Contrast-dependency of audiovisual integration
Poster Presentation

Sascha Tyll
Department of Neurology II, Otto von Guericke University, Leipziger Strasse 44, 39120 Magdeburg, Germany

*Jon Driver
Institute of Cognitive Neuroscience and Department of Psychology, University

*Hans-Jochen Heinze
Department of Neurology II, Otto von Guericke University, Leipziger Strasse 44, 39120 Magdeburg, Germany

*Toemme Noesselt
Department of Neurology II, Otto von Guericke University, Leipziger Strasse 44, 39120 Magdeburg, Germany and Institute of Cognitive Neuroscience and Department of Psychology, University

     Abstract ID Number: 103
     Full text: Not available
     Last modified: March 21, 2005

Abstract
Previous studies ( e.g. Stein et al., 1994) have reported an increase of perceived brightness if a visual stimulus is paired with a sound. However, other studies (Odgaard et al., 2003) suggested that this could be due to a response bias. In the present study, we varied the contrast of a visual stimulus (high (80% hit rate)/low (60 %hit rate)) and orthogonally the presence of a sound (factor sound: present/absent). Subjects performed a visual detection task. A response bias might lead to a general increase in yes-responses independent of contrast, while a mechanism based on brightness enhancement should reveal larger audiovisual effects at low contrast in accord with Weber-Fechner-Law. We found significantly higher accuracy (indicated by both hit rate and also d’) and faster RTs for low contrast stimuli in the presence but not in the absence of sounds but not for high contrast visual stimuli (Brightness-Sound-interaction, p<0.05). These results accord with the Weber-Fechner-law and suggest that audiovisual integration does affect brightness enhancement.
This finding is further corroborated by preliminary fMRI results suggesting that crossmodal brightness enhancement is modulated in unimodal visual cortex. Together, both behavioural and neurophysiological results point at contrast/brightness enhancement as one effect of audiovisual integration.