Re: effect of phase on pitch ("Steven M. Boker" )

Subject: Re: effect of phase on pitch
From:    "Steven M. Boker"  <sboker(at)CALLIOPE.PSYCH.ND.EDU>
Date:    Thu, 5 Feb 1998 14:15:37 -0500

Bert Schouten <Bert.Schouten(at)LET.RUU.NL> writes: >Perceptual effects of phase on pitch or timbre could be epiphenomena >of a mechanism needed for sound localization. We need some form of >phase-locking in the auditory nerve in order to be able to compare >the signals from the two ears. In natural environments the ear >receives no phase information about the sound source, so pitch and >timbre cannot normally be based on temporal information, but the >sensitivity to temporal differences between the two ears may >influence pitch or timbre whenever headphones are used or when >phones are inserted into animals' ear canals. > This argument seems almost right, although I'd add that phase information is highly predictive of self-motion. Thus there may be a strong localization component of phase both for objects and for self-location within the frame of reference. Similarly, phase change is correlated with object acceleration within an environment. If an sound source starts to move toward the listener and there is a reflecting wall behind the sound source, both the sound source acceleration and the acceleration of the source relative to the wall would be predictable from the phase changes of the direct and the reflected sound. There is some research (see Stoffrengen's recent paper for an overview) into perception of self motion through auditory cues. I argue that a large proportion of that information is contained in phase. However, if we are to maintain Pitch Constancy (similar to color constancy) for moving objects, phase changes must be removed from the perception of pitch and relegated to motion detection. There is some error in this process. The error can be most readily seen in an environment where the subject is wearing headphones, because then the phase changes are decoupled from the other sensory modes of information about self-motion. It is partly this multi-modal self motion information that allows the phase information to be removed from the incoming auditory signal and pitch constancy to be attained. Cheers, Steve --- Steven M. Boker 219-631-4941 (office) sboker(at) 219-631-8883 (fax) 219-257-2956 (home) Dept. of Psychology, University of Notre Dame, Notre Dame, IN 46556

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