interaction between endogenous and exogenous orienting in crossmodal attention

Scandinavian Journal of Psychology, 2012, 53, 303–308 DOI: 10.1111/j.1467-9450.2012.00957.x

Cognition and Neurosciences

Interaction between endogenous and exogenous orienting in crossmodal

attention

XIAOXI CHEN,1 QI CHEN,2 DINGGUO GAO1 and ZHENZHU YUE1

1Department of Psychology, Sun Yat-sen University, China2Center for Studies of Psychological Application and Department of Psychology, South China Normal University, China

Chen, X., Chen, Q., Gao, D. & Yue, Z. (2012). Interaction between endogenous and exogenous orienting in crossmodal attention. Scandinavian Journal ofPsychology 53, 303–308.

Using a cue-target paradigm, we investigated the interaction between endogenous and exogenous orienting in cross-modal attention. A peripheral (exoge-nous) cue was presented after a central (endogenous) cue with a variable time interval. The endogenous and exogenous cues were presented in one sensorymodality (auditory in Experiment 1 and visual in Experiment 2) whereas the target was presented in another modality. Both experiments showed a signifi-cant endogenous cuing effect (longer reaction times in the invalid condition than in the valid condition). However, exogenous cuing produced a facilitatoryeffect in both experiments in response to the target when endogenous cuing was valid, but it elicited a facilitatory effect in Experiment 1 and an inhibitoryeffect in Experiment 2 when endogenous cuing was invalid. These findings indicate that endogenous and exogenous cuing can co-operate in orientingattention to the crossmodal target. Moreover, the interaction between endogenous and exogenous orienting of attention is modulated by the modalitybetween the cue and the target.

Key words: Endogenous orienting, exogenous orienting, crossmodal, spatial attention, cuing effect.

Zhenzhu Yue, Department of Psychology, Sun Yat-sen University, 510275 Guangzhou, P.R. China. Tel: +86-20-84114266; fax: +86-20-84114266;e-mail: [email protected]

INTRODUCTION

Covert attention (i.e., without eye movements) to a particularevent around us is regarded as the result of the cooperationbetween endogenous (voluntary) and exogenous (reflexive) atten-tional orienting mechanisms (Mondor & Amirault, 1998; Santan-gelo & Spence, 2008). Endogenous orienting is commonlytriggered by an arrow presented at the location of fixation, inwhich the arrow predicts the target location in most of the trials.Exogenous orienting can be triggered by a salient sensory event atthe peripheral field, in which the abrupt onset has no prediction tothe location of a target. During spatial orienting of visualattention, some researchers have suggested that these two kinds oforienting may involve separate attention mechanisms, butshare the same attention resource (Berger, Henik & Rafal, 2005;Mueller & Humphreys, 1991; Santangelo & Spence, 2008). More-over, the interaction between these two orienting mechanisms isobserved in both directions: voluntary on reflexive and reflexiveon voluntary (Berger et al., 2005; Mueller & Humphreys, 1991;Mueller & Rabbitt, 1989; Theeuwes, 1991).Recent studies have investigated the relationship between them

in the multisensory circumstance, besides the interaction betweenthe endogenous and the exogenous systems in the visual modality(Koelewijn, Bronkhorst & Theeuwes, 2009; Mazza, Turatto,Rossi & Umilta, 2007; Santangelo, Olivetti Belardinelli, Spence& Macaluso, 2009; Santangelo & Spence, 2007). Adopting a dou-ble-cue target paradigm, in which a target was preceded by endog-enous and exogenous cues, researchers explored the interactionbetween the endogenous and the exogenous cues when they werepresented crossmodally (Koelewijn et al., 2009; Santangelo et al.,2009). For example, Koelewijn et al. explored whether an endog-enous visual cue could suppress the auditory exogenous orienting

