Multisensory enhancement of localization with synergetic visual-auditory cues

Multisensory enhancement of localization with synergetic visual-auditory cues Martine Godfroy (mgodfroy@imassa.fr), Cognitive Science Department, Institut de Medecine Aerospatiale du Service de Sante des Armees, B.P.73, 91223 Bretigny sur Orge Cedex, France Corinne Roumes ( croumes@imassa.fr) Cognitive Science Department, Institut de Medecine Aerospatiale du Service de Sante des Armees, B.P.73, 91223 Bretigny sur Orge Cedex, France multimodal localization task was never explored. In addition, the simultaneous presentation of spatially congruent visual and auditory cues was mostly studied considering detection of a target (Frasinetti et al., 2002), orientation toward a target (Stein et al., 1988, 1989) or reduction in response latencies (Hugues et al., 1994; Frens et al., 1995, Colonius & Arndt, 2001) rather than purely localization capability. When shown, increase in precision of the localization was restricted to the analysis of an angular value, expressing the stimulus-response discrepancy in polar coordinates. The purpose of this experiment was to evaluate multisensory integration in a two-dimensional localization task and qualify the nature of a cross modal benefit that could be obtained when the spatial information in the two modalities was convergent. We suggested a separate analysis of the localization performance for the azimuth and elevation components of the response, as a function of target double pole coordinate system in which the origin coincides with the center of the head. This procedure should reveal the contribution of the auditory modality into the bimodal localization performance, given the initial differences in coding the position of an auditory target in azimuth (Interaural Time and Level differences) and in elevation (monaural spectral shape cues). Indeed, as a consequence of this specific coding, auditory resolution differs in the horizontal and the vertical dimension while the visual resolution, associated to a retinotopic coding, is isotropic in space. The investigation of criterion we assumed to be relevant for the task was performed. Centering, precision, dispersion and orientation of the responses were successively examined to determine a potential benefit and the modal contribution of a bimodal visual-auditory target presentation. Abstract Enhanced behavioral performance mediated by multisensory stimuli has been shown using a variety of measures, including response times, orientation behavior and even simple stimulus detection. In the particular case of the study of saccadic response to unimodal or bimodal stimuli, Corneil et al. (2002) were able to show that the bimodal visual-auditory saccades benefited from the accuracy of visual saccades at saccadic response time (SRTs) typical of auditory saccades. However, there has been little evidence of multisensory mediated improvement in stimulus localization. Recently, Hairston et al. (2003) shows improvement in visual-auditory localization performance (variability) for induced myopia while no benefit was reported for normal vision. Using a similar experimental design, taking into account two space dimensions, azimuth vs. elevation, we examined the ability of human subjects to localize visual, auditory and combined visual-auditory targets for stimuli considered optimal for the given task. The results showed significant improvement in bimodal localization when compared with the more accurate modality, visual, as measured with multi criterion data (precision, dispersion and orientation of the response patterns). Furthermore, the 2D analysis of combined visual- auditory target localization performance, for azimuth and elevation response components, underlines the role of the auditory system in the determination of the response characteristics. The data suggested that visual-auditory localization performance benefited from the “best of the two worlds” (Corneil et al., 2002), in that it was improved only in the horizontal plane, and restricted to the response criterion where audition is more reliable than vision. Introduction The literature dealing with intersensory perception first dealt with the phenomena of sensory illusions, the most well known being the ventriloquism effect (Howard and Templeton, 1966) and the McGurk effect (McGurk and McDonald, 1976). Both these “on-line” effects result from discrepancies, either spatial and/or temporal between the two unimodal components of the stimulation. The much more ecological situation, in which visual and auditory signals are synergetic, i.e. in terms of spatial and temporal congruence, has been rarely investigated systematically in a localization task. Furthermore, to our knowledge, taking into consideration the two dimensions (azimuth and elevation) of the observer’s perceptive field for a Materia ls and methods Participants Ten adults, aged 22 to 50 years, took part in the experiment. They all had a minimum of 20/20 visual acuity (if need be, corrected). Their audiometric capacities were also normal, with age related variations. All were naive regarding the setup configuration (number and positions of the auditory sources).