Klein 1999 Inhibition

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346 Copyright © 1999 American Psychological Society VOL. 10, NO. 4, JULY 1999

PSYCHOLOGICAL SCIENCE

Research Article

INHIBITION OF RETURN IS A FORAGING FACILITATOR

IN VISUAL SEARCH

Raymond M. Klein and W. Joseph MacInnes Department of Psychology and Faculty of Computer Science, Dalhousie University, Halifax, Canada

Abstract—Using overt orienting, participants searched a complex

visual scene for a camouflaged target (Waldo from the “Where’s

Waldo?™ ” books). After several saccades, we presented an uncamou-

flaged probe (black disk) while removing or maintaining the scene,

and participants were required to locate this probe by foveating it.

Inhibition of return was observed as a relative increase in the time

required to locate these probes when they were in the general region of

a previous fixation, but only when the search array remained present.

Perhaps also reflecting inhibition of return, preprobe saccades showed

a strong directional bias away from a previously fixated region.

Together with recent studies that replicate the finding of inhibition at

distractor locations following serial but not parallel visual search—so

long as the search array remains visible—these data strongly support the proposal that inhibition of return functions to facilitate visual

search by inhibiting orienting to previously examined locations.

Immediately following a peripheral stimulus (cue), there is often a

short-lived increase in processing efficiency for nearby stimuli. This

phasic improvement has been attributed to automatic (exogenous) ori-

enting of attention toward the cue (see Klein, Kingstone, & Pontefract,

1992; Posner, 1980). In the absence of motivation to maintain atten-

tion at the cued location, this early facilitation is followed (or accom-

panied) by a longer lasting inhibition (Posner & Cohen, 1984) that has

been called inhibition of return (IOR; see Taylor & Klein, 1998b, for

a review).1 Extending Posner and Cohen’s (1984) interpretation of

IOR as an inhibitory mechanism that would encourage the sampling of new information in the visual field, Klein (1988) proposed that IOR

might facilitate visual search when each display item requires an atten-

tion-demanding inspection to determine if it is the target (cf. Treisman

& Gelade, 1980). Inhibitory tagging of display items that have already

been examined attentively would, by repelling attention, help the

observer avoid reinspecting them.

Klein (1988) tested this functional explanation of IOR by present-

ing luminance-detection probes immediately after the subject had per-

formed an easy (preattentive; target “pops out”) or difficult (requiring

serial allocation of attention to array items) visual search (see Fig. 1).

The probes occurred on half of the trials and were presented at loca-

tions where there had been an item in the search display (on probes)

or at locations where no item had been presented (off probes). The

rationale was straightforward: “In serial search if the presumed allo-cation of attention to each item is followed by inhibition of return, then

detection of on-probes should be delayed compared with off-probes”

(Klein, 1988, p. 430). This is precisely what Klein (1988) found using

parallel search to control for other factors, such as masking and

expectancies (see Table 1). This previous study thus provides support

for an intuitively appealing view of IOR as a foraging facilitator.

IOR AS A FORAGING FACILITATOR:

CHALLENGES AND REBUTTALS

Although several challenges to the functional interpretation of IOR

as a foraging facilitator materialized in the years following Klein’s

(1988) article, more recent findings rebut these challenges.

First, evidence began to accumulate that it might not be attention

that was inhibited but rather processes more closely related to

responding. Initial attempts to obtain IOR using nonspatial discrimi-

nation tasks were unsuccessful (Kwak & Egeth, 1992; Pontefract &

Klein, 1988, described in Klein & Taylor, 1994; Tanaka & Shimojo,

1996; Terry, Valdes, & Neill, 1994). Because performance on such

tasks is sensitive to the locus of attention, the fact that IOR did not

influence such tasks challenged the assumption that attention is inhib-

ited in IOR. Indeed, on the basis of this finding and the fact that IOR

does not affect the perceived temporal order of stimuli (Maylor, 1985;

see Klein, Schmidt, & Müller, 1998, for a review), Klein and Taylor

(1994) proposed (see also Schmidt, 1996a, 1996b, and Tanaka & Shi-

mojo, 1996, for similar proposals) that it was not attention that was

inhibited in IOR but rather responding toward stimuli appearing at

locations for which there had previously been an oculomotor program

(cf. Rafal, Calabresi, Brennan, & Sciolto, 1989). If correct, this pro-

posal would undermine the functional interpretation of IOR as a for-

aging facilitator, which is predicated on the inhibition of attention.

