Stimulus congruence and the Simon effect

Summary A standard experimental procedure was implemented with novel response requirements to assess the hypothesis that the Simon effect is attributable not to the irrelevant stimulus-response relationship, but to the congruence between stimulus attributes. The stimulus ensemble consisted of the words LEFT and RIGHT, one of which was presented on each trial to the left or right of a central fixation point. The distinctive feature of the task is that subjects were asked to respond, by laterally placed keys, whether or not the stimulus word was in accord (i. e., congruent) with its location on the display. Asking subjects to judge stimulus congruence directly enables the effect of congruence to be assessed, as well as independent estimates of the two irrelevant S-R relationships that apply in the task — that is, between the response location and (1) the stimulus location (the Simon effect) and (2) the stimulus word (the reverse Simon effect). Marked effects were obtained in all three cases. Stimulus congruence remains in contention as a factor in the explanation of the Simon effect, but the strong effects of irrelevant S-R factors suggest that a more comprehensive account of the Simon effect is needed. An explanation in terms of stimulus salience, based on an interactive activational model, is briefly discussed.     

Action-feature integration blinds to feature-overlapping perceptual events: Evidence from manual and vocal actions

Previous studies showed that the identification of a left- or right-pointing arrowhead is impaired when it appears while planning and executing a spatially compatible left or right keypress (Müsseler & Hommel, 1997a). We attribute this effect to stimulus processing and action control operating on the same feature codes so that, once a code is integrated in an action plan, it is less available for perceptual processing. In three pairs of experiments we tested the generality of this account by using stimulus–response combinations other than arrows and manual keypresses. Planning manual left–right keypressing actions impaired the identification of spatially corresponding arrows but not of words with congruent meaning. On the contrary, planning to say “left” or “right” impaired the identification of corresponding spatial words but not of congruent arrows. Thus, as the feature-integration approach suggests, stimulus identification is impaired only with overlap of perceptual or perceptually derived stimulus and response features while mere semantic congruence is insufficient.     

Action-feature integration blinds to feature-overlapping perceptual events: evidence from manual and vocal actions

Previous studies showed that the identification of a left- or right-pointing arrowhead is impaired when it appears while planning and executing a spatially compatible left or right keypress (Müsseler & Hommel, 1997a). We attribute this effect to stimulus processing and action control operating on the same feature codes so that, once a code is integrated in an action plan, it is less available for perceptual processing. In three pairs of experiments we tested the generality of this account by using stimulus-response combinations other than arrows and manual keypresses. Planning manual left-right keypressing actions impaired the identification of spatially corresponding arrows but not of words with congruent meaning. On the contrary, planning to say "left" or "right" impaired the identification of corresponding spatial words but not of congruent arrows. Thus, as the feature-integration approach suggests, stimulus identification is impaired only with overlap of perceptual or perceptually derived stimulus and response features while mere semantic congruence is insufficient.     

Coding left and right

The present study compared the processing of direction for up and down arrows and for left and right arrows in visual displays. Experiment 1 demonstrated that it is more difficult to deal with left and right than with up and down when the two directions must be discriminated but not when they must simply be oriented to. Experiments 2 and 3 showed that telling left from right is harder regardless of whether the responses are manual or verbal. Experiment 4 showed that left-right discriminations take longer than up-down discriminations for judgments of position as well as direction. In Experiment 5 it was found that position information can intrude on direction judgments both within a dimension (e.g., a left arrow to the left of fixation is judged faster than a left arrow to the right of fixation) and across dimensions (e.g., judging vertically positioned left and right arrows is more difficult than judging horizontally positioned left and right arrows). There was indirect evidence in these experiments that although the spatial codes for up and down are symmetrical, the codes for left and right may be less so; this in turn could account for the greater difficulty of discriminating left from right.     

