A Simon effect for stimulus-response duration

A non-spatial variant of the Simon effect for the stimulus-response (S-R) feature of duration is reported. In Experiment 1 subjects were required to press a single response key either briefly or longer in response to the colour of a visual stimulus that varied in its presentation duration. Short keypresses were initiated faster with short than with long stimulus duration whereas the inverse was observed with long keypresses. In Experiment 2 subjects were required to press a left or right key (according to stimulus form) either briefly or longer (according to stimulus colour). The stimuli concurrently varied in their location (left or right) and duration (short or long), which were both task irrelevant. Approximately additive correspondence effects for S-R location and S-R duration were observed. To summarize, the results suggest that the irrelevant stimulus features of location and duration are processed automatically and prime corresponding responses in an independent manner.     

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.     

Interference effects in an auditory Stroop task: congruence and correspondence

Two auditory Stroop experiments are reported in which subjects responded vocally to the gender of the speaker of stimulus words. The interference effects found were broadly similar to those of a manual-response auditory Stroop paradigm although response-set effects appeared to operate in the data. In all experimental conditions responses were slower to stimulus words which named potential responses than to those words which did not. Such effects have not been found in previous manual-response experiments and it is suggested that the relatively high degree of S-R and of ideomotor compatibility in the vocal response task, compared with the manual task, may be responsible for this difference between the paradigms.The second experiment enabled a comparison to be made between the effects of congruence between relevant and irrelevant elements of the Stroop stimulus and the effects of correspondence between the response and the irrelevant aspect of the stimulus. A predominant influence of congruence was found when the subject responded using words semantically related to speaker gender, but an effect of correspondence was obtained when an arbitrary pairing of response word and speaker gender was required.     

Anticipatory response control in motor sequence learning: evidence from stimulus-response compatibility

Three experiments using a serial four-choice reaction-time (RT) task explored the interaction of sequence learning and stimulus-based response conflict. In Experiment 1, the spatial stimulus-response (S-R) mapping was manipulated between participants. Incompatible S-R mappings produced much higher RTs than the compatible mapping, but sequence learning decreased this S-R compatibility effect. In Experiment 2, the spatial stimulus feature was made task-irrelevant by assigning responses to symbols that were presented at unpredictable locations. The data indicated a Simon effect (i.e., increased RT when irrelevant stimulus location is spatially incompatible with response location) that was reduced by sequence learning. However, this effect was observed only in participants who developed an explicit sequence representation. Experiment 3 replicated this learning-based modulation of the Simon effect using explicit sequence-learning instructions. Taken together, the data support the notion that explicit sequence learning can lead to motor 'chunking', so that pre-planned response sequences are shielded from conflicting stimulus information.     

A feature-integration account of sequential effects in the Simon task

Recent studies have shown that the effects of irrelevant spatial stimulus-response (S-R) correspondence (i.e., the Simon effect) occur only after trials in which the stimulus and response locations corresponded. This has been attributed to the gating of irrelevant information or the suppression of an automatic S-R route after experiencing a noncorresponding trial—a challenge to the widespread assumption of direct, intentionally unmediated links between spatial stimulus and response codes. However, trial sequences in a Simon task are likely to produce effects of stimulus- and response-feature integration that may mimic the sequential dependencies of Simon effects. Four experiments confirmed that Simon effects are eliminated if the preceding trial involved a noncorresponding S-R pair. However, this was true even when the preceding response did not depend on the preceding stimulus or if the preceding trial required no response at all. These findings rule out gating/suppression accounts that attribute sequential dependencies to response selection difficulties. Moreover, they are consistent with a feature-integration approach and demonstrate that accounting for the sequential dependencies of Simon effects does not require the assumption of information gating or response suppression.     

Effects of irrelevant spatial S-R compatibility depend on stimulus complexity

Summary Choice-reaction time is known to depend on the spatial correspondence of stimulus and response, even if the stimulus location is irrelevant to the task (Simon effect). An experiment investigated whether this effect depends on stimulus complexity — i. e., on whether properties of the stimulus render stimulus discrimination easy or difficult. It was hypothesized that high demands on discrimination slow down the processing of stimulus identity in relation to location, so that the facilitating or conflicting location code has more time to decay, thus losing impact on response selection. In fact, the results revealed an effect of irrelevant spatial S-R correspondence with easy, but not with difficult, stimulus discrimination. This finding resolves an apparent contradiction between the results of several previous experiments on the Simon effect.The other central argument rests on findings of Stoffer (1991) obtained with a single frame. These, however, have recently been challenged by Hommel (1993 b).     

