Perceived modulation magnitudes of second‐formant, center‐frequency variations

Abstract

Speech signals convey information via rapid changes in formant frequencies. Listeners can reliably judge the relative “modulation magnitude” of frequency modulations [e.g., H. Fastl, Hear. Res., 59–69 (1982)]. Listeners were asked if they could also judge modulation magnitude for center‐frequency‐modulated formants by presenting pairs of 500‐ms stimuli with centered, “notchlike” modulations drawn from synthetic continua with varying notch duration (30–300 ms) or depth (50–500 Hz). The first, reference, stimulus (either a low‐ or high‐modulation extreme of a continuum) was assigned a reference magnitude (1 for low‐modulation‐reference trial blocks; 10 for high‐). Listeners assigned a relative “modulation strength” (1 to 10) to the second stimulus. Judged magnitude appears as an uneven perceptual surface in the magnitude × depth × duration space: Highest modulation strengths are heard for deep‐long stimuli; deep‐short stimuli have slightly lower judged magnitudes; shallow‐long modulations are much weaker; shallow‐short modulations are the weakest. The possible relation between perceived modulation magnitude and judgments of articulatory‐phonetic differences will be discussed. [Work supported in part by NIH‐NINCDS and the Louisiana Lions Eye Foundation.]