A note about insensitivity to pitch-change direction

Electrophysiological and Psychophysical Measures of Temporal Pitch Sensitivity in Normal-hearing Listeners

To obtain combined behavioural and electrophysiological measures of pitch perception, we presented harmonic complexes, bandpass filtered to contain only high-numbered harmonics, to normal-hearing listeners. These stimuli resemble bandlimited pulse trains and convey pitch using a purely temporal code. A core set of conditions consisted of six stimuli with baseline pulse rates of 94, 188 and 280 pps, filtered into a HIGH (3365-4755 Hz) or VHIGH (7800-10,800 Hz) region, alternating with a 36% higher pulse rate. Brainstem and cortical processing were measured using the frequency following response (FFR) and auditory change complex (ACC), respectively. Behavioural rate change difference limens (DLs) were measured by requiring participants to discriminate between a stimulus that changed rate twice (up-down or down-up) during its 750-ms presentation from a constant-rate pulse train. FFRs revealed robust brainstem phase locking whose amplitude decreased with increasing rate. Moderate-sized but reliable ACCs were obtained in response to changes in purely temporal pitch and, like the psychophysical DLs, did not depend consistently on the direction of rate change or on the pulse rate for baseline rates between 94 and 280 pps. ACCs were larger and DLs lower for stimuli in the HIGH than in the VHGH region. We argue that the ACC may be a useful surrogate for behavioural measures of rate discrimination, both for normal-hearing listeners and for cochlear-implant users. We also showed that rate DLs increased markedly when the baseline rate was reduced to 48 pps, and compared the behavioural and electrophysiological findings to recent cat data obtained with similar stimuli and methods.

On the utility of perceptual anchors during pure-tone frequency discrimination

Perceptual anchors are representations of stimulus features stored in long-term memory rather than short-term memory. The present study investigated whether listeners use perceptual anchors to improve pure-tone frequency discrimination. Ten amateur musicians performed a two-interval, two-alternative forced-choice frequency-discrimination experiment. In one half of the experiment, the frequency of the first tone was fixed across trials, and in the other half, the frequency of the first tone was roved widely across trials. The durations of the interstimulus intervals (ISIs) and the frequency differences between the tones on each trial were also manipulated. The data were analyzed with a Bayesian model that assumed that performance was limited by sensory noise (related to the initial encoding of the stimuli), memory noise (which increased proportionally to the ISI), fluctuations in attention, and response bias. It was hypothesized that memory-noise variance increased more rapidly during roved-frequency discrimination than fixed-frequency discrimination because listeners used perceptual anchors in the latter condition. The results supported this hypothesis. The results also suggested that listeners experienced more lapses in attention during roved-frequency discrimination.

Sequential dependencies in pitch judgments

Studies that measure pitch discrimination relate a subject's response on each trial to the stimuli presented on that trial, but there is evidence that behavior depends also on earlier stimulation. Here, listeners heard a sequence of tones and reported after each tone whether it was higher or lower in pitch than the previous tone. Frequencies were determined by an adaptive staircase targeting 75% correct, with interleaved tracks to ensure independence between consecutive frequency changes. Responses for this specific task were predicted by a model that took into account the frequency interval on the current trial, as well as the interval and response on the previous trial. This model was superior to simpler models. The dependence on the previous interval was positive (assimilative) for all subjects, consistent with persistence of the sensory trace. The dependence on the previous response was either positive or negative, depending on the subject, consistent with a subject-specific suboptimal response strategy. It is argued that a full stimulus + response model is necessary to account for effects of stimulus history and obtain an accurate estimate of sensory noise.

Differential recognition of pitch patterns in discrete and gliding stimuli in congenital amusia: evidence from Mandarin speakers

This study examined whether "melodic contour deafness" (insensitivity to the direction of pitch movement) in congenital amusia is associated with specific types of pitch patterns (discrete versus gliding pitches) or stimulus types (speech syllables versus complex tones). Thresholds for identification of pitch direction were obtained using discrete or gliding pitches in the syllable /ma/ or its complex tone analog, from nineteen amusics and nineteen controls, all healthy university students with Mandarin Chinese as their native language. Amusics, unlike controls, had more difficulty recognizing pitch direction in discrete than in gliding pitches, for both speech and non-speech stimuli. Also, amusic thresholds were not significantly affected by stimulus types (speech versus non-speech), whereas controls showed lower thresholds for tones than for speech. These findings help explain why amusics have greater difficulty with discrete musical pitch perception than with speech perception, in which continuously changing pitch movements are prevalent.