Greg Detre
Friday, 26 May, 2000
Human consciousness is just about the last surviving mystery � Dennett (1991)
Every period in the relatively brief history of neursocience has considered that it had a special, sometimes even ultimate insight into the neural mechanisms of conscious awareness � Lawrence Weiskrantz (1991)
difficult to define the term �consciousness� (e.g. Wilkes, 1988)
although we have a subjective sense of what we mean, satisfactory formal definitions are difficult
the term is perhaps simply too corase to use theoretically
Block (1995)
many accounts of consciousness run into difficulty because they fail to make the distinction between:
phenomenal consciousness = the raw �feel� of experience
access consciousness = the accessibility of experience to verbal report and use in intentional control
Tulving (1985)
3 types of consciousness:
anoetic (non-knowing) � simple awareness of external stimuli
nooetic (knowing) � awareness of symbolic representations of the world
autonoetic (self-knowing) � awareness of self and personal experience extended in time
Farthing (1992)
distinction between:
primary consciousness � simple perceptual awareness of external and internal stimuli
reflective consciousness � �thoughts about one�s own conscious experiences per se�
Natsoulas (1978)
distinguished among seven different ways in which the term �consciousness� has been used
also (Chalmers, 1996; Mersel & Bisiach, 1988; Milner & Rugg, 1991; Weiskrantz, 1997)
cognitive scientists: variety of perspectives of approaching the phenomena of consciousness:
1950s + 60s
excitement about possibilities of understanding the neurophysiological basis of �states� of consciousness
after ground-breaking discoveries about the reticular activating system and conscious awareness (Moruzzi & Magoun, 1949)
discovery of REM sleep (Aserinsky & Kleitman, 1953)
1960s + 70s
observations of commissurotomy (split-brain) patients (Sperry, 1966; Bogen, 1969; Gazzaniga, 1970)
suggested possible existence of independent systems of consciousness in each hemisphere
�/span> speculative theorising (Popper & Eccles, 1977; Puccetti, 1981; Spring & Deutsch, 1985)
1970s + 80s
brain-damaged patients exhibited preserved access to non-conscious/implicit knowledge
despite profound impairment of conscious/explicit knowledge
e.g. blindsight (lesions to striate cortex deny conscious perception of vis stimuli can still �guess their location + other attributes (Weiskrantz, 1986, 1997)
e.g. amnesic patients who lack explicit/conscious memory of recent experiences, but can exhibit non-conscious or implicit memory for aspects of those experiences, e.g. priming + skill-learning (Schacter, 1987)
e.g. similar kinds of dissociations in aphasia, alexia, unilateral neglect etc. (Schacter, McAndrews and Moscovitch, 1988)
discovery of analogous phenomena in normal subjects (Schacter & Buckner, 1998; Stadler & Frensch, 1997)
�/span> variety of proposals concerning the nature, functoin and neural basis of consciousness (Milner & Rugg, 1991)
also: unawareness of deficit (anosognosia)
brain-damaged patients who claim to be entirely unaware of the existence of obvious deficits
not systematic approach (because of psychodynamic approaches to the issue)
historical review (McGlynn & Schacter, 1989)
contemporary approaches (Ramachandran, 1995, 1998)
1990s
rapid development of functional neuroimaging � applications to consciousness-related issues
e.g. non-conscious aspects of perception (Sahraie et al., 1997; Whalen et al., 1998)
e.g. development of automatic habits (Raichle et al., 1994)
e.g. distinctions among conscious and non-conscious forms of memory (Schacter et al., 1996; Squire et al., 1992)