Failure of the extended contingent attentional capture account in multimodal settings

Does CUD measure interhemispheric transfer time? The allocation of attention influences the Poffenberger effect

A simple reaction time (SRT) difference between responses to visual stimuli presented ipsilaterally and contralaterally to the responding hand, known as the Poffenberger effect or the crossed-uncrossed difference (CUD), has been commonly interpreted as a measure of interhemispheric transfer time (IHTT). However, the validity of this interpretation, and the measure's reliability have been debated. The present study aimed at obtaining reliable evidence of the influence of spatial attention on the CUD, which would provide an argument against the classical structural interpretation of CUD. To meet the high statistical power requirements, over 100 thousand SRTs in total were collected from 12 participants. The task had three stimulus presentation conditions differing in the degree of stimulus location uncertainty: blocked (no uncertainty), randomized (full uncertainty), and mixed (25% uncertainty). The results showed robust effects of location uncertainty, proving spatial attention's contribution to the CUD. Further, we observed a strong visual-field asymmetry reflecting the right hemisphere specialization in target detection and spatial reorienting. Lastly, despite exceptional reliability of the component SRT measures, the CUD reliability was still too low to justify using this measure as an index of individual differences.

Multisensory top-down sets: Evidence for contingent crossmodal capture

Numerous studies that have investigated visual selective attention have demonstrated that a salient but task-irrelevant stimulus can involuntarily capture a participant's attention. Over the years, a lively debate has erupted concerning the impact of contingent top-down control settings on such stimulus-driven attentional capture. In the research reported here, we investigated whether top-down sets would also affect participants' performance in a multisensory task setting. A nonspatial compatibility task was used, in which the target and the distractor were always presented sequentially from the same spatial location. We manipulated target-distractor similarity by varying the visual and tactile features of the stimuli. Participants always responded to the visual target features (color); the tactile features were incorporated into the participants' top-down set only when the experimental context allowed for the tactile feature to be used in order to discriminate the target from the distractor. Larger compatibility effects after bimodal distractors were observed only when the participants were searching for a bimodal target and when tactile information was useful. Taken together, these results provide the first demonstration of nonspatial contingent crossmodal capture.

Endogenous attention modulates attentional and motor interference from distractors: evidence from behavioral and electrophysiological results

Selective visual attention enhances the processing of relevant stimuli and filters out irrelevant stimuli and/or distractors. However, irrelevant information is sometimes processed, as demonstrated by the Simon effect (Simon and Rudell, 1967). We examined whether fully irrelevant distractors (task and target-irrelevant) produce interference (measured as the Simon effect), and whether endogenous orienting modulated this interference. Despite being fully irrelevant, distractors were attentionally coded (as reflected by the distractor-related N2pc component), and interfered with the processing of the target response (as reflected by the target-related lateralized readiness potential component). Distractors' attentional capture depended on endogenous attention, and their interference with target responses was modulated by both endogenous attention and distractor location repetition. These results demonstrate both endogenous attentional and motor modulations over the Simon effect produced by fully irrelevant distractors.

The premotor theory of attention as an account for the Simon effect

The Simon effect refers to the phenomenon that responses are faster when the irrelevant location of a stimulus corresponds with the response location than when these locations do not correspond. In the current paper we examined the viability of an updated version of the premotor theory of attention (PMTA) as an account for the Simon effect. Two predictions were evaluated. First, in the case of focused attention at the relevant target position a strong reduction of the Simon effect should be observed as the Simon effect according to PMTA crucially depends on attentional orienting. Secondly, if attention is directed towards a location then this orienting by itself should already be sufficient for producing a Simon effect, as stimulus presence is not required. Our data confirmed these predictions thereby supporting the relevance of the PMTA for the Simon effect.

The components of visual attention and the ubiquitous Simon effect

Spatial responding is influenced by the degree of correspondence between the stimulus-response (S-R) code activated by the target's task-irrelevant location and the S-R code activated by the target's non-spatial, task-relevant feature. A generally accepted explanation of this "Simon effect," named after its discoverer, is that there is a natural tendency to respond towards the source of stimulation. First we will review the ubiquity of the Simon effect. Then we will review the literature, including our own studies when appropriate, that has explored the relationship between the Simon effect and the components of attention: alertness, orienting and executive control, with an emphasis on visual orienting. The Simon effect is reduced when participants are not alert and when executive control is effective in filtering out the irrelevant location information. When attention is oriented endogenously, or is captured exogenously by uninformative peripheral stimulation, the Simon effect is additive with attentional facilitation (i.e., the Simon effect is the same magnitude for targets presented at attended and unattended locations). Yet, some forms of orienting, such as orienting directed by gaze and biased by inhibition of return, modulate the Simon effect. We will explore the implications of these patterns of additivity and interaction for our understanding of both the Simon effect and spatial attention.

Endogenous orienting modulates the Simon effect: critical factors in experimental design

Responses are faster when the side of stimulus and response correspond than when they do not correspond, even if stimulus location is irrelevant to the task at hand: the correspondence, spatial compatibility effect, or Simon effect. Generally, it is assumed that an automatically generated spatial code is responsible for this effect, but the precise mechanism underlying the formation of this code is still under dispute. Two major alternatives have been proposed: the referential-coding account, which can be subdivided into a static version and an attention-centered version, and the attention-shift account. These accounts hold clear-cut predictions for attentional cuing experiments. The former would assume a Simon effect irrespective of attentional cuing in its static version, whereas the attention-centered version of the referential-coding account and the attention-shift account would predict a decreased Simon effect on validly as opposed to invalid cued trials. However, results from previous studies are equivocal to the effects of attentional cuing on the Simon effect. We argue here that attentional cueing reliably modulates the Simon effect if some crucial experimental conditions, mostly relevant for optimizing attentional allocation, are met. Furthermore, we propose that the Simon effect may be better understood within the perspective of supra-modal spatial attention, thereby providing an explanation for observed discrepancies in the literature.

Multisensory integration affects ERP components elicited by exogenous cues

Previous studies have shown that the amplitude of event related brain potentials (ERPs) elicited by a combined audiovisual stimulus is larger than the sum of a single auditory and visual stimulus. This enlargement is thought to reflect multisensory integration. Based on these data, it may be hypothesized that the speeding up of responses, due to exogenous orienting effects induced by bimodal cues, exceeds the sum of single unimodal cues. Behavioral data, however, typically revealed no increased orienting effect following bimodal as compared to unimodal cues, which could be due to a failure of multisensory integration of the cues. To examine this possibility, we computed ERPs elicited by both bimodal (audiovisual) and unimodal (either auditory or visual) cues, and determined their exogenous orienting effects on responses to a to-be-discriminated visual target. Interestingly, the posterior P1 component elicited by bimodal cues was larger than the sum of the P1 components elicited by a single auditory and visual cue (i.e., a superadditive effect), but no enhanced orienting effect was found on response speed. The latter result suggests that multisensory integration elicited by our bimodal cues plays no special role for spatial orienting, at least in the present setting.