B.2.7.1. Perceptual load

First, these experiments seemed to confirm the perceptual load hypothesis (Lavie, 2005), since AC decreased with increasing the perceptual load in both experiments. Increasing the perceptual load seemed to impede the exogenous influence of an irrelevant distractor on attentional orienting. Lavie (2005) argued that these effects can take place in perceptual processing as early as in primary visual cortex (Schwartz, Vuilleumier, Hutton, Maravita, Dolan, & Driver, 2005). Consistently, Torralbo and Beck (2008) proposed and supported a neurally plausible definition of perceptual load, based on the biased competition hypothesis. They claimed that the perceptual load results from the competition for representation taking place in the visual cortex. Increasing the competition, either through the set size or through the target-distractors similarity, results in a greater demand of top-down biasing in favour of the target. Consistently, Emerson and Kramer (1997) showed that the exogenous effect of a salient onset distractor was reduced by contextual manipulations, notably by increasing the number of non-salient offset distractors. This biased-competition account of perceptual load is also congruent with the present results. Indeed, if increasing the set size strengthened the competition between items, then, the exogenous influence of the salient distractor should decrease with the number of items. On the contrary, the target selection was less strongly determined by this competition, thanks to the spatial endogenous cueing. Therefore, the AC effect should decrease when the set size increased, as was the case in both experiments.