Role of superior colliculus in audio-visual redundancy gain
Poster Presentation

Angelo Maravita
Dipartimento di Psicologia, Università degli Studi di Milano-Bicocca, Milano, Italy

Silvia Savazzi
Dipartimento di Scienze Neurologiche e della visione, Università di Verona, Italy

Emanuela Bricolo
Dipartimento di Psicologia, Università degli Studi di Milano-Bicocca, Milano, Italy

Valentina Penati
Dipartimento di Psicologia, Università degli Studi di Milano-Bicocca, Milano, Italy

Carlo Alberto Marzi
Dipartimento di Scienze Neurologiche e della visione, Università di Verona, Italy

     Abstract ID Number: 120
     Full text: PDF
     Last modified: June 27, 2005

Abstract
The superior colliculus is known to be a critical structure for multimodal integration in lower species and may be an important candidate for multimodal integration in humans as well. In particular one could hypothesize that simple auditory and visual stimuli must be integrated in the superior colliculus in order to efficiently orient spatial attention in extrapersonal space.
In this experiment we tested for the importance of the superior colliculus for audio-visual integration by using a simple reaction time task. Normal participants responded as fast as possible to either single (auditory or visual) or bimodal audio-visual stimuli presented at fixation. Response to bimodal stimuli was faster than that to single stimuli of either modality, a well-known phenomenon named Redundant Target Effect.
Critically, however, the speed advantage for double bimodal stimuli (the so-called Redundancy Gain) could be explained by a neural co-activation mechanism when the visual stimulus was made of red monochromatic light, while it could be ascribed to probabilistic summation when a monochromatic purple colour was used. Since the superior colliculus cannot detect purple stimuli, this result suggests that it represents a crucial structure for multimodal integration between simple visual and acoustic stimuli in humans.