Perceptual Asymmetries and Categorical Boundaries in Pitch Discrimination of Musical Intervals.

Abstract

Purpose: While overall accuracy in pitch discrimination is a common metric, error patterns can reveal fundamental properties of the auditory system. This study analyzes data from a pitch discrimination task to investigate specific perceptual asymmetries and the presence of categorical perception for musical intervals in normal-hearing adults.

Methods: Twenty normal-hearing adults (aged 36–72) completed two interval discrimination tasks using piano tones centered on C3 (130 Hz) and C4 (261 Hz). The analysis focused on (1) the directionality of errors (systematic misclassification of higher tones as "lower") and (2) confusion matrices to identify perceptual boundaries between adjacent semitones.

Results: A significant directional asymmetry was found, particularly in the C4 range, where participants were more likely to misclassify a higher-frequency tone as "lower" than the reference (Binomial test, p = 0.02). Confusion matrices revealed that 60% of all errors occurred between adjacent semitones (e.g., D# vs. E), indicating sharp perceptual boundaries consistent with categorical perception. This asymmetry was more pronounced at higher frequencies and was correlated with age (r = -0.52, p = 0.02 for C4 performance)

Conclusion: Pitch perception is not a symmetric process. The observed perceptual compression in the higher frequency range and the clustering of errors at semitone boundaries suggest that listeners employ categorical judgments, likely influenced by musical experience and psychoacoustic constraints. These findings highlight the importance of analyzing error patterns, not just accuracy, to understand the underlying mechanisms of auditory perception.