Task 6 Flashcards
Complete commissurotomy
Surgical cutting of the corpus callosum
Block-design test
A subject is required to use a set of colored blocks (cubes with a different color on each side) to construct a pattern that matches a sample pattern shown in a picture.
Chimeric figures
Pictures where the left half comes from one face and the right half comes from another face
Visual completion
A phenomenon observed when using chimeric stimuli, in which patients perceive figures as complete when they had only seen half of the figure in either the LFV or
RVF.
Cross-cueing
Situations where one hemisphere is able to guess what the other hemisphere has seen/felt by noticing the other hemisphere’s overt responses to the situation.
5 hallmarks of split-brain syndrome
- Response x visual field interaction
- Hemispheric specialization
- Left hemisphere confabulation
- Split attention
- Impaired midline comparisons
Conscious unity, split perception model
The split-brain patient is one conscious agent, in whom visual perception remains
unintegrated across hemifields
Integrated information theory (IIT)
Consciousness arises when a system has a rich representation repertoire and its subsystems are strongly interconnected. When integration within a subsystem is larger than the connection between systems, consciousness will arise as a function of the subsystem instead of the system as a whole.
Global workspace (GW) theory
The cerebral hemispheres house a global workspace, which receives information from and projects to many cortical modules. Only information
processed by the GW reaches consciousness.
Recurrent processing (RP) theory
Consciousness can arise through local RP between cortical modules, even in the absence of global or integrative cortical processes. However, such
local processing only leads to the phenomenal consciousness that is otherwise inaccessible and unreportable. For unified reportable consciousness, strong integration between the
hemispheres is still needed
Corpus callosum
Mostly connects homotopic (corresponding) points between the 2 cerebral lobes
Anterior commissure
Connects portions of the anterior temporal lobes and the amygdala
Limitations of split brain research
- The brains of split-brain patients are not normal, because these patients had severe epilepsy before the commissurotomy
- The number of subjects in such studies is relatively small
- Split-brain subjects show considerable variability among themselves
- In some of these patients, the right hemisphere has a relatively enhanced speech recognition capability. This could be due to pre-surgery changes
- After the surgery each hemisphere may acquire some functions that it did not have prior to surgery
Unilateral testing
Testing each of the hemispheres independently
Tachistoscope (T-scope)
Typically refers to a device or setup used to present stimuli to only one hemisphere of the brain at a time. It consists of a screen or display that can be positioned so that each half of the visual field is presented to a different eye, and consequently, a different hemisphere of the brain
Cross-modal matching procedure
Participants are typically presented with stimuli in one sensory modality (e.g., visual stimuli) and asked to match them to corresponding stimuli in another sensory modality (e.g., tactile or auditory stimuli).
Eccles’ criterion
Conservative, interactionist dualism viewpoint; In this view, language centers receive knowledge from an immaterial consciousness, and can make introspective verbal reports (IVRs) about it
Materialistic view
Higher-level conscious processes (above mere sensory perception) are highly correlated with the presence of linguistic circuits normally associated found only
in the left hemisphere, and IVR is the most useful indicator of consciousness, though not necessarily the only one.
Emergent interactionism theory
Consciousness is identified with holistic properties of neural activity and plays a causal role in controlling behavior. Sees split-brain patients as having two consciousnesses
The Alien Hand
Incidental independent actions of the left hand that are experienced by some split-brain patients. Some of these incidents seem to show conflicts between the 2
hemispheres
Experiment with Patient NG
- NG was presented with an array of stimuli and then with 4 pictures of herself, asked to point out which one she likes best
- Showed shock and amusement, but when asked what was in the picture she did not know
- On later test she made correct identification (“Probably me” and then “yes that is a picture of me”) which might be cross-cueing
Experiment with patient LB
- LB was asked to rate cards with pictures with “thumbs-up” and “thumbs-down”
- Was presented with pictures, including one of Hitler, was asked if he recognized anyone
- He recognized Hitler and then gave it a thumbs-down and tried to write something on his hand when asked who it was
- After being asked some more questions they then guessed it was Hitler
Patient PS
A split-brain patient (anterior commissure left intact), 15-year-old right-handed, left-hemisphere dominant boy whose right hemisphere could not speak during initial testing, but it could spell words by arranging Scrabble letters with the left hand.
Gazzaniga’s left-brain interpreter theory
- The mind/brain is made up of independent modules that cannot make verbal responses, but only produce other types of overt responses.
- The modules are unconscious, because we don’t have introspective access to them and we cannot make introspective verbal reports on their activities, but we may be aware of their outputs/responses.
- A special module (the interpreter system) tries to interpret the actions of the modules
Response x visual field interaction
When a stimulus is presented to only one visual field, the patient can only respond adequately with the hand controlled by the same part of the brain that is responsible for processing the visual field.
Hemispheric specialization
The phenomenon that each hemisphere is better at certain tasks.
Left hemisphere confabulation
Verbal post hoc confabulations occur after the response is made with the left hand.
Split attention
Each hemisphere may have its own independent focus of attention.
Impaired midline comparisons
Split-brain patients are incapable of comparing stimuli across the visual midline.
Criticisms of Gazzanigas interpreter theory
- The frequency of right-hemisphere language ability may be underestimated by counting split-brain patients whose right hemispheres were damage by epilepsy before surgery.
- A right hemisphere without language can be active, spontaneous and perform complex tasks involving space perception and spatial construction
Choice blindness
- Subjects are asked to choose between 2 options (e.g. which of 2 people they find more attractive).
- After the choice is made, the experimenter sometimes swaps the choice outcome, and now presents the rejected option to the subject as the one that was chosen.
- If the subject is asked why he had chosen this option, the most frequent response is confabulation
