Bayesian fusion of visual and auditory stimuli during saccades: an inverted ventriloquist effect
Single Paper Presentation

Maria Concetta Morrone
Faculty of Psychology, Vita-Salute S Raffaele University

Paola Binda

Aurelio Bruno

David Charles Burr
Dipartimento di psicologia, Università di Firenze

     Abstract ID Number: 36
     Full text: Not available
     Last modified: March 12, 2006
     Presentation date: 06/19/2006 10:00 AM in Hamilton Building, Foyer
     (View Schedule)

Abstract
During a critical period just before and during saccades, visual space is grossly distorted, undergoing a strong compression towards the saccadic target (Ross et al., Naure, 1997). In this study we investigated spatial localization of peri-saccadic visual and/or auditory stimuli. Subjects were asked to report which of two stimuli (both visual, acoustic or bi-modal) was more ''rightward'': one displayed centrally well before the saccade, the other peri-saccadically at a variable position. Peri-saccadic auditory clicks were perceived veridically (as given by the PSE of the psychometric function), with a similar precision (slope of the psychometric function) as during fixation. Peri-saccadic visual blobs, however, were seen mislocalized towards the saccadic target, with far less precision than during fixation (similar acoustic precision). Audio-visual stimuli were mislocalized much less than the visual stimuli presented on their own. The perceived position of the bimodal stimuli was well-predicted by assuming statistically optimal Bayesian combination of visual and auditory signals. The accuracy of the bimodal localisation was also better than either the visual or acoustic stimulus presented in isolation, again quantitatively predictable from Bayesian fusion. The results provide further support for the idea that distorted saccadic perception may result from optimal trans-saccadic integration (Niemeyer et al., Nature, 2003), and for a Bayesian explanation of the ventriloquist effect (Alais and Burr, Curr. Biol., 2004).