� 2012 The Authors.Scandinavian Journal of Psychology � 2012 The Scandinavian PsychologicalRoad, Oxford OX4 2DQ, UK and 350 Main Street, Malden, MA 02148, USA

to a visual target. A central arrow indicated the possible side of avisual target and an irrelevant peripheral auditory cue (whitenoise) was inserted between the visual endogenous cue and thevisual target. The exogenous cue came either from the left or rightloudspeaker and was valid or invalid with respect to the locationof a target, or it was neutral and came from both loudspeakers atthe same time. Participants reported the elevation of the visual tar-get regardless of visual hemifields. Their results showed thatalthough the validity of endogenous cue was 100%, the auditoryexogenous cuing had a significant effect on the reaction times,with shorter reaction time in the valid condition than in the invalidcondition. The exogenous orienting attention was not suppressedby endogenous engagement, indicating the automatic manner ofthe exogenous attention in the multisensory settings (Koelewijnet al., 2009).Moreover, at the neural level, a recent functional magnetic reso-

nance imaging (fMRI) study by Santangelo et al. (2009) providedthe initial neural evidence that the task-irrelevant exogenous cuescould interact with endogenous processing. In their experiment,task-irrelevant non-predictive auditory stimuli were presented inthe time interval between the visual endogenous cue and thevisual target, and participants were required to discriminate thevisual target in the left or right hemifield. They observed neuroan-atomical dissociation between the endogenous and exogenous ori-enting systems, that is, the activation of the temporo-parietaljunction (TPJ) and inferior frontal gyrus (IFG) was involved withthe endogenous attention, while the activation of the superior pari-etal gyrus (SPG) was associated with the exogenous attention.However, the imaging data also showed that two types of cuesinteracted and jointly affected the activation of the TPJ and SPG,supporting that the task-irrelevant exogenous cue could interactwith the endogenous processing.

Associations. Published by Blackwell Publishing Ltd., 9600 Garsington. ISSN 0036-5564.

Fi ti 500Fixation 500ms

Endogenous cue (High tone, Low tone) 100mstone,

SOA 200, 500, 800ms

Exogenous cue (White noise) 100ms

304 X. Chen et al. Scand J Psychol 53 (2012)

In the above studies, researchers manipulated the modalities ofboth cues and targets on how a crossmodal exogenous cue inter-acted with the intramodal ongoing endogenous processing in thevisual or auditory modality, that is, the modality of the endoge-nous cue was the same as the modality of the target, while themodality of the exogenous cue was different from that of thetarget. Therefore, the exogenous orienting of spatial attention wasnot suppressed by endogenous attention control, given that themodality of the exogenous cue was different from those of theendogenous cue and the target (Koelewijn et al., 2009; Mazzaet al., 2007; Santangelo et al., 2009; van der Lubbe & Postma,2005). However, no studies have as yet examined how these twoorienting systems interacted for the control of attention when theydirected attention to a crossmodal target.The present study aimed to investigate the interaction between

endogenous and exogenous attention orienting to a crossmodaltarget. Instead of presenting the endogenous and exogenous cuesfrom different modalities, both endogenous and exogenous cueswere presented in the same modality which differed from themodality of target. An exogenous cue was presented between anendogenous cue and a target, and participants were required todistinguish the target. The validity of the endogenous cue was75%, while the validity of the exogenous cue was 50%. More-over, the interaction between endogenous and exogenous orient-ing of spatial attention might rely on their time course. Hence, wealso manipulated stimulus onset asynchrony (SOA) between theendogenous and exogenous cues to explore the interactionbetween them in the short, medium and long time course respec-tively (Berger et al., 2005; Green, Teder-Salejarvi & McDonald,2005). In Experiment 1, we investigated how auditory endoge-nous and exogenous cues directed spatial attention to a visual tar-get. In Experiment 2, we examined how visual endogenous andexogenous cues directed spatial attention to an auditory target. Itmight be the modality difference between the two cues that causesthe results that the exogenous cue was not influenced by theendogenous cue from another modality (Koelewijn et al., 2009;Mazza et al., 2007; Santangelo et al., 2009; van der Lubbe &Postma, 2005). Adopting endogenous and exogenous cues fromthe same modality and by manipulating the crossmodal relation-ship between the cue and the target in the present study, we pre-dicted that we should observe interaction between the endogenousand exogenous cues in directing spatial attention to crossmodaltargets. Moreover, considering the different abilities of capturingattention between visual and auditory stimuli (Spence & Driver,1998), we predicted that the pattern of interaction between thetwo types of cues will vary as a function of the modality relation-ship between the cue and the target.

