Abstract
Although faces are often included in the broad category of emotional visual stimuli, the affective impact of different facial expressions is not well documented. The present experiment investigated startle electromyographic responses to pictures of neutral, happy, angry, and fearful facial expressions, with a frontal face direction (directed) and at a 45° angle to the left (averted). Results showed that emotional facial expressions interact with face direction to produce startle potentiation: Greater responses were found for angry expressions, compared with fear and neutrality, with directed faces. When faces were averted, fear and neutrality produced larger responses compared with anger and happiness. These results are in line with the notion that startle is potentiated to stimuli signaling threat. That is, a forward directed angry face may signal a threat toward the observer, and a fearful face directed to the side may signal a possible threat in the environment.
Highlights
The difference between face direction was not significant, but there was a trend toward greater startle when the faces were directed to the side, F(1, 29) 1⁄4 3.84, p 1⁄4 .06, Z2 1⁄4
We compared the startle response to pictures of faces with a forward direction with faces directed to the side
Our analyses of the long lead i-Perception interval condition revealed that directed angry faces elicited greater startle than averted angry faces
Summary
Thirty people (13 men, 17 women, age range 17–40, mean age 22.0 years) participated in the study. The participants were instructed not to drink caffeinated beverages or use nicotine-containing substances for 3 hr prior to the experiment. They were told that they could withdraw from the study at any time without giving any reason. The startle-eliciting noise was presented 250 or 3500 ms after picture onset. Startle-eliciting stimulus was presented at every trial (once per picture). The sampling rate was 1000 Hz. Participants rated the pictures for valence, arousal, and domination in the room adjacent to the experimental chamber. Participants used the mouse pointer to indicate the level of valence, arousal, and domination elicited by each picture using a visual analog scale (VAS) on a computer screen. The program for the VAS was written in, and controlled by, MATLAB version 8.3 with Psychophysics toolbox (Brainard, 1997)
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