The authors have declared that no competing interests exist.
Conceived and designed the experiments: CL XF. Performed the experiments: CL. Analyzed the data: CL. Contributed reagents/materials/analysis tools: XF CL. Wrote the paper: CL JL MJF XF.
In a paradigm combining spatial Stroop with spatial cueing, the current study investigated the role of the presence vs. absence of placeholders on the reduction of the spatial Stroop effect by peripheral cueing. At a short cue-target interval, the modulation of peripheral cueing over the spatial Stroop effect was observed independently of the presence/absence of placeholders. At the long cue-target interval, however, this modulation over the spatial Stroop effect only occurred in the placeholders-present condition. These findings show that placeholders are modulators but not mediators of the reduction of the spatial Stroop effect by peripheral cueing, which further favor the cue-target integration account.
The spatial coding of location is an important cognitive skill. Consequently, how its mental representation is built up and how this representation affects organization of actions have attracted considerable research interest. Spatial coding of this type has been examined in a variety of conflicting tasks used to examine spatial congruency effects, including stimulus-stimulus (S-S) congruency effects, such as the spatial Stroop effect (SSE), and the stimulus-response (S–R) congruency effect, as in the case of the Simon effect
In a version of the spatial Stroop task, an up or down-pointing arrow appears randomly above or below a fixation point. Although participants are asked to discriminate the direction of the arrow while ignoring its location, they typically make faster and more accurate responses to congruent stimuli (i.e., an up-pointing arrow located above the fixation sign) than to incongruent ones (i.e., a down-pointing arrow located above the fixation sign)
In a Simon task, responses are usually faster and more accurate when the stimulus appears in the same relative location as the response, even if the stimulus location is irrelevant to the task
Results from previous studies have indicated that the occurrence of spatial pre-cues indicating one of the possible target locations has an effect on spatial congruency effects, which have been interpreted as modulation of peripheral cueing on the building up of spatial code representations, with weaker spatial codes at attended than unattended locations
Several accounts have been proposed to explain this modulation of spatial attention over spatial congruency effects. According to the attention shift account
According to a revised version of the referential coding account, Danziger and colleagues
Although these two explanations could account for the pattern of spatial Stroop reduction on cued trials, they can not explain why such an effect is absent for S–R congruency effects such as Simon or compatibility effects
Considering the whole set of data regarding the modulation of spatial cueing on the spatial Stroop effect
These authors assume that the integration of cue and target spatial codes within the same event or object file means that no extra spatial code is created when the target appears, as it will not be treated by the perceptual system as a new object, for which a new location code would be needed, but as an update of the object representation triggered by the cue, to which only the direction information is added. This integration process thus helps to separate in time the processing of the two conflicting dimensions (the spatial location and its direction) of the target stimulus, as the distracting location dimension of the arrow target links with an event (the cue) that occurred at an earlier point in time. The separation in time of these two perceptual codes could then underlie the reduction in the spatial congruency effect observed for valid trials, as the irrelevant location dimension would have largely decayed by the time the relevant direction dimension was coded (see
The strongest evidence favoring this view comes from two recent studies
The fact that the rectangle object had an influence on the allocation of attention and its modulation over the spatial Stroop effect
The main purpose of the present study was to examine whether the spatial Stroop effect would be reduced by peripheral cueing in the absence of placeholders, and whether this reduction varies with the SOA between the cue and the target (see the right column in
The left column represents placeholder present condition and the right column represents placeholder absent condition.
Moreover, we compared a situation where placeholders were absent, to a condition where placeholders were present along the whole trial (see
For the current manipulation, the attentional shift account will predict the spatial Stroop effect to be smaller on cued than uncued trials for both the placeholder present and absent conditions, because a similar shift of attention towards the cue should occur at the short and long cue-target intervals, provided that the cueing effect is facilitatory in both conditions, as observed in the previous studies with placeholders present
Also, Danziger et al. (2001)’ referential coding account will predict the spatial Stroop effect to be smaller on cued than uncued trials for both the placeholder present and absent conditions and invariant of SOAs, given that target is coded left–right relative to the central fixation cross and the cue on cued trials, but is coded left-right relative to the central fixation cross on uncued trials.
