Is conscious perception gradual or dichotomous? A comparison of report methodologies during a visual task☆
Section snippets
Background
In a recent article published in Psychological Science, Sergent and Dehaene (2004) argue that the distinction between conscious and unconscious perception is dichotomous, and that a sharp transition can be identified between the two. Their argument is opposed to the view that there is a continuum of the “clarity” with which a perception is conscious (Mangan, 2001). Their argument is based on three experiments in which subjects use a continuous scale in an all-or-none fashion.
In the reported
Method
Fourteen subjects (5 male, 9 female, age between 18 and 65, mean 35.2) participated in the study. All subjects had normal or corrected-to-normal vision.
Stimuli were textured displays also used by Kolb and Braun (1995) but as grey lines on white background in stead of white lines on black background as white on black was found to result in an overly early ceiling effect due to high perceiver sensibility. The images consisted of a series of oriented-element textures. The “target” consisted of
Relation between display time and PAS awareness score
The association between display time and PAS score can be described using an ordinal regression model (ORM) (Harrell, 2001) which is a generalization of the logistic regression model to be used when the observed response is ordered and categorical. Since PAS rating was reported either verbally or using a keyboard we fitted an ORM with display time and report type as factors. Display time was found to be a significant factor (p < .0001) with an odds ratio of 4.19 for a 10 ms increase in duration.
Discussion
It seems a reasonable assumption that PAS ratings should correlate with other relevant measures such as display time and correctness. As it is evident in Fig. 2, Fig. 3, this is indeed the case. Furthermore, PAS does not change substantially as a function of report modality, which, we believe, is a further consolidation of the measure.
The strongest line of evidence for the validity of the PAS scale as a reflection of conscious perception is however the subjects’ own reports that it is the case.
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Morten Overgaard was supported for this work by a grant from Carlsberg Foundation.