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Journal of Applied Research in Memory and Cognition 1 (2012) 73–79
Contents lists available at SciVerse ScienceDirect
Journal of Applied Research in Memory and Cognition
journa l homepage: www.e lsev ier .com/ locate / ja rmac
arget article
isruption of verbal-spatial serial memory by extraneous air-traffic speech�
ébastien Tremblaya,∗, Fabrice B.R. Parmentierb,c, Helen M. Hodgettsd,obert W. Hughesd,1, Dylan M. Jonesc,d
Université Laval, Québec, CanadaSchool of Psychology, University of the Balearic Islands, SpainSchool of Psychology, University of Western Australia, AustraliaCardiff University, Wales, UK
r t i c l e i n f o
rticle history:eceived 22 November 2011eceived in revised form 27 March 2012ccepted 1 April 2012vailable online 11 April 2012
a b s t r a c t
The disruptive impact of task-extraneous air-traffic radio speech on a task involving the serial-recallof combined verbal and spatial stimuli (7 letters and their locations) that were broadly analogous toinformation about aircraft callsigns and movements was examined. Regardless of the dimension to berecalled (identity or spatial location), accuracy was significantly disrupted by the air-traffic speech. Prior
eywords:hort-term memoryackground speechinding
knowledge as to which dimension to recall did not affect accuracy and did not interact with the disruptiveeffect of air-traffic speech, but did extend the time to initiate a response to the first item. The results arediscussed with reference to theories of the irrelevant sound effect and stimulus-dimension binding inshort-term memory. The vulnerability of cognitive processing related to air-traffic management andsimilar work environments is also discussed.
pplie
ir-traffic control © 2012 Society of A. Introduction
Memory for spatial and verbal sequential information is criti-al to the operations of both air-traffic controllers and pilots (e.g.,ronlund, Ohrt, Dougherty, Perry, & Manning, 1998; Nicholls et al.,007) but a substantial body of evidence suggests that the presencef background speech—intrinsic to the flight environment—couldompromise such capacities appreciably. Despite its essential con-ribution to very many cognitive activities (Marshuetz, 2005), theapacity to process and maintain serial order information is highlyulnerable to disruption by the mere presence of backgroundound. Even at low intensities, certain classes of background sound,uch as narrative speech—which participants are instructed tognore—can disrupt recall of a sequence of verbal items by some
0% to 50% (e.g., Ellermeier & Zimmer, 1997; Tremblay & Jones,998). The disruption is not only marked but also very reliableinternal consistency of .85; see Ellermeier & Zimmer, 1997) and� This research was supported by a research grant from the Spanish Ministry ofcience and Innovation (PSI2009-08427) to F. Parmentier, a research grant from theustralian Research Council (DP0773836) to M. Maybery, F. Parmentier and D. Jones,nd funds from a EUROCONTROL (Brussels, Belgium) CARE Innovative Action.∗ Corresponding author at: School of Psychology, 2325 rue des Bibliothèques,niversité Laval, Québec, QC G1V0A6, Canada, Tel.: +1 418 656 2131x2886;
ax: +1 418 656 3343.E-mail address: [email protected] (S. Tremblay).
1 Present address: Department of Psychology, Royal Holloway, University of Lon-on, UK.
211-3681/$ – see front matter © 2012 Society of Applied Research in Memory and Cognttp://dx.doi.org/10.1016/j.jarmac.2012.04.004
d Research in Memory and Cognition. Published by Elsevier Inc. All rightsreserved.
stable both within (Jones, Macken, & Mosdell, 1997) and betweentesting sessions (Hellbrück, Kuwano, & Namba, 1996). The currentstudy investigates whether air-traffic radio speech (akin to the so-called ‘partyline’) disrupts verbal and spatial memory; furthermore,it is the first to examine whether the number of sequence dimen-sions that must be retained (i.e., verbal or spatial information, orboth) interacts with any impairment by the speech.
