The Effect Of Language On Categorical Perception Of Facial Expressions

Categorical perception(CP) effect of facial expression is that facial expressions varying continuously are perceived in human brain as belonging to qualitatively discrete categories,with a clear categorical boundary between different emotional expressions. A defining feature of CP is enhanced performance(i.e., accuracy, reaction time, discriminability) between stimuli which span the categorical boundary compared to discrimination between stimuli from one category, when the stimuli are separated by the same physical distance.Many studies demonstrate that adult humans show CP for human emotional faces. While,it is still debated whether the effect can be accounted for solely by perceptual differences(structural differences among emotional faces) or whether additional conceptual knowledge(i.e., language) is required. Based on one prospective, there exist certain perceptual classification mechanisms which are specifically tuned to facial features that represent each particular expression, suggesting that CP of facial expression is modulated by perception,rather than driven by language. Another prospective contends that the structural information in the face is not sufficient for CP of facial expression to occur, proposing that naming facilitates the effect of CP. Limited research has specifically examined whether CP of facial expression is influenced by language. The current study aimed to examine whether verbal interference affects CP effect by a CP paradigm.Experiment 1 investigated the effect of interference and facilitation of verbal processing.Our Baseline condition, No Interference condition and Verbal Prompt condition all showed that subjects perceived these facial expressions in a categorical fashion. However, the discrimination of between-category stimuli dropped to the level of within-category stimuli,leading to the disappearance of CP effect in Verbal Interference condition.In the second experiment we compared the effects of verbal interference at encoding,during storage, and at both these stages in the discrimination task. By manipulating the stage of verbal interference, we found that the impairment depended on the type of stimuli. In terms of within-category pairs, most interference was found in the Storage Interference and Both condition. Regarding cross-category pairs, interference was found in all three interference conditions. Interference during both encoding and storage produced more impairment than during encoding, storage or no interference.In the third experiment, by employing a variation of the visual oddball paradigm, we investigated whether N2 b and P3 b can be modulated by the categorical origin of the frequent and rare stimuli and by verbal interference. ERP results suggested that deviant faces depicting a different emotion evoked an earlier attentional N2 b wave complex, together with an earlier P3 b. In the No Interference condition, between-category faces evoke an enhanced P3 b than within-category faces, while this differences disappeared in the Interference condition.This pattern of behavioral and neurophysiological results suggests that categorical perception is driven by language.