However, in numerous laboratories, IOR has recently been observed to

have an impact on nonspatial discrimination tasks. For example, using

a short (100-ms) cue-target stimulus onset asynchrony (SOA) with a

variety of longer ones, Lupiáñez, Milán, Tornay, Madrid, and Tudela

(1997) found IOR with both simple detection and color discrimination

tasks (though with the discrimination task, IOR appeared at longer

SOAs than with the detection task). In addition, Pratt, Kingstone, and

Khoe (1997) have found evidence for IOR in a form discrimination

task (see also Cheal, Chastain, & Lyon, 1998), and Handy, Jha, and

Mangun (1999) have demonstrated a d ' effect using a go/no-go size

discrimination task. Whatever the cause of the discrepancy,2 the fact

Address correspondence to Raymond Klein, Department of Psychology,

Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada; e-mail:

[email protected].

1. We use the term IOR (which we think has been overextended recently in

the literature on cognitive inhibition) to refer to inhibition generated by and

measured in spatial behavior.

2. More than one cause is likely responsible. Although a time-course differ-

ence works well for resolving the discrepancy between Lupiáñez et al. (1997) and

Pontefract and Klein (1988), both of whom used a cue-target paradigm, a differ-

ent explanation is needed for the dissociation (IOR with detection and localiza-

tion, but not with color or form discrimination) reported by Tanaka and Shimojo

(1996), who used a target-target paradigm with relatively long intertrial intervals.

In this case, IOR from the preceding target may be masked by a response-repeti-

tion heuristic (cf. Keele, 1973, pp. 91–93). Compared with a simple detection

task, in a complex discrimination task, there will be greater utility for the subject

to bypass the response selection stage by just repeating the previous response

when the subject notices that a similar target has appeared on successive trials.




Raymond M. Klein and W. Joseph MacInnes

that IOR can be obtained with nonspatial discriminations reopens the

possibility that attention is inhibited from returning to previouslyinspected locations (see Taylor & Klein, 1998a).

A second challenge came from studies suggesting that IOR could

be maintained at only one location—the one most recently stimulated.

Pratt and Abrams (1995) presented a cue at either one or, in succes-

sion, both possible target locations before presenting a target. In the

two-cue condition, they found inhibition only at the most recently

cued location. Gibson and Egeth (1994) explained this result and

applied it to their own findings by proposing that IOR generated by a

cue was canceled by presentation of a subsequent stimulus at a task-

relevant location, a mechanism they called disinhibition of return.

Although Pratt and Abrams (1995; Abrams & Pratt, 1996) observed

IOR only at the most recently cued location or region, Tipper, Weaver,

and Watson (1996) disputed this finding, and more recently, Kingstone

and his colleagues (Danziger, Kingstone, & Snyder, 1998; Snyder &Kingstone, in press) provided compelling evidence for IOR at more

than one location. Similarly, Klein et al. (1998) showed that disinhibi-

tion of return is an unlikely mechanism that is not needed to explain

Gibson and Egeth’s (1994) pattern of results.

Finally, failures to replicate the original finding of IOR following

serial visual search (Wolfe & Pokorny, 1990; see also Klein & Taylor,

1994) provided a direct challenge to the functional interpretation of

IOR. Recently, the pattern reported by Klein (1988) was replicated in

two different laboratories, but only when the search array remained

visible when the probe was delivered (Müller & von Mühlenen, 1999;

Takeda & Yagi, in press).3 Takeda and Yagi conducted a close replica-

tion of Klein (1988). Their data are shown in Table 1, along with

Müller and von Mühlenen’s remarkably similar pattern. The demon-

stration (Abrams & Dobkin, 1994; Tipper, Driver, & Weaver, 1991;

Tipper, Weaver, Jerreat, & Burak, 1994) that IOR may be tagged to

objects (rather than, or in addition to, environmental locations) pro-

vides a theoretical rationale for the importance of maintaining the dis-play elements in order to observe IOR after a visual search task: If,

during visual search, IOR tags objects in the scene once they have

been inspected, then when the scene is removed (and the objects,

therefore, disappear), the inhibition should likewise be removed.

Indeed, Tipper, who has been a consistent adherent of the view that

IOR functions to facilitate visual search, has made precisely this sug-

gestion (Tipper et al., 1994, pp. 495–496).