1.1. Air-traffic control, short-term memory, and irrelevant speech
The management of air traffic involves short-term memory forboth verbal and spatial information and also entails a high degreeof exposure to task-extraneous sound. The air-traffic controllermust serially track aircraft on the radar, updating his/her mentalmodel to take into account aircraft entering and departing the flightspace, often in the presence of distracting background speech. Forpilots, background sound comprises not only colleagues’ conver-sations and direct air-traffic control (ATC) communications, butalso shared radio traffic between ATC and other aircraft in thevicinity. Pilots claim that this ‘party-line’ is important for main-taining situation awareness (see Endsley, 1995) by helping themto build up a mental representation of the situation (Hodgettset al., 2005; Pritchett & Hansman, 1993); however, the partylinehas been shown to increase workload and decrease performance
(Boehm-Davis, Gee, Baker, & Medina-Mora, 2010; Hoogeboom,Joose, Hodgetts, Straussberger, & Schaefer, 2004). Pilots’ mentalrepresentation of other aircraft positions is achieved by encodingtogether verbal identity (call-sign) and inferred spatial positionition. Published by Elsevier Inc. All rights reserved.
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4 S. Tremblay et al. / Journal of Applied Rese
Pope, Houghton, Jones, Parmentier, & Farmer, 2002). For con-rollers, the radar screen provides an external aid to help supporthis mental picture, but still altitude information must be boundith lateral position to create a three-dimensional spatial represen-
ation (Wickens, Mavor, & McGee, 1997). Spatial as well as verbalask elements are vulnerable to the effects of extraneous speech.or example, spatial awareness of the movements of aircraft cane impaired by other subsequent verbal information (Nichollst al., 2007). Similarly, background speech impairs a spatial conflictetection task, contrary to the idea of a modular cognitive systemPope, Houghton, Jones, & Parmentier, 2003). Given the importancef short-term memory for flight task activities (Gronlund et al.,998; Shorrock, 2005) and the peculiar vulnerability of short-termemory to disruption by background sound, it is critical to evaluate
he effect that partyline speech may have on such flight-task per-ormance. In the present article, we begin to address this neglectedssue through a novel extension of laboratory work on the effectsf irrelevant sound on short-term memory performance.
A typical irrelevant-sound experiment requires participantso recall in strict serial-order seven sequential, visually pre-ented verbal items, with the key finding being that backgroundound substantially impairs serial recall relative to quiet (for aeview, see Jones, Hughes, & Macken, 2010). A leading theoreti-al account of this phenomenon supposes that the disruption isue to interference-by-process: The presence of identifiable acous-ic changes in the sound (the changing-state effect; Jones, Madden, &
iles, 1992; Tremblay & Jones, 1998) results in the obligatory seri-tion (or ordering) of the sound’s changing elements which in turnonflicts with the similar but deliberate process of seriating (or seri-lly rehearsing) the to-be-remembered sequence (Jones, Beaman,Macken, 1996). Thus, in contrast to popular modular conceptions
f STM (e.g., Baddeley, 1990) and similar concepts of modality-ased pools of cognitive resources often found in the engineeringsychology literature (e.g., Wickens, 1992), STM is construed onhe non-modular account as a unitary workspace where the pro-essing of relevant and irrelevant streams can clash irrespective ofheir modality source (e.g., visual, auditory) and representationalode (e.g., verbal, spatial) so long as they are subject to similar pro-esses, for example, the processing of order information (BeamanJones, 1997; Jones & Macken, 1993) or the extracting of semantic
nformation (Marsh, Hughes, & Jones, 2009).
.2. Binding in STM and interference-transfer
Most serial-memory studies require participants to retain therder of a single attribute of the stimuli, usually their verbal identitye.g., Jones et al., 1992; Salamé & Baddeley, 1989), or occasion-lly their spatial location (e.g., Jones, Farrand, Stuart, & Morris,995; Tremblay & Macken, 2001). However, stimuli are not uni-imensional and numerous tasks—such as that of the air-trafficontroller—involve integrating information pertaining to differ-nt dimensions (e.g., verbal and spatial) of a stimulus. Indeed, anncreasing number of studies have begun to define the capacityf STM in terms of integrated objects and to report evidence ofinding between, for example, verbal and spatial features (e.g.,rabhakaran, Narayanan, Zhao, & Gabrielli, 2000; Wu, Chen, Li,an, & Zhang, 2007). With the proposition of binding in STM comeuestions regarding the effect of interference, and whether effectsn such integrated objects can also be accommodated within annterference-by-process approach.
