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Title: Aging effect of perceptual processing on face encoding : an event-related potential study
Authors: Chan, SCC 
Lam, LH
Keywords: Aging
Electroencephaolography (EEG)
Issue Date: 2016
Source: The 22nd Annual Meeting of the Organization for Human Brain Mapping (OHBM), Geneva, Switzerland, 26-30 June 2016, poster number 1748 (Poster) How to cite?
Abstract: Introduction: While semantic face encoding strategy is shown to be beneficial for face recognition (Kirchhoff et al., 2012), how the holistic and perceptual processing of face configuration could enhance encoding and subsequent face recognition is not readily studied. It was suggested that elderly individuals showed attention deterioration on face configural information during face encoding, especially at the eye region (Slessor et al., 2013). It is postulated that increased attention on different facial configurations during encoding would be beneficial for elderly. This study aimed to examine the aging effect of perceptual processing of facial configuration on encoding in terms of event-related potential (ERP) N170 for attention and N250 for familiarization and to investigate the differential effects of perceptual processing at different sites (eye-level vs mouth-nose region) of facial configurations on these biomarkers.
Methods: Five adult (mean age (SD)=25.2 (4.9) years) and 6 elderly (mean age (SD)=62.3 years) subjects were recruited, and they were cognitively intact as confirmed by Montreal Cognitive Assessment (Wong et al., 2009). They participated in an experiment adopted from a repetition priming paradigm used by Xue et al. (2011) and were randomized into either eye-level or nose-month encoding groups. In the encoding phase, each subject was asked to study emotionally neutral and novel Chinese faces for four times under spaced learning manner (ITI between 1500 and 2500ms) either in a control or experimental condition. In a control (holistic strategy) condition, each trial started with a 1-s fixation followed by a face stimulus lasting for 2s. The subject needed to press a button when a blank screen was randomly appeared after the face. In an experimental (perceptual strategy) condition, the stimulus presentation of the 1st and 2nd exposures is the same as in control. In the 3rd and 4th exposures, instead of a blank screen, a prompt randomly appeared to ask the subject to compare eye-level or nose-mouth features and responded by pressing a button (Fig. 1). There were 60 faces in five blocks for each condition. After a half-hour break, each subject was presented with 240 faces for 2s with half were previously presented. At the end of the trial, the subject determined if the face had been previously viewed and rated the confidence level of the response (low, moderate and high). A 64-channel electroencephalogram was concurrently recorded using NeuroScan software in a sound-proof chamber. Face recognition performance in terms of hit rate and discriminability index (d-prime) were compared between groups. Repeated measures ANOVA was used to examine the main and interaction effects of groups, strategies, sites of facial feature for encoding and midline/lateral electrode sites in terms of N170 and N250 grand-averaged amplitudes.
Results: The mean hit rate and d-prime were .62 and .63 for adult group and .58 and .53 for elderly group, respectively. No significant differences were obtained between two groups. Repeated measures ANOVA showed a marginal significant groupstrategy site interaction in lateral sites of N170 (120-180ms) [F(1,7)=2.65, p=.15]. Post-hoc analysis revealed more negative at left electrodes when adult group viewed faces with eye-level comparison (p=.15). For N250 (220-290ms), significant group x strategy x site interaction effect was found in midline sites [F(1,7)=11.12, p<.01]. Post-hoc analysis showed more negative-going N250 amplitudes in eye comparison task of elderly group (p<.1) (Fig. 2 & 3).
Conclusions: The preliminary results suggest that cortical activation of attention for face configuration appeared to be more symmetrical among elderly. Besides, perceptual processing of face configuration, especially at the eye level, would be beneficial for aged individuals to encode face. This sheds light that the perceptual strategy could have the therapeutic value to enhance face-related memory functions of those with cognitive declines.
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