Academic journal article Perception and Psychophysics

Unconscious Processing of Color and Form in Metacontrast Masking

Academic journal article Perception and Psychophysics

Unconscious Processing of Color and Form in Metacontrast Masking

Article excerpt

Three experiments employed a metacontrast masking procedure to examine the extent and nature of priming effects from visual stimuli not consciously perceived. The results showed effects of unconscious stimuli on subsequent target responses that (1) were more consistent, reliable, and not subject to strategic control, as compared with consciously perceived stimuli (Experiment 1); (2) produced both facilitation and interference of subsequent processing (Experiment 2); and (3) did not influence indirect response-related levels of processing (Experiment 3). These results demonstrate that color and form attributes of unconscious stimuli are sufficiently registered within the visual system to influence behavior, and that some of these unconscious effects occur at early levels of stimulus encoding, prior to higher level perceptual and response-related processes.

While performing a given task, such as making a cup of tea, one can be distracted by all sorts of things; a misplaced pan, for example, can cause a delay in, and modification of, the plan of action. Often these distractions go unnoticed, but they may nonetheless automatically activate and alter the perceptual and motor systems, especially when certain stimulus features, such as the color or shape of objects, are shared. The role of visual awareness in generating facilitation and inhibition of subsequent perceptual and response processing was investigated in this study using a metacontrast masking paradigm that allowed the presentation of stimuli below a conscious threshold for awareness (for a review on metacontrast masking, see Breitmeyer & Öðmen, 2000). The main question addressed was whether or not a stimulus has to be consciously registered in order for it to have an influence on other stimuli and, particularly, at what levels this unconscious influence occurs.

As early as the 1950s and '60s, studies showed a dissociation between phenomenal reports of observers and their physiological and overt responses (Fehrer & Biederman, 1962; Fehrer & Raab, 1962; Lazarus & McCleary, 1951). For example, Fehrer and her colleagues demonstrated that when participants were asked to respond with a speeded buttonpress to the first stimulus seen, they responded faster when there was a preceding metacontrast masked stimulus, despite reporting having been unaware of it. This speeded response suggests that, although observers often do not report awareness of the masked stimuli, these stimuli may initiate a motor response.

More recently, the role of awareness in perceptual and response-related processing has been the subject of much interest and debate. Since the elegant studies by Marcel (1983) demonstrating unconscious semantic priming, numerous studies have examined whether unconscious visual stimuli influence the perceptual and response- related processing of other stimuli. In one of these studies, Schwarz and Mecklinger (1995) used a backward pattern-masking procedure and demonstrated that, although participants were unable to consciously report the identity (objective thresholding procedure) of flanking letter distractors, they nonetheless produced slower responses when these flankers were incongruent with the target letter. Similar results have been reported using a metacontrast masking procedure with shapes (Klotz & Neumann, 1999) and colors (Schmidt, 2000, 2002), and have shown that unconscious stimuli may automatically influence actions (Schmidt, 2002; Vorberg, Mattler, Heinecke, Schmidt, & Schwarzbach, 2003). Other studies, using patterned masks, have also shown influences on subsequent responses from unconscious, semantically related stimuli (Abrams, Klinger, & Greenwald, 2002; Dehaene et al., 1998; Greenwald, Draine, & Abrams, 1996; Klinger, Burton, & Pitts, 2000), including numeric stimuli assigned to shared response mappings (Naccache, Blandin, & Dehaene, 2002). An event-related potential study suggests that these unconscious semantic processing effects reflect automatic spreading of activation to semantically related stimuli, possibly in the ventral visual pathway (Kiefer, 2002; Kiefer & Brendel, 2006). …

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