Consciousness in the core sense refers to a state or continuum in which we are able to feel, think and perceive. Certain popular and social science usages, such as class consciousness, consciousness raising and self consciousness, refer to the content, style or objects of consciousness rather than the primary fact of being aware.
Consciousness is paradoxical because we have direct and immediate personal knowledge of it, but, at the same time, it seems to evade the explanatory frameworks of the social and natural sciences. Let us assume that it can be shown that a particular group of neurons in the brain fires whenever the observer sees something red, and that another group of neurons fires whenever the observer sees something green. This might explain how the observer can make different responses to different colours, but does not seem to explain the subjective appearance of those colours. Acquisition of the appropriate linguistic usages of the term red (as a child) might explain why we can all agree that ripe strawberries and English post boxes are red, but can it explain their redness? This point is illustrated in the puzzle of the inverted spectrum; suppose what you see as having the subjective quality of redness, I see as having the subjective quality of greenness. We nevertheless can agree in our use of colour names because the same (publicly describable) objects always cause similar (private) sensations for a given individual.
Philosophers have given the name qualia to specific sensory qualities, such as the smell of freshly baked bread, the sound of a breaking glass, or the colour and texture of the bark of an oak tree. To know these things vividly and precisely, it is not good enough to be told about them, one must experience them for oneself. Consciousness seems to depend on a privileged observer and unique viewpoint, and it might be argued that the subjective aspects of consciousness are thus outside the explanatory systems of science which are based on shared knowledge (Nagel 1986), and, by extension, beyond all socially constructed meanings.
William James (1890) provided a critique and synthesis of the nineteenth-century debate about whether the mind originated from the material brain or a nonmaterial soul. He concluded that thought was founded on brain physiology but followed its own laws. His analysis of consciousness began with introspection. Consciousness, or the stream of thought, is continuous and ever-changing. Thought is personal, related to an ‘I’ or self; it always has objects; it is selective and evaluative. Consciousness has a span: there are a limited number of objects which we can attend to simultaneously, and there is a span of immediate memory, for events which are just past and have not yet left consciousness.
Problems with introspection as a scientific tool contributed to the ascendancy of behaviourism from the 1920s to the 1950s. Behaviourists held that behaviour could be observed unambiguously, but mental states could not. Establishing the laws relating stimuli and responses would provide a complete explanation of behaviour, denying a causal status to mental events; consciousness was redundant.
With the growth of cognitive psychology in the 1960s, the causal status of mental events was re-affirmed; cognition (by analogy with computer programs) was identified as the processing of information received by the senses. It became legitimate to investigate such topics as mental imagery, objective measures such as reaction times providing corroboration of subjective reports. Much of cognitive processing, including early stages of perceptual analysis, was shown to be unavailable to consciousness, which was linked with focal attention.
Compelling evidence that consciousness depends upon specific brain functions comes from studies of patients with brain injuries. If the visual cortex on one side of the brain is destroyed following a stroke, vision is lost in the opposite half of the visual field. Such patients report a complete absence of any visual sensations from the blind hemifield. Some of these patients nevertheless can point, quite accurately, to a visual target in the ‘blind’ hemifield, while denying that they see anything. There is thus a dissociation between the conscious experience of seeing and the visual processing required for pointing; vision without conscious awareness is termed ‘blindsight’ (Weiskrantz 1986). If right parietal cortex is damaged, patients tend to exhibit a syndrome known as unilateral neglect. They appear not to be conscious of bodily or extra-personal space on the side opposite the lesion. The sensory input appears to be intact, because if a stimulus is applied in isolation to the neglected side, it can usually be detected. However, under everyday conditions patients may misjudge the centre of doors, eat only the right half of food on a plate or dress only the right half of the body. Bisiach and Luzzatti (1978) have shown that unilateral neglect applies to imagined as well as real scenes. It would appear that conscious awareness of an external world, of the body, and of an imagined scene, requires brain processes over and above the simple registration of sensory inputs. A key component of consciousness is deliberate or voluntary action: Luria (1973) described patients who, after massive frontal lobe lesions, were completely passive, expressed no wishes or desires and made no requests. Luria showed that this was a disturbance only of the higher forms of conscious activity, not a global paralysis or stupor. Involuntary or routine behaviours were intact or intensified, emerging sometimes at inappropriate moments, due to the loss of conscious regulation. Incidental stimuli such as the squeak of a door could not be ignored; a patient might respond involuntarily to an overheard conversation with another patient, while being unable to respond directly to questions.
