Simon congruency effects based on stimulus and response numerosity

Three choice reaction time experiments documented a Simon-type congruence effect involving the numbers of stimuli and responses. In Experiment 1 the stimulus consisted of one or two high- or low-pitch tones, and participants were required to respond with one or two taps of a response key depending on stimulus pitch. Responses were faster when the number of tones matched the required number of response taps than when these numbers mismatched. Experiment 2 showed that a weaker version of this effect can also be obtained using visual stimuli, and Experiment 3 showed that the analogous effect can even be obtained, albeit very weakly, with bimodal stimuli. There was also evidence that the number of stimuli affected the rate of emitting the two-tap response. These results indicate that stimulus numerosity is processed automatically to the level at which it can affect the selection and possibly the execution of a varying number of responses.     

Simon congruency effects based on stimulus and response numerosity

Three choice reaction time experiments documented a Simon-type congruence effect involving the numbers of stimuli and responses. In Experiment 1 the stimulus consisted of one or two high- or low-pitch tones, and participants were required to respond with one or two taps of a response key depending on stimulus pitch. Responses were faster when the number of tones matched the required number of response taps than when these numbers mismatched. Experiment 2 showed that a weaker version of this effect can also be obtained using visual stimuli, and Experiment 3 showed that the analogous effect can even be obtained, albeit very weakly, with bimodal stimuli. There was also evidence that the number of stimuli affected the rate of emitting the two-tap response. These results indicate that stimulus numerosity is processed automatically to the level at which it can affect the selection and possibly the execution of a varying number of responses.     

Stimulus-response compatibility for absolute and relative spatial correspondence in reaching and in button pressing

Three experiments tested whether stimulus-response (S-R) compatibility might be a function of absolute (as opposed to relative) spatial correspondence-that is, the distance between a stimulus and the place of response. Experiment 1 studied reaching movements toward one of two targets in response to one of six visual stimuli. Stimulus-response pairs that shared relative position were faster than those that did not, and reaction time was faster when the stimulus and one of the potential targets were in close proximity. In Experiment 2 the same effects were found when the hands started from a different position, implicating stimulus target distance, rather than stimulus-hand distance as the critical variable. Experiment 3 employed keypress responses instead of reaches, and the distance effect was nearly absent. The implications of these results are discussed in terms of categorical (e.g. left-right) vs. quantitative (e.g. distance) S-R variables in spatial compatibility.     

Transfer of orthogonal stimulus-response mappings to an orthogonal Simon task

When up-down stimulus locations are mapped to left-right keypresses, an overall advantage for the up-right/down-left mapping is often obtained that varies as a function of response eccentricity. This orthogonal stimulus-response compatibility (SRC) effect also occurs when stimulus location is irrelevant, a phenomenon called the orthogonal Simon effect, and has been attributed to correspondence of stimulus and response code polarities. The Simon effect for horizontal stimulus-response (S-R) arrangements has been shown to be affected by short-term S-R associations established through the mapping used for a prior SRC task in which stimulus location was relevant. We examined whether such associations also transfer between orthogonal SRC and Simon tasks and whether correspondence of code polarities continues to contribute to performance in the Simon task. In Experiment 1, the orthogonal Simon effect was larger after practising with an up-right/down-left mapping of visual stimuli to responses than with the alternative mapping, for which the orthogonal Simon effect tended to reverse. Experiment 2 showed similar results when practice was with high (up) and low (down) pitch tones, though the influence of practice mapping was not as large as that in Experiment 1, implying that the short-term S-R associations acquired in practice are at least in part not modality specific. In Experiment 3, response eccentricity and practice mapping were shown to have separate influences on the orthogonal Simon effect, as expected if both code polarity and acquired S-R associations contribute to performance.     

Stimulus-response compatibilities between vertically oriented stimuli and horizontally oriented responses: the effects of hand position and posture

Stimulus-response (S-R) compatibility effects between vertically oriented stimuli (above or below fixation) and horizontally oriented responses (left or right switch deflections by a single hand) have been shown to depend both on which hand responds (Bauer & Miller, 1982) and on the location at which the response is made (eccentricity on a frontoparallel line; Michaels, 1989). In the latter study, hand position and hand posture were confounded, so it is unclear which variable determined the compatibility effect. In Experiment 1, the importance of effector position was tested. Vertically oriented stimuli were paired with a horizontal response solicited at different locations but always involving the same hand posture. Compatibility effects emerged, and their direction depended on position. In Experiment 2, the compatibilities were not evident in a simple reaction time paradigm, so the effect was not due to differential ease of responses. In Experiment 3, a change in hand posture (palm up or palm down) at the same location (the body midline) also affected the compatibilities. It was concluded that the S-R compatibility of orthogonally oriented stimuli and responses is influenced by (1) which hand responds, (2) the location of that hand, and (3) its posture. The results imply that both postural and positional states of the action system affect S-R compatibility.     

