Effect of removing physiologically relevant sound-localization parameters on tuning properties of barn owl tectal neurons

Abstract

Barn owls use the interaural time difference (ITD) for locating sounds in azimuth and the interaural level difference (ILD) for locating sounds in elevation. Neurons in the optic tectum have spatially restricted receptive fields. Recently, Keller et al. [Hearing Res. 118, 13–34 (1998)] have demonstrated that the spatial patterns of responses were almost indistinguishable in response to virtual [stimuli filtered with head-related transfer functions (HRTFs)] and to free-field stimulation in neurons of the inferior colliculus. The inferior colliculus provides input to the optic tectum. The spatial restriction of tectal neurons is mainly due to their sensitivity to ITD and ILD. This paper deals with the effect of removing ITD and/or ILD from the virtual stimuli on the tuning of tectal neurons. HRTFs of two barn owls were recorded, and noise stimuli with ITDs, ILDs, filtered with HRTFs, filtered with HRTFs but containing no ITDs, and filtered with HRTFs but without ILDs were used in the experiments. Preliminary results suggest that removal of ITDs or ILDs caused a substantial loss of spatial tuning in tectal neurons. These results support earlier findings that suggested an essential role of the tectal neurons in sound-localization behavior. [Work supported by GIF.]