DOES INHIBITION OF RETURN GUIDE NATURAL

VISUAL SEARCH?

Our purpose in conducting the present study was twofold: (a) to

determine whether IOR would be observed in the behavior of the ocu-lomotor system when an observer was searching a complex scene for

a camouflaged target and (b) to replicate and extend the finding that

the maintenance of IOR depends on the persistence of the scene being

searched. To accomplish these goals, we presented observers with pic-

tures taken from the “Where’s Waldo?TM” series of picture books,

wherein Waldo (a curly-haired man with a walking stick, red-and-

white striped shirt, and blue slacks) is hidden in a variety of dense and

colorful environments. A long-robed, white-haired wizard is an alter-

nate or additional target in some of the pictures. We presented each

picture superimposed on a central fixation disk whose removal sig-

naled the participants to look for Waldo until they detected a probe

stimulus (reappearance of the disk in a new location), at which time

they were to reacquire it. We placed this probe carefully on the picture

after several saccades had been made; when the probe appeared, thepicture either was simultaneously removed or continued to be dis-

played. The probe was placed on an equi-eccentric circle around the

current fixation such that one of the possible probe locations was the

immediately preceding fixation location (one-back; Experiment 1) or

the fixation immediately preceding that one (two-back; Experiment 2),

and the remaining locations varied in angular separation from this

location (see Figs. 2 and 3). We expected that if IOR were present, sac-

cadic reaction times (SRTs) would increase the closer the probe was to

a previous fixation. If IOR were coded in relation to the scene (rather

than space per se), then maintenance of IOR would depend on main-

tenance of the scene (IOR would not be observed when the scene was

removed).

VOL. 10, NO. 4, JULY 1999 347

Fig. 1. Hypothesized distribution of inhibition of return in visual

search. Filled circles in the top rectangle indicate the locations of dis-

play items in a search task on a target-absent trial. The middle rectan-

gles illustrate that following a difficult search task (serial), inhibitory

tags are left behind at each distractor location “visited” by attention; in

contrast, inhibition is not left behind at distractor locations following

an easy (parallel) search task. Probes presented in new locations

(“Off”) and locations previously occupied by distractors (“On”) are

illustrated in the bottom rectangles. (Redrawn from Klein, 1988.)

3. Klein (1988) found evidence of inhibitory tagging in visual search even

though (as in Wolfe & Pokorny, 1990, and his own later studies) the search

array in this study was removed prior to presentation of the luminance probe.

That maintenance of the search array is necessary to observe IOR following

search suggests (Müller & von Mühlenen, 1999) a possible explanation for this

discrepancy: In Klein’s initial experiments (1988), conditions may have been

optimal for visible persistence of the search scene (high-luminance setting on

a Tektronix 604 oscilloscope with p31 phosphor in a dark room) after the

search array was “turned off.”




Inhibition of Return Facilitates Foraging

A general goal of the project was to bring a degree of ecologicalvalidity into the IOR literature. Of course, the “Where’s Waldo?” pic-

tures and task are no more natural than driving a car or conducting a

search on the World Wide Web. However, because they are much more

complex and interesting than the displays and tasks typically used in

studies of attention, they provide an excellent environment for explor-

ing natural search behavior. Finally, besides generating reaction times

to probe stimuli delivered by the experimenter, our method also pro-

vides a rich source of information on oculomotor behavior during the

search task itself.

METHOD

Participants

Eight adult volunteers, including one of the authors (W.J.M.), par-

ticipated in Experiment 1; 6 new adult volunteers participated in

Experiment 2. All were either students or employees of Dalhousie

University.

Stimuli and Apparatus

Stimuli were eight scenes scanned from three “Where’s Waldo?TM”

books4 and modified for our requirements. We chose pictures in which

there was a relatively high density of distracting information, in which

there was no black and very little dark gray, and in which Waldo, when

present (in half the pictures), and the potential distractors were rela-

tively small. The fixation and probe stimuli were black circles thatsubtended 0.5° of visual angle and had transparent centers 0.1° in

diameter. Stimuli were presented on a 17-in., SVGA,ViewSonic mon-

itor (640 × 480 pixels, 256 colors) in an area measuring 25.0° (width)× 19.4° (height) at a viewing distance of 71 cm. Scenes were drawn or

modified in a single screen refresh.

An EyeLink TM video-based eye-tracking system was used to mon-

itor each participant’s direction of gaze every 4 ms with a resolution of

0.1° or better. With this system, information about changes in direction

of gaze was available to the experimental program within approxi-

mately 20 ms.

