Can attention modulate non-conscious processing ?

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Recent research has also overturned another classic dogma in cognitive psychology: the idea that subliminal priming effects are automatic, rigid and independent of the subject's strategies or attention. The classic theory (Posner & Snyder, 1975) coincides a whole series of properties: the rapid, parallel, uncontrollable, non-intentional and non-conscious character of so-called "automatic" cognitive operations is contrasted with the slow, serial, controlled, intentional and conscious character of so-called "strategic" operations. There is little doubt that a distinction of this kind should be maintained, but the idea of a perfect dichotomy, with no overlap between automatic and controlled processes, has been undermined by the observation that attention and conscious strategies can modulate cognitive operations right down to the lowest level of perception. It therefore seems logical to postulate that subliminal priming may also be under the influence of conscious strategies.

The accuracy of this hypothesis was demonstrated in several stages. Firstly, it has been shown that subliminal priming depends on temporal attention: a subliminal stimulus that occurs at an unexpected time ceases to give rise to significant priming effects in response times (Naccache, Blandin & Dehaene, 2002). The same applies to spatial attention: the effect of a stimulus masked by meta-contrast varies according to whether or not its spatial position receives attentional amplification (Kentridge, Nijboer & Heywood, 2008).

Perhaps more surprisingly, the instructions given to the subject also modulate the influence of non-conscious priming on semantic processing and decision-making. In the numerical classification task, the same numbers may or may not induce an unconscious priming effect, depending on whether or not they are part of the list expected by the participants, and also on the strategy adopted to respond to the task. In a Stroop-inspired interference situation, the unconscious influence of non-congruent cues is modulated according to the recovery of cognitive control induced on the previous trial (Kunde, Kiesel & Hoffmann, 2003).

In Abstract, this research demonstrates that cognitive strategies, once consciously prepared, are then likely to be partially executed on a non-conscious target. The links between attention and consciousness thus appear to be more complex than initially thought. On the one hand, a non-conscious stimulus can have its processing modulated by attention - although paying attention to it is not enough to bring it into consciousness. On the other hand, even a subliminal stimulus can attract attention - the orientation of attention is therefore, at least in part, a non-conscious process. Although this question remains debated (Wyart & Tallon-Baudry, 2008), the only link between attention and consciousness seems to be that an act of directing attention - voluntary or attracted by the stimulus itself - is indispensable for access to consciousness (Dehaene & Naccache, 2001).