Stability in the speech system: How neural encoding consistency shapes behavioral categorization and language function

Abstract

Speech perception requires listeners to contend with highly variable acoustic input to construct stable linguistic categories. Recent work has shown that listeners differ in their categorization consistency—the degree to which categorization responses vary for the same stimuli across different trials. Crucially, differences in consistency predict a wide range of real-world outcomes, including language and reading ability in children and adults. However, the mechanisms underlying these differences remain poorly understood. Here, we evaluate the hypothesis that inconsistent categorization is driven by inconsistent encoding of the acoustic information at the neural level. Using electroencephalography, we measured the consistency of the N1 and P3 components in an oddball task. The auditory N1 captures early, pre-attentional encoding processes, while the P3 reflects higher level categorization judgements in the oddball design. Listeners heard steps along speech continua involving bilabial and velar stop consonants while EEG recording took place. We then predicted listeners’ categorization consistency at the behavioral level using the visual analog scaling task from the consistency of their neural responses. Preliminary results suggest a relationship between the consistency of the N1 and the behavioral response, bolstering the idea bottom up noise at the neural level is responsible for differences in categorization consistency.