Greg Detre
Tuesday, 08 May, 2001
Larry Weiskrantz
Consciousness society
there�s a lot to learn from brain damage about consciousness - neuropsychology
Sherrington, disconnection in the spinal cord - intact function without conscious awareness
damage to medial temporal cortex � amnesia, no loss of IQ, only the laying down of memories is impaired (and possibly some retrograde amnesia) (Memento)
semantic knowledge retained even though episodic memory lost (�You never know who might have pins in their hand�)
Weiskrantz with Elizabeth Warren(???) - classical conditioning (light � puff of air in eye)
present words uniquely identified by first three letters � amnesics were better than controls after 24 hours
disconnection between the capacity and awareness of the capacity
this can be seen in every cognitive capacity in psychology
unilateral neglect � independent of head-movement
prospagnosia � lie detectors
even in aphasia, subjects show intact ability to process language, even though they can�t use it
Tyler: their response to a keyword degrades in the same way that normal people�s do (e.g. syntantic/grammatic errors)
Whitehead quote (Introduction to mathematics, 1948, pg 61) � cognitive operations are like cavalry movements � rare, at decisive moments
if visual cortex is damaged, they say they can�t see (what about monkeys???) � if only one hemisphere, then only half visual field affected � but if both hemispheres�
distinguishing colour in blindsight � distinguishing qualia without qualia
not only in vision � deaf hearing, numbsense
possibilities:
stray light hitting the other visual field
not a complete visual cortex lesion
John Barbera pupilometry � measure diameter of pupil, cycles per grating, visual acuity
GY � the most heavily tested patient in the history of neuroscience (New Scientist)
showed blindsight victim mimicking orientation of laser pointer in blind visual field � showed it to Dennett (Consciousness Explained, 1991, pg 332, GY not DB)
depends on how fast you move the pointer � didn�t do the experiment then, but did later � Dennett turned out to be right
it�s important that it�s a red laser
red spot-green spot � colour contrast - the pupil is biased towards red � pupil responding to the unseen after-effect of unseen colour contrast
superior colliculus (mid-brain + medial cortical)) lights up in the unaware state, but in the aware state the dorsolateral + prefrontal lights up � can�t say whether it�s gradual, because it�s a binary situation
the whole pattern of brain activity changes between aware-unaware state
his own position: conscious = being able to tell or express (the medium is the message) � being able to report consciousness
linking prefrontal to a communication system, but prefrontal seems a bit crowded for consciousness
he�s only interested in awareness of ongoing events in someone who�s not comatose � offline judgement based on online activity
blindsight victims don�t bump into things after the first week � blindsight monkeys aren�t noticeably different from normal monkeys
what if we were to reward subjects, like monkeys???
�must wear sunglasses in bright sunlight, but doesn�t know why�
Gazzaniga denied that blindsight was anything about microscopic movements of eye. required Purkinje eye tracker � image follows the eye movement
Callie + Sperry
Emmett�s law
Dennett has this counter-intuitive Multiple Drafts theory of
mind (cf Searle) � scientific approach to consciousness, try and narrow down
what sort of brain activity gives rise to consciousness � is there anything
about the particular pathway in blindsight that isn�t conscious but still
functional
discounts epiphenomenalism
at least Memento amnesics don�t get bored � or do they � do their responses modify in a bored-like fashion over time???
what if you invert the image in unilateral neglect (left
half of burning house)???
assume if it�s object-level, then it will be as though right way up
how does blindsight affect Dennett???
can you point to anything about the particular pathway
affected in blindsight that might give rise to consciousness � anything about
the complexity of computation, causal role, particular physiology etc.???
is it an issue of geographic localisation of the particular areas???
who noticed blindsight first???
does this point towards epiphenomenalism??? zombies???
can you help people/improve their vision in any way with
follow-on techniques???
if you go on giving practice to subjects in the blind field, they get better � like physiotherapy � continuum of blindsight???
is this related to intuition in normals???
could blindsight be a problem with expression � the language centre can�t see it, but rest of self can
what about non-external senses, e.g. hunger???
is this related to anasognosia???
what about brain imaging in blindsight victims � can we trace the knock-on effects (or lack of effect) of the missing visual cortex???
implications for identity theory??? problem of other minds (can�t judge from non-linguistic behaviour)???
relevance for Julian Jaynes???
primesight, grimesight
related to split-brain patients???
how functional are these people in daily life???
use blackout/tunnel contact lenses???
need we necessarily discount epiphenomenalism as a result of blindsight findings??? no� it could be that there are redundant evolutionarily ancient non-conscious visual mechanisms (e.g. superior colliculus) that are coming into play when these blindsight-related bits of the cortex are damaged, in which case we would expect blindsight to be different in some ways to human sight, and for the unaware bits that light up to perform the processing that the visual cortex usually does