Design and Procedure

Each experiment consisted of a block of 288 trials in which each of

the eight Waldo pictures was used equally often. The sequence of

events in a typical trial is shown in Figure 2. Each trial began when the

subject pressed the space bar to indicate that he or she was looking atthe fixation circle at the center of the screen. If fixation was stable, a

picture was displayed. The fixation stimulus remained present for an

additional 700 ms, and participants were instructed to maintain fixa-

tion until it disappeared and then to begin searching. Participants were

told to search for the wizard if they found Waldo in a particular pic-

ture. Examples of Waldo and the wizard were shown to subjects who

were not already familiar with them. Waldo was present in half the pic-

tures, and the wizard in none, so that participants would continue

searching pictures that had become familiar. Participants were

informed that on most trials, after a random period, the fixation disk

would be presented somewhere on the screen, and that when it reap-

peared they should stop searching and shift their gaze to it as quickly

as possible. On half the trials, at the time of this probe presentation,

the search picture remained present until the probe was fixated; on theremaining half of the trials, the picture was removed, leaving only the

probe present on a gray screen.

Any saccades or drifts (of more than 1°) that occurred before the

removal of the fixation dot resulted in a warning beep and recycling of

the trial. Once the fixation dot was removed, subjects were free to

search the picture as they saw fit. After a variable number of saccades

(minimum of 4), the probe was presented (approximately 20 ms after

saccade termination) at a location determined by the current and pre-

vious fixation positions according to the following procedures (illus-

trated in Fig. 3a). In Experiment 1 (one-back condition), the current

348 VOL. 10, NO. 4, JULY 1999

4. The displayed scenes were excerpted from three books by Martin Hand-

ford (Grolier Ltd., London).From Where’sWaldo?” (1987), we used theBeach,

theMuseum, theDepartment Store (withWaldo), andthe Fair; from FindWaldo

Now (1988), we used Once Upon a Saturday Morning (with Waldo) and The

Last Days of the Aztecs (with Waldo); and from The Giant Waldo Search

(1989), we used The Great Ball Game Players (with Waldo) and the Deep Sea

Divers.Additional information about the scenes is available from the authors.

Table 1. Difference in probe reaction time (in milliseconds) between targets presented at locationsoccupied by distractors and targets presented at new locations following serial and parallel search inrecent studies

Search Inferred

Study Serial Parallel inhibition of return

Klein (1988, Experiment 1) 39 7 32Klein (1988, Experiment 2) 62 16 46

Display maintainedTakeda and Yagi (in press, Experiment 2) 63 36 27Takeda and Yagi (in press, Experiment 3) 68 35 33Müller and von Mühlenen (1999, Experiment 2) 108 71 37

Display removedTakeda and Yagi (in press, Experiment 1) 54 49 5Müller and von Mühlenen (1999, Experiment 1) 42 39 3

Note. The data are from target-absent trials and are collapsed across set size (see Klein, 1988, for a justification).





gaze position became the center of an imaginary circle with a radius

equal to the distance between the current and penultimate (immedi-

ately preceding) fixation. Possible probe locations were centered on

the circumference of this circle, appearing equally often at the follow-

ing six angles relative to the previous fixation location: 0°, 60°, 120°,

180°, 240°, and 300°. Probe presentation was delayed if the calculat-

ed radius was less than 1° or would place any one of the possible

probes off the screen. If no suitable gaze position could be found with-

in 12 saccades, the trial was terminated without a warning beep. In

Experiment 2 (two-back condition), probe locations were determined

in the same manner except that the radius was based on the ante-

penultimate fixation (i.e., preceding the one used in Experiment 1; see

Fig. 3a).

A saccade was said to acquire the probe if the landing coordinates

of the saccade were within 1° of the probe’s center. All other fixationlocations were classified as misses. The primary dependent variable

was the SRT to acquire the probe when it was acquired within one sac-

cade.

RESULTS AND DISCUSSION

Probe Acquisition

Trials were excluded from this analysis if there was a blink (4.1%,

Experiment 1; 11.9%, Experiment 2) or a probe could not be delivered

(5.6%, Experiment 1; 20.4%, Experiment 2). Across the remaining tri-

als, probes were acquired in one saccade more frequently when the

scene was removed (63.1%) than when it remained present (44.6%),

F (1, 12) = 69.6, p < .001, a difference likely due to increased salience

of probes that were not superimposed on a complex scene. The reac-

tion times of these saccades provided the primary data for testing the

hypotheses.

