Localization and unification of unimodal and multimodal objects in older adults

Localization of speakers and differentiation of speakers in space are demanding tasks in central object representation. The perception of spatial objects depends on the integration of sensory information from different modalities. Crossmodal interactions during perception of audio-visual objects in terms of spatial alignment/displacement have been extensively studied in young adults. Still, it is unclear how both systems interact at peripheral positions, where spatial representations of objects are less precise. In old adults central processing mechanisms are declined and crossmodal interactions might be of great significance in object localization. The present study investigates acuity of localization of static acoustic, visual and audio-visual objects in young and old adults in free-field. Subject had to localize either acoustic or visual stimuli. The acoustic and visual signals of an audio-visual stimulus were spatially congruent or incongruent and subjects were asked to localize the acoustic signal. At frontal positions localization of audio-visual stimuli was strongly biased towards the visual signals. At peripheral positions, subjects localized the sound source at a position intermediate between the acoustic and visual signal. The results suggest that the influence of the visual system is reduced towards the periphery, while the auditory system has a stronger impact in localization in the periphery. The amount of unification increased as a function of spatial position and age. Thereby, old adults showed a higher amount of unification at largest spatial disparities. Young and old adults performed equally at the largest disparity at the most peripheral position which points to an increased match of sensory information in the peripheral, monocular visual field. These results suggest that the amount of unification depends on the dimension of spatial resolution