Numerosity and rhythmicity in stimulus-response compatibility

When people must respond discriminatively to 1 or 2 stimuli by making 1 or 2 taps of a response key, they initiate the response more rapidly when the correct number of taps matches the number of stimuli (compatible condition) than when it mismatches (incompatible condition; J. O. Miller, S. G. Atkins, & F. Van Nes, 2005). Miller et al. sometimes found an effect of compatibility on response execution time, as reflected in the interresponse intervals between successive taps. The authors report 2 further experiments (N = 8 participants) in which they generalized the numerosity compatibility effects on response-initiation time and interresponse intervals to 2- versus 3-stimulus sequences. In addition, they varied gap length between stimuli to see whether the rhythm of the stimulus would influence that of the response. Weak rhythmicity effects were repeatedly found, but those were too small to suggest a plausible alternative explanation for the numerosity compatibility effect on response-initiation time.     

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.     

Numerosity and Rhythmicity in Stimulus-Response Compatibility

When people must respond discriminatively to 1 or 2 stimuli by making 1 or 2 taps of a response key, they initiate the response more rapidly when the correct number of taps matches the number of stimuli (compatible condition) than when it mismatches (incompatible condition; J. O. Miller, S. G. Atkins, & F. Van Nes, 2005). Miller et al. sometimes found an effect of compatibility on response execution time, as reflected in the interresponse intervals between successive taps. The authors report 2 further experiments (N=8 participants) in which they generalized the numerosity compatibility effects on response-initiation time and interresponse intervals to 2- versus 3-stimulus sequences. In addition, they varied gap length between stimuli to see whether the rhythm of the stimulus would influence that of the response. Weak rhythmicity effects were repeatedly found, but those were too small to suggest a plausible alternative explanation for the numerosity compatibility effect on response-initiation time.     

Control of stimulus-response translation in dual-task performance

In contradiction to stimulus-response- (S-R-) translation bottleneck models of dual-task control, stimulus processing in a primary task is affected by its compatibility with the response in a secondary, later performed task (Hommel, 1998a)- an indication of parallel S-R translation. Here we show that this backward-compatibility effect is independent of working-memory load, whether this is induced by an extra memory task (Experiment 1) or by increasing the number of S-R alternatives in the primary task (Experiment 2). However, backward effects occur even when the secondary task is no longer carried out (Experiment 3) and they are strongly affected by the inconsistency of previously used S-R mappings (Experiment 4). These findings suggest that S-R translation is (or can be) capacity-independent and automatic even under multiple-task conditions, and that it is mediated by direct S-R associations that emerge after only little practice.     

A role for set in the control of automatic spatial response activation

Spatial stimulus-response (S-R) compatibility effects are widely assumed to reflect the automatic activation of a spatial response by the spatial attributes of a stimulus. The experiments reported here investigate the role of the participant's set in enabling or interacting with this putatively automatic spatial response activation. Participants performed a color discrimination task (Experiment 1) or a localization task (Experiment 2). In each experiment, two different S-R mappings were used and a task-cue indicated the appropriate mapping on each trial. S-R compatibility and the time between the task-cue and target were manipulated, and compatibility effects were assessed as a function of (a) the time between the task-cue and the stimulus, and (b) whether the S-R mapping repeated or switched on consecutive trials. Critically, whether response mappings repeated or switched on consecutive trials determined the relation between compatibility effects and the time between task-cue and stimulus. These results are discussed in terms of an interaction between automatic spatial response activation and the participant's set.     

The prevalence effect in two-dimensional stimulus-response compatibility is a function of the relative salience of the dimensions

When stimulus-response (S-R) sets vary along horizontal and vertical dimensions, a right-left prevalence effect is often obtained in which the horizontal compatibility effect is larger than the vertical compatibility effect. Vu and Proctor (2001) showed that the prevalence effect varies as a function of the dimension made salient by the response configuration. A salient features coding interpretation of this result implies that manipulating the salience of the stimulus display should produce similar results and that S-R translation should be fastest when salient features of the stimulus and the response sets correspond. Experiment 1 manipulated spatial proximity to make the vertical or the horizontal stimulus dimension salient. Neutral displays yielded a typical right-left prevalence effect, and this effect was enhanced by horizontal-salient displays and eliminated by vertical-salient displays. Experiments 2 and 3 showed that the benefit for horizontal (or vertical) compatibility was larger when the salient features of both the stimulus and the response sets emphasized the horizontal (or the vertical) dimension than when only one did. The results support salient features coding as an explanation for the prevalence effect obtained with two-dimensional S-R arrangements.     

