An Implementation of Virtual Acoustic Space for Neurophysiological Studies of Directional Hearing

Abstract

Sound produced by a free-field source and recorded near the cat’s eardrum has been transformed by a direction-dependent ‘Free-field-to-Eardrum Transfer Function’ (FETF) or, in the parlance of human psychophysics, a ‘Head-Related-Transfer-Function’ (HRTF). We prefer to use here the term FETF since, for the cat at least, the function includes significant filtering by structures in addition to the head. This function preserves direction-dependent spectral features of the incident sound that, together with interaural time and interaural level differences, are believed to provide the important cues used by a listener in localizing the source of a sound in space. The set of FETFs representing acoustic space for one subject is referred to as a ‘Virtual Acoustic Space’ (VAS). This term applies because these functions can be used to synthesize accurate replications of the signals near the eardrums for any sound-source direction contained in the set.1–6 The combination of VAS and earphone delivery of synthesized signals is proving to be a powerful tool to study parametrically the mechanisms of directional hearing. This approach enables the experimenter to control dichotically with earphones each of the important acoustic cues resulting from a free-field sound source while obviating the physical problems associated with a moveable loudspeaker or an array of speakers.KeywordsReceptive FieldSound SourceAuditory CortexInteraural Level DifferenceDirectional HearingThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.