The Simon effect and visual motion

Summary S-R compatibility and Simon effects were studied for real visual motion. In Experiment 1, two small stimulus lights were constantly visible, 5° to the left and right of fixation; after a random delay, one began to move at 2°/s. In Experiment 2, a single stimulus light moving at 2°/s suddenly appeared 5° to the left or right of fixation, i. e., motion onset and stimulus onset coincided. In both experiments, subjects responded by a key press with their left or right index finger as soon as they detected motion. In Condition A responses were made to the position (left or right) from which the motion started, irrespective of its direction (position compatibility); in Condition B responses were made to the direction of motion (leftward or rightward) irrespective of whether motion started to the left or to the right of fixation (direction compatibility). The results show strong compatibility effects for both position and direction of motion in both experiments. A Simon effect, however, occurred only when position was task irrelevant in Experiment 1; no Simon effect was found in Experiment 2. The data only partly confirm previous results obtained with apparent motion. The selective lack of a Simon effect supports the integrated model of Umiltá and Nicoletti (1992), which requires orienting of attention for the Simon effect to occur. It is specifically assumed that this attention-orienting is triggered only by the saccade program and does not extend to the pursuit program that is initiated by smooth stimulus motion.     

Attention shifts and the Simon effect: a failure to replicate Stoffer (1991)

The Simon effect refers to the intrusion of an irrelevant spatial dimension in the selection of a response to a stimulus. Recently, Stoffer (1991) proposed a specific role for attention orienting in the Simon effect. According to Stoffer, attentional shifts from an initial fixation point to a stimulus location are associated with the generation of a spatial code which specifies the position of the stimulus in relation to the last attended location. This spatial code forms the basis for the Simon effect because it is used to specify the selection of the right or left response. Three experiments were performed to examine further the attention-shift hypothesis forwarded by Stoffer. Experiment 1 was an attempt to replicate Stoffer (1991), but failed to do so. Experiments 2 and 3 were designed to optimize conditions for replicating crucial aspects of Stoffer's findings, but also failed to yield support for the attention-shift account.     

Spatial Simon effects with nonspatial responses

Recent studies have shown that spatial Simon effects can be modulated by short-term associations that are set up as a result of task instructions. I examined whether spatial Simon effects can also be produced by short-term associations even when the responses are unrelated to spatial position. Participants were to say “cale” or “cole” on the basis of the direction of arrows (i.e., left or right), the meaning of words (i.e.,left orright), and the color of squares presented left or right of the screen center. Responses to squares were faster when the correct response was associated with the same position as the irrelevant position of the square (e.g., say “cale” to a square on the left when “cale” was assigned to the wordleft and the left arrow). This new type of stimulus-response compatibility effect provides the first evidence for short-term associations that involve mode-independent representations.     

语音反应方式下情绪效价对空间Simon效应的影响

通过3个实验考察语音反应方式下情绪效价对空间Simon效应的影响。实验1采用空间Simon任务范式考察语音反应方式下空间Simon效应的存在;实验2增加刺激的情绪效价维度,采用同样任务考察无关情绪效价对空间Simon效应的影响;实验3在实验2基础上进一步探讨当情绪效价为相关维度时对空间Simon效应的影响。研究结果表明:语音反应方式下,只有当情绪效价为相关维度时,才会对空间Simon效应产生影响,且该影响主要表现在积极效价对认知控制的促进作用而导致空间Simon效应减小或消失,此结果与极性编码一致性假说一致,也拓宽了躯体特异性假说,扩展了以往对情绪影响空间认知的理解。     

The SNARC effect: an instance of the Simon effect?

Our aim was to investigate the relations between the Spatial-Numerical Association of Response Codes (SNARC) effect and the Simon effect. In Experiment 1 participants were required to make a parity judgment to numbers from 1 to 9 (without 5), by pressing a left or a right key. The numbers were presented to either the left or right side of fixation. Results showed the Simon effect (left-side stimuli were responded to faster with the left hand than with the right hand whereas right-side stimuli were responded to faster with the right hand), and the SNARC effect (smaller numbers were responded to faster with the left hand than with the right hand, whereas larger numbers were responded to faster with the right hand). No interaction was found between the Simon and SNARC effects, suggesting that they combine additively. In Experiment 2 the temporal distance between formation of the task-relevant non-spatial stimulus code and the task-irrelevant stimulus spatial code was increased. As in Experiment 1, results showed the presence of the Simon and SNARC effects but no interaction between them. Moreover, we found a regular Simon effect for faster RTs, and a reversed Simon effect for longer RTs. In contrast, the SNARC effect did not vary as a function of RT. Taken together, the results of the two experiments show that the SNARC effect does not simply constitute a variant of the Simon effect. This is considered to be evidence that number representation and space representation rest on different neural (likely parietal) circuits.     