The basic method of the experiment is straightforward, placeholder boxes were present on half of trials but they were absent on the other half. Thus, cues and targets could appear either in objects or in an essentially blank display. We mainly wanted to investigate whether cueing would modulate the spatial Stroop effect in the placeholder-absent condition, and whether it would do in a similar or different way as it does in the placeholder-present condition reviewed above.
Eighteen undergraduate students (7 males and 11 females) were paid to participate in this experiment. All participants had normal or corrected-to-normal vision and were naïve as to the purpose of the experiment. Written consent was obtained from all participants prior to participation. The protocol was approved by the institutional review board (IRB) at the institute of psychology, Chinese Academy of Sciences.
Stimuli presented on a super VGA high-resolution color monitor. A computer, running E-Prime 1.1 software, controlled the presentation of stimuli, timing operations, and data collection. Participants viewed the monitor from a distance of 57 cm in a dimly lit room.
For all trials, the display sequence in a trial differed depending on whether placeholder boxes were present. Two typical trial sequences for each display type are illustrated in
Each trial began with a central fixation cross (0.8°×0.8°) and two circular boxes separately located at the left and right of it for placeholder-present display but only with the cross for placeholder-absent display. After 1 s, a red cue flickered at the left or righ of the fixation cross with equal probability for 100 ms. Following a further interval of 0 or 500 ms from the cue offset (depending on the SOA), the imperative arrow appeared, which was left or right pointing. The target remained visible until the subject responded or for 1000 ms if no response was emitted. Then the next trial began. The interval between trials was 500 ms and the screen remained white throughout this interval.
There were two sessions of 544 trials each, with a rest interval of 5 min between them. Each session consisted of two large blocks corresponding respectively with placeholder-present and placeholder-absent conditions with a rest interval of 60 s between them and their order was randomized. Each block included one practice block of 16 trials followed by two test blocks of 128 trials. Each test block corresponded with one SOA and their order was random.
All participants were instructed to complete the two sessions of trials. Responses were made with the index fingers of both hands, pressing the C and M keys on the computer keyboard for left and right responses, respectively. In one session of trials, the response location was compatible with the direction of arrow, i.e., pressing the C key when the arrow was left pointing and pressing the M key when it pointed right, regardless of the arrow’s location, while the reverse mapping was used in the other session of trials, on which the response location was incompatible with the direction of the arrow, i.e., pressing the M key when the arrow was left pointing and pressing the C key when it pointed right, regardless of the arrow’s location. The order of the two sessions was counterbalanced across participants. The response keys and computer screen were aligned such that the fixation point and the midway point between the two response keys were on the participant’s sagittal midline. Participants were firmly instructed to maintain fixation and to respond to the targets as quickly and accurately as possible.
The experiment had a 2 (display type: placeholder-present, placeholder-absent)×2 (cueing: cued, cued)×2 (spatial Stroop: congruent, incongruent)×2 (compatibility: compatible, incompatible)×2 (SOA: 100 ms, 600 ms) design, with 32 observations per experimental condition. Compatibility refers to whether the location of arrow and response location are compatible, and spatial Stroop refers to whether the location of arrow and its direction are congruent.
Mean reaction times (RTs, in ms) and percentage errors (PEs) are presented in
Placeholder Present | Placeholder Absent | |||||||
100 ms SOA | 600 ms SOA | 100 ms SOA | 600 ms SOA | |||||
Cued | Uncued | Cued | Uncued | Cued | Uncued | Cued | Uncued | |
CC | 416(1.6) | 420(1.9) | 427(1.6) | 430(2.1) | 422(2.1) | 433(2.8) | 421(2.3) | 428(3.5) |
CI | 442(2.3) | 446(1.4) | 446(1.4) | 453(3.3) | 444(1.9) | 452(2.3) | 446(2.3) | 450(1.4) |
IC | 434(3.0) | 463(5.0) | 437(2.8) | 460(5.7) | 433(4.3) | 461(5.4) | 440(4.2) | 451(3.6) |
II | 437(2.1) | 478(4.5) | 443(2.6) | 465(3.6) | 443(2.3) | 475(3.0) | 457(4.0) | 471(3.6) |
CC
Errors. sented in
The analysis for long SOA revealed that cueing,
The analysis of the placeholder-present data showed that cueing,
In the error analysis, there was a main effect of cueing,
As in the previous studies
Also replicating previous studies
In experiment 2, we used a vertical display (i.e, up/down pointing arrows appearing above/below fixation) to see whether the pattern of results observed in experiment 1 would occur in a procedure where only spatial Stroop (i.e., S-S congruency) is measured. This change allowed to measure a pure spatial Stroop effect that results from the conflict of the direction of arrow and its location without the confound of the conflict between arrow location and response location, given that the responding hand (whether left or right) was orthogonal to the location and direction of the arrow (top/bottom, up/down)
Twenty-four undergraduate students (10 males and 14 females) were paid to participate in this experiment. All participants had normal or corrected-to-normal vision and were navïe as to the purpose of the experiment. Written consent was obtained from all participants prior to participation. The protocol was approved by the institutional review board (IRB) at the institute of psychology, Chinese Academy of Sciences.
