FREE-FIELD BINAURAL UNMASKING IN BUDGERIGARS (MELOPSITTACUS-UNDULATUS)

The detection of signals in noise is important for understanding bath the mechanisms of hearing and how the auditory system functions under more natural conditions. In humans, the auditory system gains some imp rovement if the signal and noise are separated in space (binaural mask ing release). Birds with small heads are at a disadvantage in separati ng noise and signal sources relative to large mammals, because interau ral time differences are much smaller. Two binaural phenomena in budge rigars related to the detection of tones in noise were examined. Budge rigars show 8 dB of free-field binaural masking release when signal an d noise are presented to their right side and correlated noise is pres ented to their left side. Budgerigars also show a spatial masking rele ase of 9 dB when a signal and noise are separated in azimuth by 90 deg rees. These results are similar to those found in humans and other mam mals with much larger heads.