The perceptual flow of phonetic information

Abstract

Over a long and distinguished career, Randy Diehl has elucidated the brain mechanisms underlying spoken language processing. The present study touches on two of Randy’s central interests, phonetic features and Bayesian statistics. How does the brain go from sound to meaning? Traditional approaches to the study of speech intelligibility and word recognition are unlikely to provide a definitive answer. A finer-grained, Bayesian-inspired approach may help. In this study, listeners identified 11 Danish consonants spoken in a Consonant + Vowel + [l] environment. Each syllable was filtered so that only a portion of the original audio spectrum was presented. Three-quarter-octave bands of speech, centered at 750, 1,500, and 3,000 Hz, were presented individually and in combination. The conditional, posterior probabilities associated with decoding the phonetic-features Voicing, Manner, and Place of Articulation were computed from confusion matrices to delineate the perceptual flow of phonetic information processing. Analysis of the conditional probabilities associated with both correct and incorrect feature decoding suggest that Manner of articulation is linked to the decoding of Voicing (but not vice-versa), and that decoding of Place of articulation is associated with decoding of Manner of articulation (but not the converse). Such feature-decoding asymmetries may reflect processing strategies in which the decoding of lower-level features, such as Voicing and Manner, is leveraged to enhance the recognition of more complex linguistic elements (e.g., phonetic segments, syllables, and words), especially in adverse listening conditions. Such asymmetric feature decoding patterns are consistent with a hierarchical, perceptual flow model of phonetic processing.