Historically, STM research has focused on the recall of eithererbal or spatial information (not dual-feature recall) thus prevent-
ng the detection of potential synergies between such dimensions,nd bringing into question the generalizability of existing theo-ies of interference to integrated representations such as thoseikely to be involved in flight-task performance. Recent evidencen Memory and Cognition 1 (2012) 73–79
suggests that dual-feature stimuli, when encoded as integratedobjects, can lead to a transfer of the interference typically observedfor one constituent feature to another. For example, a manipula-tion of the phonological similarity of consonants presented visuallyat different spatial locations showed that participants’ memoryfor the spatial locations was reduced when the consonants werephonologically similar (Guérard, Tremblay, & Saint-Aubin, 2009).Remarkably, the effect was observed regardless of whether or notparticipants were cued as to which feature would be tested (loca-tions or consonants), suggesting that the integration of verbal andspatial information is at least partly automatic upon presentationof dual-feature stimuli (although see Elsley & Parmentier, 2009,regarding some role of attention in cross-modal binding). Furtherevidence of cross-modal interference through binding comes froma recognition study of consonants (identity, location, or both):When features were encoded as integrated objects, articulatorysuppression even impaired recognition of new location probeswhich could be rejected solely on the basis of location, a spatialrather than verbal judgment (Morey, 2009). These studies suggestthat integration may bestow on individual features a propensityto interference typically associated with the other feature (i.e.,interference-transfer).
1.3. Present study
The current study investigated the impact on short-term mem-ory of background air-traffic speech. In particular, we examined therole of focal-task encoding requirements—whether verbal or spa-tial dimensions had to be retained or whether both dimensionshad to be retained—to examine whether one or both dimen-sions are impaired by air-traffic speech, either independently orthrough interference-transfer. Our approach sits on a particu-lar point within a Cognitive System Engineering framework (e.g.,Rasmussen, Pejtersen, & Goodstein, 1994). In this framework,applied cognitive research can be decomposed into four key steps:cognitive processes testing (initial laboratory experiments), func-tions testing (laboratory methods within a basic context); functionstesting within complex simulations; and behavioral observa-tion within an experimental operational setting. This continuumreflects research development from defining the problem-space totesting solutions, each stage requiring a different balance betweenecological validity and experimental control. Laboratory studiesmay seem far removed from the real world but allow for theinvestigation of specific factors; field studies capture the naturalistcontext of situations but the lack of empirical precision preventsthe formulation of any causal claims and limits the ability to gener-alize conclusions (Parasuraman, Sheridan, & Wickens, 2008). Giventhe relatively new concepts under investigation and a need tofirst define the problem-space, the current study uses cognitiveprocesses-centered testing in order to first establish basic effectsof verbal and spatial binding and their susceptibility to disruptionfrom background speech. Our intention therefore was not to sim-ulate the ATC/pilot setting in any detail but to design a task thatwould allow us to examine some of the key cognitive processesinvolved in that setting, namely keeping track of the temporal orderof incoming verbal and spatial information.
Participants were to recall in serial-order, either the identity(symbolizing call-signs) or location (symbolizing aircraft position)of seven sequentially presented consonants whilst in the pres-ence of air-traffic radio speech or quiet. Participants were eitherprovided with prior knowledge (PK) of which dimension (verbalor spatial) was to be recalled on a given trial (‘PK-yes’), or the
recall-dimension cue was delayed until after stimulus presenta-tion (‘PK-no’). Because in the ‘PK-yes’ condition no benefit wouldbe gained from maintaining both the identities and positions ofthe seven stimuli, it was assumed that participants would code the
arch in Memory and Cognition 1 (2012) 73–79 75
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Fig. 1. Illustration of the task at the time of recall. Consonants presented sequen-
S. Tremblay et al. / Journal of Applied Rese
timuli in terms of either their identities or positions, but not both.n the PK-no condition, however, it seems likely that participants
ould have to represent the identity and position of each stimu-us either as two separate objects in memory, or represent eachtimulus such that both identity and position is bound into a singlebject.
