B.2.7.2.2. Influences on controlled processes

The fact that endogenous orienting and resisting interference were similarly influenced by WM suggested that both processes were linked in some way. The most straightforward hypothesis was that they depended on a similar process. As argued in introduction, both processes were endogenously driven, and depended strongly on the active maintaining of a goal. This was also the case in the cited experiments of Unsworth et al. (2004) and of Han and Kim (2004). On this basis, the biased-competition model of WM (Sala & Courtney, 2007) provides a simple account of these influences of WM. On the one hand, loading WM with a dual task led to complicate the task model by increasing the goal number (Duncan et al., 2008, see also Kimberg & Farah, 1993; 2000; Watson & Humphreys, 1997). This amounted to increase the competition between the goals and, thus, to increase the risk of neglecting one of them or of activating it insufficiently. On the other hand, both endogenous orienting and resisting interference also depended on a goal to do so, just as did the second task. Therefore, adding a second task could impair both of these attentional processes, through task goal competition. Moreover, the limited WM capacities vary among people. Thus, the WM-induced impairments of both endogenous processes might be found to be correlated.

In the no-distractor condition, the target had not to be searched for, but only to be selected, and then processed, suggesting that this was the attentional focalizing that was disrupted by loading WM. Clearly, this focalizing process was endogenously-driven: the target was not salient and was indicated by a central arrow. Logically, WM load might have impeded this focalizing process itself, but the reason why would be quite peculiar. It seems more probable that WM actually interfered with the goal of focalizing attention. This under-activation of the goal could have led to a sub-optimal endogenous focalizing.

Obviously, all processes need not be similarly sensitive to goal deactivation. The strength of alternative responses should also be considered. A task might be more sensitive to WM load as the competition from alternative responses increases, for the goal activation should have to be stronger. This might explain why WM load effects were less easily observed in non-competitive tasks than in competitive ones (Lavie & de Fockert, 2005; Mitchell et al., 2004; Unsworth et al., 2004). Finally, the biased competition perspective (Sala & Courtney, 2007; Courtney et al., 2007) could also account for the stronger influence of executive WM tasks relative to mnesic WM ones (Han & Kim, 2004). Indeed, an executive WM task is more complex, and calls for a more complex task model than a simple memorization task. The greater number of coactivated -and thus competing- goals should restrain or decrease their respective activations, owing to competition, and thus increasing the risk to impair performance.