Mean SRT for trials on which the probe was acquired in the first

saccade (see Fig. 4) were subjected to a 2 (one- vs. two-back) × 2

(scene removed vs. maintained) × 4 (angular distance5 from the previ-

ous fixation) mixed analysis of variance. There was a significant main

VOL. 10, NO. 4, JULY 1999 349

A

B1-back

2-back

3-back

Potential Probe Locationsin Experiment 1 (one back)

Gaze Position attime of probe

Saccade Path0°

-120°

180°

-60°

120°

2

3

60°

1

Fig. 3. Placement of probes (a) and method of analyzing the direction

of freely executed saccades as a function of the angular difference

between a saccade and preceding fixation locations (b). In (a), the last

three saccades prior to probe presentation are shown. The empty cir-

cle shows the location of gaze at the time of probe presentation, and

the solid circles show the six possible locations for the probe target in

Experiment 1. Only one probe location was selected for each trial.

Each of these six locations was used equally often, but for purposes of analysis, the locations were collapsed on the basis of the absolute dif-

ference in direction between the probe target and the penultimate fix-

ation location (marked 0°). The checkerboard-filled circle marks the

location of the antepenultimate fixation that was used to generate the

probe locations in Experiment 2. In (b), four saccades preceding the

delivery of the probe target are shown, along with the angular differ-

ence between the last saccade in this sequence and each of the three

preceding fixations.

5. For present purposes, the six different angles were collapsed into four

angular distances: 0°, ±60°, ±120°, and 180° (as shown in Fig. 3a).

Fig. 2. Sequence of displays in the experiments. The participants indi-

cated when they were ready while fixating the disk at the center of a

blank display (a). The search array (shown here as a brick-wall pat-

tern; see the text for a description) was then added (b). Removal of the

fixation disk was the signal to begin the search (c). After four or more

saccades (d), a probe stimulus (reappearance of the fixation disk) was

presented on an imaginary circle that was centered about the present

fixation and had a radius equal to the distance between the current and

penultimate (Experiment 1) or antepenultimate (Experiment 2) fixa-

tions. When the probe appeared, the search array either remained or

was removed (e). See the text and Figure 3 for further details.





effect of scene removal, F (1, 12) = 28.5, p < .001, reflecting longer

SRTs when the scene was removed (257.7 ms) than when it remained

present (209.9 ms) during probe presentation. Sensory or motor mech-

anisms could be responsible for this difference. As an example of the

former, the global transient associated with removal of the scene might

have masked the local transient associated with the onset of the probe

(as occurs in change blindness; see Simons & Levin, 1997, p. 263),

thus delaying its perception. Alternatively, removing the visual data

used to compute oculomotor parameters for the Waldo search might

have caused a refractory period for the programming of subsequent

saccades, until clearing and resetting of the visual-motor representa-

tions was completed. The results strongly favor this possibility: Sac-

cades that were made immediately after probe presentation but were

not directed to the probe showed the same cost (46.4 ms) of scene

removal as did saccades that immediately acquired the probe.

The main effect of angular distance was significant, F (3, 36) =8.03, p < .001, as was the predicted interaction between angular dis-

tance and scene removal, F (3, 36) = 8.15, p < .001. This pattern was

further qualified by a three-way interaction involving experiment, F (3,

36) = 3.299, p < .05. To determine whether the results supported the

predictions outlined earlier, we analyzed the two conditions (scene

removed and scene maintained) separately for the presence of IOR.

There were no significant effects or interactions (all F s < 1) when

the scene was removed: The time to find the target was unaffected by

its angular distance from the immediately preceding fixation (one-

back) or the fixation before that one (two-back). In contrast, when the

scene was maintained, the effect of angular distance was significant,

F (3, 36) = 16.24, p < .001, as was the interaction with experiment,F (3,

36) = 3.12, p < .05.