Based on the non-modular conception of STM embodied withinhe interference-by-process framework, irrelevant speech wasxpected to disrupt both spatial and verbal recall (see Jones et al.,995). Based on theories of binding, we would expect universal
nterference in the PK-no condition due to a transfer of irrelevantpeech interference in the spatial task when verbal and spatialeatures are bound. Or, if participants integrate features automati-ally, regardless of instructions, interference-transfer could impairoth verbal and spatial memory in both PK conditions. If verbalnd spatial features are integrated automatically at presentation,e would expect overall equivalent performance in both PK con-itions; however if features are not fully integrated into objects,oorer performance should be observed in the PK-no condition ashis would entail a higher memory load.
Unlike most past studies of serial memory, we also measuredesponse times as well as recall accuracy. RT measures are relativelyarely used (e.g., Anderson, Bothell, Lebiere, & Matessa, 1998), buthere is evidence that RT can be useful in elucidating the mech-nisms at play in serial-recall tasks (e.g., Maybery, Parmentier, &ones, 2002).
. Method
.1. Participants
Thirty-six Cardiff University psychology undergraduates partic-pated in the experiment for course credit. All reported normal ororrected-to-normal vision and normal hearing.
.2. Apparatus/materials
The visual stimuli were generated using Visual Basic 6 andresented on a PC. For each trial the to-be-remembered visualequence consisted of seven randomly selected consonantsexcluding W and Y) each placed in a square (40 × 40 pixels; screenet to 800 × 600 pixels). The consonants (black; Arial bold font; 30ixels) were presented sequentially at the rate of 1 s−1 with no
nter-stimulus interval, and could appear at one of the fixed set of9 locations chosen randomly but with the constraint that no twotimuli would spatially ‘overlap’ each other.
For the irrelevant speech trials, radio speech signals wereecorded and edited from live ATC communications from Chicago’Hare Ground Control over the internet (Cyberair Airpark, 2000).2
en 18 s samples were produced, each edited to remove unin-elligible segments and any silent periods beyond 500 ms. Theounds were approved by Eurocontrol Subject Matter ExpertsSME) as being highly representative of ATC conversations. Therrelevant messages were presented stereophonically over head-hones at approximately 65 dB(A), from the onset of the firsto-be-remembered item until the end of the retention interval.
.3. Design
A four-factor (7 × 2 × 2 × 2) mixed-design was used withhree repeated-measures factors: serial position (seven levels),
2 We used these recordings as they had produced clear irrelevant speech effectsn another study on distraction and air traffic control we happened to be conductingt the time we carried out the present experiment.
tially are re-presented simultaneously to participants with a cue at the bottom ofthe screen indicating what aspect of the stimuli to recall (locations in this example).
dimension (verbal or spatial), and background condition (speechand quiet) and one between-subjects factor (PK). For both PK con-ditions, 40 experimental trials comprised 10 trials from each ofthe dimension × background condition (2 × 2) configurations (ran-domly selected for each given trial).
2.4. Procedure
The 36 participants were randomly split into two groups (18in ‘PK-yes’ and 18 in the ‘PK-no’ condition). Each participant wastested individually in a sound-attenuated testing booth. They weregiven instructions regarding the serial-recall task, and told to ignoreany sound as they would not be tested on any aspect of it. Each trialwas structured as follows: Clicking the START button initiated thetrial. Following a delay of 500 ms the word CALLSIGNS or LOCA-TIONS appeared at the bottom of the screen for 2000 ms to indicatewhich dimension of the ensuing stimuli was to be recalled, i.e., theidentity or the locations of the consonants. In the ‘PK-no’ conditiona ####### pattern appeared instead. After a delay of 1000 ms,the first visual stimulus was presented. A retention interval of 10 sfollowed the last item, during which participants were expectedto continue sub-vocally rehearsing the to-be-remembered infor-mation. Such a retention interval is typical of irrelevant-soundeffect paradigms, and also ecologically valid given the multitaskingaspect of ATC which can entail delays between aircraft monitoringand taking subsequent action. All 7 presented stimuli then reap-peared simultaneously albeit with the 7 letters rearranged amongstthe 7 locations (Fig. 1). At this point also, in the ‘PK-no’ condi-tion, the word CALLSIGNS or LOCATIONS appeared. Participantsused the mouse to click on the appropriate items in the orderthey believed they had originally been presented. The color of anitem changed once chosen and responses could not be repeatedor altered. Participants were instructed to recall each sequence asquickly and accurately as possible. Four practice trials preceded theexperiment proper, one for each of the dimension × backgroundsound factor combinations. The experiment took approximately25 min.
