Coding of Spatiotemporal features of the auditory scene in the owl's midbrain

Abstract

Localization of spatiotemporally-dynamic sound stimuli is an important ability for interacting with the environment. In this thesis, I studied how space-specific cells in the external nucleus of the barn owl inferior colliculus (ICx) respond to complex sound stimuli to better understand how space-time stimulus features are computed within spatial receptive fields. Receptive fields of ICx cells showed asymmetric surround in the azimuth dimension where suppression from frontal space was stronger. A model based on the non-uniform distribution of space within ICx accounted for increased asymmetry in the surround with tuning eccentricity. Response to moving sound stimuli showed that direction selectivity in ICx cells is dependent on the history of excitation in a manner consistent with adaptation. Asymmetry in the spatial receptive field predicted the direction and strength of direction selectivity. Receptive field asymmetry and direction selectivity were correlated with tuning eccentricity such that more peripherally tuned cells showed stronger preference for sounds moving toward the front. Using each cell's adaptation properties, temporal summation of response suppression accurately predicted directional responses. This thesis contributed to the understanding computation within SRFs of the auditory system by showing (1) representation of sensory space can have a direct effect on functional interactions between cells and (2) direction selectivity can emerge through adaptation. These findings have important implications for elucidating the neural representation of stimulus features within dynamic auditory scenes.