The processing of interaural level differences (ILDs) is crucial for locating high frequency sounds in the horizontal plane. A wealth of data supports the view that ILDs are computed in the lateral superior olive (LSO) due to an integration of two monaural inputs: an ipsilaterally driven excitation and a contralaterally driven inhibition. However, my recent data show that the medial nucleus of the trapezoid body (MNTB), the source of contralaterally driven inhibition to LSO, is inhibited by sound at the ipsilateral ear. I also find that the inhibition is age-dependent. The goal of this project is to determine the effect of ipsilateral inhibition to MNTB in young and adult animals when acoustically realistic ILDs are presented. A first experiment will study the ILDs that occur in the free field. This will involve recording cochlear microphonics or measuring sound intensity near the tympanic membrane as a sound source is positioned at various azimuthal locations. After obtaining the free field data, I will perform in vivo recordings from the MNTB and measure responses to binaural stimuli whose ILDs correspond to known locations in the horizontal plane. By comparing responses to binaural stimuli with responses to appropriate monaural, contralateral stimuli, the effects of the ipsilateral inhibition will be inferred. I will also investigate the effect of inhibition on spike timing and reliability by examining its effects on phase locking and spike rate variability.