Shallice (1982) has proposed that the frontal lobes are part of a supervisory attentional system which controls and modulates the routine, involuntary and habitual processes of behaviour and perception, and it is tempting to identify conscious thought with the normal operation of systems of this kind. Velmans (1992) has argued, however, that it is mistaken to abandon a first-person for a third-person perspective in this way, and that it is focal attention, not consciousness, which has a role in human information processing.
What are the developmental origins of consciousness? Vygotsky (1986) saw individual subjective awareness as secondary and derivative of social awareness; an internalization of processes and concepts derived from the wider culture via speech (Kozulin 1990). In keeping with this view, the ability to monitor one’s own experiences and the intentions of others are facets of the same developmental achievement (meta-representation). According to Perner (1991), children below the age of 4 years do not know that they have intentions: moreover, in solving a puzzle they did not know whether they chose the right answer because they knew it was correct, or by guessing.
Social and cognitive theories of consciousness are broadly compatible with a functionalist stance on the mind-body problem. Thus, Dennett (1991) has argued that enough is now known, from psychology, social sciences, neuroscience and computer science, to provide an explanation (in principle) of consciousness. Only the philosophers’ puzzles remain, and Dennett marshals arguments to strip them of their power: qualia, for instance, are ultimately nothing more than the sum total of our reactive dispositions, and there is no Cartesian theatre where conscious events are played out for us.
Crick (1994) argues that a neurophysiology of consciousness is within the scope of science. It should be possible, for example, to identify the neural correlates of visual awareness. Neurons in higher visual areas, such as V4 and V5, have responses which correlate more closely with perceptual responses than do neurons in lower visual areas such as VI: V4 cells responding to colour patches are influenced in their firing by surrounding colour patches in a way that parallels human perception of colour; cells in VI tend simply to respond to the wavelength of light. Crick reviews evidence that ‘back projections’ from higher to lower visual areas are important in visual awareness; they may unify the isolated visual features which bottom-up, hierarchical analysis has identified.
The demystification of consciousness by such means is unlikely to satisfy everyone, and for many, the paradox endures. Penrose (1994), for example, implies that the primacy of conscious experience places it outside the functionalist paradigm. He explains with great clarity fundamental problems in the theory of computation and quantum physics, and argues (more obscurely) that there is a deep connection between these problems and that of consciousness.
Michael Wright
Brunel University
References
Bisiach, E. and Luzzatti, C. (1978) ‘Unilateral neglect, representational schema and consciousness’, Cortex 14.
Crick, F. (1994) The Astonishing Hypothesis: The Scientific Search for the Soul, New York.
Dennett, D.C. (1991) Consciousness Explained, New York.
James, W. (1890) The Principles of Psychology, New York.
Kozulin, A. (1990) Vygotsky’s Psychology: A Biography of Ideas, New York.
Luria, A.R. (1973) The Working Brain: An Introduction to Neuropsychology, Harmondsworth.
Nagel, T. (1986) The View from Nowhere, Oxford.
Penrose, R. (1994) Shadows of the Mind, Oxford.
Perner, J. (1991) Understanding the Representational Mind, Cambridge, MA.
Shallice, T. (1982) ‘Specific disorders of planning’, Philosophical Transactions of the Royal Society of London 298.
Velmans, M. (1992) ‘Is human information processing conscious?’, Behavioral and Brain Sciences 14.
Vygotsky, L.S. (1986) Thought and Language, ed. A.Kozulim, Boston, MA.
