Eye movements reflect acoustic cue informativity and statistical noise

Abstract

Listeners rely on highly variable, non-discrete acoustic information to understand spoken messages. The present ‘visual world’ eye-tracking study investigated whether the amount of acoustic cue variation affected Cantonese listeners’ perception of speech contrasts. Participants saw pictures of word pairs which were identical except for initial consonants (unaspirated versus aspirated). Auditory stimuli were continua of increasing VOT presented in bimodal distributions. The amount of acoustic variation varied between conditions: high-variance versus low-variance. Generalised Additive Modelling analyses showed that, in the low-variance condition, eye movements reflected cue values: there was differential fixation behaviour for category means, boundaries, and peripheries. In contrast, in the high-variance condition, the acoustic cue had little effect: fixation behaviour was similar across the different acoustic cue values. This demonstrates listeners’ high sensitivity to the discriminative value of acoustic cues. How much cue dimensions are utilised depends on their variance.