Lexical effects on phonetic categorization: the role of stimulus naturalness and stimulus quality.

A series of experiments was conducted to determine whether the effects of lexical status on phonetic categorization were influenced by stimulus naturalness (replicating M. W. Burton, S. R. Baum, & S. E. Blumstein, 1989, who manipulated the intrinsic properties of the stimuli) and by stimulus quality (presenting the stimuli in white noise). The experiments compared continua varying in voice onset time (VOT) only to continua covarying VOT and amplitude of the burst and aspiration noise in no-noise and noise conditions. Results overall showed that the emergence of a lexical effect was influenced by stimulus quality but not by stimulus naturalness. Contrary to previous findings, significant lexical effects failed to emerge in the slower reaction time ranges. These results suggest that stimulus quality contributes to lexical effects on phonetic categorization, whereas stimulus naturalness does not.