Perception without awareness: perspectives from cognitive psychology
Introduction
Questions regarding whether stimulus information is perceived even when there is no awareness of perceiving have been the focus of considerable research and discussion for many years. One reason for this continual interest in perception without awareness is that the very idea that perception occurs when there is no awareness of perceiving is inconsistent with the conventional belief that the perception of stimulus information capable of influencing feelings, thoughts or actions is always accompanied by an awareness of perceiving. Given this belief, any evidence that perception is not necessarily accompanied by an awareness of perceiving attracts attention because it challenges the idea that perception implies consciousness.
In the first part of this paper, we describe a conceptual framework for classifying studies of visual perception which, contrary to the conventional belief that perception implies consciousness, show that stimulus information can be perceived even when there is no awareness of perceiving. Although many different methods have been used to investigate perception without awareness, the vast majority of studies represent one of the four basic experimental approaches illustrated in Fig. 1. What the figure shows is that the studies can be classified in terms of (a) the experimental logic used to demonstrate perception without awareness and (b) the method used to control or vary awareness. By far the most frequently followed experimental logic has been to demonstrate a dissociation between two different measures of perception. One measure is assumed to assess perception with awareness, whereas the second measure is assumed to be sensitive to perception without awareness. An alternative but less frequently used experimental logic has been to contrast perception with and without awareness. The goal of these studies has been to establish qualitative differences in the consequences of perceiving with and without awareness. In studies based on either experimental logic, awareness of the critical stimuli has been controlled in one of two ways. In some studies, awareness has been controlled by manipulating the stimulus conditions, whereas in other studies, awareness has been controlled by instructing observers on how to distribute their attention. In general, the results of studies in which any of the four approaches have been adopted show that observers can perceive critical stimuli even when they are unaware of the stimuli. Taken together, the results of these studies provide considerable evidence that perception without awareness is a valid or useful concept in the sense that it leads to verifiable predictions regarding how people perceive the world.
In the second part of the paper, we consider how information perceived without awareness influences conscious experience. The goal of the vast majority of studies to date has been simply to show that information is perceived without awareness. However, a potentially more interesting and important issue concerns how information perceived without awareness, or in other words unconsciously perceived information, influences conscious experience. We describe a number of studies which assess the influence of stimuli perceived without awareness on the conscious experiences associated with perceiving other visual stimuli. The results of these studies show not only that visual stimuli are perceived when there is no awareness of perceiving but that visual stimuli perceived without awareness can both bias which stimuli are perceived with awareness and influence how stimuli are consciously experienced.
Section snippets
Dissociations between measures
In the majority of studies investigating perception without awareness, the basic experimental logic has involved demonstrating a dissociation between two measures of perception. One measure is assumed to assess the stimulus information that is perceived with awareness, or in other words, conscious perception, whereas the second measure is assumed to assess the stimulus information that is perceived without awareness. The logic of using dissociations to demonstrate perception without awareness
Contrasts between perception with and without awareness
As an alternative to establishing dissociations between measures, it is also possible to demonstrate perception without awareness using a single measure of perception, if there are theoretical/conceptual reasons to believe that the selected measure will reveal qualitatively different results depending on whether information is perceived with or without awareness. The logic underlying this alternative approach is based on the assumption that information perceived with awareness enables a
Conscious experience and perception without awareness
Now that it is firmly established that the concept of perception without awareness is valid in the sense that it leads to verifiable predictions, an obvious next step is to examine the functions of perception without awareness. One question that can be asked is how does information that is perceived without awareness influence conscious experience? This question has received relatively little attention in experimental studies to date because the goal of the vast majority of studies has been
Concluding comments
After more than a century of research studies investigating perception without awareness, it is possible to conclude with considerable confidence that stimulus information can be perceived even when there is no awareness of perceiving. This conclusion is supported both by the results of studies demonstrating dissociations between measures of perception with awareness and measures sensitive to perception without awareness and by the results of studies showing that perception with and without
Acknowledgements
Preparation of this paper was supported in part by a research grant from the Natural Sciences and Engineering Research Council of Canada (NSERC) to P.M.M. and by a postgraduate scholarship from NSERC to D.S.
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