We expected that when the scene was maintained, the slowestSRTs would be to probes presented in the same location as a previous

fixation (0°), and that there would be a monotonic decrease in SRT

with increasing angular distance from this location. Precisely this pat-

tern was observed in the two-back condition; in the one-back condi-

tion, the pattern was similar except that SRTs to targets presented at

the immediately prior fixation (0°) were faster than expected. The two-

back data (which were collected to help address this unexpected find-

ing) suggest that one or more processes were operating in the one-back

condition to mask the inhibitory effect in the 0° location. The most

recently encoded region of the scene is likely to be the most accurate-

ly represented, so changes (e.g., probe presentation) in this region may

be more conspicuous than other changes. Alternatively, facilitation,

akin to that elicited in a peripheral cuing paradigm, might mask the

inhibition in this region. Although there are reasons to favor the con-spicuity account,6 whatever the explanation, the important point is that

in the two-back condition, when both processes would be less likely to

be operating, the data pattern obtained was precisely the pattern pre-

dicted by the proposal that IOR was operating in this task.

Saccades Prior to Probe Presentation

If IOR is elicited following each fixation, then the “freely” gener-

ated saccades made by our participants prior to the appearance of the

probe should show evidence of this inhibition. We explored this possi-

350 VOL. 10, NO. 4, JULY 1999

Fig. 4. Saccadic reaction time when the first posttarget saccade

acquired the probe target. Results are shown separately for Experiment

1 (a), with probes at the one-back location, and Experiment 2 (b), with

probes at the two-back location. Within-subjects 95% confidence

intervals, appropriate for comparing different angular distances from

the same curve, were generated according to Loftus and Masson

(1994) using the Distance × Subject MSE s from analyses of variance

done separately for the scene-maintained and scene-removed condi-

tions of each experiment.

6. First, the viability of the facilitation account depends on the spread of

inhibition exceeding the spread of facilitation, a relation that has not yet beendemonstrated. Second, if facilitation were operating, we ought to have seen evi-

dence of it in the scene-removed condition. Finally, we split SRTs to probe tar-

gets (in the scene-maintained condition) in the one-back study on the basis of

the preceding fixation duration. The analysis supports the conspicuity account

in that following longer-than-average fixations (which permit more encoding),

there was a 20-ms advantage for targets at the location of preceding fixation

compared with targets ±60° from this location; this advantage was not present

following shorter-than-average fixations. This is not what would be expected

from a facilitation account, because if facilitation is initiated when a location is

fixated, and begins to decay from this point, then measured IOR should be larg-

er following longer-than-average fixation durations.





bility by examining the angle between a preprobe saccade’s vector and

the vector connecting the launching point for that saccade with the

previous fixation for all preprobe saccades that would have allowed

the delivery of a probe (see Method section). The relative angles were

first sorted into six equal pie-shaped regions, with one centered on the

vector from the preceding fixation (0°) and the remaining five going

around an imaginary circle (as in Fig. 3a), and the six regions werethen collapsed as in the SRT analysis (see footnote 5). This process

was repeated (see Fig. 3b) using the fixation before the immediately

preceding fixation (two-back) and the fixation before that one (three-

back). As can be seen in Figure 5, there was a very strong tendency for

saccades made during search to be launched in directions away from

previous landing positions. The proportion of saccades whose direc-

tion would shift gaze in the direction of previous fixations was rela-

tively low, and there was, in each case, a significant effect of angular

distance in the form of a monotonic gradient—one-back: F (3, 36) =

41.1, p < .001; two-back: F (3, 36) = 25.2, p < .001; three-back: F (3,

36) = 13.18, p < .001.

Although it is theoretically appealing to assert that IOR causes this

directional bias in oculomotor search, it is also possible that the ocu-

lomotor bias causes IOR. Because oculomotor responses are likelyinitiated by a winner-take-all algorithm mediated by lateral inhibition

(and implemented in the superior colliculus), any asymmetric prepa-

ration would result in inhibition of the least-prepared saccades.

Although we believe that both behavioral and neurophysiological

studies may be able to distinguish between these alternatives,7 for pre-

sent purposes we need not be disturbed by the cause-effect ambiguity,

because either way the visual system is keeping track of regions of the

scene that need not be reexamined.

SUMMARY AND CONCLUSION

There are three main findings from this study of oculomotor

behavior during search of complex scenes. First and foremost, when

probe targets were presented in a scene during search, participants

were slower to find (saccade to) them when they were in the gener-

al region of preceding fixations than when they were in a new

region. This finding is precisely what is predicted by the proposal

that the function of IOR is to facilitate foraging (Klein, 1988; Pos-

ner & Cohen, 1984; Tipper et al., 1994). Moreover, the monotonic

function relating SRT to angular distance (particularly in Experiment

2) is consistent with the idea that there is a gradient of inhibition

around a previously attended (Maylor & Hockey, 1985) or fixated

region.