3. Results
3.1. Accuracy
For a measure of recall accuracy the strict serial-recall crite-rion was adopted, i.e., recalled items were scored as correct only
76 S. Tremblay et al. / Journal of Applied Research in Memory and Cognition 1 (2012) 73–79
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ig. 2. Percentage of correct serial-recall for the verbal and spatial tasks in the extonditions.
f they corresponded exactly to the position in which they hadeen presented. The average percentage of correct responses wasrst analyzed in a 2 (PK: yes, no) × 2 (task: spatial, verbal) × 2background condition: speech, quiet) × 7 (serial position) ANOVA.owever, since the PK condition did not affect performance signif-
cantly (p > .20, �p2 = .07) nor interact with any other variable (all
nteractions with PK, p > .20, �p2 < .02), a simpler analysis excluding
K is reported below.Fig. 2 shows the mean percentage of correct recall in the ver-
al and spatial variants of the task and under each of the twoackground conditions. A 2 × 2 × 7 ANOVA revealed that perfor-ance was superior in the verbal task compared to the spatial,
(1, 35) = 30.60, MSE = 1485.68, p < .001, �p2 = .47. Irrelevant speech
ed to a significant decrease in recall performance, F(1, 35) = 41.21,SE = 575.59, p < .001, �p
2 = .54. The effect of serial position waslso significant, F(6, 210) = 48.24, MSE = 260.19, p < .001, �p
2 = .58.he overall effect of irrelevant speech was similar for both tasks, asndicated by the absence of an interaction between task and back-round condition, F(1, 35) = 2.89, MSE = 453.84, p = .10, �p
2 = .08.urther contrasts confirmed that the effect of speech was significantoth in the verbal task, F(1, 35) = 31.50, MSE = 574.40, p < .001, and
n the spatial task, F(1, 35) = 15.25, MSE = 455.03, p < .001. Similarhapes of the serial position function were observed for the verbalnd spatial task, as indicated by the absence of a task by serial posi-ion interaction, F(6, 210) = 1.69, MSE = 184.02, p = .13, �p
2 = .05. Theffect of speech was stronger in middle-list serial positions than atarly or late serial positions, as corroborated by a significant back-round condition by serial position interaction, F(6, 210) = 6.33,SE = 161.72, p < .001, �p
2 = .15. However, this effect was accentu-ted in the spatial task compared to the verbal, and complicated byhe relatively small recency effect observed in the spatial quiet con-ition compared to the other conditions and the somewhat more
rregular pattern in the spatial conditions, as indicated by the sig-ificant triple interaction, F(6, 210) = 3.26, MSE = 161.10, p < .001,p
2 = .09. Further analyses confirmed that the effect of speech wastronger in the middle-list positions by comparing the speechnd quiet conditions in terms of the quadratic trend of the serial
osition curve. A stronger curvature was observed in the speechondition than in the quiet condition for both the verbal task,(1, 35) = 13.46, MSE = 147.90, p < .001, and the spatial task, F(1,5) = 6.73, MSE = 149.87, p = .01.us speech and quiet conditions, for the PK-yes (left panel) and PL-no (right panel)
3.2. Response times
Median RTs for correctly recalled items were measured from thepresentation of the response screen to the first response (‘initiationtime’) and from response-to-response from then on. Generally, thepattern can be described as follows: RTs were longer for the firstitem than for all subsequent items, among which little variationwas observed except for a trend for a slight reduction across serialpositions 2–7. As evident in Fig. 3, which shows the median RT inthe verbal and spatial tasks for correct responses across positions1–7 in the two PK conditions and in the two background conditions,differences between conditions mainly occurred at serial position1. We therefore confine the analysis to these initiation times.
3.3. Initiation times
A 2 (PK: yes, no) × 2 (task: verbal, spatial) × 2 (backgroundcondition: speech, quiet) ANOVA was conducted on the averagemedian RT for correct responses at serial position 1 as a mea-sure of the cost of initiating the response sequence. Initiation timewas significantly longer in the ‘PK-no’ condition than the ‘PK-yes’,F(1, 34) = 9.37, MSE = 1666613, p = .004, �p
2 = .22; longer in the ver-bal task than the spatial, F(1, 34) = 13.13, MSE = 271834, p < .001,�p
2 = .28; and marginally longer in the speech condition than thequiet condition, F(1, 34) = 3.82, MSE = 185365, p = .06, �p
2 = .10. Allother effects and interactions were non-significant (p > .1).
