Showing that the race model inequality is not violated

Role of audiovisual synchrony in driving head orienting responses

Many studies now suggest that optimal multisensory integration sometimes occurs under conditions where auditory and visual stimuli are presented asynchronously (i.e. at asynchronies of 100 ms or more). Such observations lead to the suggestion that participants' speeded orienting responses might be enhanced following the presentation of asynchronous (as compared to synchronous) peripheral audiovisual spatial cues. Here, we report a series of three experiments designed to investigate this issue. Upon establishing the effectiveness of bimodal cuing over the best of its unimodal components (Experiment 1), participants had to make speeded head-turning or steering (wheel-turning) responses toward the cued direction (Experiment 2), or an incompatible response away from the cue (Experiment 3), in response to random peripheral audiovisual stimuli presented at stimulus onset asynchronies ranging from -100 to 100 ms. Race model inequality analysis of the results (Experiment 1) revealed different mechanisms underlying the observed multisensory facilitation of participants' head-turning versus steering responses. In Experiments 2 and 3, the synchronous presentation of the component auditory and visual cues gave rise to the largest facilitation of participants' response latencies. Intriguingly, when the participants had to subjectively judge the simultaneity of the audiovisual stimuli, the point of subjective simultaneity occurred when the auditory stimulus lagged behind the visual stimulus by 22 ms. Taken together, these results appear to suggest that the maximally beneficial behavioural (head and manual) orienting responses resulting from peripherally presented audiovisual stimuli occur when the component signals are presented in synchrony. These findings suggest that while the brain uses precise temporal synchrony in order to control its orienting responses, the system that the human brain uses to consciously judge synchrony appears to be less fine tuned.

Redundancy gain for semantic features

In a go/no-go experiment, semantic redundancy gain was assessed for responses to single written words. Specifically, we asked participants to respond only to words whose meaning matched at least one semantic target feature-that is, the target category (e.g., animal), the target color (e.g., gray), or both. On redundant-target trials, the word (e.g., elephant) matched both semantic target features (i.e., gray and animal). On single-target trials, the word (e.g., beaver) matched one target feature (i.e., animal) and a nontarget feature (i.e., brown). We observed shorter reaction times in the redundant-target condition than in the faster single-target condition. Hence, the present study provides the first evidence that redundancy gain is not limited to responses to redundant proximal stimulus features but can also be observed for responses to semantic feature information.

Statistical measures for workload capacity analysis

A critical component of how we understand a mental process is given by measuring the effect of varying the workload. The capacity coefficient (Townsend & Nozawa, 1995; Townsend & Wenger, 2004) is a measure on response times for quantifying changes in performance due to workload. Despite its precise mathematical foundation, until now rigorous statistical tests have been lacking. In this paper, we demonstrate statistical properties of the components of the capacity measure and propose a significance test for comparing the capacity coefficient to a baseline measure or two capacity coefficients to each other.