Blank 100ms

Target 100ms

Fig. 1. Examples of experimental paradigms in Experiment 1. Participantsmaintained the fixation upon a centrally located cross throughout all trials.An exogenous cue (white noise) was presented after an endogenous cue(pure tone with high or low frequency) with variable inter-stimulusintervals. Participants were required to discriminate the color of a visualtarget (yellow or red).

EXPERIMENT 1

Using a double-cue target paradigm, we explored the interactionbetween endogenous and exogenous orienting of attention incrossmodal processing. Both endogenous and exogenous cueswere presented in the auditory modality, while the target was pre-sented in the visual modality. A 2 · 2 · 3 within-participantsdesign was adopted with three factors: Endogenous Cue Validity(75% valid, 25% invalid), Exogenous Cue Validity (50% valid,50% invalid), and SOA (200 ms, 500 ms, and 800 ms).

� 2012 The Authors.Scandinavian Journal of Psychology � 2012 The Scandinavian Psychological

Method

Participants. Twenty undergraduate students of the Sun Yat-senUniversity (11 men and 9 women; mean age 25.1 years; age range19–30 years; all right-handed) participated in this experiment. Allparticipants had normal or corrected-to-normal vision and reportednormal hearing. Participants were informed about the experimen-tal procedure and were naive to the purpose of the experiment.They completed consent forms before taking part in the experi-ment and were paid for their participation. This study wasapproved by the Academic Committee of Department of Psychol-ogy in Sun Yat-sen University.

Stimuli and apparatus. Stimulus presentation was controlled by aprogram of E-Prime 1.2 (Psychology Software Tools, 1996–2006). Participants sat in a dimly lit room approximately 80 cmfrom a computer screen (LCD monitor, 20 in., 60 Hz refresh rate).Auditory stimuli were presented via two loudspeakers, whichwere placed behind the monitor, 80 cm away from participantsand either 15� to the left or right from the midline of participants.All auditory stimuli used in the experiment were pure tones of70 dB, including a total of 10 ms rise and 10 ms fall time. Visualstimuli were presented on the computer monitor and at the samelocation as the auditory stimuli.

Design and procedure. The sequence of a trial is illustrated inFig. 1. At the beginning of each trial, a white fixation crossappeared at the center of the screen, and participants wereinstructed to maintain fixation during the whole trial. After500 ms, an endogenous cue burst from both speakers for 100 ms,which was a pure tone with high (1000 Hz) or low (300 Hz) fre-quency. Participants perceived the tone as if it was presented fromthe center of the screen. For half of the participants, the high fre-quency indicated that the target would be presented on the rightside of the screen in 75% of the trials (valid trials), and for theother half, the high frequency tone indicated the left side in 75%of the trials (valid trials). After a varied SOA (200 ms, 500 ms,800 ms) an exogenous cue (white noise burst) with a validity of50% was present for 100 ms from the left or right loudspeaker.

Associations.

Scand J Psychol 53 (2012) Endogenous and exogenous orienting 305

Then after 100 ms interval, a dot as a visual target (diameter 0.2�of visual angle) was presented at either 15� left or right to the fixa-tion for 100 ms. Participants were instructed to identify the colorof the dot as either yellow or red and to respond with either left orright index finger as quickly and accurately as possible. The aver-age inter-trial interval (ITI) was 1000 ms, and was randomizedbetween 900 ms to 1100 ms.For each SOA condition, there were altogether 192 trials of

valid endogenous cues (75% of the trials) in which the auditorycue and visual target were presented on the same side and 64 trialsof invalid endogenous cues (25% of the trials) in which the audi-tory cue and visual target were presented on opposite sides. Halfof the exogenous cues’ locations were congruent with the targetlocations, and the other half were incongruent. All experimentalconditions and response mappings were counter-balanced acrossparticipants. Participants practiced 20 trials before the formalexperiment began, and they were allowed to rest after every 96 tri-als during the formal phase.

