The perception of frequency peaks and troughs in wide frequency modulations

This work was concerned with the perception of "instantaneous pitch" in continuously frequency modulated sounds. In experiment 1, a 70-dB sinusoidal carrier, close to 1 kHz, was modulated by the exponential of periodic functions corresponding to the sum of a few sinusoids [e.g., sin(at)+sin(3at)]. Each modulation had a fundamental frequency (a/2 pi) of 1.5 Hz and was symmetric on the dimensions of time and log frequency. Thirty listeners identified discrete melodic motifs within these stimuli. The pitches of the identified notes mainly corresponded to the local frequency maxima; generally, the local minima were not heard as auditory "events" (pitch singularities). A similar perceptual asymmetry was not observed for comparable sequences of discrete tones. In experiments 2-4, frequency difference limens were measured for the maxima and minima of continuous frequency modulations, using an adaptive forced-choice method. Sinusoidal carriers were modulated by the exponential of one cycle of a 5-Hz cosine function, starting at phase pi or phase 0 and giving an overall frequency swing of about 0.5 oct. For maxima and minima around 1 kHz, frequency shifts of maxima were better detected than frequency shifts of minima, by an average factor of 2. Generally, this asymmetry did not decrease as a function of subjects' training in the discrimination task, and was still present when frequency minima were given a 6-dB intensity advantage over frequency maxima. No explanation was found for the advantage of frequency maxima with respect to perceptual salience (experiment 1) or discriminability (experiments 2-4).