TASK 6 - DUAL CONSCIOUSNESS Flashcards
1
Q
commissurotomy
A
= surgical transection of corpus callosum
- shows that the corpus callosum is critical for communicating information between hemispheres
- full commissurotomy: involving transection of corpus callosum + anterior commissure
- -> effective in controlling seizures: : seizures typically begin in one hemisphere and spread rapidly to the opposite hemisphere
- -> has psychological effects
- -> harmful effects are limited to experimental situations and patients can function normally in daily life
2
Q
split-brain research
A
- make interpretations that go beyond the experimental data
- can only show what separated right and left hemispheres are capable of learning to do –> not what the connected hemispheres normally do in normal brains
3
Q
split-brain research
- interpretation of results
A
- should be interpreted with caution for several reasons:
1. brains of split-brain patients are not entirely normal (afflicted with epilepsy) and cannot be generalised to normal brains
2. relatively small number of split-brain subjects leading to small sample numbers in studies
3. split-brain subjects show considerable variability due to differences in amount and location of damage prior to surgery
4. functional reorganisation may have occurred prior to surgery (one hemisphere acquires other hemisphere’s functions)
5. after surgery each hemisphere might acquire functions it did not have prior to surgery as it can learn independently
4
Q
split-brain research
- unilateral testing
A
- limit stimulus inputs to single hemisphere to test two hemispheres independently
- subjects: right-handed patients in whom language production mechanisms are in left hemisphere
5
Q
unilateral testing
1. visual-tactile association
A
= ask to identify objects by touch alone (inside box)
- subjects stuck hand through a hole in the side of the box to feel objects
a) right hand: naming possible
b) left hand: no naming but still knew what left hand had felt because could show how to use it (e.g. spoon)
a) left hemisphere knew what object right hand felt + named it
b) right hemisphere could not name what the left hand felt –> but it knew what left hand felt because showed how to use it
6
Q
unilateral testing
- projection tachistoscope (T-scope)
A
= lateralise visual stimuli:
- focus on central cross –> visual stimulus was flashed on either left or right side –> flash was so brief that subjects did not have time to move their eyes during flash
- test left + right hemispheres separately for recognition of visual stimuli
a) LVF = no naming (see nothing) - -> cross-modal matching procedure = select matching object with left hand seen in LVF
- when nude shown to LVF, couldn’t name but showed embarrassment –> left hemisphere tried to make sense of right hemisphere’s actions
b) RVF = naming - right hemisphere knows, understands concepts (having to do with functional relational between objects), initiated automatic emotional reaction
- right hemisphere could also select objects that “go with” the object one saw
7
Q
results of projection tachistoscope (T-scope)
- visuospatial superiority of right hemisphere
A
- block-design test: use set of coloured blocks (each side has a different colour) to construct a pattern that matches the sample pattern in a picture
- sample pattern remains visible during construction test
a) left hand: easy + quick
b) right hand = difficult/impossible
a) RH = superior in non-verbal tasks, particularly visuospatial tasks involving drawing + construction - more of a “manipulospatial” superiority of RH: limited to tasks that require some sort of manipulation of objects in space, construction, tactile recognition (rather than general visuo-spatial superiority)
b) LH = superior in verbal + conceptual tasks
8
Q
results of projection tachistoscope (T-scope)
- face recognition
A
b) RH is better at recognising faces
- chimeric figures test: flash composite pictures of faces (left half from one face and right half from different face) on T-scope
a) verbal response controlled by LH: choose right half of face
b) pointing response controlled by RH: patients choose face that matched left half (better)
- Gazzaniga + LeDoux: RH superiority limited to tests involving similar faces –> hard to discriminate between different faces
- -> differences between LH and RH are relative not absolute
- visual completion: subjectively see figure as complete although they’ve only seen half (possibly Gestalt principle of good continuation)
- -> greatest soon after surgery, over time decreases and patient notices incomplete visual field
9
Q
dual consciousness model
- Sperry
A
- based on hallmarks of split-brain
- other-minds problem: the speaking LH has no direct knowledge of the RH –> can only make inferences based on emotional reaction or behaviour initiated –> to LH, RH is the “other mind”
- -> patients don’t experience this
- general question: is RH conscious or not?
- -> LH seems to function normally, making introspective verbal reports (IVR) in casual conversation
- -> hypothesis: due to separation, each hemisphere has own centre of consciousness
- criterion of intelligent behaviour: intelligent behaviour (= adaptive to current situation + controlled by flexible thought processes) as sufficient evidence from which to infer consciousness
10
Q
dual consciousness model
- evidence
A
- Sperry supports notion of dual consciousness in split-brain patients
- RH shows perceptual awareness + conscious thinking by the criterion of a pattern of intelligent behaviour
- only by the narrow criterion of IVR could RH-consciousness be denied
- also indicates RH self-awareness (not necessarily identical to left)
- -> self-concept depends on reflective consciousness (largely verbal) –> non-verbal RH probs doesn’t have a highly developed concept
11
Q
dual consciousness model
- evidence of conscious thinking in RH
1. cognitive tasks
A
- intelligent action follows from thinking in visuospatial mental images
- intelligent behaviour of independent RH is influenced by conscious but non-verbal thinking
- -> horse photo flashed to RH: could draw what goes with it without knowing what it was (LH couldn’t figure out that it was a saddle) –> could draw what he saw (horse) –> LH could then infer from the horse that what he drew before was a saddle (“oh it was a saddle!”)
12
Q
dual consciousness model
- evidence of conscious thinking in RH
2. volition
A
- alien hand (left) as support for independent initiation of voluntary action, which supports independent consciousness
13
Q
dual consciousness model
- evidence of conscious thinking in RH
3. cross-cueing
A
= deliberate attempts of the RH to send info to the LH via overt responses
- picture of aunt shown to right hemisphere –> left hand drew first letter of name on right hand –> said name
- only shows short-term goals in response to immediate demands, no long-term plans
- inadvertent cross-cueing = spontaneous but unintentional responses (interpreted by LH)
- -> nude/ colour task –> emotional response
14
Q
dual consciousness model
- evidence of conscious thinking in RH
4. self-recognition
A
= minimum criterion for self-awareness + a self-concept
- z-lens experiment: peeps could examine photo while LH couldn’t see
- emotional responses (thumbs up/down) in RH indicate sense of self-values which were interpreted by the left hemisphere
- spelling of P.S.’s right hemisphere
15
Q
language + brain modularity
A
- Gazzaniga argues that RH of most split-brain patients aren’t conscious
- -> BUT there are exceptions –> some do: correlates with RH language ability
- e.g. patient P.S: self-concept where sometimes answers even depended on hemisphere, understood action verbs, emotional reaction communicated to LH BUT anterior commissure wasn’t cut so direct emotional communication was possible
- those without language ability, didn’t show any ability to carry out complex cognitive tasks beyond basic perceptual recognition