Results and discussion

Reaction Times (RTs) that were three standard deviations (SD)away from the mean in each experimental condition were consid-ered as outliers. RTs beyond 200–1200 ms (Santangelo et al.,2009), wrong responses, and outliers were eliminated from finalanalyses (9.2% of trials). A 2 · 2 · 3 (Endogenous Cue Validity[valid, invalid] · Exogenous Cue Validity [valid, invalid] · SOA[200 ms, 500 ms, 800 ms]) analyses of variance (ANOVA) wasperformed on mean reaction times. The distribution of the elimi-nated trials did not change significantly across the different condi-tions in Experiment 1 and 2. An overview of the mean reactiontimes and their standard errors for each condition are shown inTable 1.The three-way ANOVA revealed a significant main effect of

Endogenous Cue Validity, F (1, 19) = 21.63, p < 0.001, indicat-ing that participants responded more rapidly when the target waspresented at the valid location (483 ms) than when it was pre-sented at the invalid location (518 ms). The main effect of Exoge-nous Cue Validity was significant, F (1, 19) = 19.99, p < 0.001(valid 494 ms vs. invalid 507 ms), indicating that participantsresponded more rapidly when the target was presented at the validlocation than when it was presented at the invalid location. Themain effect of SOA was also significant, F (2, 38) = 21.20,p < 0.001, showing that participants’ responses were significantlymore rapid in case of the SOA of 500 and 800 ms (494 and495 ms, respectively) than in case of the SOA of 200 ms(513 ms).

Table 1. Mean reaction times (ms) and standard error (SE) in all the experime

SOA(ms) 200 500

Endogenous validity Invalid Valid Invalid

Exogenous validity Invalid Valid Invalid Valid Invalid

Experiment 1 541 (15) 522 (13) 498 (11) 491 (12) 521 (13)Experiment 2 557 (26) 570 (26) 562 (26) 547 (24) 550 (27)


Moreover, the interaction between Endogenous Cue Validityand Exogenous Cue Validity was significant, F (1, 19) = 8.50,p < 0.01 (see Fig. 2). On the one hand, when the endogenous cuewas valid, there was a significant exogenous cuing effect (valid479 ms vs. invalid 487 ms, t (19) = )2.92, p < 0.01). When theendogenous cue was invalid, the exogenous cuing effect was alsosignificant (valid 509 ms vs. invalid 527 ms, t (19) = )4.40,p < 0.001). The exogenous cuing effect was larger when theendogenous cue was invalid than when the endogenous cue wasvalid (18 ms vs. 8 ms, p < 0.01), indicating that the effect ofexogenous cuing was modulated by the endogenous cue. Toreduce the possibility that larger cuing effects were elicited due tolonger reaction times, these effects were further testified by calcu-lating the ratio of exogenous (or endogenous) cuing effect to thereaction time in each condition, respectively. The results of t-testsshowed that there existed significant difference between the cuingeffects in two conditions, t (19) = 3.27, p < 0.01. On the otherhand, a valid endogenous cue facilitated target discriminationregardless of the validity of the exogenous cue (cuing effect was40 ms when the exogenous cue was invalid, t (19) = )4.42,p < 0.001 and 30 ms when the exogenous cue was valid,t (19) = )4.66, p < 0.001). The endogenous cuing effect was lar-ger when the exogenous cue was invalid than when exogenous cuewas valid (p < 0.001), indicating that exogenous orienting couldalso modulate endogenous orienting of attention. In addition, therewere no significant interactions that involved the SOA factor (allps > 0.1), indicating that the orienting of voluntary attention wasrelatively stable and it influenced the upcoming attention shift bythe onset of the exogenous cue during its whole time course.The results of Experiment 1 demonstrated that both the endoge-

nous and the exogenous auditory cues could facilitate attentionalorienting to visual targets. Valid endogenous auditory cuesspeeded up the discrimination of the following visual targets, andvalid exogenous auditory cues facilitated the processing of visualtargets as well, as compared with invalid endogenous and exoge-nous cues, respectively. Moreover, there existed interactionbetween the endogenous and exogenous cues, that is, mutualinfluences between the two types of cue. The cue validity effectof the endogenous cue was larger when the exogenous cue wasinvalid than when valid, and the validity effect of the exogenouscue was larger when the endogenous cue was invalid than whenvalid. These results suggested that the endogenous cue and theexogenous cue in the auditory modality compensated each otherin biasing spatial attention towards visual targets.Previous studies have showed that an auditory cue facilitated

the orienting of the visual target but not vice versa (Spence &Driver, 1997; Theeuwes, 1991). However, there is also strong

ntal conditions of Experiment 1 and Experiment 2

800

Valid Invalid Valid

Valid Invalid Valid Invalid Valid Invalid Valid

498 (11) 480 (10) 475 (11) 519 (13) 507 (12) 482 (11) 472 (10)564 (27) 555 (25) 543 (26) 552 (25) 568 (27) 557 (25) 550 (27)

Associations.

