Peter Wühr

A response-discrimination account of the Simon effect.

Simon effects might partly reflect stimulus-triggered response activation. According to the response-discrimination hypothesis, however, stimulus-triggered response activation shows up in Simon effects only when stimulus locations match the top-down selected spatial codes used to discriminate between alternative responses. Five experiments support this hypothesis. In Experiment 1, spatial codes of each response differed by horizontal and vertical axis position, yet one axis discriminated between alternative responses, whereas the other did not. Simon effects resulted for targets on discriminating axes only. In Experiment 2, both spatial axes discriminated between responses, and targets on both axes produced Simon effects. In Experiment 3, Simon effects resulted for a spatial choice-reaction task but not for a go/no-go task. Even in the go/no-go task, a Simon effect was restored when a two-choice reaction task preceded the go/no-go task (Experiment 4) or when participants initiated trials with responses spatially discriminated from the go response (Experiment 5).

Exploring trial-by-trial modulations of the Simon effect.

The present study investigates sequential modulations of the Simon effect. The Simon effect involves faster responses to spatially corresponding than to noncorresponding stimuli, even when stimulus position is irrelevant. Recently, the Simon effect has been shown to decrease or to disappear after noncorresponding predecessor trials. Possible explanations for these sequential modulations include (a) the gating of position-based response activation (conflict monitoring), (b) repetition or alternation effects, and (c) the interaction between feature integration (binding) processes and stimulus-response (S-R) correspondence. Three experiments tested different predictions of these models by comparing Simon effects after neutral trials with those after corresponding and noncorresponding trials, respectively, and by varying the stimulus-onset asynchrony (SOA) between and within experiments. Experiments 1 and 2 revealed large Simon effects after corresponding trials, intermediate Simon effects after neutral trials, and small (or no) Simon effects after noncorresponding trials. Moreover, some systematic effects of S-R repetitions and S-R alternations were observed. Finally, the sequential modulations were maximal at short SOAs and decreased with increasing SOA, but still occurred at an SOA of 6 seconds. The results seem to exclude repetition or alternation effects as the main cause of sequential modulations of the Simon effect, but both conflict monitoring and binding may contribute to these effects.

Sequential modulations of correspondence effects across spatial dimensions and tasks.

In two experiments, we explored sequential modulations of correspondence effects in a prime-target paradigm. In Experiment 1, the participants responded to the direction of target arrows that were preceded by prime arrows with a corresponding or noncorresponding direction. This produced a prime-target correspondence effect that was reduced when the preceding trial contained a noncorresponding prime-target event. This sequential modulation of the correspondence effect was observed even when neither stimuli nor responses were repeated from one trial to the next, ruling out explanations of sequential modulations in terms of stimulus or response repetitions. Experiment 2 combined the prime-target correspondence effect with a Simon-type correspondence effect. Both effects were reduced following noncorrespondence of the same type and, to a lesser extent, following noncorrespondence of the other type. Altogether, these results suggest that part of the sequential modulation of correspondence effects reflects an adaptation to a preceding response conflict independently of the peripheral stimulus events that produced this conflict.

Post-conflict slowing: cognitive adaptation after conflict processing

The aftereffects of error and conflict (i.e., stimulus or response incongruency) have been extensively studied in the cognitive control literature. Each has been characterized by its own behavioral signature on the following trial. Conflict leads to a reduced congruency effect (Gratton effect), whereas an error leads to increased response time (post-error slowing). The reason for this dissociation has remained unclear. Here, we show that post-conflict slowing is not typically observed because it is masked by the processing of the irrelevant stimulus dimension. We demonstrate that post-conflict slowing does occur when tested in pure trials where helpful or detrimental impacts from irrelevant stimulus dimensions are removed (i.e., univalent stimuli).

A Case for Inhibition : Visual Attention Suppresses the Processing of Irrelevant Objects

The present study investigated the ability to inhibit the processing of an irrelevant visual object while processing a relevant one. Participants were presented with 2 overlapping shapes (e.g., circle and square) in different colors. The task was to name the color of the relevant object designated by shape. Congruent or incongruent color words appeared in the relevant object, in the irrelevant object, or in the background. Stroop effects indicated how strong the respective area of the display was processed. The results of 4 experiments showed that words in the relevant object produced larger Stroop effects than words in the background, indicating amplification of relevant objects. In addition, words in the irrelevant object consistently produced smaller Stroop effects than words in the background, indicating inhibition of irrelevant objects. Control experiments replicated these findings with brief display durations (250 ms) and ruled out perceptual factors as a possible explanation. In summary, results support the notion of an inhibitory mechanism of object-based attention, which can be applied in addition to the amplification of relevant objects.