Second, this inhibition was not observed if the search array was

removed when the probe was delivered. This finding is consistent with

evidence showing that IOR is attached to objects in a scene (e.g.,

Abrams & Dobkin, 1994; Tipper et al., 1991, 1994) and also replicates

and extends recent demonstrations (Müller & von Mühlenen, 1999,

Experiments 1 and 2; Takeda & Yagi, in press) that IOR measured in

manual reaction time to probes following serial search depends on

maintenance of the search array (as predicted by Tipper et al., 1994).

Third, the freely executed saccades of participants prior to the pre-

sentation of the probe showed the same bias that was evident in the

time to acquire the probe; that is, each saccade was more likely to

repeat the previous direction than to reverse it. This is precisely what

one would expect if the IOR that was seen in the time to find the probe

was operating equivalently on the freely made saccades during search.

And it is precisely such freely made saccades during visual search of

a scene that ought to be influenced by inhibition serving as a foragingfacilitator.

REFERENCES

Abrams, R.A., & Dobkin, R.S. (1994). Inhibition of return: Effects of attentional cuing on

eye movement latencies. Journal of Experimental Psychology: Human Perception

and Performance, 20, 467–477.Abrams, R.A., & Pratt, J. (1996). Spatially diffuse inhibition affects multiple locations: A

reply to Tipper, Weaver, and Watson. Journal of Experimental Psychology: Human

Perception and Performance, 22, 1294–1298.

Cheal, M.L.,Chastain, G., & Lyon,D.R. (1998). Inhibition of return in identification tasks.

Visual Cognition, 5, 365–388.

Danziger, S., Kingstone, A., & Snyder, J. (1998). Inhibition of return to successively stim-

ulated locations in a sequential visual search paradigm. Journal of Experimental

Psychology: Human Perception and Performance, 24, 1467–1475.

Gibson, B.S., & Egeth, H. (1994). Inhibition and disinhibition of return: Evidence from

temporal order judgments. Perception & Psychophysics, 56, 669–680.

Handy, T.C., Jha,A.P., & Mangun, G.R. (1999). Promoting novelty in vision: Inhibition of

return modulates perceptual-level processing. Psychological Science, 10, 157–161.

Keele, S.W. (1973). Attention & human performance. Pacific Palisades, CA: Goodyear.

VOL. 10, NO. 4, JULY 1999 351

Fig. 5. Percentage of freely executed (saccadic) eye movements made

prior to probe presentation in various directions relative to the imme-diately previous fixation (one-back), the fixation prior to the immedi-

ately previous one (two-back), and the fixation before that one

(three-back) (see Fig. 3b).

Acknowledgments—The research described here was supported by a Nat-ural Sciences and Engineering Research Council of Canada CollaborativeProjects Grant (“Selection of Objects by the Primate Oculomotor System”)to R. Klein (principal investigator), D. Munoz, P. McMullen, and T.Trappenberg.

7. A behavioral approach we are pursuing using the same “Where’s

Waldo?” materials is to instruct the observer to look for something interesting

and remain fixated on it until a probe is detected or the trial ends. Under such

conditions, voluntary oculomotor preparation would be unwarranted, so if

probes delivered near previous fixations are inhibited, it would be reasonable

to assume that IOR precedes, and possibly causes, the asymmetric motor prepa-

ration observed here.





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Klein, R.M. (1988). Inhibitory tagging system facilitates visual search. Nature, 334,430–431.

Klein, R.M., Kingstone, A., & Pontefract, A. (1992). Orienting of visual attention. In K.Rayner (Ed.), Eye movements and visual cognition: Scene perception and reading(pp. 46–65). New York: Springer-Verlag.

Klein, R.M., Schmidt, W.C., & Müller, H.J. (1998). Disinhibition of return: Unnecessaryand unlikely. Perception & Psychophysics, 60, 862–872.

Klein, R.M., & Taylor, T.L. (1994). Categories of cognitive inhibition, with reference toattention. In D. Dagenbach & T.H. Carr (Eds.), Inhibitory processes in attention,

memory, and language (pp. 113–150). San Diego: Academic Press.Kwak, H., & Egeth, H. (1992). Consequences of allocating attention to locations and to

other attributes. Perception & Psychophysics, 51, 455–464.Loftus, G.R., & Masson, M.E.J. (1994). Using confidence intervals in within-subject

designs. Psychonomic Bulletin & Review, 1, 476–490.Lupiáñez, J., Milán, E.G., Tornay, F.J., Madrid, E., & Tudela, P. (1997). Does IOR occur

in discrimination tasks? Yes, it does, but later. Perception & Psychophysics, 59,1241–1254.