Fi ti 500xa on ms

Endogenous cue (arrow) 100ms

>

SOA 200, 500, 800ms

Exogenous cue (White dot) 100ms

Blank 100ms

Target 100ms

Fig. 3. Examples of experimental paradigms in Experiment 2. Anexogenous cue (white dot) was presented after an endogenous cue (centralarrowhead) with variable inter-stimulus intervals. Participants were askedto judge the frequency of a target tone (high or low).

Fig. 2. Mean RTs with confidential intervals are shown as a function ofthe endogenous and exogenous cue validity in Experiment 1. Significantdifferences between two conditions are marked with an asterisk(p < 0.05).


evidence supporting the idea that a visual cue facilitates thediscrimination of an auditory target (Green & McDonald, 2006;Li, Wu & Touge, 2010). It is currently controversial whether thevoluntary and reflexive shift of attention is similar betweenauditory and visual modalities. To test the differential effects ofinteraction between the endogenous and exogenous cues for thevisual and the auditory systems engaged in a spatial attention task,we reversed the modality of the cue and the modality of the targetand conducted Experiment 2.

EXPERIMENT 2

By manipulating both the endogenous and exogenous cue fromvisual modality and target from auditory modality, we exam-ined the interaction between the endogenous and the exogenousorienting to the crossmodal target. A 2 · 2 · 3 within-partici-pants design was adopted with three factors: Endogenous CueValidity (75% valid, 25% invalid), Exogenous Cue Validity(50% valid, 50% invalid), and SOA (200 ms, 500 ms, and800 ms).

Method

Participants. Twenty-two new undergraduates of the Sun Yat-senUniversity (14 men, 8 women; mean age 23.6 years; age range20–31 years; all right-handed) participated in this experiment. Allparticipants had normal or corrected-to-normal vision and reportednormal hearing. Participants were informed about the experimen-tal procedure and were naive to the purpose of the experiment.They completed consent forms before taking part in the experi-ment and were paid for their participation. This study wasapproved by the Academic Committee of Department of Psychol-ogy in Sun Yat-sen University.


Stimuli, design, and procedure. The procedure is shown in Fig. 3.A central arrowhead (1� · 1�) was adopted as the endogenous cueindicating the possible location of an auditory target and was pre-sented on the screen for 100 ms. After a varied SOA (200 ms,500 ms, 800 ms) an exogenous cue (a white dot, diameter 0.2� ofvisual angle) was presented from either side of the screen (15� tothe left or right of the central fixation) for 100 ms. The auditorytarget emitted from either loudspeaker randomly. Participantswere asked to judge whether the frequency of a target tone washigh or low (high 1000 Hz, low 300 Hz). All the other experi-mental settings, design, and procedure were identical to those inExperiment 1.

Results and discussion

Reaction times beyond 200–1200 ms, wrong responses, and out-liers were eliminated from final analyses (7.8% of trials).A 2 · 2 · 3 (Endogenous Cue Validity [valid, invalid] · Exoge-nous Cue Validity [valid, invalid] ·SOA [200 ms, 500 ms,800 ms]) ANOVA on mean reaction times revealed that a maineffect of Endogenous Cue Validity was significant, F (1, 21) =4.82, p < 0.05, with participants responding more rapidly whenthe target was presented at the expected location (552 ms) thanwhen it was presented at the unexpected location (560 ms). Themain effect of Exogenous Cue Validity was not significant, F (1,21) = 0.109, p = 0.745, indicating that the cuing effect was rela-tively small when a visual exogenous cue directed attention to anauditory target.The interaction between Endogenous Cue Validity and Exoge-

nous Cue Validity was significant, F (1, 21) = 7.03, p < 0.05 (seeFig. 4). Further simple effect analyses showed a marginally signif-icant exogenous cuing effect (valid 546 ms vs. invalid 558 ms)when the endogenous cue was valid (t (21) = )1.99, p = 0.05).And the exogenous cue triggered an inhibitory effect (valid567 ms vs. invalid 552 ms) when the endogenous cue was invalid(t (21) = 2.04, p = 0.06). The endogenous cuing effect was evi-dent when exogenous cue was valid (t (21) = )3.48, p < 0.001),but did not reach significance when exogenous cue was invalid (t(21) = )0.86, p = 0.399). In addition, the main effect of SOA andinteractions that involved SOA were not significant (all ps > 0.1),

Associations.