The apparatus were identical to the experiment 1. The procedure was identical to the experiment 1, apart from the following changes: Participants only completed one session. The target was an arrow pointing either up or down, and the display was vertical. For half participants, the task was to press the C key (left response) when the arrow pointed up, and the M key (right response) when it pointed down, regardless of the arrow’s location above or below fixation, while the reverse mapping was used for the other half participants.
The experiment had a 2 (display type: placeholder-present, placeholder-absent)×2 (cueing: cued, cued)×2 (spatial Stroop: congruent, incongruent)×2 (SOA: 100 ms, 600 ms) design, with 32 observations per experimental condition.
Mean RTs and PEs are presented in
Placeholder Present | Placeholder Absent | |||||||
100 ms SOA | 600 ms SOA | 100 ms SOA | 600 ms SOA | |||||
Cued | Uncued | Cued | Uncued | Cued | Uncued | Cued | Uncued | |
Congruent | 471(3.6) | 469(2.9) | 469(2.6) | 474(5.1) | 478(4.0) | 483(5.2) | 474(5.5) | 487(4.4) |
Incongruent | 487(4.7) | 513(5.6) | 483(5.3) | 508(8.1) | 492(6.2) | 522(7.4) | 503(6.5) | 514(8.5) |
The analysis showed main effects of two variables, cueing,
The analysis showed again main effects of two variables, cueing,
The ANOVA on PEs revealed a main effect of cueing,
As in Experiment 1 and the previous studies
The current study investigated the role of the presence/absence of placeholders on the reduction of the spatial Stroop effect by peripheral cueing. We found that the typical spatial Stroop modulation by cueing occurred in both the placeholder present and absent conditions at the 100 ms SOA between the cue and the target. Such modulation survived up to 600 ms SOA when placeholders were present, while no modulation was observed at this SOA when placeholders were absent.
As reviewed in the introduction, there exist three possible hypotheses that have been used to explain the reduction of spatial Stroop by peripheral cueing. According to the
Similarly, the
All these findings, however, thoroughly reconcile with the event integration account
Interestingly, the event integration account also predicts that no IOR would be observed in a difficult discrimination task, as the one used in the current experiments. According to this account, IOR is considered as a cost in detecting new information at a location where a peripheral cue appeared before (i.e., at a location where an object representation was just opened)
Altogether, we may conclude that the reduction of spatial Stroop by peripheral cueing might arise from cue-target integration processes. More importantly, we report evidence showing that the temporal window for object-file integration can be extended in time. The significant reduction of spatial Stroop observed at the 600 ms SOA when placeholders are presented (but not when they are absent) provides evidence that cue-target integration, although reduced, can survive up to 600 ms. Evidence for a similar extension of the temporal window for integration was observed by Akyürek, Toffanin, and Hommel (2008) in an Attentional Blink paradigm. In this case the temporal extension, rather than being stimulus-driven as in our case, depended on the expectation about the duration of the first stimulus to be integrated. The expectation for a longer duration of the first stimulus (T1) increased its integration with the following stimulus (T2). In a different study by Chica, Charras, and Lupiáñez (2008)
Therefore, these results together with the evidence reported in the current paper support the role of spatio-temporal overlap in object-file integration processes. Whereas integration occurs quite automatically as a direct consequence of this spatio-temporal overlap, the temporal window for integration can be modulated both endogenously
We wish to thank Bruce Milliken and Derrick Watson for their helpful comments on previous versions of the manuscript. Raw data from the two reported experiments are freely available upon request.