To enable a listener to localize a sound source, the auditory system suppresses echoes that result from reflections of the sound off nearby objects. Psychoacoustic experiments have provided evidence that some of this suppression occurs within a group of nerve cells--the cochlear nuclear complex--which is the first integrative stage in the auditory system. Anatomical and physiological experiments on brain slices that include the cochlear nuclei have identified neurons in the upper portion of the cochlear nuclear complex that are candidates for mediating the echo suppression effect. The major purpose of these experiments is to examine, physiologically, the suppression of echoes in the cochlear nuclear complex and to determine whether the suppression is due to the candidate neurons. Microelectrode recordings are made from single neurons to various sound stimuli to study the effects of echo suppression, since even though echos are suppressed for localization of a sound, they do make a contribution to perception of the sound. Responses of neurons to pairs of stimuli will be recorded to determine whether and under what conditions the response to a second click is suppressed by the first. Also, responses will be recorded from different neurons in the lower cochlear nucleus to determine whether there are neurons that do not show echo suppression.
