5.3.1.1. Method

Participants. Thirty undergraduate psychology students at the University of Lyon II in France participated in the experiment as partial fulfillment of their course requirements. They were native French speakers (mean age of 24 years old, ranging from 19 to 31 years old). Nineteen participants were female and 12 were male. They were selected without regard to any specific measurement of emotion or emotional difficulty.

Materials. The colour words were four French words, bleu, rouge, vert, and jaune (blue, red, green, and yellow); their respective colour patches were also used. The words were presented in Courier 48 bold black type on a white screen. The colour patches were four squares (12 x 12 cm) painted blue, red, green, and yellow. Two schematic faces, one expressing negative emotion and the other, positive emotion, were acquired from Lundqvist, Esteves, and Öhman (1999) to serve as emotional stimuli. A neutral face was created from two previous faces, using imaging software (see appendix 1). Each face was the same size as the coloured squares. Stimuli were presented on a 14” computer monitor that was connected to a Power Mac. Psyscope software version 1.0.2b4 (Cohen, MacWhinney Flatt, & Provost, 1993) controlled stimulus presentation. A voice key device was used to record response latencies.

Design. A 2 (Stroop congruency condition: colour word and colour patch) x 4 (emotional valence: positive, neutral, negative face, and absence of face) x 2 (block of trials) factorial design was used. Subjects participated in 80 trials, divided into two blocks; each block of 40 trials included 10 trials with the negative face, 10 with the positive, 10 with the neutral and 10 with no face. Three different lists were prepared for the presentation order of trial and selected randomly in each block. In each list, after counterbalancing face valence and Stroop congruency level, trials were selected randomly by drawing lots to avoid heavy repetition of a particular face or response.

Procedure. Participants were instructed to name the colour of the colour patch as quickly and as accurately as possible. After training trials, the experimenter answered any participant questions and ensured that they had understood all instructions. Each trial started with a central fixation point (+) for 700 ms, which was replaced by a colour word for 600 ms. After the offset of the colour word, the schematic face was presented immediately for 30 ms. Finally, the colour square appeared with an ISI of 90 ms and disappeared when the participant pronounced the first syllable of the colour name (see Figure 8). A voice key recorded response latencies and, simultaneously, responses were listed and checked by the experimenter for artefacts and participant errors. There were six training trials that were performed without an emotional face.

Figure 8. Example of a trial used in Experiment 1.