A temporal window for lateralization of interaural time difference by barn owls

Abstract

Lateralization of interaural time difference by barn owls (Tyto alba) was studied in a dichotic masking experiment. Sound bursts consisted of two parts: binaurally time-shifted noise, termed the probe, was inserted between masking noise. The owls indicated that they detected and lateralized the time-shift in the probe by a head turn in the direction predicted from sign of the time-shift. The general characteristics of head turns in response to this stimulus was similar to the head turns elicited by free-field stimulation or to head turns in response to presentation of the probe alone. The owls could easily lateralize stimuli containing long probes. The number of correct turns decreased as probe duration decreased, demonstrating that the masking noise interfered with the owls' ability to lateralize the probe. The minimal probe duration that the animals could lateralize ("minimal duration") became shorter as burst duration decreased. Minimal duration ranged from 1 ms to 15 ms for the two subjects and burst durations from 10 to 100 ms. These findings suggested that owls possess a temporal window. A fitting procedure proposed by Moore et al. (1988) was used to determine the shape of the temporal window. The fitting procedure showed that the shape of the owls' binaural temporal window could be described by the same algorithms as the human monaural temporal window. Thus, the temporal window is composed of a short time constant that determines the central part of the window, and a longer time constant that determines the shape at the skirts of the window.