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Vowel normalization, speech perception
Abstract:
Listeners adjust their vowel perception to the characteristics of a particular speaker. Six experiments investigated whether speech-specific signal characteristics influence the occurrence and amount of such normalization. Previous findings were replicated with first formant (F1) manipulations of naturally recorded speech; target sounds on a [pIt] (low F1) to [pEt] (high F1) continuum were more often labeled as [pIt] after a precursor sentence with a high F1, and more often labeled as [pEt] after one with a low F1 (Exp. 1). Normalization was also observed, though to a lesser extent, when these materials were spectrally rotated, and hence sounded unlike speech (Exp. 2). No normalization occurred when, in addition to spectral rotation, the silent intervals and pitch-movement were removed and the syllables were temporally reversed (Exp. 3), despite spectral similarity of these precursors to those in Exp. 2. Reintroducing only pitch movement (Exp. 4), or silent intervals (Exp. 5), or spectrally-rotating the stimuli back (Exp. 6), did not result in normalization, so none of these factors alone accounts for the effect's disappearance in Exp. 3. These results show that normalization is not specific to speech, but still depends on more than the overall spectral properties of the preceding acoustic context.
