The mental state in which one experiences, notices, and is directly apprised of one's own "percepts, "memories, emotions, beliefs, thoughts, and actions.
Books on memory tend to shy away from the discussion of consciousness and related issues. This is surprising on the one hand yet understandable on the other. It is surprising because the relation of consciousness to memory is of great importance in memory research ("amnesia, "declarative memory, "episodic memory), and conscious awareness is a major "criterion in the "zeitgeist "taxonomy of memory "systems. Avoiding the discussion of consciousness is, however, understandable, because despite many centuries of systematic thinking, and the fact that we all know subjectively what it is, consciousness is still an "enigma. All authors point to the great difficulty in even defining it (e.g. Crick and Koch 1992; Searle 1992; Block 1995). Because we know so little about consciousness, many authors also believe that premature definitions are counterproductive.
The purpose of this discussion is to outline briefly only very limited aspects of conscious awareness that are directly relevant to the discussion of memory. To do so, we must, first, and in spite of the aforementioned caveat, attempt to formulate an operational, heuristic definition of the subject of discussion. This definition does not aspire to explain what conscious awareness is in the context of a theory of mind and brain, it merely delineates the subject.1 Second, as the terms 'consciousness', 'conscious', 'awareness', and 'conscious awareness' are often used interchangeably in the literature, the meaning of these terms as intended in this book should be clarified before further use.
Consciousness is an umbrella term that refers to a particular type of mental faculty, state, and process in living systems, which involves subjective experiencing of ongoing occurrences. "Stimuli are sensed and perceived by their perceiver in a private version, with phenome-nological qualities that are transparent to the "subject only.2 Emotions, beliefs, thoughts, and actions involve private experiences as well, inaccessible to the outside observer. Consciousness could also involve reflexive perception of oneself, or 'self-consciousness'.3 Consciousness is treated in a variety of contexts in philosophical discourses, whose spectrum of discussion ranges from issues of soul and self, to speculations about emergent properties of highly complex systems (e.g. Kant 1781; James 1890; Freud 1900; Bergson 1908; Ryle 1949; Edel-man 1990,1995; Dennett 1991; Searle 1992; Crick 1994; Damasio 2000; for a tiny glimpse of the sophistication of treatment of consciousness in eastern philosophy, see Harvey 1990; Keown 2000). Consciousness is manifested in multiple varieties, differing along the "dimensions of arousal, "attention, qualia experience, and reflexivity. For example, there are states of altered consciousness on waking up from deep sleep, or in some diseases (e.g. "dementia), or under the influence of drugs, or in meditation. Consciousness is assumed to mean very different things in different species (Ristau 1991; Heyes and Huber 2000). Being conscious refers to the exercising of some or another variety of consciousness.
Awareness per se refers here to the ability of the central nervous system to sense and process ongoing stimuli from the outside world, irrespective of the particular state of consciousness. This is a "reductionist use of the term. According to this use, awareness of a target stimulus can be inferred objectively from observing the input-output relationships, provided appropriate "controls for input-output causality are being used. Hence the brain could react to information and use it to act on the world, without the subject, as the active agent, paying attention and becoming directly apprised of this information. Examples in humans are non"declarative memories, such as "habit, "skill, and "priming. Or consider an even simpler case, the stimulus that evokes the gill withdrawal reflex in *Aplysia; it makes sense to talk about Aplysia being aware of this stimulus, but it is questionable whether the slug is really conscious of the stimulus; so far we have no "method to determine if it is and if so, to what degree.4
Conscious awareness is a higher form of awareness. To say that the subject is consciously aware of something is to say that in addition to the nervous system of the subject being aware of this thing, the subject is also conscious that this thing happens. A subject may, of course, be in a fully conscious state but unaware of the target information. Stating that the subject is specifically conscious of the target information implies that the subject is also aware of this information; however, the use of the solo term conscious (or consciousness) in experimental science might be somewhat problematic from the point of view of pragmatics. This is because these terms, as noted above, are used in a broad spectrum of conceptual frameworks, some of which do not necessarily refer to concrete behaviour. Conscious awareness intends to connote a more tangible cognitive state, of being directly apprised of one's ongoing behavioural acts, and fits better to be used in the context of experimental science. This is, therefore, the term preferred in this book. Note that many authors do equate 'conscious' with 'aware', yet still use the term 'consciously aware', which in this case becomes a redundancy ("Ockham's razor).