Dilution of compatibility effects in Simon-type tasks depends on categorical similarity between distractors and diluters

The presence of a distracting stimulus during performance of the Stroop color-naming task leads to dilution of the Stroop effect. Because the automatic activation of word meaning may interfere with the task-relevant stimulus feature (text color; stimulus-stimulus [S-S] interference) and the response (saying the text color; stimulus-response [S-R] interference), it is unclear which of these types of interference is diluted. We introduce a new dilution paradigm using word- and arrow-based Simon tasks, in which only S-R interference is present. Participants made a left or right response to a central color target. A task-irrelevant location-word (Experiment 1) or arrow (Experiment 2) distractor adjacent to the target produced S-R compatibility effects. An additional neutral word or symbol series (diluter) was sometimes presented on the opposite side of the target from the distractor. The compatibility effect was smaller when the distractor and diluter category domains matched than when they mismatched. This result provides evidence that S-R compatibility effects are susceptible to the presence of diluters that are categorically similar to the distractors.     

Auditory stimulus-response compatibility: Is there a contribution of stimulus-hand correspondence?

 Simon, Hinrichs, and Craft found that when subjects responded to a tone in the left or right ear with a left or right keypress, both ear-response-location correspondence and ear-hand correspondence affected reaction time. This outcome is in contrast to results obtained for auditory and visual Simon tasks (i.e., tasks in which stimulus location is irrelevant) as well as results obtained in visual stimulus-response (S-R) compatibility studies, which show only an effect of spatial S-R correspondence. Experiment 1 was a replication of Simon et al.'s experiment in which spatial mapping and hand placement (uncrossed, crossed) were varied. The results were inconsistent with those of Simon et al., showing no ear-hand compatibility effect. Experiment 2 was a second replication with an additional condition examined in which the stimuli were visual locations. The results showed no contribution of stimulus-hand correspondence for either auditory or visual stimuli. Experiment 3 was a replication of another experiment by Simon et al. in which tone pitch was relevant and tone location irrelevant. Like Simon et al.'s data, our results showed no indication that stimulus-hand correspondence is a significant factor. Overall, our results imply that regardless of whether tone location is relevant or irrelevant, ear-response-location correspondence is the only factor that contributes to S-R compatibility in auditory two-choice reaction tasks. Received: 15 March 1999 / Accepted: 8 June 1999     

Is automatic imitation a specialized form of stimulus–response compatibility? Dissociating imitative and spatial compatibilities

In recent years research on automatic imitation has received considerable attention because it represents an experimental platform for investigating a number of interrelated theories suggesting that the perception of action automatically activates corresponding motor programs. A key debate within this research centers on whether automatic imitation is any different than other long-term S-R associations, such as spatial stimulus-response compatibility. One approach to resolving this issue is to examine whether automatic imitation shows similar response characteristics as other classes of stimulus-response compatibility. This hypothesis was tested by comparing imitative and spatial compatibility effects with a two alternative forced-choice stimulus-response compatibility paradigm. The stimulus on each trial was a left or right hand with either the index or middle finger tapping down. Speeded responses were performed with the index or middle finger of the right hand in response to the identity or the left-right spatial position of the stimulus finger. Two different tasks were administered: one that involved responding to the stimulus (S-R) and one that involved responding to the opposite stimulus (OS-R; i.e., the one not presented on that trial). Based on previous research and a connectionist model, we predicted standard compatibility effects for both spatial and imitative compatibility in the S-R task, and a reverse compatibility effect for spatial compatibility, but not for imitative compatibility, in the OS-R task. The results from the mean response times, mean percentage of errors, and response time distributions all converged to support these predictions. A second noteworthy result was that the recoding of the finger identity in the OS-R task required significantly more time than the recoding of the left-right spatial position, but the encoding time for the two stimuli in the S-R task was equivalent. In sum, this evidence suggests that the processing of spatial and imitative compatibility is dissociable with regard to two different processes in dual processing models of stimulus-response compatibility.     

The role of instructions,practice, and stimulus-hand correspondence on the Simon effect

Numerous studies of two-choice reaction tasks, including auditory and visual Simon tasks (i.e., tasks in which stimulus location is irrelevant) and visual compatibility tasks, have found that only spatial stimulus-response (S-R) correspondence affected S-R compatibility. Their results provided no indication that stimulus-hand correspondence was a significant factor. However, Wascher et al. (2001) suggested that hand coding plays a role in visual and auditory Simon tasks when the instructions are in terms of the finger/hand used for responding. The present experiments examined whether instructing subjects in terms of response locations or fingers/hands influenced the Simon effect for visual and auditory tasks. In Experiments 1-3, only spatial S-R correspondence contributed significantly to the Simon effect, even when the instructions were in terms of the fingers/hands. However, in Experiment 4, which used auditory stimuli and finger/hand instructions, the contribution of stimulus-hand correspondence increased with practice.     

