Clarifying the neurophysiological basis of the other-race effect

Vizioli, Luca (2012) Clarifying the neurophysiological basis of the other-race effect. PhD thesis, University of Glasgow.

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The other race effect (ORE) is a well-known phenomenon whereby individuals tend to identify more accurately faces from their same-race (SR) as opposed to faces from the other-race (OR). First reported by Feingold (1914), almost a hundred years ago, since then the ORE has found consistent support at the behavioural level. In spite of a general consensus regarding the robustness of this effect, theoretical accounts have thus far failed to reach an agreement concerning the causes underlying this phenomenon. Two main strands exist within the academic literature, differing on the alleged roots of the ORE. One regards this phenomenon as stemming from different levels of expertise individuals hold with SR and OR face (i.e. the expertise based accounts); the other advocates the importance of social cognitive factor (i.e. the social cognitive accounts). Neuroimaging data can provide important insights in understanding the basis of the ORE. These studies though have thus far failed to reach a degree of consistency. EEG data for example are highly contradictory. A number of studies report no race sensitivity on the N170 face preferential component, while others show that this component is in fact modulated by race. However, discrepancy is found even amongst the study reporting N170 modulation to race, with some showing larger N170 to SR faces, while others revealing the opposite pattern. Similarly, fMRI data show the same degree of inconsistency, especially with regards to the role played by the fusiform face area (FFA). The aim of this thesis is to clarify the neurphysiolological basis of the ORE in order to gain further insights into its origins. To this end three studies (two employing EEG and one fMRI) were designed to answer three main questions related to the ORE: when, how and where in the brain does this phenomenon occur.

The first study investigates the conjoint effects of race and the face inversion effect (FIE - regarded as a marker of configural face processing) on the N170. Interestingly, no race modulations on this ERP component were observed for upright faces. Race however impacted upon the magnitude of the electrophysiological FIE, with SR faces leading to greater recognition impairment and eliciting larger N170 amplitudes compared to inverted OR faces. These results indicate that race impacts upon early perceptual stages of face processing and that SR and OR faces are processed in a qualitatively different manner.

The second study exploites the advantages conferred by adaptation paradigm to test neural coding efficiency for faces of different races. An unbiased spatiotemporal data-driven analysis on the newly developed single-trial repetition suppression (srRS) index, which fully accounts for the paired nature of the design, revealed differential amounts of repetition suppression across races on the N170 time window. These data suggest the SR faces are coded more efficiently than OR faces and, in line with the previous results, that race is processed at early perceptual stages.

The final study investigates whether and where in the brain faces are coded according to the laws predicted by valentine’s norm based multidimensional face space model. Representational Dissimilarity Matrices (RDM) showed that faces are coded as a function of experience within the dominant FFA according to the laws of valentine’s theoretical framework

Importantly in all experiments I tested both Western Caucasian (WC) and East Asian (EA) observers viewing WC and EA faces. A crossover interaction between the race of the observers and that of the face stimuli is in fact crucial to genuinely relate any observed effect to race, and exclude potential low level confounds that may be intrinsic in the stimulus set.

These data, taken together indicate that the ORE is an expertise based phenomenon and that it takes place at early perceptual level of face processing.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Other-race effect, brain imaging, fMRI, EEG, face processing, cognitive neuroscience
Subjects: B Philosophy. Psychology. Religion > BF Psychology
Colleges/Schools: College of Science and Engineering > School of Psychology
Supervisor's Name: Rousselet, Dr. G.A.R.
Date of Award: 2012
Depositing User: Mr Luca Vizioli
Unique ID: glathesis:2012-4112
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 28 Mar 2013 11:33
Last Modified: 28 Mar 2013 11:33

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