Influence of irrelevant information on human performance: Effects of S-R association strength and relative timing

Six experiments examined effects of stimulus-response (S-R) association strength and relative timing on the magnitude of consistency effects for irrelevant information in Stroop-like tasks. Keypresses were made to two-dimensional stimuli (a colour or location word surrounded by a coloured rectangle or arrow), with the irrelevant information presented simultaneously with or prior to the relevant information. With simultaneous presentation, irrelevant information affected performance regardless of whether its S-R association was weak or strong, if the relevant S-R association was weak (e.g., colour word to keypress). However, a weak irrelevant S-R association (location word to keypress) had little effect when paired with a strong relevant S-R association (arrow direction to keypress), except when the stimulus onset asynchrony (SOA) between the irrelevant and relevant information was 300 ms. When the relevant information was colour, the effect of an irrelevant colour word persisted at a 500-ms SOA but that of an irrelevant physical colour did not, reflecting different decay functions for irrelevant verbal and non-verbal information. The persisting effect of an irrelevant colour word was reduced by articulatory suppression and eliminated at extended SOAs of 3 s. The results indicate that whether the consistency effect patterns are symmetric or asymmetric is determined by the relative strengths of the relevant and irrelevant S-R associations, as specified by the criteria of conceptual and mode similarity. The magnitude of the consistency effect is also a function of the temporal overlap of the resulting response activation, which is determined primarily by mode similarity.     

A Simon effect in memory retrieval: Evidence for the response-discrimination account

According to the traditional view, the effects of irrelevant stimulus location on the selection of a spatial response to a nonspatial stimulus feature (Simon effect) result from long-term associations between spatial stimulus codes and spatially corresponding response codes. According to an alternative view, the response-discrimination account, Simon effects arise from interactions between spatial stimulus codes and response labels in working memory (WM). The latter account predicts Simon effects when participants use spatial labels for response representation in WM, even when the actual responses have no spatial features (e.g., saying the word "plate"). The prediction was tested in an experiment, in which participants first encoded two words at different locations, and then responded to a stimulus by saying the word from the location indicated by stimulus color. The manipulation concerned the correspondence between irrelevant location of the colored stimulus and the retrieval cue for the vocal responses (i.e., word location in the encoding display). A Simon effect in memory retrieval was observed, supporting the response-discrimination account.     

A memory-based, Simon-like, spatial congruence effect: Evidence for persisting spatial codes

The Simon effect refers to the finding that in a task where stimulus location is irrelevant, reaction time is faster when stimulus and response locations are congruent than when they are not. Dominant theories of the Simon effect have generally attributed this spatial congruence effect to a spatial code automatically generated upon stimulus presentation. A common assumption of these theories is that this spatial code decays in less than a few hundred milliseconds following stimulus onset. We report two working-memory experiments suggesting a reexamination of this assumption—a Simon-like spatial congruence effect persisted over a delay of as long as 2400 ms. We propose that, in addition to generating short-lived perceptual codes, spatial information may be coded in working memory as part of the context associated with stimulus events. When reactivated by cues from the original event, such information may influence response selection and produce spatial congruence effects (in this case, positive when participants made a “yes” response and negative when they made a “no” response).     

Interactions between stimulus-stimulus congruence and stimulus-response compatibility

According to a central claim of Kornblum's dimensional-overlap model, response-related processes do not start before stimulus-related processes have been completed, which implies an additive relationship between effects of stimulus-stimulus congruence and stimulus-response compatibility. Three experiments were conducted to test this prediction. In Exp. 1, additive effects of color-word congruence (Stroop effect) and irrelevant spatial S-R compatibility (Simon effect) were in fact obtained. However, interactions between congruence and compatibility were observed in Exp. 2, where flanker-target congruence was varied, and in Exp. 3, where inter-level congruence of multi-level letters was manipulated. It is argued that these findings are inconsistent with the seriality assumption of the dimensional-overlap model, but that they support models claiming a temporal overlap of stimulus and response processing instead.     

The influence of dimensional overlap on location-related priming in the Simon task

Choice reaction times are shorter when stimulus and response locations are compatible than when they are incompatible as in the Simon effect. Recent studies revealed that Simon effects are strongly attenuated when there is temporal overlap with a different high-priority task, accompanied by a decrease of early location-related response priming as reflected in the lateralized readiness potential (LRP). The latter result was obtained in a study excluding overlap of stimulus location with any other dimension in the tasks. Independent evidence suggests that location-related priming might be present in conditions with dimensional overlap. Here we tested this prediction in a dual-task experiment supplemented with recording LRPs. The secondary task was either a standard Simon task where irrelevant stimulus location overlapped with dimensions of the primary task or a Stroop-like Simon task including additional overlap of irrelevant and relevant stimulus attributes. At high temporal overlap, there was no Simon effect nor was there stimulus-related response priming in either condition. Therefore stimulus-triggered response priming seems to be abolished in conditions of limited capacity even if the likelihood of an S–R compatibility effect is maximized.     

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 the Simon effect: toward a conceptual clarification.

The current view that the Simon effect (Simon & Small, 1969) reflects stimulus-response compatibility (SRC) is questioned. Previous accounts of the Simon effect have overlooked stimulus congruity (SC), the correspondence relation borne by the two simultaneous aspects of the stimulus, a factor inevitably confounded in the Simon paradigm with irrelevant spatial S-R correspondence. The Hedge and Marsh (1975) reversal effect, replicated in Experiment 1, is reinterpreted as decisive evidence that the Simon effect is entirely accounted for by SC. Furthermore, in Experiment 2 irrelevant S-R correspondence was manipulated in the absence of any variation of SC, and the Simon effect vanished. It is concluded that the Simon effect, contrary to current opinion, represents a spatial variant of the Stroop effect and is irrelevant to the SRC issue. The view that mental operations proceed automatically at the stage of response determination loses one of its strongest empirical arguments.     

