Transfer of response codes from choice-response to go/no-go tasks

The present study investigated the conditions for observing the Simon effect in go/no-go tasks. The Simon effect denotes faster and more accurate responses when irrelevant stimulus location and response location correspond than when they do not correspond. In four experiments, participants performed both in a choice-response task (CRT) and in a go/no-go task, and we varied the order and the similarity of the tasks. In the CRT, participants pressed a left key to one stimulus colour and a right key to another stimulus colour; in the go/no-go task, participants pressed one (e.g., left) key to one stimulus colour and refrained from responding to the other stimulus colour. As expected, Simon effects were consistently observed in the CRT. In contrast, Simon effects in the go/no-go task were only observed when it followed the CRT and when the mapping of stimulus colours to response locations was preserved between tasks (i.e., in Experiment 4). Results suggest that transfer of a particular S–R rule including response location from the CRT to the go/no-go task was responsible for the Simon effect in the latter task. In general, results are consistent with a response-discrimination account of the Simon effect.     

Inverting the Simon effect by intention

Summary The Simon effect indicates that choice reactions can be performed more quickly if the response corresponds spatially to the stimulus - even when stimulus location is irrelevant to the task. Two experiments tested an intentional approach to the Simon effect that assigns a critical role to the cognitively represented action goal (i. e., the intended action effect). It was assumed that the direction of the Simon effect depends on stimulus-goal correspondence, that is, that responses are faster with spatial correspondence of stimulus and intended action effect. Experiment 1 confirmed that the direction of the Simon effect was determined by spatial correspondence of stimulus and intended action effect, the latter having been manipulated by different instructions. Experiment 2 indicated that effects of correspondences unrelated to the action goal (i. e., stimulus to hand location or to anatomical mapping of the hand), contributed additively to the resulting Simon effect. It is discussed how current approaches to the Simon effect can be elaborated to account for these results.     

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.     

Processing irrelevant location information: Practice and transfer effects in choice-reaction tasks

Left or right keypresses to a relevant stimulus dimension are faster when the stimulus location, although irrelevant, corresponds with that of the response than when it does not. This phenomenon, called the Simon effect, persisted across 1,800 trials of practice, although its magnitude was reduced. Practice with the relevant stimulus dimension presented at a centered location had little influence on the magnitude of the Simon effect when irrelevant location was varied subsequently, and practice with location irrelevant prior to performing with location relevant slowed responses. After practice responding to stimulus location with an incompatible spatial mapping, the Simon effect was reversed (i.e., responses were slower when stimulus location corresponded with response location) when location was made irrelevant. When the response keys were labeled according to the relevant stimulus dimension (the Hedge and Marsh [1975] task variation), this reversal from practice with a spatially incompatible mapping was found for both the congruent and the incongruent relevant stimulus-response mappings. Thus, task-defined associations between stimulus location and response location affect performance when location is changed from relevant to irrelevant, apparently through producing automatic activation of the previously associated response.     

Perceptual and attentional factors in encoding irrelevant spatial information

Numerous studies found superior performance when the irrelevant location of a stimulus and response location were corresponding than when they were not corresponding (Simon effect), suggesting that stimulus location is processed in an obligatory manner. The present study compared Simon effects from the location of a relevant (i.e., to-be-attended) object to those from the location of an irrelevant (i.e., to-be-ignored) object. In four experiments, participants were presented with a rectangular frame and a square, with the relevant object in green or red color and the irrelevant object in gray or white color. Participants’ task was to respond with a lateral keypress to the color of the relevant object, and we varied spatial correspondence between the location of the relevant or the irrelevant object and the response, respectively. Results consistently showed larger Simon effects from the location of the relevant than from the irrelevant object, even when the irrelevant object was made very salient. These results suggest that location processing is largely confined to relevant (i.e., attended) objects, stressing the role of attention shifts for location encoding.     

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.     

The enhanced Simon effect for older adults is reduced when the irrelevant location information is conveyed by an accessory stimulus

The Simon effect, better performance when irrelevant stimulus location corresponds with the response location than when it does not, typically is larger for older than younger adults. However, Simon and Pouraghabagher [Simon, R. J., & Pouraghabagher, A. R. (1978). The effect of aging on the stages of processing in a choice reaction time task. Journal of Gerontology, 33, 553-561] found no age difference using an accessory-stimulus Simon task in which the relevant dimension was the color of a visual stimulus and the irrelevant dimension the location of a tone. Experiment 1 confirmed that older adults show a larger Simon effect than younger adults for the visual Simon task and that this age-related deficit is reduced or eliminated for the auditory-accessory task. Experiment 2 provided evidence suggesting that a small part of the age-related deficit in the visual Simon task is due to having to code the location of the relevant stimulus, but Experiment 3 showed that the majority of the deficit is due to the relevant and irrelevant information being conveyed by the same stimulus. Reaction-time distribution analyses show similar functions for younger and older adults, suggesting that the time course of activation is similar for both age groups.     

