Elsevier

Consciousness and Cognition

Volume 15, Issue 4, December 2006, Pages 700-708
Consciousness and Cognition

Is conscious perception gradual or dichotomous? A comparison of report methodologies during a visual task

https://doi.org/10.1016/j.concog.2006.04.002Get rights and content

Abstract

In a recent article, [Sergent, C. & Dehaene, S. (2004). Is consciousness a gradual phenomenon? Evidence for an all-or-none bifurcation during the attentional blink, Psychological Science, 15(11), 720–729] claim to give experimental support to the thesis that there is a clear transition between conscious and unconscious perception. This idea is opposed to theoretical arguments that we should think of conscious perception as a continuum of clarity, with e.g., fringe conscious states [Mangan, B. (2001). Sensation’s ghost—the non-sensory “fringe” of consciousness, Psyche, 7, 18]. In the experimental study described in this article, we find support for this opposite notion that we should have a parsimonious account of conscious perception. Our reported finding relates to the hypothesis that there is more than one perceptual threshold [Merikle, P.M., Smilek, D. & Eastwood, J.D. (2001). Perception without awareness: perspectives from cognitive psychology, Cognition, 79, 115–134], but goes further to argue that there are different “levels” of conscious perception.

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.

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