Abstract
Integration of sensory information across multiple senses is most likely to occur when signals are spatiotemporally coupled. Yet, recent research on audiovisual rate discrimination indicates that random sequences of light flashes and auditory clicks are integrated optimally regardless of temporal correlation. This may be due to 1) temporal averaging rendering temporal cues less effective; 2) difficulty extracting causal-inference cues from rapidly presented stimuli; or 3) task demands prompting integration without concern for the spatiotemporal relationship between the signals. We conducted a rate-discrimination task (Exp 1), using slower, more random sequences than previous studies, and a separate causal-judgement task (Exp 2). Unisensory and multisensory rate-discrimination thresholds were measured in Exp 1 to assess the effects of temporal correlation and spatial congruence on integration. The performance of most subjects was indistinguishable from optimal for spatiotemporally coupled stimuli, and generally sub-optimal in other conditions, suggesting observers used a multisensory mechanism that is sensitive to both temporal and spatial causal-inference cues. In Exp 2, subjects reported whether temporally uncorrelated (but spatially co-located) sequences were perceived as sharing a common source. A unified percept was affected by click-flash pattern similarity and the maximum temporal offset between individual clicks and flashes, but not on the proportion of synchronous click-flash pairs. A simulation analysis revealed that the stimulus-generation algorithms of previous studies is likely responsible for the observed integration of temporally independent sequences. By combining results from Exps 1 and 2, we found better rate-discrimination performance for sequences that are more likely to be integrated than those that are not. Our results support the principle that multisensory stimuli are optimally integrated when spatiotemporally coupled, and provide insight into the temporal features used for coupling in causal inference.
Highlights
Multisensory interactions are beneficial to the observer as they can facilitate detection in noisy environments, improve accuracy of perceptual judgements, and allow for faster reactions to sensory events [1]
Temporal causal inference with stochastic audiovisual sequences brief glimpse of movement with an audible rattling noise will increase the probability that you notice the snake and correctly localise where it is hiding, as well as reducing the time to turn around and run
Determining whether sensory information should be integrated based on a shared origin is referred to as casual inference [2]
Summary
Multisensory interactions are beneficial to the observer as they can facilitate detection in noisy environments, improve accuracy of perceptual judgements, and allow for faster reactions to sensory events [1]. Information about the timing of events across modalities is discarded in rate estimation as this task requires monitoring the density of events within a temporal window substantially broader than that used to judge temporal coincidence In such a scenario, observers are presumably relying on other casual-inference cues, such as spatial proximity, to judge whether the sources should be integrated [2, 5, 22]. A third plausible hypothesis is that observers are able to integrate separate rate estimates without any regard for the probability the sources share a common origin This flexible coupling of information across the auditory and visual senses has been demonstrated previously. We examined whether there were observable differences in rate discrimination in the presence of temporal conflict, based on whether it was more likely the participant perceived the auditory and visual sequences as sharing a common origin or separate origins
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