.) This is a continuation of research attempting to identify neural substrates of sound localization relevant to human hearing. Neurons in the cat central auditory system will be tested to determine if they are monaural directional (MD) or binaural directional (BD), two means of deriving directional selectivity for broad band noise (BBN). Properties of MD and BD cells will be evaluated in the cat inferior colliculus (IC) to determine where and how MD sensitivity is synthesized. Superior colliculus (SC) neurons will be evaluated for MD sensitivity. To determine the role of the dorsal cochlear nucleus (DCN), neurons in auditory cortex (AI) and SC will be tested after transection of DCN output fibers. Experiments on MD sensitivity in squirrel monkey auditory cortex are also proposed. Neural sensitivity to sound movement in high frequency neurons will be studied in cat AI neurons using ear plugs to determine whether movement sensitivity derives from monaural cues, binaural cues, or both. Whether the azimuth tuning of cortical cells in cat BD cells to noise stimulation reflects a linear summation of sensitivity to binaural disparities in constituent spectral components will be tested by comparing azimuth function for noise with that obtained from the linear sum of azimuth functions for tonal stimuli with frequencies distributed throughout the band pass of the noise. In all, seven hypotheses will be specifically tested.
