Speaker

Prof. Mike McBeath

Title

""Breakdowns in the Correspondence between Acoustic Frequency and Auditory Pitch""

Abstract

Most people including many physicists and musicians think of auditory pitch as a perceptual dimension that corresponds almost one-to-one with the physical dimension of acoustic frequency. This way of thinking stems in part from an attempt to characterize perceptual components, such as pitch, loudness, and timbre, in terms of elegant mathematical constructs, such as orthogonal dimensions. However, such elegant descriptions may fail to adequately represent the perceptual components because they do not accurately reflect the manner in which the components are actually used in environmental contexts. In this talk I will describe three studies that demonstrate a variety of ways in which the simple correspondence between pitch and frequency breaks down. The underlying theme will be that the perception of pitch evolved as a characteristic used to help parse sounds and specify auditory objects in the processing of auditory scenes.

Brief Summary of the Three Studies

In the first study we used Shepard tones (tones comprised of energy only at octave multiples) and replicated that pitch can be divided into at least two major dimensions, tone height (e.g. A1 vs. A2 vs. A3, () and tone chroma (e.g. A vs. B vs. C, (). The findings confirm that the chromatic dimension captures virtually all of the variance in melodic recognition, and suggest that the height dimension is correlated with timbre. The second study examined the phenomena of virtual pitch; the percept of hearing a missing fundamental when presented with tones that only have energy at higher harmonics. The findings confirm that listeners can perceive the missing fundamental even when presented with only a prime-numbered series of harmonics. They support that pitch is specially attuned to recognize the harmonically rich acoustic pattern found in natural resonant sources. The third study examined the percept of tones that were dynamically swept in frequency and intensity (e.g. Doppler shifted tones). The findings confirm that dynamic intensity changes can dramatically effect the percept of pitch. They support that this distortion can facilitate auditory source parsing because it reflects a correlation between changes in the intensity and frequency of natural sources. The findings of all three studies provide strong evidence against the notion of pitch as a simple dimension corresponding simply to acoustic frequency and instead support that it is a characteristic that reflects the complex energy patterns associated with natural acoustic objects. In my talk, I will be reviewing three studies that I have done. I refer you to three articles, each one relevant to one of the studies.

1. Shepard, R.N. (1964). Circularity in judgments of relative pitch. Journal of the Acoustical Society of America, 36, 2346-2353.

2. Hartmann, W.M. (1996). Periodicity, and auditory organization. Journal of the Acoustical Society of America, 100(6), 3491-3502.

3. Neuhoff, J.G. & McBeath, M.K. (1997). Overcoming naive mental models in explaining the Doppler shift: An illusion creates confusion. American Journal of Physics, 65(7), 618-621.