Fig. 4. Mean RTs with confidential intervals are shown as a function ofthe endogenous and exogenous cue validity in Experiment 2. Significantdifferences between two conditions are marked with an asterisk(p < 0.05).

Scand J Psychol 53 (2012) Endogenous and exogenous orienting 307

indicating that the modulation patterns between endogenous andexogenous cues were not affected by endogenous orienting pro-cess (at least CTOA of 1000 ms).In Experiment 2, there existed interplay between the visual

endogenous and exogenous cues in directing attention to the audi-tory targets. The facilitatory cuing effect of the endogenous cuewas observed only when the exogenous cue was valid, and thefacilitatory cuing effect of the exogenous cue was observed onlywhen the endogenous cue was valid. On the other hand, the exog-enous cuing induced an inhibitory effect when the endogenouscue was invalid, and the endogenous cuing induced a null effectwhen the exogenous cue was invalid. In contrast to the pattern ofresults in Experiment 1, the results here suggested that the effectsof the endogenous and exogenous cues in the visual modality co-existed, and they tended to co-direct the spatial attention orientingto the auditory targets: one type of cue contributed to attentionalorienting to the auditory target only when the other type of cuefully functioned as well.Unlike the facilitatory cuing effect of the exogenous cue when

the endogenous cue was valid, an inhibitory cuing effect of theexogenous cue was observed when the endogenous cue was inva-lid. The suppression of reflexive orienting during the voluntaryre-orienting process (i.e. in the condition that the endogenous cuewas invalid) might be due to a trend of inhibition of return (IOR).IOR is generally produced when attention is summoned to thecued location and then moved to a new location. As the conse-quence of the invalid endogenous cuing, the reflexive exogenouscuing dominated the orienting process to the crossmodal targets.Thus, a valid visual exogenous cue did not facilitate the process-ing of the auditory target when visual attention was focused on aninvalid location, because the visual exogenous cue did not attractattention as efficiently as the auditory exogenous cue (Spence &Driver, 1997; Theeuwes, 1991).


GENERAL DISCUSSION

In this study, we aimed at exploring the interaction betweenendogenous and exogenous cues of the same modality duringorienting attention to crossmodal targets. The endogenous and theexogenous cues were always presented in the same modality(auditory in Experiment 1 and visual in Experiment 2), while thetarget was presented in a different modality. Our results showedthat the endogenous and the exogenous orienting systems inter-acted with each other, and the pattern of interaction depended onthe ‘auditory – visual’ or the ‘visual – auditory’ relationshipbetween the cue and the target. When the modality relationshipbetween the cue and the target was ‘auditory – visual’, the cuevalidity effect of one type of cue was significantly larger when theother type of cue was invalid than valid. When the modality rela-tionship between the cue and the target was ‘visual – auditory’,however, the cue validity effect of one type of cue was significantonly when the other type of cue was also valid. The different pat-terns of interaction between the two types of cue in Experiment 1and 2 may be due to the lower spatial localizing abilities in theauditory system than in the visual system (e.g. Mazza et al., 2007;Shimojo & Shams, 2001). Specifically speaking, in terms of thecombination of auditory endogenous and exogenous cues, due totheir worse localizing abilities, when one type of cue was notfunctioning well (invalid), the other type of cue had to compen-sate for the cost in order to effectively guide spatial attention tothe location of the visual target. On the other hand in terms of thecombination of visual exogenous and endogenous, due to theirbetter localizing abilities, the two types of cue co-directed in guid-ing visuospatial attention so that one cue could facilitate atten-tional orienting only when the other cue was effective as well.There has also been previous evidence suggesting the bidirec-

