Elevation sensitivity in the cat’s thalamo-cortical auditory system: Role of monaural spectral and binaural disparity cues

Abstract

High-frequency neurons in auditory cortex (AI) and medial geniculate (MGB) of anesthetized cats are differentially sensitive to monaural and binaural directional cues present in broad-band noise. Binaural directional (BD) cells depend upon binaural stimuli for azimuth sensitivity, whereas monoaural directional (MD) cells are sensitive to the direction of monaural stimuli. In the MGB, neurons’ spatial receptive fields (SRFs) were obtained using noise bursts presented throughout the frontal hemifield and sound pressure levels that varied over an 80-dB range. BD cells were broadly tuned to elevation. Those that received excitatory input from one ear and exhibited binaural inhibition or mixed interactions had SRFs that extended throughout one lateral hemifield. Predominantly binaural cells exhibited strong binaural facilitation and had SRFs that formed a vertical band in front of the head. MD cells’ SRFs varied considerably, some were focal areas restricted in azimuth and elevation. Others consisted of multiple areas that in some cases showed level-dependent changes in location. The elevation sensitivity of MD cells was nearly identical under monaural and binaural conditions showing that it derived from monaural spectral cues. AI units showed similar response properties. [Work supported by NIDCD.]