Evidence for gating of direct response activation in the Simon task

TheSimon effect denotes faster responses when the task-irrelevant stimulus position corresponds to the response position than when it does not. Accounts of this effect assume that stimulus position automatically activates a spatially corresponding response while the correct response is being computed. Yet the Simon effect has been found to be reduced after noncorresponding trials. Some authors have interpreted these sequential modulations of the Simon effect as evidence for a mechanism gating positionbased response activation. Alternatively, sequential modulations have been explained in terms of feature-integration processes, which depend upon the fact that different sequences of spatial-correspondence conditions covary with different degrees of feature overlap between subsequent trials. The present study investigates whether sequential modulations of the Simon effect can occur when feature overlap in the different conditions is the same. Therefore, a Simon task with four stimulus positions and two response positions was used. Sequential modulations of the Simon effect were found in trial sequences with constant amounts of feature overlap between trials. Although the feature-integration account cannot explain this result, it is consistent with the idea of a gating (i.e., cognitive control) mechanism.     

Effects of saccades and response type on the Simon effect: If you look at the stimulus,the Simon effect may be gone

The Simon effect has most often been investigated with key-press responses and eye fixation. In the present study, we asked how the type of eye movement and the type of manual response affect response selection in a Simon task. We investigated three eye movement instructions (spontaneous, saccade, and fixation) while participants performed goal-directed (i.e., reaching) or symbolic (i.e., finger-lift) responses. Initially, no oculomotor constraints were imposed, and a Simon effect was present for both response types. Next, eye movements were constrained. Participants had to either make a saccade toward the stimulus or maintain gaze fixed in the screen centre. While a congruency effect was always observed in reaching responses, it disappeared in finger-lift responses. We suggest that the redirection of saccades from the stimulus to the correct response location in noncorresponding trials contributes to the Simon effect. Because of eye–hand coupling, this occurred in a mandatory manner with reaching responses but not with finger-lift responses. Thus, the Simon effect with key-presses disappears when participants do what they typically do—look at the stimulus.     

Time course of the Simon effect in pointing movements for horizontal, vertical, and acoustic stimuli: evidence for a common mechanism

In the Simon effect, responses to a non-spatial attribute are faster when the irrelevant spatial position of the stimulus corresponds to the position of the response. It was suggested that there are two distinct mechanisms involved in the Simon effect. In the visuomotor Simon effect, the stimulus transiently activates the corresponding response which results in a decaying Simon effect function (i.e., the Simon effect decreases in slower reaction time [RT]-bins). In contrast, the cognitive Simon effect arises from a conflict between stimulus and response codes and is associated with a stable Simon effect function (i.e., the Simon effect is the same in fast and slow RT-bins). We recorded RTs and motor parameters of pointing movements in a Simon paradigm. Consistent with the previous research, the time course of the Simon effect in RTs was stable with vertical visual and horizontal acoustic stimuli (cognitive Simon tasks), but decreased with horizontal visual stimuli (visuomotor Simon task). In contrast, the Simon effect in motor parameters decreased across RT-bins in all conditions, supporting the idea that only a single, common mechanism underlies the Simon effect.     

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.     

Lateralized warning tones produce typical irrelevant-location effects on choice reactions

Simon, Acosta, and Mewaldt (1975) reported an experiment in which a 200-Hz warning-tone, presented in the left or right ear, was followed by an imperative stimulus of 500 Hz in either ear, to which a left- or right-key press was to be made. Simon et al. found a correspondence effect for warning location and response location (i.e., faster reactions when warning and response locations corresponded than when they did not) when the stimulus-response mapping was incompatible but not when it was compatible. These findings stand in contrast to typical results of (1) a correspondence effect for irrelevant location information when the mapping is compatible and (2) a reversed correspondence effect (i.e., faster responses when stimulus and response location do not correspond) when the mapping is incompatible. We conducted a direct replication of Simon et al.’s experiment and another experiment that differed only in the imperative stimulus being visual, in order to determine whether there are unique aspects of their method that yield atypical results. Our results failed to replicate those reported by Simon et al. but instead showed the patterns of correspondence effects typically found with other procedures, suggesting that the warning-signal method produces irrelevant-location effects consistent with those produced by other methods.     

The Simon Effect in Action: Planning and/or On‐Line Control Effects?

Choice reaction tasks are performed faster when stimulus location corresponds to response location (Simon effect). This spatial stimulus–response compatibility effect affects performance at the level of action planning and execution. However, when response selection is completed before movement initiation, the Simon effect arises only at the planning level. The aim of this study was to ascertain whether when a precocious response selection is requested, the Simon effect can be detected on the kinematics characterizing the online control phase of a non‐ballistic movement. Participants were presented with red or green colored squares, which could appear on the right, left, above, or below a central cross. Depending on the square's color, participants had to release one of two buttons (right/left), then reach toward and press a corresponding lateral pad. We found evidence of the Simon effect on both action planning and on‐line control. Moreover, the investigation of response conflict at the level of previous trials (i.e., n?1), a factor that might determine interference at the level of the current response, revealed a conflict adaptation process across trials. Results are discussed in terms of current theories concerned with the Simon effect and the distinction between action planning and control.     

