B.1.3.1.3. Procedure

First, a fixation cross was presented for 800 ms, followed by a 1000 ms black background. Then, the search display appeared until the participants answered by pressing one of two predefined buttons with their dominant middle and index fingers, according to whether the target (i.e. "the only vertically gaped item") was open on top (H button) or on bottom (B button). They were instructed to respond as quickly as possible without making errors. In half of the trials, all display items were of the same size (homogeneous condition). In the other half, each item was of a different size (heterogeneous condition). In both conditions, the target could be large, medium or small, in equal proportions. Participants were explicitly informed that each item had the same probability to be the target. The two conditions were presented randomly. They completed two mixed blocks of 108 trials, separated by a break. RTs less than 200 ms and more than 2000 ms were discarded, considered as anticipation or inattention responses. Discarded trials counted for less than 1 % of the total number of trials.

Figure 1:Synopsis of the visual search task, for Experiments 2 and 3. Only the low oad condition (3 items) was presented. For the display search (last figures on the right), a no-distractor condition was shown on top, and a salient distractor condition on bottom.

Figure 2: Distribution par quintiles des TR pour les expériences 1 (haut), 2 (milieu) et 3 (bas), en fonction de la condition de pertinence et de la taille de la cible. Les barres représentent 1 E.-S.