Re: front to rear reversals (William L Martens )

Subject: Re: front to rear reversals
From:    William L Martens  <wlm(at)U-AIZU.AC.JP>
Date:    Wed, 19 Jan 2000 10:18:43 +0900

With regard to Tim Cox's observation on front to rear reversals in binaural recordings, I have made this distinction: Discussion of the problem of front/rear reversals is clarified if the distinction is made between the subjective experience of the observer and the overt behavioral responses that the observer makes in listening experiments. When the observer is forced to make a choice between two response categories for free-field source incidence angle, front versus rear, then it is possible to have front/rear reversals. In studies of this sort (e.g., Blauert, 1969/70) there is a correct answer, as the sound source is actually located to the front or the rear of the observer. When, however, observers are asked to examine the subjective experience they have during earphone listening, it is no longer appropriate to use the term front/rear reversal, as the true report on the observer's auditory spatial image is the only correct answer. Of course, if a frontally positioned sound source is recorded binaurally, we can ask earphone listeners to make a choice about where they think the sound source was during recording; but this is a different question than that regarding where the auditory spatial image is actually located in the observers perceptual space. For many observers a dry (non-reverberant) binaural recording of a frontally-positioned sound source will result in a spatial image that is located intracranially (inside the head). This phenomenon underscores the importance of clearly stating the nature of the judgment that the observer must make in a spatial listening task. Much of the spatial hearing literature employing earphone presentation obscures this issue by calling judgments about auditory images localization judgments. The distinction must be made between the observer's localization performance and the observer's ability to report the direction and distance of an auditory image experienced during earphone listening. Even when broadband stimuli are reproduced via precisely calibrated earphones, there is no guarantee that veridical perception will result. One reason is that veridical perception of sound-source location often is not observed in free-field listening. This observation and others led Shaw (1982) to propose that earphone studies of spatial imagery be termed either ``space perception'' or ``sound localization.'' -- William L. Martens, Ph.D. Associate Professor Multimedia Systems Lab URL: University of Aizu TEL: [+81](242)37-2791 Aizu-Wakamatsu 965-8580, Japan FAX: [+81](242)37-2731

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