assumptions

are undermined by findings from the three experiments described here.

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Symbolic processing and attentional control

The assumption that participants encode centrally presented (endogenous)

cues as symbols (e.g., see Greene et al., 2009; Hommel & Akyurek, 2009;

Pratt et al., 2010) is examined first. A central feature of symbolic processing

is that the visual form of the symbol is immaterial. The word ‘‘duck’’ neither

looks, walks, nor quacks like a duck; the relationship between the symbol

and the aquatic bird it denotes is essentially arbitrary. A striking feature of

findings from Experiments 1 and 2 is that attentional effects of centrally

presented cues were critically dependent upon visual features of the cue

display. Bilateral cues elicited covert visual orienting at the long, cue�target

SOA, but single, visually symmetric, central cues failed to elicit any orienting

effects at all. There were no reliable effects of symmetric central cues on

covert attention at either brief (0 ms, 150 ms) or long (500 ms) cue�target

SOAs, even when the spatial extent of the single cues matched that of the

bilateral cues. These results extend and clarify our earlier finding that

ostensibly symbolic cues that possessed the visual feature of asymmetry (the

letters d and b) elicited clear orienting effects, although similarly symbolic,

but visually symmetric central letters (X, T, v, o) were ineffective as spatial

cues. Although it is often difficult to draw conclusions from null results, in

this case the null finding (no effect of symmetric central cues on attention)

stands in stark contrast to a substantial series of positive results, in which

precisely the same stimulus distinction (X vs. T) in the context of asymmetric

cue displays, gave rise to highly reliable orienting effects*even when the cue

discrimination was performed not in high resolution central vision, but

peripherally (Lambert, 2006; Lambert & Duddy, 2002; Lambert, Norris,

Naikar, & Aitken, 2000), and even when the cues were both peripheral and

low in contrast. Lambert and Shin (2010) observed highly reliable orienting

in response to peripheral X, T cues when stimulus contrast was reduced to

10%. Thus in cueing paradigms, the presence of spatial correspondence

between target location and visual features of the cue display appears to be a

critical factor that influences whether attentional effects will, or will not, be

observed.

Conscious control and covert orienting

A second assumption commonly made in studies purporting to assess

endogenous orienting, is that orienting in response to arbitrary, symbolic

cues is accessible to, and indeed is driven by, conscious control. This

assumption is undermined by our observation that in all three experiments

covert orienting was unaffected by conscious control. In Experiments 1 and

2, a conscious attempt to follow experimental instructions, by orienting in

response to clearly discriminable cues failed to elicit any orienting effects,

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when the cues lacked the feature of spatial correspondence. In Experiment 3,

cues that did possess the feature of spatial correspondence elicited clear

orienting effects, but the magnitude of these effects was uninfluenced by

whether participants were aware or remained unaware of the predictive

utility of the letter cues. Thus, in this situation, consistent with the recentfindings of Risko and Stolz (2010), conscious awareness of the predictive

relationship between cues and targets appeared to be independent of the

attentional effects elicited by those cues.

A closely similar pattern of results has recently been reported by Peterson

and Gibson (in press). These authors found that when coloured circles (blue

vs. pinkish purple) were used as cues, no reliable orienting effects were

observed. However, when the circles were rendered visually asymmetric, by

adding small gaps on the left or right of the cue, clear orienting effects wereobserved. Furthermore, as in the present study, attentional effects elicited by

the asymmetric circle cues were independent of participants’ conscious

awareness of the predictive utility of the cues, with respect to target location.

In the field of consciousness studies, much research has aimed to

demonstrate the existence of nonconscious mental process (e.g., perception

without awareness, learning without awareness), and the existence of

conscious versions of these processes has been taken as self-evident (e.g.,

see Holender, 1986; Shanks & St. John, 1994). We suggest that scientists andscholars may need to reverse this mental set when approaching the topic of

covert visual orienting. The question of whether covert orienting in response

spatial cues is accessible to conscious control processes does not have a self-

evident answer*empirical evidence is required. The current results, together

with earlier studies provide ample evidence that covert visual orienting in

response to spatial cues can occur even when participants are unaware of the

cue�target relationship (Lambert et al., 1999; Risko & Stolz, 2010).

