Developmental trends in the facilitation of multisensory objects with distractors

Sensory integration and the ability to discriminate target objects from distractors are critical to survival, yet the developmental trajectories of these abilities are unknown. This study investigated developmental changes in 9- (n=18) and 11-year-old (n=20) children, adolescents (n=19) and adults (n=22) using an audiovisual object discrimination task with uni- and multisensory distractors. Reaction times (RTs) were slower with visual/audiovisual distractors, and although all groups demonstrated facilitation of multisensory RTs in these conditions, children’s and adolescents’ responses corresponded to fewer race model violations than adults’, suggesting protracted maturation of multisensory processes. Multisensory facilitation could not be explained by changes in RT variability, suggesting that tests of race model violations may still have theoretical value at least for familiar multisensory stimuli

Neural responses in parietal and occipital areas in response to visual events are modulated by prior multisensory stimuli

The effect of multi-modal vs uni-modal prior stimuli on the subsequent processing of a simple flash stimulus was studied in the context of the audio-visual 'flash-beep' illusion, in which the number of flashes a person sees is influenced by accompanying beep stimuli. EEG recordings were made while combinations of simple visual and audio-visual stimuli were presented. The experiments found that the electric field strength related to a flash stimulus was stronger when it was preceded by a multi-modal flash/beep stimulus, compared to when it was preceded by another uni-modal flash stimulus. This difference was found to be significant in two distinct timeframes--an early timeframe, from 130-160 ms, and a late timeframe, from 300-320 ms. Source localisation analysis found that the increased activity in the early interval was localised to an area centred on the inferior and superior parietal lobes, whereas the later increase was associated with stronger activity in an area centred on primary and secondary visual cortex, in the occipital lobe. The results suggest that processing of a visual stimulus can be affected by the presence of an immediately prior multisensory event. Relatively long-lasting interactions generated by the initial auditory and visual stimuli altered the processing of a subsequent visual stimulus.status: publishe

Grand averages for UNI (red) and MULTI (green) difference waves.

<p>Grey boxes show time points at which a permutation test indicated a significant difference between the waveforms. The x-axis represents time relative to the first flash. The time of the second flash (67 ms) is marked on the x-axis.</p

The effects of modality dominance and accuracy on motor reaction times to unimodal and bimodal stimuli

PURPOSE: Despite limited understanding of the underlying neural mechanisms involved in merging various sensory inputs and, in turn, the construction of a unified representation of the environment, it would appear that multisensory stimuli have a facilitating effect on information processing. It was the aim of this study to investigate multisensory processing using patterns of motor reaction times (MRTs) on a simple discrimination task as a means of categorizing groups of individuals. METHOD: Twenty-six adults were presented with temporally and spatially coincident unimodal (auditory or visual) and bimodal (auditory and visual) stimuli (100 ms duration), consisting of blue flashes as invalid (Vi) and red flashes as target (Vt) stimuli, and 500 Hz tones as invalid (Ai) and 600 Hz tones as target (At) stimuli. Overall, eight stimulus conditions were used: Ai, Vi, AiVi, At, Vt, AiVt, AtVi, and AtVt. Participants were required to press a button immediately in response to target stimuli: MRTs and response accuracy were recorded. Participants were subdivided into groups of visual dominant [Vis-Dom (n=16)] where MRT for Vt < At and auditory dominant [Aud-Dom, n=10] where MRT for At < Vt. RESULTS: Both Vis-Dom and Aud-Dom groups showed similar levels of facilitation for duel target bimodal stimuli (AtVt), i.e., MRTs were approximately 60 ms faster compared to unimodal stimuli and single target bimodal stimuli. Furthermore, MRTs to single target bimodal stimuli mirrored MRTs to unimodal stimuli, i.e., Vis-Dom and Aud-Dom participants' MRT were faster to AiVt and AtVi stimuli, respectively. An increase in speed, for all stimulus conditions, was also associated with high response accuracy. CONCLUSION: MRTs are partly dependent on an individual's dominant modality and performance accuracy. Nevertheless, maximum facilitation is achieved with duel target bimodal stimuli

Timing Diagram.

<p>Diagram showing various responses to a simultaneous flash/beep stimulus at time zero. A1 – Primary Auditory Cortex, V1 – Primary Visual Cortex, PL – Parietal Lobes. See text for explanation of numbered points.</p