Factors affecting relative pitch perception
Sounds that evoke a sense of pitch are ubiquitous in our environment and important for speech, music, and auditory scene analysis. The frequencies of these sounds rarely remain constant, however, and the direction and extent of pitch change is often more important than the exact pitches themselves. This dissertation examines the mechanisms underlying how we perceive relative pitch distance, focusing on two types of stimuli: continuous pitch changes and discrete pitch changes.
In a series of experiments testing continuous pitch changes, listeners heard pure-tone frequency sweeps and reported whether they moved up or down. Sweeps varied in the extent of frequency change, the rate of frequency change, and sweep center frequency. Results provide evidence for a sampling mechanism in which listeners extract the start and end pitches of each sweep and then compare them to determine sweep direction. A comparison of performance between frequency regions shows a smaller effect of sweep rate at high frequencies (>6 kHz), suggesting that the mechanism by which listeners extract start/end pitches at low frequencies is based on temporal pitch processing.
To examine discrete frequency changes, nonmusicians, amateur musicians, and formally trained “expert” musicians heard two different pitch-intervals and were asked to indicate which was larger. Intervals varied in the size of the comparison interval and were presented in both low and high frequency regions. Expert musicians performed significantly better than other listeners, while amateur musicians performed similar to nonmusicians. Contrary to previous studies, all groups demonstrated better performance for smaller intervals. A comparison of frequency region also suggests a potential difference in listening strategy between groups: nonmusicians produced higher thresholds at high frequencies but amateur and expert musicians did not.
Overall, results provide novel evidence for the role of a sampling mechanism in sweep-direction identification, and present a previously undocumented effect of standard interval size in pitch-interval perception. The effects of frequency region found in both contexts furthermore suggests that temporal pitch processing mechanisms are used at low frequencies, and that different listening strategies may be used for relative pitch perception at higher frequencies where temporal pitch cues are less reliable.