Furthermore, conscious control failed to modulate the visual orientingeffects that were observed in Experiment 3, and covert orienting effects were

not observed in Experiments 1 and 2 when participants attempted to orient

in response to cue displays that contained no spatial correspondences

between cue features and target location. This evidence is consistent with a

theoretical view of attention (see later) which contends that covert orienting

in response to spatial precues is nonconscious and inaccessible to conscious

control.

In studies of spatial precueing (see Wright & Ward, 2008) for acomprehensive review), several conceptually independent factors are often

copresent. These factors include the predictive utility of the cues, spatial

correspondence between features of the cue display and target location,

strategic instructions to orient in response to the cues, and prior learning

history in which participants have oriented attention in response to stimuli

such as arrows, faces gazing to one side, or new peripheral objects. Clearly, in

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order to isolate the role of these factors in the control of covert orienting it is

necessary to manipulate each of them independently. The pattern of results

observed in this study, together with data reported by Lambert and Duddy

(2002), Lambert et al. (2006), and Lambert and Shin (2010) suggests that (1)

spatial correspondence is a critically important factor for eliciting covertvisual orienting in response to spatial cues, and (2) conscious strategic

control does not appear to play a causal role in this situation. Conscious

awareness of the cue�target relationship appears to be neither a necessary

condition (Experiment 3; Lambert, 2004; Lambert et al., 1999), nor a

sufficient condition (Experiments 1 and 2; Lambert et al., 2006) for covert

orienting to be observed.

Attentional cueing and spatial correspondence learning

The pattern of results reported here and in other studies of spatial cueing can

be explained in terms of the spatial correspondence framework introduced

by Lambert and Duddy (2002) and by Lambert et al. (2006). An important

feature of this framework is that it contends that attentional behaviour in

studies using both central and peripheral cueing procedures can be explained

in terms of, spatial correspondence learning, rather than in terms of the two

processes embodied in the theoretical dichotomy characterized variously asendogenous versus exogenous, voluntary versus reflexive, stimulus driven

versus goal driven, and so on. According to our framework, in visual cueing

tasks participants are highly sensitive to the spatial relationships that obtain

between visual objects in the cue display and the location of the target, when

it appears. Clearly, this framework is consistent with peripheral cueing

studies which show rapid orienting effects when the location of the target

and the location of an abrupt onset or peripheral visual change correspond

(Cheal & Lyon, 1991; Muller & Rabbitt, 1989). It can also explain the rapidand strong orienting effects that are seen in bilateral cueing studies, when the

location of one type of cue object usually corresponds with the location of

the target (Lambert & Duddy, 2002, Exps. 1 and 3A). The latter findings are

predicted by the spatial correspondence framework, but problematic for the

endogenous*exogenous theoretical dichotomy, because visual orienting in

this situation is goal directed. Thus, rapid orienting in response to peripheral

objects can be driven by a temporary attentional set (‘‘Orient towards the

X’’) which might be described as endogenous, as well as by a long-term, andrelatively ‘‘hard wired’’ attentional set which predisposes individuals to

orient towards new objects or salient visual changes in the periphery (Schreij,

Theeuwes, & Olivers, 2010). We contend that participants readily learn

spatial correspondences between target location and the location of a cue

object, and deploy this learning in the control of covert attention. As

explained earlier, cue�target spatial correspondences are reduced when

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participants are presented with bilateral cue displays which are visually

symmetric, and in agreement with the spatial correspondence learning

approach, visual orienting effects are reduced in this situation (Lambert &

Duddy, 2002, Exps. 2 and 3B). The spatial correspondence framework can

also explain the finding that orienting in response to asymmetric central cuestakes longer to develop than orienting in response to peripheral cues (Cheal

& Lyon, 1991; Muller & Rabbitt, 1989), because in this case the spatial

correspondences between the cue and target displays are driven by the

spatial arrangement of features within the cue object, rather than by

variation in the overall location of cues (Lambert et al., 2006).

