STUDY 2 Ocular Exploration of Emotional Facial Expression: 7 Days Citalopram vs Placebo

Volunteers and design
Recruitment and screening measures were the same as in Study 1, but only individuals with High Ns were selected (⩾16 on neuroticism scale of the EPQ) (Eysenck and Eysenck, 1975). Forty-seven participants were recruited from the general population; five were excluded owing to history of depression (before data collection and randomized group allocation), and six owing to bad quality of data recording (after data collection; four from the citalopram, two from the placebo group). Three more participants (2 from the citalopram, 1 from the placebo group) were excluded as outliers (see definition above), leaving a total sample of 33 (20 males, mean age=23.6±6.1 years), of which 16 received citalopram (10 males, mean N=18.44±2.4) and 17 placebo (10 males, mean N=19.76±1.8). Participants were randomly allocated to receive identical capsules of citalopram 20 mg or placebo, instructed to take them every day after breakfast, and tested on the seventh day of administration, avoiding caffeinated drinks from 2 h before testing.

Gender discrimination task and eye-movement recording
The experimental methods were the same as in Study 1.

Facial expression recognition task (FERT)
In this study, participants performed an additional task (FERT) previously shown to be sensitive to antidepressant manipulation (Harmer, 2008), where subjects are asked to label emotional facial expressions presented on a screen for 500 ms at intensities varying between 10 and 100%. Correct responses and misclassifications are recorded, and accuracy is measured calculating the average expression intensity threshold needed to correctly identify each emotion (Chan et al, 2007). Eye movements were not recorded during the FERT.

Statistical analysis
The analysis methods were the same as in Study 1. In the repeated-measures ANOVAs, treatment group (drug vs placebo) was entered as the between-subjects variable. A correlation analysis was also run between eye-movement parameters and facial expression intensity threshold values for correct emotion recognition on the FERT, to explore whether emotion recognition accuracy was related to patterns of ocular face exploration.