Research Article Inferior Frontal Regions Underlie the Perception of Phonetic Category Invariance

ABSTRACT—The problem of mapping differing sensory stimuli onto a common category is fundamental to human cognition. Listeners perceive stable phonetic categories despite many sources of acoustic variability. What are the neural mechanisms that underlie this perceptual stability? In this functional magnetic resonance imaging study, a short-interval habituation paradigm was used to investi-gate neural sensitivity to acoustic changes within and be-tween phonetic categories. A region in the left inferior frontal sulcus showed a pattern of activation consistent with phonetic invariance: insensitivity to acoustic changes within a phonetic category and sensitivity to changes be-tween phonetic categories. Left superior temporal regions, in contrast, showed graded sensitivity to both within- and between-category changes. These results suggest that perceptual insensitivity to changes within a phonetic cat-egory may arise from decision-related mechanisms in the left prefrontal cortex and add to a growing body of liter-ature suggesting that the inferior prefrontal cortex plays a domain-general role in computing category representa-tions. Mapping differing sensory stimuli onto a common category is fundamental to human cognition. For instance, multiple views of a given face are mapped to a common identity, visually distinct objects (e.g., cups) are mapped to the same object category, and acoustically distinct speech tokens are resolved to the sam