In the final type of situation, examined in Experiments 1 and 2, and by

Lambert et al. (2006), when participants are presented with visually

symmetric, centrally located cues there are no spatial correspondences,either between target location and cue location, or between target location

and the spatial arrangement of visual features within the cue. The two

experiments reported here show that, in agreement with the spatial

correspondence learning approach, visual orienting effects in response to

these cues are weak at best, and probably nonexistent. According to the

theory of endogenous and exogenous orienting, it should be possible to shift

attention under endogenous control via symbolic encoding of any type of

easily discriminable cue stimulus, especially stimuli such as letters which arefamiliar verbal symbols. However, when letters are used as spatial cues, their

attentional effects depend crucially on their visual features.

It is worth noting that the spatial correspondence framework can also

accommodate findings that certain classes of central cues (arrows, faces

gazing to one side) are associated with automatic orienting effects, that are

difficult to modify via top-down control (Friesen et al., 2005; Tipples, 2008).

These findings have been interpreted as problematic for the endogenous�exogenous theoretical dichotomy (see Gibson & Kingstone, 2006). However,within the spatial correspondence framework, these effects can be inter-

preted in the same manner as orienting in response to peripheral cues, as

arising from long-term attentional sets, associated with overlearning (arrow

cues), and/or from a relatively hard wired disposition to orient in response to

certain classes of biologically important stimuli (faces, new peripheral

objects).

Results from Experiment 3, together with earlier findings (Lambert et al.,

1999), suggest that the learning process whereby spatial orienting is affectedby spatial correspondences between cue and target stimuli can be character-

ized as implicit. These findings are therefore consistent with accounts in

which implicit learning plays a pivotal role in the control of spatial attention

(Chun, 2000; Risko & Stolz, 2010). Furthermore, the observation that effects

of spatial cues on attention appear to be independent of conscious awareness

of the cue�target relationship is consistent with the hypothesis that visual

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orienting effects are subserved by dorsal visual stream processing of the cue

stimulus (Lambert & Shin, 2010). Dorsal visual stream encoding is thought

to occur independently of conscious awareness (Milner & Goodale, 2006). In

support of this dorsal stream attention hypothesis (DSAH), Lambert and

Shin (2010) reported a dramatic dissociation between effects of reduced

luminance on visual orienting in response to peripheral cue letters, and on

conscious perception of the same letters. Conscious perception of low

contrast peripheral letters was massively impaired, but the visual orienting

effects elicited by low and high contrast letters were closely similar. This

dissociation is consistent with the dorsal stream hypothesis because, unlike

the ventral stream, the dorsal visual stream is composed almost entirely of

cells arising from magnocellular (M) layers of lateral geniculate nucleus

(LGN), and it is known that M cells respond to well to low contrast visual

stimuli. Two further pieces of evidence are also consistent with the DSAH.

First, Lambert et al. (2011, Experiment 1) recorded high density EEG while

participants oriented in response to spatial cues. Source localization

provided electrophysiological evidence for rapid activation of the dorsal

stream in response to peripherally presented letter cues. Second, it appears

that patient DF, studied extensively by Milner and Goodale (2006), is able to

shift attention appropriately, in response to peripheral letter cues (Lambert

et al., 2011, Experiment 2). DF exhibits severe agnosia for visually presented

objects, shapes, and letters, having suffered extensive damage to the ventral

visual stream, but also displays accurate visually guided reaching behaviour.

The latter ability is thought to be mediated by processing within the dorsal

visual stream, which remains intact in this patient. Thus, the dorsal stream

attention hypothesis predicts that DF should also be able to orient

appropriately in response bilaterally presented peripheral cues, despite being

unable to discriminate the cue letters consciously. Lambert et al. (2011,

Experiment 2) tested this prediction experimentally, and observed that DF

did indeed respond more rapidly to objects presented at the cued location,

while denying any conscious awareness of the cue letters themselves.

