Comparing Individual Differences Across Spectral Contrast Effects With Speech and Non-Speech Stimuli

Abstract

Auditory enhancement is a type of context effect, observed when an individual target component within a masking complex tone becomes perceptually more prominent when the masker-target combination is preceded by a copy of the masker, leading to lower detection thresholds of the target. Context effects can also influence the perception of speech sounds. For instance, the identity of a vowel can be influenced by the spectral content of the preceding sentence. Both auditory enhancement and vowel spectral contrast effects suggest the existence of a perceptual process that favors new acoustic events over ongoing energy, yet it remains unclear whether the same neural mechanisms are responsible for both. This study tested the hypothesis that both effects reflect the same underlying mechanisms by determining whether individual differences in performance are correlated between the two tasks. Thirty normal-hearing native speakers of American English completed both an auditory enhancement task and a vowel categorical boundary task in a counterbalanced order. Robust context effects were observed in the speech and non-speech tasks. Listeners produced an average auditory enhancement effect exceeding 17 dB. The spectrally contrastive precursor sentence induced an average perceptual shift in the categorical boundary of nearly three steps on a 10-step vowel continuum for the vowel identification task. Despite inter-individual performance variability in both tasks, there was no significant correlation between the two context effects. This result suggests that the two effects may not share the same underlying mechanisms.