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A widely accepted assumption is that the boundary between conscious and unconscious perceptual processes is most appropriately defined in terms of a threshold for discriminative responding. Although many studies have been based on this assumption, no generally accepted conclusions have emerged concerning whether or not unconsciously perceived visual stimuli lead to semantic analysis. In the present studies, the boundary between conscious and unconscious perceptual processes was equated with a subjectively-defined threshold based on claimed awareness rather than an objective threshold based on discriminative responding. The results of two experiments involving a Stroop-priming task indicated that masked colour words presented above and below a subjective threshold were effective primes for the subsequent naming of colour patches. More importantly, the results also indicated that primes presented above and below a subjective threshold had qualitatively different effects; variations in the proportion of trials on which primes and targets were congruent led to the adoption of a predictive strategy when the primes were presented above the subjective threshold, but no evidence for the adoption of a predictive strategy was found when the primes were presented below the subjective threshold. It is concluded that a subjectively-defined awareness threshold captures the phenomenological distinction between conscious and unconscious experiences and provides a basis for establishing the qualitative differences that distinguish conscious from unconscious perceptual processes.

The results of four experiments provide evidence for controlled processing in the absence of awareness. Participants identified the colour of a neutral distracter word. Each of four words (e.g., MOVE) was presented in one of four colours 75% of the time (Experiments 1 and 4) or 50% of the time (Experiment 2 and 3). Colour identification was faster when the words appeared in the colour they were most often presented in relative to when they appeared in another colour, even for participants who were subjectively unaware of any contingencies between the words and colours. An analysis of sequence effects showed that participants who were unaware of the relation between distracter words and colours nonetheless controlled the impact of the word on performance depending on the nature of the previous trial. A block analysis of contingencyunaware participants revealed that contingencies were learned rapidly in the first block of trials.Experiment 3 showed that the contingency effect does not depend on level of awareness, thus ruling out explicit strategy accounts. Finally, Experiment 4 showed that the contingency effect results from behavioural control and not from semantic association or stimulus familiarity. These results thus provide evidence for implicit control. Implicit Control 3Contingency Learning without Awareness: Evidence for Implicit Control Cognitive processes that are controlled are conventionally assumed to operate in a slow, effortful, and voluntary manner (Posner & Cohen, 1984;Posner & Snyder, 1975; Shiffrin & Schnieder, 1977). Thus, when researchers discuss the influence of "controlled" processes, it is typically assumed that such processes are explicit (i.e., conscious; cf., Besner & Stolz, 1999). As such, the term "implicit control" would seem to be nonsensical, because "implicit" (i.e., unconscious) seems to preclude the possibility of control. However, etymologically speaking this is not a necessary conclusion. The Oxford English Dictionary (2001) Evidence for cognitive control, which is assumed to be explicit and strategic in nature, has been drawn from the Stroop literature (Stroop, 1935). In the Stroop task, identification of the print colour of colour words is slower when the word and ink colour are incongruent (e.g., the word GREEN in orange; GREEN orange ) than when they are congruent (e.g., ORANGE orange ; see MacLeod, 1991, for a review). Probably the most important demonstration of putatively controlled processes in the Stroop literature is the proportion congruent effect. The proportion congruent effect refers to the finding that the size of the Stroop effect is influenced by the proportion of congruent items in a block of trials (Lindsay & Jacoby, 1994;Logan & Zbrodoff, 1979). Specifically, the Stroop effect is much larger in a high proportion congruent block of trials than in a low proportion congruent block of trials. This effect is commonly attributed to Implicit Control 4 participants explicitly learning to predict the colour from the word. Specifically, because the word us...

The separate semantic and response competition interactions between colour and word processing in a manual Stroop task were evaluated by comparing three trial types. Identity trials are both semantically compatible and response compatible (e.g., BLUE in the colour blue), different response trials are both semantically incompatible and response incompatible (e.g., BLUE in the colour green, where blue and green have different response keys), and same response trials are semantically incompatible and response compatible (e.g., the word BLUE in the colour red, where blue and red have the same key press response). Ink colours were embedded in two different word types, colour words, and colour associates. The results using colour words replicated the findings of De Houwer ( 2003) and demonstrated both a semantic effect (a difference between same response trials and identity trials) and response competition (a difference between same response trials and different response trials). In contrast, the results using colour associates provided evidence for only a semantic effect. These findings support interpretations of the colour associate Stroop effect that attribute the effect to semantics, but challenge Klein's (1964) response competition account andSharma andMcKenna's (1998) claim that the effect of colour associates is dependent on verbal responding. The results confirm that the Stroop colourword task appears to involve at least two mechanisms, a semantic mechanism and a response competition mechanism.

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