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Discrete repetition effects for visual words compared to faces and objects, but no modulation by expectation: An event-related potential study
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Poster A128 in Poster Session A, Tuesday, October 24, 10:15 am - 12:00 pm CEST, Espace Vieux-Port
Bingbing SONG1, Werner Sommer2, Urs Maurer134; 1Department of Psychology, The Chinese University of Hong Kong, Hong Kong, China, 2Institut für Psychologie, Humboldt-Universitaet zu, Berlin, Germany, 3Brain and Mind Institute, The Chinese University of Hong Kong, Hong Kong, China, 4Centre for Developmental Psychology, The Chinese University of Hong Kong, Hong Kong, China
Introduction: Repetition suppression (RS) refers to the reduction in neuronal responses to repeated stimuli as compared to non-repeated stimuli. Previous studies have reported RS for various stimulus categories, such as faces and words, but it remains unclear whether the timing of these effects differs between stimulus categories. Moreover, in previous functional magnetic resonance (fMRI) imaging studies with faces RS was modulated by repetition probability (expectation), also known as P(rep). Because P(rep) effects with visual non-face stimuli were inconsistent, P(rep) effects may depend on the expertise of the stimulus category. The visual expertise hypothesis can be tested by including written words, for which literate individuals have expertise. Moreover, using time-sensitive EEG allows to assess the temporal order of RS and P(rep) effects and to test for differences between stimulus categories. Method: Data from 33 native Cantonese speakers (16 females, mean age = 20.19 years, range = 18-28) are reported. Participants were presented with stimulus pairs of Asian faces (subcategories: male, female), written Chinese words (subcategories: living, non-living things), and animal pictures (subcategories fish, birds). The second stimulus of a pair could be the same as the first stimulus (repetition trials) or different (alternation trials). The sub-category of S1 served as a cue to signal P(rep) of S2, e.g., a living word could signal a high repetition probability (75%) and a low alternation probability (25%). Following the presentation of each stimulus pair, participants classified the sub-category of S1 (e.g., living vs. non-living) by button press. EEG data were analyzed using Topographic Analyses of Variance (TANOVA) on raw ERPs that estimate differences between entire ERP maps by generating a randomized distribution of dissimilarity of map differences between conditions. To identify the temporal dynamics of repetition effects and P(rep) following S2 onset, we ran time point-by-time point TANOVA separately for each stimulus category with factors Repetition (repeated vs. alternated) and Expectation (expected vs. unexpected), followed up by pairwise contrasts. Results: TANOVA revealed significant repetition effects after the onset of the second stimulus across multiple time intervals from 92-560ms for words, from 207-358ms for faces, and from 324-486ms for objects. Repetition effects were not modulated by expectation in any of these analyses. Irrespective of expectation, pairwise TANOVA contrasts showed larger repetition effects for written words compared to faces (152-262, 282-456ms) and objects (150-238, 265-440ms), and for faces compared to objects (213-332ms). Conclusion: The findings suggest that repetition effects occur for all stimulus categories, but that the timing of these effects differs. Repetition effects were earlier for expertise stimuli (words and faces) than non-expertise stimuli (animals). However, stimulus properties, such as spatial frequency, seem to further influence the occurrence and direction of repetition effects. Finally, while some spatially sensitive fMRI studies had revealed modulation of repetition effects by expectation, no evidence of such a modulation was observed in our study with temporally-sensitive EEG, underlining the importance of time resolution for investigating neural processing.
Topic Areas: Reading,