Poster E71, Thursday, August 22, 2019, 3:45 – 5:30 pm, Restaurant Hall
Individual differences in bottom-up and top-down processing in speech perception as reflected by beta and gamma oscillations
Jinghua Ou1, Sam-Po Law2;1University of Chicago, 2University of Hong Kong
Introduction Most, if not all, cognitive processes involve interactions between bottom-up and top-down processing. Neurophysiologically, the ascending and descending information is proposed to be conveyed via distinct frequency bands (Arnal & Giraud, 2012; Fontolan, Morillon, Liegeois-Chauvel, & Giraud, 2014; Wang, 2010). Specifically, intracortical recordings from human auditory cortex have directly linked beta (i.e. 𝛽) to information transfer in the top-down direction, whereas gamma (i.e. 𝛾) in the bottom-up direction. The present study seeks to further elucidate the functional specificity of these neural oscillations (i.e. 𝛽 and 𝛾) in the domain of speech perception. To this end, beta and gamma activities were examined among individuals exhibiting different patterns of speech perception, and further correlated with behavioural measures reflecting top-down and bottom-up mechanisms in speech processing. Methods Data were based on two groups of native Cantonese speakers participating in a passive oddball paradigm using EEG (Ou & Law, 2017). They differed in discrimination sensitivity to two rising tones (d': t(36) = 15.2, p < .0001) but both had non-distinctive production, [–Pro+Per] and [–Pro–Per]. Event-related spectral perturbation (ERSP) difference spectrograms (deviant-standard) in beta (12-30 Hz), and gamma (30-50 Hz) bands were subjected to non-parametric bootstrap resampling to detect significant group differences. Two behavioural measures of speech perception - discrimination sensitivity d’ (taken to reflect the quality of internal representation, i.e. top-down knowledge) and RT (taken to reflect both bottom-up and top-down processes) were then correlated with neural oscillatory activities in order to reveal the functional relevance of different frequency bands. Given that beta is suggested to subserve top-down processes and gamma bottom-up processes, we expect to observe significant group differences in beta, which may further be related to differences in d’. Additionally, beta and gamma may contribute differentially to individual differences of RT between the two groups. Results and Discussion Significant group differences were observed in beta from 170 to 280 ms (p < .05, N = 1000 permutations), with reduced beta power observed in [–Pro–Per]. No group differences in the gamma waveform reached significance (all p > .05). We found significant correlation between beta and d' (r = .705, p = .001) for [–Pro–Per], but not in the [–Pro+Per] (r < - .069, p > .05). RTs in the two groups showed significant correlations with different frequency bands, with a significant RT-beta correlation observed in [–Pro–Per] (r = - .651, p = .003) but a RT-gamma correlation in [–Pro+Per] (r = .580, p = .009). Based on the current findings, we propose that beta, implicated in top-down processing, reflects individual differences in the quality of phonological representations among the [-Pro-Per] participants, further leading to variations in d’ and RT; on the other hand, gamma, involved in bottom-up processing, reflects individual differences in acoustic encoding among the [-Pro+Per] participants, resulting in differences in RT.
Themes: Speech Perception, Perception: Auditory
Method: Electrophysiology (MEG/EEG/ECOG)