Stimulus-Response Compatibility and Motor-Programming Effects: A Test of Theoretical Accounts of Compatibility

Traditional mental coding accounts of stimulus-response (S-R) compatibility suggest that the S-R translation stage is the locus for the effect (Umilta & Nicoletti, 1990; Wallace, 1971). However, recent response-priming accounts have suggested that the S-R translation and response-programming stages may interact to produce S-R compatibility effects (Kornblum, Hasbroucq, & Osman, 1990; Wickens. 1984; Zelaznik & Franz, 1990). Our study investigated the nature of the relation between these two stages relative to the S-R compat- ibility effect. Subjects performed a choice reaction-time task in response to visual stimuli. The critical manipulations in the study were of compatibility and response programming. The analysis revealed a significant compatibility effect but no interaction between the factors affecting compatibility and those affect- ing response programming. The results were consistent with the notion that the S-R translation stage of information processing is the locus of S-R compatibility effects. Thus S-R compatibility is an effect of the mental operations that occur within the S-R translation stage of human information processing.     

Division of attention: The single-channel hypothesis revisited

Two experiments are reported in which subjects performed two forced-paced serial reaction time tasks separately and together at their maximum sustainable rates of information processing. Experiment 1 investigated the effects on the relationship between single- and dual-task performance of using tasks with the same or different input and output modality characteristics; an additional condition tested the effects on this relationship of using tasks with higher S-R compatibility. Experiment 2 investigated the effects on the relationship between single- and dual-task performance of varying information load (number of S-R alternatives). No significant differences were found in subjects' capacities to process information in single- and dual-task conditions. This finding was unaffected by: (a) the absolute information levels of the tasks, (b) whether inputs and/or outputs involved the same or different modalities, or (c) the level of S-R compatibility. The data from both experiments provide strong support for the single-channel hypothesis.     

Working memory involvement in dual-task performance: Evidence from the backward compatibility effect

In three experiments, the authors supported the hypothesis that parallel response activation seen in dual-task performance results from holding Task 2 rules in working memory (WM) while performing Task 1. To this end, the authors used the backward compatibility effect (BCE; quicker primary responses when the Task 2 response is compatible with codes of Task 1) as a marker for parallel response activation and manipulated WM load. Increasing the number of primary task rules from two to four did not modulate BCE, replicating Hommel and Eglau (2002), but a higher load condition, involving six primary task rules, reduced the BCE to nonsignificant levels. Experiment 3 further showed that WM is loaded by rules associating abstract stimulus categories to responses, and not by rules tt associate individual stimuli to responses (S-R rules).     

Somatosensory prior entry

The perceived timing of sensory events does not necessarily match the actual timing. In the present study, we investigated the effect of location of attention on the perceived timing of somatosensory stimuli. Participants judged the temporal order of two taps, delivered one to each hand, with taps presented at different elevations (upper and lower) on the opposing hands. The task was to discriminate the elevation of the tap presented first (or second). This vertical discrimination task was orthogonal to the horizontal attentional cuing manipulation, removing the response bias confound that has undermined earlier studies investigating the impact of attention on the perceived timing of sensory stimuli. We manipulated spatial attention either (1) exogenously (Experiment 1) in 13 participants, using brief taps to either the left or right hand, or (2) endogenously (Experiment 2) in 22 participants, using centrally presented symbolic cues. The results supported the hypothesis that attended stimuli are perceived more rapidly than unattended stimuli. This effect was larger when attention was exogenously manipulated. Previous research has demonstrated a similar effect for visual stimuli. The present study, which extends this result to somatosensory perception, indicates that the phenomenon may represent a more global feature of the perceptual system, which is possibly mediated by a common modality-independent mechanism.     

The Lateral Coding of Rotations

A number of experimental studies have consistently shown the locus of spatial S-R compatibility effects to be the selection of the response within an abstract memory code. The purpose of the present study was to test, in the particular case of wheel rotations, the general proposition that any response that a subject internally codes in terms of left and right may be interfered with by the lateral location of the stimuli in a Simon paradigm. Experiment 1 showed that the auditory Simon effect occurred in a task where the subjects had to rotate a steering wheel bimanually either clockwise or counterclockwise according to sound pitch, despite the fact that responses of this kind are undefined with respect to laterality. Experiment 2 confirmed this result in a unimanual rotation condition and suggested that the ear-rotation compatibility effect may be added to the effect of a biomechanical factor, pronation versus supination, supporting the idea of an abstract motor code. In Experiment 3, subjects rotated the steering wheel with their hands on the lowest part of the wheel. When the response movement made the spot of a C.R.T. move laterally in accordance with the performed rotation, the subjects coded their response directly in terms of its effect on the visual display. For subjects not receiving visual feedback, no compatibility effect occurred. However, the individual data were compatible with the notion that some subjects in this group coded their responses in terms of wheel rotations, and others in terms of hand movements.