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RIC: Research Interest Comparator |
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Affiliation: University of Texas Southwestern Medical Center
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Home Page: http://innovation.swmed.edu
1274 CONSCIOUSNESS
distinguished between “phenomenal consciousness”
(the raw “feel” of experience) and “access consciousness”
(the accessibility of experience to verbal report
and use in intentional control), claiming that various
analyses of consciousness run into difficulty because
they fail to make such a distinction. Tulving (1985) had
previously distinguished among three types of consciousness:
anoetic (nonknowing), which entails simple
awareness of external stimuli; noetic (knowing), which
involves awareness of symbolic representations of the
world; and autonoetic (self-knowing) consciousness,
which involves awareness of self and personal experience
extended in time. Farthing (1992) offered a
distinction between primary consciousness—simple perceptual
awareness of external and internal stimuli—and
reflective consciousness—“thoughts about one’s own
conscious experiences per se” (1992, p. 13). Natsoulas
(1978) distinguished among seven different ways in
which the term “consciousness” has been used, and numerous
other distinctions among forms or types of consciousness
could be cited (cf. Chalmers, 1996; Marcel
and Bisiach, 1988; Milner and Rugg, 1991; Weiskrantz,
1997).
Definitional problems notwithstanding, cognitive neuroscientists
have approached phenomena of consciousness
from a variety of perspectives. During the 1950s
and 1960s there was great excitement about possibilities
for understanding the neurophysiological basis of
“states” of consciousness, spurred on by the groundbreaking
discoveries by Moruzzi and Magoun (1949)
concerning the reticular activating system and conscious
awareness, and stimulated by the discovery of rapid eye
movement sleep (Aserinsky and Kleitman, 1953). A new
and startling perspective on consciousness was provided
by observations of commissurotomy, or split-brain, patients
that began to appear in the 1960s and 1970s. Led
by such investigators as Sperry (1966), Bogen (1969),
and Gazzaniga (1970), studies of split-brain patients produced
striking observations that suggested the possible
existence of independent systems of consciousness in
each hemisphere. These observations provided fertile
ground for theorizing about consciousness—much of it
rather speculative—in neuroscience, psychology, and
philosophy (cf. Popper and Eccles, 1977; Puccetti, 1981;
Springer and Deutsch, 1985).
While much of the initial excitement surrounding
split-brain studies developed during the 1960s and early
1970s, a different sort of phenomenon began to capture
the attention of cognitive neuroscientists during the late
1970s and 1980s: Demonstrations that various kinds of
brain-damaged patients exhibit preserved access to nonconscious
or implicit knowledge despite a profound impairment
of conscious or explicit knowledge. Perhaps
the best known and most arresting example is that of
blindsight, where patients with lesions to striate cortex
who deny conscious perception of visual stimuli nonetheless
can “guess” their location and other attributes
(e.g., Weiskrantz, 1986, 1997). Similarly, amnesic patients
who lack explicit or conscious memory for their
recent experiences can exhibit nonconscious or implicit
memory for aspects of those experiences, as exemplified
by such phenomena as priming and skill learning
(Schacter, 1987). Similar kinds of dissociations have
been observed in patients with aphasia, alexia, and unilateral
neglect, among others (Schacter, McAndrews,
and Moscovitch, 1988), and have led to the discovery of
analogous phenomena in normal subjects (for recent reviews,
see Schacter and Buckner, 1998; Stadler and
Frensch, 1997). These dissociations have led to a variety
of proposals concerning the nature, function, and neural
basis of consciousness (see Milner and Rugg, 1991).
The 1980s also witnessed renewed attention to another
neuropsychological phenomenon with important
implications for thinking about consciousness: unawareness
of deficit, or anosognosia. The observation that
some brain-damaged patients claim to be entirely unaware
of the existence of deficits that are all too obvious
to others was first reported in the late nineteenth and
early twentieth centuries. Unfortunately, implications of
the phenomenon for understanding the nature of conscious
experience were not pursued systematically, perhaps
because of the prevalence of psychodynamic
approaches to the issue (for historical review, see Mc-
Glynn and Schacter, 1989). However, stimulated largely
by the pioneering research of Bisiach and his colleagues
concerning anosognosia in neglect patients (Bisiach and
Geminiani, 1991), the central importance of anosognosia
and related phenomena for theories of consciousness
has come to be more widely appreciated (see Prigatano
and Schacter, 1991, and more recent work by Ramachandran,
1995, 1998, for an overview of contemporary
approaches).
With the rapid development of functional neuroimaging
during the 1990s, we are beginning to witness the first
applications of imaging technologies to consciousness-related
issues, ranging from nonconscious aspects of perception
(Sahraie et al., 1997; Whalen et al., 1998) to the
development of automatic habits (Raichle et al., 1994)
and distinctions among conscious and nonconscious
forms of memory (Schacter et al., 1996; Squire et al.,
1992). Although the use of neuroimaging to understand
problems related to consciousness is just beginning, we
can expect many more such studies in the future.
The chapters in this section provide a broad overview
of approaches to consciousness in contemporary cognitive
neuroscience that summarize in some depth the
Extraction Method: Keyword Count with Lexical Variants Added-
Eliminated words list: MedlinePlus List
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Similarity Method: Weighted Keyword Count
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Weighting Method: Term Frequency * Inverse Document Frequency
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Database: Medline Updates from current year
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Publication Type: All
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Score Calculation Method: Cosine Similarity Method
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Results computed on: 6/9/2006