The role of attention for the Simon effect

Summary It has been claimed that spatial attention plays a decisive role in the effect of irrelevant spatial stimulus-response correspondence (i. e., the Simon effect), especially the way the attentional focus is moved onto the stimulus (lateral shifting rather than zooming). This attentional-movement hypothesis is contrasted with a referential-coding hypothesis, according to which spatial stimulus coding depends on the availability of frames or objects of reference rather than on certain attentional movements. In six experiments, reference objects were made available to aid spatial coding, which either appeared simultaneously with the stimulus (Experiments 1–3), or were continuously visible (Experiments 4–6). In contrast to previous experiments and to the attentional predictions, the Simon effect occurred even though the stimuli were precued by large frames surrounding both possible stimulus positions (Experiment 1), even when the reference object's salience was markedly reduced (Experiment 2), or when the precueing frames were made more informative (Experiment 3). Furthermore, it was found that the Simon effect is not reduced by spatial correspondence between an uninformative spatial precue and the stimulus (Experiment 4), and it does not depend on the location of spatial precues appearing to the left or right of both possible stimulus locations (Experiment 5). This was true even when the precue was made task-relevant in order to ensure attentional focusing (Experiment 6). In sum, it is shown that the Simon effect does not depend on the kind of attentional operation presumably performed to focus onto the stimulus. It is argued that the available data are consistent with a coding approach to the Simon effect which, however, needs to be developed to be more precise as to the conditions for spatial stimulus coding.     

Peripheral spatial cues modulate spatial congruency effects: Analysing the “locus” of the cueing modulation

The spatial Stroop effect (slower left/right responses to left/right pointing arrows when they appear at spatially incongruent than at congruent locations) has often been used to examine the processing of irrelevant spatial information. We present data from two experiments in which the magnitude of such location-based interference is drastically reduced when the location of the arrow is precued by a spatial noninformative cue. The main aim of the present study was to clarify whether such modulation takes place at perceptual or at response-related stages of processing. First, we manipulated the spatial compatibility between the direction of the arrow and the location of the response so that each subject would respond with spatially compatible vs. incompatible key presses for each half of the experiment. We found that such manipulation did not have any effect on the standard reduction of the congruency effect by peripheral cues. In a second experiment, subjects made left/right key presses to directional arrows pointing bottom/up, which could appear equally often at left/right/bottom/up locations. In cued trials, we found a reduction of the congruency effect on the vertical axis (stimulus location-direction congruency), whereas congruency was unaffected by cueing in targets presented on the horizontal axis (stimulus-response location congruency). According to these results, we conclude that spatial noninformative cues modulate spatial Stroop interference by reducing the conflict between stimulus dimensions at perceptual- rather than motor-related stages of processing.     

Arrows don’t look at you: Qualitatively different attentional mechanisms triggered by gaze and arrows

Eye gaze conveys rich information concerning the states of mind of others, playing a critical role in social interactions, signaling internal states, and guiding others’ attention. On the basis of its social significance, some researchers have proposed that eye gaze may represent a unique attentional stimulus. However, contrary to this notion, the majority of the literature has shown indistinguishable attentional effects when eye gaze and arrows have been used as cues. Taking a different approach, in this study we aimed at finding qualitative attentional differences between gazes and arrows when they were used as targets instead of as cues. We used a spatial Stroop task, in which participants were required to identify the direction of eyes or arrows presented to the left or the right of a fixation point. The results showed that the two types of stimuli led to opposite spatial interference effects, with arrows producing faster reaction times when the stimulus direction was congruent with the stimulus position (a typical spatial Stroop effect), and eye gaze producing faster reaction times when it was incongruent (a “reversed” spatial Stroop effect). This reversed Stroop is interpreted as an eye-contact effect, therefore revealing the unique nature of eyes as special social-attention stimuli.     

S-R compatibility effects due to context-dependent spatial stimulus coding

Responses are faster with spatial S-R correspondence than with noncorrespondence (spatial compatibility effect), even if stimulus location is irrelevant (Simon effect). In two experiments, we sought to determine whether stimuli located above and below a fixation point are coded as left and right (and thus affect the selection of left and right responses) if the visual context suggests such a coding. So, stimuli appeared on the left or right eye of a face’s image that was tilted by 90° to one side or the other (Experiment 1) or varied between upright and 45° or 90° tilting (Experiment 2). Whether stimulus location was relevant (Experiment 1) or not (Experiment 2), responses were faster with correspondence of (face-based) stimulus location and (egocentrically defined) response location, even if stimulus and response locations varied on physically orthogonal dimensions. This suggests that object-based spatial stimulus codes are formed automatically and thus influence the speed of response selection.     

