Flanker and Simon effects interact at the response selection stage

The present study aimed at investigating the processing stage underlying stimulus–stimulus (S–S) congruency effects by examining the relation of a particular type of congruency effect (i.e., the flanker effect) with a stimulus–response (S–R) spatial correspondence effect (i.e., the Simon effect). Experiment 1 used a unilateral flanker task in which the flanker also acted as a Simon-like accessory stimulus. Results showed a significant S–S Congruency × S–R Correspondence interaction: An advantage for flanker–response spatially corresponding trials was observed in target–flanker congruent conditions, whereas, in incongruent conditions, there was a noncorresponding trials’ advantage. The analysis of the temporal trend of the correspondence effects ruled out a temporal-overlap account for the observed interaction. Moreover, results of Experiment 2, in which the flanker did not belong to the target set, demonstrated that this interaction cannot be attributed to perceptual grouping of the target–flanker pairs and referential coding of the target with respect to the flanker in the congruent and incongruent conditions, respectively. Taken together, these findings are consistent with a response selection account of congruency effects: Both the position and the task-related attribute of the flanker would activate the associated responses. In noncorresponding-congruent trials and corresponding-incongruent trials, this would cause a conflict at the response selection stage.

The Effects of Accessory Stimuli on Information Processing: Evidence from Electrophysiology and a Diffusion Model Analysis

People typically respond faster to a stimulus when it is accompanied by a task-irrelevant accessory stimulus presented in another perceptual modality. However, the mechanisms responsible for this accessory-stimulus effect are still poorly understood. We examined the effects of auditory accessory stimulation on the processing of visual stimuli using scalp electrophysiology (Experiment 1) and a diffusion model analysis (Experiment 2). In accordance with previous studies, lateralized readiness potentials indicated that accessory stimuli do not speed motor execution. Surface Laplacians over the motor cortex, however, revealed a bihemispheric increase in motor activation—an effect predicted by nonspecific arousal models. The diffusion model analysis suggested that accessory stimuli do not affect parameters of the decision process, but expedite only the nondecision component of information processing. Consequently, we conclude that accessory stimuli facilitate stimulus encoding. The visual P1 and N1 amplitudes on accessory-stimulus trials were modulated in a way that is consistent with multisensory energy integration, a possible mechanism for this facilitation.

Binding of Event Files in a (go/no-go) Simon Task With an Accessory Peripheral Signal

To understand the relation between the Simon effect and the time course of relevant and irrelevant code activations, we presented the response signal before or simultaneously with a go/no-go signal in an accessory Simon task. A peripheral accessory signal could appear before, simultaneously with or after the go/no-go signal. We observed a Simon effect when the accessory signal was presented just before or simultaneously with the go signal, irrespective of the delay between response and go/no-go signal. The Simon effect reversed when the accessory signal was presented 150 ms after the go signal when response information was presented first and the participants had to make a go/no-go decision afterwards or when they had to select a response when the go signal appeared. The reversal did not occur when both decisions were required at the same time. Our data suggest that the integration and release of event files are involved in the occurrence of the reversal. Response activation induced by the accessory stimulus facilitates/interferes with the response when it is presented before the event file is integrated. When the accessory stimulus is presented after integration, the automatically activated response is inhibited, causing a delay in the corresponding reaction times.