Social situations are strongly influenced by the way that individuals respond to others' facial expressions, which convey a wealth of information about a person's mental state such as the mood and intentions. Ethyl alcohol is often involved as a neuropharmacological factor in such situations and alcohol has been shown to alter facial perception to make some faces appear more attractive. It therefore appears that facial expression may influence behaviour to a greater extent under the effects of alcohol. We were interested in whether ethyl alcohol altered the ability to derive intentional cues from facial observation, or inhibit responses to those cues. To explore this issue, we used a simple two choice reaction time task in 8 healthy, right handed non-smoking males of BMI = 18-21 in a double-blind, placebo-controlled crossover design. Blood alcohol levels were raised to about 0.15%. Participants were required to press a right key when a central arrow pointed right and left when it pointed left. An eye-movement within a computer-generated facial expression (composite of 100 real faces) seen for 1000ms provided pre-cue information that was always valid. The imperative stimuli would appear 500-3000ms (random) after the face disappeared. In the first block of trials (n = 40) the eyes within the face were made to move 10 degrees to either the right or left or remain stationary. In the second block of trials (n = 40), the eye shift occurred concurrently with a smile or a frown. The smile meant that the cue was valid but a frown indicated an invalid cue. Participants were told this. A second condition also explored performance when the imperative arrow appeared on the left or right of the screen rather than in the centre. The results of this study provide insights into the effect of alcohol on the behavioural response to facial expression.
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