This study investigated whether categorical perception—a phenomenon observed in speech perception—extends to the discrimination of vowel-like timbre qualities. Categorical perception occurs when continuous acoustic variations are perceived as distinct categories, leading to better discrimination near category boundaries than within a category. To test this, discrimination thresholds for the center frequency of a one-third-octave band formant introduced into the spectrum of a pink noise burst were measured in five subjects using an adaptive psychophysical procedure. Thresholds were assessed at distinctive formant frequencies of selected Polish vowels and at boundaries between adjacent vowel categories along the formant-frequency continuum. Results showed no reduction in discrimination thresholds at category boundaries, suggesting an absence of categorical perception for vowel-like timbre. One possible explanation for this finding lies in the listening mode—a concept from ecological auditory research—describing cognitive strategies in auditory tasks. The design of both the stimuli and the experimental procedure likely encouraged an acousmatic listening mode, which focuses solely on the sensory characteristics of sound, without reference to its source or meaning. This may have suppressed cues typically used in the categorical perception of speech sounds, which are associated with the communication listening mode. These findings highlight the importance of considering listening mode in future research on categorical perception of timbre and suggest that vowel-like timbre discrimination may involve perceptual mechanisms distinct from those used in speech sound discrimination.