Mixing location-relevant and location-irrelevant choice-reaction tasks: influences of location mapping on the Simon effect

The Simon effect refers to the finding that reaction times are faster when stimulus and response locations correspond than when they do not in tasks where stimulus location is defined as irrelevant. The authors examined the Simon effect for situations in which location-irrelevant trials were intermixed with trials for which stimulus location was relevant. Compatible mapping of the location-relevant trials enhanced the Simon effect relative to an unmixed condition, whereas incompatible mapping reversed the Simon effect. The reversal with incompatible mapping remained evident when task uncertainty was removed by use of a precue and was larger than the reversed effect produced by making incongruent trials more frequent than congruent trials. This result suggests that both attentional biases and task-defined associations contribute to the reversal of the Simon effect.     

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 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.     

Stimulus-response compatibility between stimulated eye and response location: implications for attentional accounts of the Simon effect

One influential theory of the Simon effect, the attention-shift hypothesis, states that attention movements are the origin of spatial stimulus codes. According to this hypothesis, stimulus-response compatibility effects should be absent when attention shifts are prevented. To test this prediction, we used monocular patches of color that required left or right key-press responses. About half of the subjects could discriminate which eye was stimulated (in a subsequent task), and showed strong spatial compatibility effects between the stimulated eye and the response location. The other half of the subjects could not make a utrocular discrimination (i.e., they could not judge which eye had received monocular stimulation), but the pattern of results was the same: the fastest reaction times were observed when the stimulated eye corresponded spatially to the required response (i.e., a Simon effect). Since the subjects presumably did not move their attention (from the subject's point of view, the stimuli were presented centrally), our results indicate that spatial codes can be produced in the absence of attention shifts. These results also show that utrocular discrimination can be assessed via indirect measures that are much more sensitive than explicit measures.     

The influence of irrelevant location information on performance: A review of the Simon and spatial Stroop effects

The purpose of this paper is to investigate the effect of irrelevant location information on performance of visual choice-reaction tasks. We review empirical findings and theoretical explanations from two domains, those of the Simon effect and the spatial Stroop effect, in which stimulus location has been shown to affect reaction time when irrelevant to the task. We then integrate the findings and explanations from the two domains to clarify how and why stimulus location influences performance even when it is uninformative to the correct response. Factors that influence the processing of irrelevant location information include response modality, relative timing with respect to the relevant information, spatial coding, and allocation of attention. The most promising accounts are offered by models in which response selection is a function of (1) strength of association of the irrelevant stimulus information with the response and (2) temporal overlap of the resulting response activation with that produced by the relevant stimulus information.     

Stimulus–response compatibility for mixed mappings and tasks with unique responses

For two stimulus locations mapped to two keypresses, reaction time is shorter when the mapping is compatible than when it is not (the stimulus–response compatibility, SRC, effect). A similar result, called the Simon effect, occurs when stimulus location is irrelevant, and colour is relevant. When compatibly mapped trials are intermixed with incompatibly mapped trials or Simon task trials, the compatibility effect is eliminated, and the Simon effect is influenced by the location mapping. In five experiments, we examined whether similar mixing effects occur when the two spatial mappings or location-relevant and location-irrelevant tasks use distinct keypresses on the left and right hands. Mixing had considerably less influence on the SRC and Simon effects than it does when the intermixed trial types or tasks share the same responses, even though response time was lengthened to a similar extent. Mixing two tasks for which stimulus location was irrelevant yielded no within-task Simon effect, but the effect was also absent when four stimuli were assigned to two responses on a single hand. The relative lack of influence of mixing on the SRC and Simon effects when the tasks have unique responses implies that suppression of direct activation of the corresponding response occurs primarily when the tasks share responses.     

Differential dynamics of spatial and non-spatial stimulus-response compatibility effects: a dual task LRP study

Choice reaction times are shorter when stimulus and response features are compatible rather than incompatible. Recent studies revealed that spatial compatibility effects in Simon tasks are strongly attenuated when there is temporal overlap with a different high-priority task. In contrast, non-spatial variants of the Simon task appear to be unaffected by task overlap. The present study used the lateralized readiness potential (LRP) within a dual task design to elucidate the dynamics underlying these differential effects for a color and a spatial variant of the Simon task. In the color version there was no sign of early response priming by irrelevant stimulus features in the LRP. The color compatibility effect was independent of task overlap and reflected in the LRP onset latency. In contrast, in the spatial version, priming by irrelevant stimulus location showed up and was mirrored by early LRP activation. Response priming and the corresponding Simon effect, however, were present only in case of little temporal overlap with the primary task. The absence of spatial compatibility effects at strong temporal overlap suggests that response conflicts due to stimulus-related priming depend on the availability of processing resources.