More support for rate-based discrimination of second formant transitions

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Abstract
Two prior studies [Besing et al., J. Acoust. Soc. Am. 81, 535 (1987); Porter et al., J. Acoust. Soc. Am. Suppl. 1 82, S81 (1987)] investigated differential thresholds for onset frequency of second formants (30-ms transitions) and for transition duration (60- and 120-ms transitions). The extent of both rising and falling (to 1800-Hz) transition was systematically varied to yield differing rates-of-change for stimuli. Transition discrimination was examined for formants isolated and in a first formant context. The question addressed was whether discrimination varied as a function of the simple stimulus dimensions of frequency and time or in relation to the more complex domain of the rate-of-change of frequency over time. Several aspects of the results supported a rate-of-change interpretation. The present study further tests that interpretation by extending observations to discrimination of onset frequency for 60- and 120-ms transitions. Results for six listeners indicate that onset-frequency discrimination of 60-ms transitions is also based on rate-of-frequency change as was the case for 30-ms transitions; discrimination of 120-ms transitions may be, in part, frequency based. In addition, rate-based discrimination appears to be nonlinear in that higher rates-of-change yield smaller difference limens relative to a reference than do lower rates-of-change. [Supported by NIH-NINCDS and the Louisiana Lions Eye Foundation.]

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