Date of Award

5-2025

Document Type

Thesis

Degree Name

Master of Arts in Psychological Science

Department

Psychology

First Reader/Committee Chair

Brunet, Nicolas Ph.D

Abstract

The N170 is an event-related potential (ERP) component commonly associated with its sensitivities to face stimuli. While mixed literature exists, the N170 has been repeatedly demonstrated to be modulated by emotion. In a highly cited study, Blau et al. (2007) found that the N170 is heavily modulated by emotional expression, with fearful expressions eliciting larger N170 amplitudes than neutral expressions. In their study, however, analysis did not account for variability in mouth positioning in fearful and neutral expressions and how this variability might influence differences observed in amplitudes of the N170. A distinctive feature in the fearful condition was the presence of exposed teeth, whereas the neutral expression did not show teeth.

In the present study, research analysis focused on how mouth variations in emotional display can modulate event-related potentials (ERPs). Participants (N=42) categorized facial stimuli by sex. Stimuli consisted of 288 images of faces, balanced for sex and race/ethnicity, with fearful, happy, or neutral expressions, and were controlled for mouth display (open mouth with visible teeth vs. closed mouth).

Results revealed that the N170 was significantly modulated by the presence of teeth, irrespective of emotion shown; however, the P100 waveform displayed significant interaction between these variables.

Overall, results showed that the N170 is not modulated by emotion, but rather the visibility of teeth, indicating that teeth may play a significant role in neural processing of facial recognition and emotion perception. Further, differences between the N170 and P100 may highlight distinct neural processing pathways for early and late face recognition that future research may look to assess.

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