Horizontal and vertical Simon effect: different underlying mechanisms?

Reaction times are usually faster when stimulus and response occur at the same location than when they do not, even if stimulus location is irrelevant to the task (Simon effect). This effect was found with both horizontal and vertical stimulus-response arrangements. The same mechanisms have been proposed to be involved in either case. Here, we compared a horizontal and a vertical Simon task by means of a RT time-course analysis of the Simon effect. Also, we analysed the lateralised readiness potential (LRP), an index of covert response-preparation processes. In the horizontal task, the Simon effect decays over time and pre-activation occurs above the motor cortex ipsilateral to the stimulus. In contrast, the Simon effect does not decay over time and no early incorrect LRP deflection is observed in the vertical task. These findings suggest that typical activation accounts can fit only the horizontal Simon effect, while a translation explanation is more suitable for the vertical Simon effect.     

Effect of conflicting cues on information processing: the 'Stroop effect' vs. the 'Simon effect'

This study examined the relationship between two sources of interference in human information processing: the Stroop effect and the Simon effect. Forty subjects pressed a left- or right-hand key in response to a Stroop color word located on the left or right side of a screen. For one group, ink color was the relevant cue and, for another group, word meaning was the relevant cue. Independent variables were: congruence, i.e., agreement or lack thereof between the ink color and meaning of the Stroop word; spatial correspondence, i.e., agreement or lack thereof between the location of the Stroop word and the location of the key used to make the response; and stimulus duration, i.e., 400 or 100 ms. Each of these variables had a significant effect on RT, and there were no significant interactions. According to Sternberg's additive-factor logic, these findings suggest that the Stroop effect (congruence) and the Simon effect (spatial correspondence) involve separate stages of processing. If one assumes that manipulation of stimulus duration effects the encoding stage, then results also suggest that neither the Stroop effect nor the Simon effect involves the stimulus encoding stage.     

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     

Co-occurrence of sequential and practice effects in the Simon task: Evidence for two independent mechanisms affecting response selection

The Simon effect refers to the observation that responses to a relevant stimulus dimension are faster and more accurate when the stimulus and response spatially correspond than when they do not, even though stimulus position is irrelevant. Recent findings have suggested that the Simon effect can be strongly modulated by prior practice with a spatially incompatible mapping and by correspondence sequence. Although practice is thought to influence conditional stimulus —response (S-R) processing, leaving response priming through the unconditional route unaffected, sequential effects are thought to represent trial-by-trial adaptations that selectively involve unconditional S —R processing. In the present study, we tested this assumption by assessing the effects of correspondence sequence both when the Simon task alone was performed and when it was preceded by a spatial compatibility task with either incompatible (Experiments 1-2) or compatible (Experiment 2) instructions. The observation that practice and correspondence sequence co-occur and exert additive effects strongly demonstrates that the two factors affect different processing routes.     

Spontaneous decay of response-code activation

Summary Two experiments investigated whether theTwo experiments investigated whether the Simon effect (i. e.., faster responses to spatially corresponding than to noncorresponding stimuli, with stimulus location being irrelevant) is affected by the frequency of noncorrespondence trials. Stimulus discriminability (Experiment 1) and immediate or delayed stimulus formation (Experiment 2) was varied in order to manipulate the temporal relationship between coding of the relevant stimulus information and of stimulus location. As was expected, the Simon effect decreased from high to low discriminability and from immediate- to delayed-stimulus formation. This is consistent with the notion of a gradual decay of location-induced response-code activation. Moreover, the Simon effect decreased with increasing frequency of noncorrespondence trials and was even reversed with higher frequency. This demonstrates strategic preparation of stimulus processing and/or response selection based on irrelevant location information. However, frequency did not modify the interaction between S-R correspondence and stimulus discriminability or stimulus formation, this suggesting that code decay is not a result of a strategy, but an automatic process.     

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.     

Between-task transfer of learning from spatial compatibility to a color stroop task

Responses to a relevant stimulus dimension are faster and more accurate when the stimulus and response spatially correspond compared to when they do not, even though stimulus position is irrelevant (Simon effect). It has been demonstrated that practicing with an incompatible spatial stimulus-response (S-R) mapping before performing a Simon task can eliminate this effect. In the present study we assessed whether a learned spatially incompatible S-R mapping can be transferred to a nonspatial conflict task, hence supporting the view that transfer effects are due to acquisition of a general "respond to the opposite stimulus value" rule. To this aim, we ran two experiments in which participants performed a spatial compatibility task with either a compatible or an incompatible mapping and then transferred, after a 5 min delay, to a color Stroop task. In Experiment 1, responses were executed by pressing one of two keys on the keyboard in both practice and transfer tasks. In Experiment 2, responses were manual in the practice task and vocal in the transfer task. The spatially incompatible practice significantly reduced the color Stroop effect only when responses were manual in both tasks. These results suggest that during practice participants develop a response-selection strategy of emitting the alternative spatial response.