The aim of theory is, of course, not only to explain attentional behaviour

in spatial cueing experiments, but also to explain attentional behaviour

outside the laboratory. The visual world outside the attention laboratory

embodies a wide variety of statistical associations between successive views

and experiences of a dynamic, but reasonably predictable environment. The

concept of spatial correspondence learning, as presented here and elsewhere

(Lambert & Duddy, 2002; Lambert et al., 2006), implies that associative

learning mechanisms, which have been applied so fruitfully to the study of

overt behaviours (e.g., Dickinson & Balleine, 2002), can also be recruited to

explain covert attentional behaviour.

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Control of spatial attention: One process or two?

The evidence described in this paper, together with a number of earlier

findings (Friesen et al., 2004, 2005; Hommel et al., 2001; Lambert & Duddy,

2002; Lambert et al., 2006; Tipples, 2002, 2008), indicate that the widely

invoked dichotomy between endogenous and exogenous control of covert

visual orienting is severely flawed at best. In light of this, it seems

appropriate to evaluate whether the single process explanation described

earlier, which attributes spatial cueing effects to a single process involving

implicit learning of spatial correspondences between cue and target displays,

and which relies on dorsal stream visual processing of cue objects, might

provide a better account of spatial cueing effects than the two-process

endogenous�exogenous model. As explained in the previous section, the

spatial correspondence framework can explain a variety of findings that are

problematic for a two-process (endogenous vs. exogenous) model. On the

other hand, the voluminous literature on spatial cueing also includes several

findings that appear to raise difficulties for the spatial correspondence

account. First, the latter account seems to be contradicted by findings that

participants are able to orient in response to central cues that comprise

directional words, such as left, right, above, below (Hommel et al., 2001;

Vecera & Rizzo, 2004; see also Gibson & Kingstone, 2006). These studies

appear to provide strong evidence that symbolic stimuli can function

effectively as spatial cues. However, directional words, like arrows and

laterally gazing eyes, have participated in a long learning history, in which

associative links between attentional behaviour and the cue word will have

been formed. Furthermore, in these studies the words employed as cues

would all have been highly primed, both by the experimental context

(participants were instructed to attend left, right, above, or below), and by

extensive repetition of the words themselves. In this highly primed state,

encoding of the cue words may have been achieved by encoding simple visual

features that distinguished between the words, rather than via full-blown

verbal�semantic processing. According to this interpretation, the crucial

feature of these studies (Hommel et al., 2001; Vecera & Rizzo, 2004) is not

that symbolic cues can elicit covert visual orienting, it is that cues that have

an overlearned relationship with orienting behaviour can elicit automatic

orienting.

In an experiment described by Ristic and Kingstone (2009) adults and

preschool children were presented with central cues that comprised visually

symmetric shapes (circles and squares). These cues elicited reliable orienting

at a brief (100 ms) SOA in preschool children, and elicited reliable orienting at

both short and long SOAs in adults. These results appear to contradict

directly our finding that visually symmetric letters failed to elicit orienting.

However, in Ristic and Kingstone’s (2009) experiment, rather than presenting

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the cues transiently, cues remained on the screen until after the target had

been presented: ‘‘Both the cue and the target remained on the screen until a

response was executed or 2300 ms had elapsed, whichever came first’’ (p. 292).

This aspect of their procedure makes it possible that response differences

could have been driven by differences in the overall configuration of the target

and cue stimulus, rather than by differences in the allocation of attention to

target locations. That is, the stimulus configurations for a valid trial (e.g.,

circle�right target or square� left target) would be more likely than the

converse stimulus configurations (circle� left target or square�right

target). Thus, response time differences could have been driven by sensitivity

to the varying probability of these different stimulus configurations, rather

than by differential allocation of spatial attention. This interpretation could

be tested by repeating their experiment, using transiently presented shapes as

cue stimuli.

