Generation of Virtual Sound Sources for Electrophysiological Characterization of Auditory Spatial Tuning in the Guinea Pig
The sound emitted by a source is distorted by the pinna, head and body. These distortions are caused by diffraction and reflections in the pinna structure and depend on the frequency and the direction of incident. They can be formally described by the transfer function H(f,ϕ,υ) (ϕ=azimuth, υ=elevation, head related transfer function, HRTF)(Blauert 1983, Wightman 1989). This function is defined as the ratio between the sound pressure at the eardrum and the sound pressure at the position of the head when no animal is present. If the sound is delivered through earphones, the hearing event will be identical to that under free field conditions provided that the sound pressure at the eardrum is the same as in the free field. This can be achieved by filtering the signal of a sound source with the corresponding HRTF of that direction and by compensating the influence of the earphone transfer function and coupling to the ear canal. In the present study we measured the HRTFs of 8 guinea pigs. The individual HRTFs were used to create virtual sound sources (VSS) which simulate free field conditions. The virtual sound sources were used for electrophysiological characterization of spatial tuning in the central nucleus of the guinea pig’s inferior colliculus.
KeywordsSound Pressure Sound Source Inferior Colliculus Interaural Time Difference Interaural Level Difference
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