Referential coding and attention-shifting accounts of the Simon effect

Summary Stoffer (1991) and Umiltá and Nicoletti (1992) have proposed an attention-shifting account of the Simon effect. However, Hommel (1993) has presented evidence suggesting that the effect can be explained in terms of referential coding, without invoking attentional shifts. Five experiments are reported here, whose primary purpose is to test implications of the referential-coding account. All of the experiments compared conditions in which a noise stimulus was presented in the position opposite the target stimulus with conditions in which it was not. Contrary to the referential-coding account, (a) the basic Simon effect was larger without a fixation point to serve as a referent than with one; (b) the noise stimulus increased the magnitude of the Simon effect when a fixation point was used, but not when there was no fixation point; and (c) the magnitude of the Simon effect obtained in the presence of a noise stimulus was reduced substantially when the noise and the target (and, if present, the fixation point) were in different colors. The results, although counter to predictions of the referential-coding account, can be accommodated by the attention-shifting account if it is assumed that a fixation point provides an anchor that minimizes attention shifts.     

Mechanisms underlying spatial coding in a multiple-item Simon task

Choice responses are faster when target position and response side correspond than when they do not, even if target position is response-irrelevant. This "Simon effect" has also been observed in case of multi-item arrays. Generally, it is assumed that an automatically generated spatial response code is responsible for the effect. The referential-coding account assumes that this code is directly related to the target, although the moment of production of the code is not fully clear. The attention-shift account assumes that the code is directly related to the direction of the most recent attentional shift. An experiment was performed in which left or right target locations were indicated by arrows occurring before (precue), simultaneous with (simcue), or after (postcue) six-element arrays. Overt responses and EEG potentials were recorded. The Simon effect was present in all conditions, and decreased when responses were slower. No relation was found between amplitude of posterior lateralized components and the magnitude of the Simon effect. A posterior contralateral negativity was also found after presenting the arrays in the precue condition, which might reflect the reorienting of attention toward the target position. The results are more favorable to the referential-coding account although this account becomes very similar to the attention-shift hypothesis as the moment of formation of the spatial response code is related to effective target onset rather than to stimulus onset.     

The functional role of attention for spatial coding in the Simon effect

Summary Two experiments investigated relative spatial coding in the Simon effect. It was hypothesized that relative spatial coding is carried out with reference to the position of the focus of visual attention. The spatial code for an imperative stimulus presented exactly at the position of focal attention should be neutral on the horizontal plane, and therefore no Simon effect should be observed. However, when the imperative stimulus is presented to the left or to the right of the current position of focal attention, the spatial code should not be neutral, thus producing a Simon effect. In both experiments, focal attention was manipulated either by a peripherally presented onset precue (Experiment 1) or by a centrally presented symbolic precue (Experiment 2). Results showed that the Simon effect was substantially reduced in both experiments when a valid precue preceded the imperative stimulus just in time to conclude refocusing of attention to the position of the imperative stimulus before it was presented. However, conditions with neutral precues yielded a normally sized Simon effect. In both experiments, the Simon effect decreased as the SOA grew when the precue was valid. At least for the Simon effect, the results can be interpreted as evidence that relative spatial coding is functionally related to the position of the focus of attention.     