A compact matrix of memory systems-by-consciousness, proposed by Tulving (1985b), illustrates the kind of interactions possible among different types of memory and consciousness. Tulving lists three varieties of consciousness, which he terms anoetic (not comprehending), noetic (comprehending), and auto-noetic (self-comprehending).5 Anoetic is similar to awareness as defined above; the subject is capable of registering, representing, and responding to aspects of the present environment, but is not consciously aware of these events. Anoetic consciousness corresponds to procedural, nondeclarative memory systems. Noetic consciousness allows the subject privately to experience and operate cognitively on objects and events and on the relations among them. This corresponds to conscious awareness as used here, and is correlated with semantic memory ("declarative memory). Autonoetic consciousness confers in addition the capability of experiencing the private phenomenological flavour of personal episodes, is correlated with "episodic, autobiographical memory, and corresponds to an advanced, reflexive form of conscious awareness as defined here.
It is hence evident from the discussion so far that consciousness is not an all-or-none state, and therefore we should indeed expect to find various degrees of conscious awareness in different species as well as in different states of the organism. Furthermore, different task conditions may involve different varieties of conscious awareness. Consider, for example, "classical conditioning; whereas simultaneous and delay conditioning require only awareness, i.e. anoetic consciousness, trace conditioning may already require conscious awareness, i.e. noetic consciousness (Clark and Squire
1998). Another noteworthy point is that the role of conscious awareness in "acquisition and in "retrieval of an item could differ. For example, learning to drive a car should better involve conscious awareness, but an expert driver can drive for hours in the absence of conscious awareness of the activation of the driving skill. Thus, conscious awareness is not a cognitive system that becomes permanently linked to particular types of memory; rather, it is a brain state, which is either obligatory, or permissive, or optional for the acquisition or retrieval of an item.
What are the brain substrates of conscious awareness? This question is the focus of many studies that combine multiple experimental methodologies, occasionally augmented by a provocative hypothesis and by input from professional philosophers (for a selection of approaches and commentaries, see Griffin 1985; Crick and Koch 1992, 1995; Nagel 1993; Bogen 1995; Weiskrantz 1995; Block 1996; Duzel et al. 1997; Clark and Squire 1998; Mcintosh et al 1999). Two major experimental methods stand out. One is the analysis of conscious awareness in brain damaged patients. These are patients that suffer from amnesia; or agnosia (the loss of ability to "recognize and identify a class of stimuli in the absence of impairment in the ability to sense these stimuli; Shallice 1988); or disconnection syndrome (a set of deficits following interruption of large tracts of nerve fibres in the brain, such as the corpus callosum; Zaidel et al. 1996). This type of approach unveils circumscribed disturbances of conscious phenomena, and identifies brain sites that subserve these phenomena. The second approach is combination of "functional neuroimaging with neuropsychology, and its main objective is to identify neural correlates of conscious awareness. It seems that conscious awareness depends on the activity of distributed brain circuits; an "homunculus explanation is currently out of favour. Thalamo*cortical circuits are the prime candidates.6 The prefrontal cortex probably plays a global, executive role ("working memory), whereas other cortici participate according to the type of information accessed. From studies of amnesics we also learn that the "hippocampal formation and adjacent cortici are particularly important for the access of items in memory to conscious awareness.
Selected associations: Attention, Declarative memory, Enigma, Persistence, Working memory
'For more on the nature of definitions, see The conceptual framework, in the introduction.
2These privately experienced qualities are called qualia (singular: quala). Qualia are types of 'sense data', i.e. entities that are assumed to exist only because they are sensed; see *stimulus. 3Some authors consider consciousness to always involve self-consciousness (e.g. Kant 1800), others do not (e.g. Searle 1992). Kant's definition draws on this relationship: 'All our cognition has twofold relation, first to the object, second to the subject. In the former respect it is related to presentation, in the latter to consciousness, the general condition of all cognition in general. (Actually consciousness is a presentation that another presentation is in me.)' (Kant 1800).
4There is also the view that we will never know what is it like to be an Aplysia (Nagel 1974).Some dispute this view (Dennett 1991).
5In Aristotelian philosophy, nous meant comprehension, or intellectual intuition (Guthrie 1981).
6These circuits are necessary but not sufficient. Conscious awareness requires more basic forms of awareness, that depend on arousal, itself controlled by the brainstem (Magoun 1952).
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