4. Discussion
The present study showed that order memory for both verbaland spatial information was disrupted by irrelevant speech. Priorknowledge of the relevant aspect of the stimuli (identity versuslocation information) did not affect accuracy and did not signifi-cantly interact with the detrimental impact of irrelevant speech,but did decrease initiation time. That spatial as well as verbalrecall was impaired by the background speech is in line with theinterference-by-process account (e.g., Jones et al., 2010) which
posits that the similarity of content of two concurrent streams ofinformation is less important than the similarity of the processbeing applied to that content (e.g., between the deliberate seriationof the to-be-remembered information and the obligatory seriation
S. Tremblay et al. / Journal of Applied Research in Memory and Cognition 1 (2012) 73–79 77
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ig. 3. Average median response times for correctly recalled items in the ‘Before’ (Panel) and spatial (right panel) tasks.
f the to-be-ignored changing-state sound). Thus, both verbal andpatial tasks may be impaired by irrelevant verbal material—andhis regardless also of the sensory modality through which they areelivered—because they involve the same fundamental process.
Feature-binding provides an alternative means of framing theresent results. Stimuli comprising a combination of features mayndergo some automatic integration (e.g., Allen, Baddeley, & Hitch,006; Gajewski & Brockmole, 2006; Treisman & Zhang, 2006) andhereby render spatial locations as sensitive to irrelevant soundnterference as verbal to-be-remembered items. This interference-ransfer from one feature to another through binding is in line withrevious work reporting a similar phenomenon with phonologi-al similarity (Guérard, Jalbert, Neath, Surprenant, & Bireta, 2009)nd articulatory suppression (Morey, 2009). The present findingsxtend this for the first time to the irrelevant sound effect using aask involving serial-recall of jointly encoded consonants or loca-ions.
The absence of a main effect of PK suggests that the mainte-ance of both verbal and spatial information is relatively automaticnd/or effortless. Despite instructions, both task dimensions mayave been retained automatically in the PK-yes condition (seeuérard, Jalbert, et al., 2009), and as such the two conditionsere equivalent. Or, if both verbal and spatial information wasaintained only in the PK-no condition, it would seem that retain-
ng the additional dimension was fairly effortless and at no costo subsequent recall performance. Participants may have main-ained the positions and identities of the stimuli as a single streamn which location and identity information were combined. Thists with the proposition that the maintenance of bound objectsay not require attentional resources beyond that necessary toaintain its constituent features (e.g., Delvenne, Cleeremans, &
aloyaux, 2010; Gajewski & Brockmole, 2006). There is strong evi-ence that organizing independent stimuli or stimulus features intosingle object or meaningful ‘chunk’ increases the net amount
f information maintainable in STM; furthermore, the capacityimit of STM is best defined in terms of objects rather than indi-
idual features (Cowan, 2001; Delvenne & Bruyer, 2004; LuckVogel, 1997; Miller, 1956), in line with Duncan’s (1984; seelso Kahneman, Treisman, & Gibbs, 1992) concept of object-basedttention.
) and ‘After’ (PK-no) conditions, for speech and quiet conditions, in the verbal (left
If participants integrate stimulus dimensions, one might expectsome sort of filtering or decomposition process at the time of recallin order to extract the relevant information from the object rep-resentation (particularly since the spatial configuration of letterswas different at presentation and recall). In effect, the sum must bedecomposed into its constituent elements before one of these ele-ments can be retrieved and produced. It could be expected thatsuch a process would slow recall, either at each serial position(repeated decomposition process), or as a one-off cost before thefirst response is produced (one-off decomposition). Although someof the initiation cost evident in the ‘PK-no’ condition may have sim-ply reflected the time to read the cue, it is possible that some ofthis cost also may have reflected a one-off decomposition process.Moreover, there was no evidence of a repeated decomposition pro-cess given that there was no RT cost associated with the ‘PK-no’condition at serial positions 2–7 (see Goschke, 2000; Monsell, 2003,for evidence of reconfiguration time costs).