A further problem for the spatial correspondence learning account of

orienting effects arises from observations that visually symmetric colour cues

appear to function effectively as cues for eliciting covert visual orienting

(Dodd & Wilson, 2009; Funes, Lupianez, & Milliken, 2007). Funes et al.

(2007) used visually symmetric coloured (red or green) patches as spatial

cues, and found reliable visual orienting effects when the delay between cues

and targets was 350 ms or longer. In Dodd and Wilson’s (2009) study,

participants initially performed a training session in which large, visually

symmetric, coloured (blue or green) patches predicted target location with

100% accuracy, and then participated in a test session in which the colour

cues were uninformative with respect to target location. During the test

session, small but reliable visual orienting effects were observed: Participants

oriented attention towards the location that had been associated previously

with the coloured central cue. Although the latter results are consistent with

the contention that learned associations between cue stimuli and orienting

behaviour play an important role in spatial cueing effects, the findings of

Dodd and Wilson and of Funes et al. appear problematic for the spatial

correspondence account of spatial cueing effects: In both studies, visually

symmetric cues that apparently lack the feature of spatial correspondence

elicited visual orienting. Three comments can be made. First, it is possible

that visually symmetric colour patches do not eliminate all opportunity for

spatial correspondence learning. In both the Funes et al. and Dodd and

Wilson studies, the presence of a target on the left would have been

associated with the presence of a specific cue colour (e.g., green) on the left

of the cue display (together with the same colour on the right), and a target

on the right would have been associated with the presence of the other cue

colour on the right of the cue display. This interpretation is directly

analogous to that applied earlier, to the finding that visually symmetric,

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bilateral cue displays elicit reliable visual orienting effects. Second, although

the results reported here, together with our earlier work (Lambert & Duddy,

2002; Lambert et al., 2006), demonstrate clearly that spatial correspondence

is a powerful factor driving covert orienting in spatial cueing paradigms,

other stimulus attributes such as colour could also play an important role. A

third comment, related to the second, is that it is not entirely clear whether

visual orienting in either the Funes et al. or Dodd and Wilson studies was

driven by the hue of the central cues. Because no attempt made to equate the

luminance of the coloured patches in either study, it is possible that the cues

differed with respect to luminance, as well as with respect to hue. This is

pertinent, because the dorsal stream is highly sensitive to luminance

distinctions, but insensitive to isoluminant colour boundaries. Further

studies that disentangle effects of cue colour and cue luminance would

resolve this issue, and would also provide a further test of the dorsal stream

attention hypothesis. In the recent study of Peterson and Gibson (in press),

coloured circles were used as cues and cue colours were matched with respect

to luminance. Interestingly, in this situation no orienting effects were

observed, at either brief or long (500 ms) SOAs. In conclusion, although

spatial correspondence learning, together with the dorsal stream attention

hypothesis can account for several findings that are difficult to explain in

terms of a two-process endogenous�exogenous model of attentional control,

it is also clear that further research will be required to delineate the

explanatory scope of this framework.

SUMMARY AND CONCLUSIONS

In Experiments 1 and 2, visual orienting effects were critically dependent

upon visual features of the stimuli employed as precues. When there were no

spatial correspondences between cue stimuli and target location, visual

orienting effects were absent, despite a conscious intention to orient in

response to the symbolic information carried by the cue. In Experiment 3,

participants oriented readily in response to precues that did possess the

feature of cue�target spatial correspondence. However, the orienting effects

observed in Experiment 3 were unaffected by whether participants were

aware or unaware of the predictive information carried by the cue letters.

These findings suggest that spatial correspondence between target location

and visual features of the cue display is a critical factor driving visual

orienting in spatial cueing paradigms, and that conscious awareness of these

spatial correspondences does not play a causal role in the covert orienting

effects that are observed in this situation.

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