Frequency scaling reduces individual differences in external‐ear transfer functions in developing cats

Abstract

There are three cues to sound location: Interaural differences in time and level and monaural spectral shape cues. The ultimate magnitudes of these cues depend largely on the linear dimensions of head and pinnae. During development, the increasing interaural distance associated with a growing head and pinnae result in cues that change substantially and continuously until maturation is complete. These experiments examined whether the intersubject differences in the directional transfer functions (DTFs), the directional components of the head‐related transfer functions, of cats during development could be reduced by scaling one set of DTFs on a log‐frequency axis. Measurements were made of both the physical dimensions of the head and pinnae and the DTFs of cats aged 4 weeks to adulthood. For each pair of subjects, an optimal frequency scaling factor was computed that minimized the differences in the DTFs. In many cases, the optimal factors for pairs of subjects were proportional to the ratios of the measured physical dimensions of the head and pinnae in those subjects. Although there were still considerable differences in the DTFs even after scaling, these data support frequency scaling as a potential method of modeling the development of the DTFs in cats. [Work supported by NIH Grant DC006865.]