tional influences between endogenous and exogenous cues. Onthe one hand, the exogenous cuing effect was modulated by thevalidity of the endogenous cue. Some studies have revealed thatthe automaticity of exogenous orienting could be influenced bytop-down factors (such as task setting and perceptual load), andexogenous cuing benefits even disappeared when attention wasfocused on a valid and predefined target location (Koelewijnet al., 2009; Koelewijn, Bronkhorst & Theeuwes, 2010;Santangelo & Spence, 2008). For instance, Santangelo and Spence(2007) demonstrated that exogenous cuing effects were modulatedby perceptual load. They manipulated the perceptual load in anattention orienting task. In the low load condition, participantswere required to discriminate the target in a cue-target task only.Whereas in the high load condition, participants performed thecue-target task and a rapid serial visual presentation (RSVP) tasksimultaneously. Their results showed that the cuing effect of theexogenous cue was suppressed under the high load condition butnot under the low load condition, indicating that the reflexive ori-enting was not truly automatic and could be influenced by the lim-itation of attention resources. On the other hand, the endogenouscuing effect was also affected by the validity of the exogenouscue. For example, Berger et al. (2005) examined the relationbetween endogenous and exogenous orienting of visual attentionwith an identification task. They found that the endogenous cuingeffect (26 ms) was significant when the exogenous cue was valid,while the endogenous cuing effect (15 ms) was only marginally

Associations.


significant when the exogenous cue was invalid, indicating thatthe exogenous orienting could interfere with the endogenous ori-enting. Therefore, the interplay patterns in the present study areconsistent with the model proposed within the visual modality –spatial orienting can be achieved by two separate orienting mecha-nisms, and these two mechanisms (endogenous and exogenousorienting) interact with each other as they compete for sharedresources (Berger et al., 2005; Mueller & Rabbitt, 1989).In addition, it should be noted that we observed a facilitatory

exogenous cuing effect in Experiment 1, whereas an inhibitoryexogenous cuing effect in Experiment 2 when the endogenous cuewas invalid (see left panel in Figs. 2 and 4). The above differencecould be due to the asymmetric effects between the auditory andvisual exogenous cues in attention capture. Some crossmodalstudies on covert exogenous orienting have demonstrated thatauditory reflexive cues are more effective than visual cues indrawing attention to a spatial location (Spence & Driver, 1997,1998). In our Experiment 1, when the auditory endogenous cuewas invalid, spatial attention was directed to the opposite side ofthe target. Due to the higher attentional capture abilities of audi-tory stimuli, the valid auditory exogenous cue could effectivelyattract attention to the target location, causing facilitatory effects.By contrast in our Experiment 2, when the visual endogenous cuewas invalid, spatial attention was directed to the opposite side ofthe target location as well. In contrast to Experiment 1, however,due to the worse attentional capture abilities of visual stimuli, thevalid visual exogenous cue could not efficiently attract attentionaway from the invalid location, leaving residual attention on theinvalid locations. Correspondingly, responses to targets on theinvalid locations were significantly faster than responses on thevalid locations, that is, an inhibitory effect. Hence, our results pro-vided the evidence that the interaction between the voluntary andthe reflexive orienting of attention were asymmetric for the visualand auditory modalities.To summarize, using a crossmodal ‘double cue – target’ para-

digm, we investigate how the endogenous and exogenous cuesinteract with each other during directing spatial attention to cross-modal targets. Our results show that the endogenous and exoge-nous cues either compensate each other or co-exist depending onthe modality relationship between the cue and the target (i.e.,‘auditory – visual’ or vice versa). In contrast to results from previ-ous crossmodal studies in which the exogenous and endogenouscues are from different modalities, our results suggest that whenthe two types of cue are from the same modality, they interactwith each other to guide attention to crossmodal targets.

The study was supported by grants from the National Natural ScienceFoundation of China (31100739, 30970895, 31070994, 31070988), theMinistry of Education of China (10YJCXLX055, 09YJAXLX026), theFundamental Research Funds for the Central Universities, Foundation forthe Author of National Excellent Doctoral Dissertation of P.R. China(200907) and Science and Technology Planning Project of GuangdongProvince, China (2008B080701041).

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Received 28 August 2011, accepted 6 March 2012

Associations.

interaction between endogenous and exogenous orienting in crossmodal attention

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