Attentional focussing and spatial stimulus-response compatibility

Summary The relative functional significance of attention shifts and attentional zooming for the coding of stimulus position in spatial compatibility tasks is demonstrated by proposing and testing experimentally a tentative explanation of the absence of a Simon effect in Experiment 3 of Umiltà and Liotti (1987). It is assumed that the neutral point of the spatial frame of reference for coding spatial position is at the position where attention is focussed immediately before exposition of the stimulus pattern. If a stimulus pattern is exposed to the right or the left of this position a spatial compatibility effect can be observed when the stimulus-response pairing is incompatible. Generalizing from this, one can say that a spatial compatibility effect will be observed if the last step in attentional focussing of the stimulus attribute specifying the response is a horizontal or a vertical attention shift. If the last step in focussing is attentional zooming (change in the representational level attended to), the stimulus pattern is localized at the horizontal and the vertical positions where the last attention shift had positioned the focus. In this case the spatial code is neutral on these dimensions and so no spatial compatibility effect should result. To test this model we conducted two experiments. Experiment 1 replicated the finding of Umiltà and Liotti that there is no Simon effect in the condition with no delay between a positional cue (two small boxes on the left or right of a fixation cross) and the imperative stimulus, whereas in the condition with a delay of 500 ms a Simon effect was observed. In a comparison condition with a single, rather large cue instead of two small boxes (forcing attention to zoom in), no Simon effect was observed under either delay condition. Experiment 2 used a spatial compatibility task proper with the same experimental conditions as Experiment 1. But in contrast to those of Experiment 1, the results show strong compatibility effects in all cue and delay conditions. The absence of a Simon effect in some experimental conditions in Experiment 1 and the presence of a spatial compatibility effect proper in all conditions in Experiment 2 are consistently accounted for with the proposed attentional explanation of spatial coding and spatial compatibility effects.     

Modes of spatial coding in the Simon task*

Many models of the Simon effect assume that categorical spatial representations underlie the phenomenon. The present study tested this assumption explicitly in two experiments, both of which involved eight possible spatial positions of imperative stimuli arranged horizontally on the screen. In Experiment 1, the eight stimulus locations were marked with eight square boxes that appeared at the same time during a trial. Results showed gradually increasing Simon effects from the central locations to the outer locations. In Experiment 2, the eight stimulus locations consisted of a combination of three frames of spatial reference (hemispace, hemifield, and position relative to the fixation), with each frame appearing in different timings. In contrast to Experiment 1, results showed an oscillating pattern of the Simon effect across the horizontal positions. These findings are discussed in terms of grouping factors involved in the Simon task. The locations seem to be coded as a single continuous dimension when all are visible at once as in Experiment 1, but they are represented as a combination of the lateral categories (“left” vs. “right”) with multiple frames of reference when the reference frames are presented successively as in Experiment 2.     

Increased spatial salience in the social Simon task: A response-coding account of spatial compatibility effects

A spatial compatibility effect (SCE) is typically observed in forced two-choice tasks in which a spatially defined response (e.g., pressing a left vs. a right key) has to be executed to a nonspatial feature of a stimulus (e.g., discriminating red from green) that is additionally connoted by a spatial feature (e.g., the stimulus points to the left or the right). Responses are faster and more accurate when the response side and the spatial stimulus feature are compatible than when they are incompatible. Previous research has demonstrated that SCEs are diminished when stimuli from only one response category are responded to in individual go/no-go tasks, whereas SCEs reemerge when two participants work jointly on two complementary, individual go/no-go tasks in a joint go/no-go task setting. This social Simon effect has been considered evidence for shared task representations. We show that SCEs emerge in individual go/no-go tasks when the spatial dimension is made more salient, whereas SCEs are eliminated in joint go/no-go tasks when the spatial dimension is made less salient. These findings are consistent with an account of social Simon effects in terms of spatial response coding, whereas they are inconsistent with an account of shared task representations. The relevance of social factors for spatial response coding is discussed.     

Action planning during the presentation of stimulus sequences: Effects of compatible and incompatible stimuli

Experimental designs that require the simultaneous perception and reproduction of a stimulus sequence could help to clarify the relationship between perception and action. This contribution examines a specific stimulus-response compatibility with the reproduction of simple stimulus sequences. In the procedure a response just prepared or one to be prepared is confronted with a new incoming stimulus that is compatible or incompatible with the response. Interference is predicted from a framework in which stimulus perception and action control are assumed to share common codes.Five arrows were successively presented at 1-s intervals. The arrows pointed either to the left or to the right with equal probability. One of the five arrows was accompanied by a randomly presented go signal. Subjects then had to reproduce the sequence by pressing corresponding left or right keys while the stimulus presentation continued. Reaction-time latencies and reaction intervals within a sequence were analyzed in six experiments. Results showed increasing reaction-time latencies the later the go signal was presented — that is, the longer the sequence to be reproduced was. In contrast to previous findings, this effect interacted with the compatibility between the arrow displayed together with the go signal and the first reaction. It is argued that the go signal initiates a transfer of a cognitive action plan to a peripheral motor program and that this process is subject to interference the more the current stimulus is at odds with one of the first parameter specification.