Object-based attentional selection can modulate the Stroop effect

The Stroop (1935) effect is the inability to ignore a color word when the task is to report the ink color of that word (i.e., to say “green” to the word RED in green ink). The present study investigated whether object-based processing contributes to the Stroop effect. According to this view, observers are unable to ignore irrelevant features of an attended object (Kahneman & Henik, 1981). In three experiments, participants had to name the color of one of two superimposed rectangles and to ignore words that appeared in the relevant object, in the irrelevant object, or in the background. The words were congruent, neutral, or incongruent with respect to the correct color response. Words in the irrelevant object and in the background produced significant Stroop effects, consistent with earlier findings. Importantly, however, words in the relevant object produced larger Stroop effects than did the other conditions, suggesting amplified processing of all the features of an attended object. Thus, object-based processing can modulate the Stroop effect.

On distractor-repetition benefits in the negative-priming paradigm

The present study investigates the effects of distractor repetitions between prime and probe displays on behaviour in the negative-priming (NP) paradigm. Investigating this condition is theoretically significant because inhibition-based accounts and episodic retrieval accounts of NP on one side and the temporal-discrimination theory on the other side make opposite predictions with regard to the effects of distractor repetition. In particular, the former accounts predict distractor-repetition benefits while the latter theory does not. Two experiments further explored the distractor-repetition effects. Experiment 1 replicated previous findings. Experiment 2 further showed that distractor-repetition benefits are still observed when the prime-display distractor and the probe-display target are not correlated. The pattern of results is consistent both with inhibition-based and with retrieval-based accounts of NP, but the results are inconsistent with temporal-discrimination theory.

Precueing spatial S-R correspondence: is there regulation of expected response conflict?

Four experiments investigated the ability to prepare for the level of forthcoming stimulus-response correspondence in choice-response tasks. In a Simon task, participants responded to the color of spatially variable stimuli with spatially variable responses. Participants were given advance information about whether a forthcoming stimulus-response event would be spatially corresponding, neutral, or spatially noncorresponding. Reliable cues decreased reaction times (RTs) in the corresponding conditions of 2- and 3-choice tasks, decreased RTs in noncorresponding conditions of a 2-choice task but not in a 3-choice task, and left RTs in neutral conditions unaffected. The pattern of results suggests that participants used reliable cues for responding to the nominally irrelevant stimulus location if the correct response could be inferred from location (attention switching). By contrast, the lack of cueing effects on performance in noncorresponding conditions of 3-choice tasks suggests that participants cannot use cues for changing the attentional weights of processing channels for different stimulus dimensions (gating). In summary, gating may be involved in the regulation of experienced response conflict, but the present results suggest that it is not involved in the regulation of expected (i.e., predicted) response conflict.

Varying the response code in the blindness to response-compatible stimuli

Previous work has indicated that action-control processes can specifically influence perceptual processes. The identification of a left- or right-pointing arrow is impaired when it appears during the preparation and execution of a compatible left-right keypress (Müsseler & Hommel, 1997a, b). The present study examines the role of the response-specifying cue in order to manipulate the coding of the action-control processes. Experiment 1 shows that the size of the perceptual impairment is not affected by whether the cue has high or little feature overlap with the to-be-performed response. Cues were omitted in Experiment 2 and participants generated their responses endogenously, but the perceptual impairment still occurred. Experiment 3 examines in more detail which feature of the response contributes to the effect. The results show that it needs both an intended action goal and a corresponding motor activity to bring about the perceptual impairment.

Can actions affect perceptual processing

Previous studies reported impairments in a perceptual task performed during the selection and execution of an action. These findings, however, always raise the question of whether the impairment actually reflects a reduction in perceptual sensitivity or whether it results only from an unspecific reduction in attentiveness given the perceptual task. Recent studies by the authors indicate that actions can also have a specific impact on perception in a dual-task situation. The identification of a left or right arrow is impaired when it appears during the execution of a compatible left or right keypress. In three experiments Signal Detection Theory is applied to test whether this impairment is also found in the sensitivity measure d′ or whether it originates only from a response tendency. The results revealed a general lower d′ for the identification of arrows that were compatible to simultaneously executed keypresses than for arrows that were incompatible. The bias measure c was small and/or did not differ between conditions. Additional analyses revealed that the impairment is due to a higher mean perceptual degradation of stimuli in the compatible condition and that it is restricted to the point in time when the central movement command is generated. Thus, actions actually seem able to affect perceptual processing.