Maylor, E. (1985). Facilitatory and inhibitory components of orienting in visual space. InM.I. Posner & O.S.M. Marin (Eds.), Attention and performance XI (pp. 189–203).Hillsdale, NJ: Erlbaum.

Maylor, E., & Hockey, R. (1985). Inhibitory component of externally controlled covert ori-enting in visual space. Journal of Experimental Psychology: Human Perception and Performance, 11, 777–787.

Müller, H., & von Mühlenen, A. (1999). Probing distractor inhibition in visual search: Inhibition of return. Manuscript submitted for publication.

Pontefract,A.J.,& Klein,R.M. (1988). Assessing inhibition of returnwith simpleand choicereaction time. Unpublished manuscript, Dalhousie University, Halifax, Canada.

Posner, M.I. (1980). Orienting of attention. Quarterly Journal of Experimental Psycholo-

gy, 32, 3–25.Posner, M.I., & Cohen, Y. (1984). Components of visual orienting. In H. Bouma & D.

Bouwhuis (Eds.), Attention and performance X (pp. 531–556). London: Erlbaum.Pratt, J., & Abrams, R.A. (1995). Inhibition of return to successively cued spatial locations.

Journal of Experimental Psychology: Human Perception and Performance, 21,1343–1353.

Pratt, J., Kingstone, A., & Khoe, W. (1997). Inhibition of return in location- and identity-based choice decision tasks. Perception & Psychophysics, 59, 964–971.

Rafal, R.D., Calabresi, P.A., Brennan, C.W., & Sciolto, T.K. (1989). Saccade preparation

inhibits reorienting to recently attended locations. Journal of Experimental Psy-

chology: Human Perception and Performance, 15, 673–685.

Schmidt, W.C. (1996a). Inhibition of return is not detected using illusory line motion. Per-

ception & Psychophysics, 58, 883–898.

Schmidt, W.C. (1996b). ‘Inhibition of return’wi thout visual input. Neuropsychologia, 34,

943–952.

Simons, D.J., & Levin, D.T. (1997). Change blindness. Trends in Cognitive Sciences, 1,

261–267.

Snyder, J.J., & Kingstone, A. (in press). Inhibition of return and visual search: How many

separate loci are inhibited? Perception & Psychophysics.

Takeda, Y., & Yagi, A. (in press). Inhibitory tagging in visual search can be found if search

stimuli remain visible. Perception & Psychophysics.

Tanaka, T., & Shimojo, S. (1996). Location vs feature: Reaction time reveals dissociation

between two visual functions. Vision Research, 36, 2125–2140.

Taylor, T.L., & Klein, R.M. (1998a). Inhibition of return: Attentional and motor bases.

Manuscript submitted for publication.

Taylor, T.L., & Klein, R.M. (1998b). On the causes and effects of inhibition of return. Psy-

chonomic Bulletin & Review, 5, 625–643.

Terry, K.M., Valdes, L.A., & Neill, W.T. (1994). Does “inhibition of return” occur in dis-

crimination tasks? Perception & Psychophysics, 55, 279–286.

Tipper, S.P., Driver, J., & Weaver, B. (1991). Object-centred inhibition of return of visual

attention. The Quarterly Journal of Experimental Psychology, 43, 289–298.

Tipper, S.P., Weaver, B., Jerreat, L.M., & Burak, A.L. (1994). Object-based and environ-

ment-based inhibition of return of visual attention. Journal of Experimental Psy-

chology: Human Perception and Performance, 20, 478–499.

Tipper, S.P., Weaver, B., & Watson, F.L. (1996). Inhibition of return to successively cued

spatial locations: Commentary on Pratt and Abrams (1995). Journal of Experimen-tal Psychology: Human Perception and Performance, 22, 1289–1293.

Treisman,A.M., & Gelade, G. (1980). A feature-integration theory of attention. Cognitive

Psychology, 12, 97–136.

Wolfe, J.M., & Pokorny, C. (1990). Inhibitory tagging in visual search: A failure to repli-

cate. Perception & Psychophysics, 48, 357–362.

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