Audio-vocal responses to repetitive pitch-shift stimulation during a sustained vocalization: Improvements in methodology for the pitch-shifting techniques

Abstract
The pitch-shift reflex is a sophisticated system that produces a “compensatory” response in voice
F0 that is opposite in direction to a change in voice pitch feedback (pitch-shift stimulus), thus
correcting for the discrepancy between the intended voice F0 and the feedback pitch. In order to more
fully exploit the pitch-shift reflex as a tool for studying the influence of sensory feedback mechanisms
underlying voice control, the optimal characteristics of the pitch-shift stimulus must be understood.
The present study was undertaken to assess the effects of altering the duration of the interstimulus
interval (ISI) and the number of trials comprising an average on measures of the pitch-shift reflex.
Pitch-shift stimuli were presented to vocalizing subjects with ISI of 5.0, 2.5, 1.0, and 0.5 s to
determine if an increase in ISI altered response properties. With each ISI, measures of event-related
averages of the first 10, 15, 20, or 30 pitch-shift reflex responses were compared to see if increases
in the number of responses comprising an event-related average altered response properties.
Measures of response latency, peak time, magnitude, and prevalence were obtained for all ISI and
average conditions. While quantitative measures were similar across ISI and averaging conditions,
we observed more instances of “non-responses” with averages of ten trials as well as at an ISI of 0.5
s. These findings suggest an ISI of 1.0 s and an average consisting of at least 15 trials produce optimal
results. Future studies using these stimulus parameters may produce more reliable data due to the
fivefold decrease in subject participation time and a concomitant decrease in fatigue, boredom, and
inattention.