4.1. Practical applications
The practical implications of our results are clear: The presenceof extraneous speech, even if irrelevant and to-be-ignored, reducescognitive performance in a task requiring recall of verbal or spatialinformation in serial-order. Such effects contradict the modular,resource-based, view that has dominated research in aviation psy-chology which focuses on the problems of resource-competitionwhen stimuli share the same modality or code (Wickens, 1992).The current findings suggest the possibility of cross-modal interfer-ence through feature-binding, whereby an automatic integrationof features blurs the proposed verbal–spatial boundary so that ver-bal stimuli disrupt spatial recall. We suggest that risk assessmentswithin a demanding ATC setting should consider the possibility thatthe handling of information combining verbal and spatial infor-mation may expose operators to interference effects previouslythought to operate more within same-modality classes of stimuli.
We also suggest that similarity of content (e.g., modality or code)
may be less important than similarity of process (e.g., processingof order information) in determining interference, and this shouldbe taken into consideration with regard to aviation tasks. Ordermemory and the encoding of stimuli comprising multiple features
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8 S. Tremblay et al. / Journal of Applied Rese
re key functions of human STM (e.g., Baddeley, 2000; Lashley,951), and the task of an air-traffic controller specifically. For exam-le, serial processing is implicated in ordering heading changes tovoid conflicts, marking flight strips after an altitude change, orven mentally simulating sequences of potential consequences oflanned actions. Ample evidence indicates that ATC performance
s related to the degree of situation awareness (e.g., Durso et al.,998; Endsley & Rodgers, 1998), and that maintaining situationwareness for air-traffic controllers (and pilots) is reliant upon STMor both the position and identity of aircraft (e.g., Banbury, Croft,
acken, & Jones, 2004). In the context of air-traffic management,rrelevant speech may disrupt the operation of re-organizing flightaper strips in a new order, which involves prospective memoryor the new order and sequential motor activity. Guidelines to air-raffic controllers may therefore need to specify precautions suchs to avoid engaging in radio-communication while reorganizingaper strips or processing visual information from the radar dis-lay (e.g., arrangement of aircraft in a circuit). Because controllingir-traffic is a dynamic complex task in which continuously chang-ng information must be processed, the temporal sequencing ofognitive activities required in a particular situation is of centralmportance.
Of course, air-traffic controllers engage in other tasks—such asisual search—that do not require serial processing and for whiche would not expect to see the same impairment as those tasks
nvolving seriation. However, it is possible that background speechay still affect task performance (e.g., increasing the time it takes
o identify a specific aircraft among others) due to a more gen-ral auditory attentional capture process (e.g., Hughes, Vachon, &ones, 2005; Parmentier, 2008). Such capture occurs typically whenhe background sound deviates unexpectedly in some way fromhe prevailing auditory context (e.g., a female voice following sus-ained exposure to a male voice; Hughes, Vachon, & Jones, 2007).ndeed, some theories of the irrelevant-sound effect posit that theetrimental impact of changing-state irrelevant sound—as well asnexpected deviant sounds—may be driven by attentional capturee.g., Chein & Fiez, 2010; Cowan, 1995; Elliott, 2002). However, aelatively large body of evidence now indicates otherwise (for aecent review, see Hughes et al., 2011). Nevertheless, we cannotule out some role for attentional capture by unexpected changesithin our air-traffic speech samples despite the fact that we took
are to edit out highly abrupt changes. Moreover, actual air-trafficpeech is likely to involve periods of continuous changing-stateound interspersed with, for example, the unpredictable onset ofpeech following a silent period or the onset of a new voice. Thus,hereas we would suggest that most of the disruptive effect wit-essed in the present study was driven by interference-by-process,
t seems likely that the air-traffic controller would be susceptible towo forms of distraction: interference-by-process and attentionalapture.
The present results add to theoretical developments by show-ng that sequences are dealt with in memory by processes that actndiscriminately on visual and auditory sources of information andlso operate across the distinction often made between verbal andpatial domains. The present study also extends this view to multi-imensional stimuli and suggests that the interference created byxtraneous speech applies irrespective of whether participants areree to focus on a particular dimension of these stimuli on the basisf prior knowledge, or must maintain more than one dimensiononcurrently.
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