Task 6 Flashcards
Dual-Consciousness
Two separate, independent centers of consciousness, one in each cerebral hemisphere
Contralateral Organization
= the left hemisphere analyzes stimuli and controls actions of the right side of the body, and the right hemisphere does the same for the left side of the body
—> normally sensory information and thoughts are shared between the two hemispheres via the corpus callosum (+ anterior commissure)
–> when the commissures are cut, then sensory inputs and thoughts cannot be transmitted directly from one hemisphere to the other
Visual Pathway
- information from the left visual field is processed in the right cerebral hemisphere (right occipital cortex)
- information from the right visual field is processed in the left cerebral hemisphere (left occipital cortex)
- the optic chiasm transmits the signals coming from the left visual field to the right hemisphere, and does the same for the right visual field
Commissurotomy
= surgical transection (cutting) of the corpus callosum
- purpose: try to control severe epilepsy
- hypothesis: a complete transection of corpus callosum and anterior commissure would prevent the conduction of epileptic seizures between two hemispheres
- no effects on daily lives
T-scope Test (projection tachistoscope test)
Procedure: subjects focused on a dot at the center of the screen, then a visual stimulus (picture or word) was flashed on either the right or the left side of the screen
Results:
- if the picture was flashed in the RVF, subjects correctly named it
- if the picture was flashed in the LVF, they could not name it
Cross-Modal Matching Procedure (T-Scope Test)
If subjects were asked to reach through an opening under the screen and feel several objects with their left hand, then they could select the object that matched the one seen in the LVF
–> the right hemisphere can understand concrete concepts having to do with functional or category relations between objects
Visual-Recognition and Naming Test
Procedure: a picture of a nude female was flashed to the LVF of a female subject
Results:
- the participant giggled and blushed, as if embarrassed
- the right hemisphere initiated an automatic emotional reaction to it –> one based on the patient’s social learning experience
- the speaking left hemisphere tried to interpret the emotional reaction
Left Hemisphere
- superior for verbal and conceptual tasks
- spontaneity behavior
Right Hemisphere
- superior for many nonverbal tasks, particularly visuospatial tasks involving drawing and construction
- copying behavior
- manipulo-spatial superiority
Face Recognition Studies
- Subjects saw a chimeric stimulus flashed on a screen
- They were asked to point to the face that was seen
- Pointing –> whole face that matched the left side of the chimeric face (right hemisphere)
- Verbally responding –> whole face that matched the right side of the chimeric face (left hemisphere)
–> the right hemisphere is better at recognizing similar faces
Visual Completion
Patients subjectively perceived figures as complete when in fact they had seen only half of the figure
–> greatest soon after surgery
–> may decrease over a period of time
John Eccles on the Question of Dual Consciousness
- the left hemisphere is a liaison cortex that transmits knowledge from an immaterial entity, the “self-conscious mind”, which has subjective conscious experience
- language centers receive knowledge from an immaterial consciousness and can make introspective verbal reports about it
Gazzaniga on the Question of Dual Consciousness
- higher-level conscious processes are highly correlated with the presence of linguistic circuits normally found only in the left hemisphere
- IVR is the most useful indicator of consciousness
Roger Sperry on the Question of Dual Consciousness
- consciousness occurs in the right hemisphere, independent of language circuits and introspective verbal reports
- intelligent behavior (behavior adaptive to the current situation and controlled by flexible thought processes rather than reflexes) is sufficient evidence from which to infer consciousness
Emergent Interactionism Theory
consciousness is identified with the holistic properties of neural activity and plays a causal role in controlling behavior
Alien Hand
Example: a patient’s left hand slammed a drawer on his right hand when his right hand reached into the drawer to get a pair of socks
–> support for independent initiation of voluntary actions –> independent consciousness
Cross-Cueing
= deliberate attempts of the right hemisphere to send information to the left hemisphere via overt responses
–> short-term voluntary action by the right hemisphere
–> the right hemisphere is conscious, independently of the left hemisphere
Inadvertent Cross-Cueing
= the left hemisphere interprets responses that were made spontaneously but unintentionally by the right hemisphere
Z-lens Experiment by Sperry et al.
Z-lens = a special contact lens that limits the subject’s vision to the left visual field (right hemisphere)
Procedure:
- the subjects viewed a series of fifty stimulus cards
- subjects should point to one of the items that they recognized on each card
- evaluate chosen item with thumbs-up/-down
–> distinctive emotional reactions and other cues enabled the left hemisphere to identify the picture correctly
Values and Self-Concept
Patient P.S. could “write out” answers to questions whose last words were flashed to his right hemisphere, with Scrabble letters with his left hand
–> his right hemisphere is conscious and has a self-concept, and a sense of personal values
–> self-generated, voluntary behavior of the right hemisphere
–> consciousness independent of the left hemisphere
Understanding Action Verbs
- the right hemispheres of P.S. and V.P., have the unusual ability to show their understanding of action verbs by performing the actions indicated by them, when the words are flashed to the right hemisphere (LVF)
- when asked to name the word that had been flashed, the left hemisphere makes a guess based on the action that was being carried out
Emotional Reactions
The right hemisphere could…
… recognize a word
… have an appropriate emotional reaction to it
… communicate the specific emotional reaction to the left hemisphere without communicating the word itself
Modules
The mind/brain system is made up of a number of modules
Modules: relatively independent functional units that can receive information, compute, store and retrieve memories, trigger emotional reactions, and produce behavior
–> nonconscious
–> not directly introspective accessible
Interpreter System
= a special module that tries to interpret the diverse actions of the various modules, explain why they occurred, and fit them into the narrative sequence of events of our lives and conscious experience
–> bound to left hemisphere –> language system
–> generates conscious emotional reactions
–> constructs systems of values and beliefs
Gazzaniga Experiment I
- different pictures were flashed simultaneously in the left and right visual field
- subject’s right hemisphere (left hand) chose a picture that went with the one it had seen in the LVF, while the left hemisphere (right hand) chose a picture that matched what it had seen in the RVF
- left hemisphere tried verbally to explain the responses
–> the left hemisphere knew only what it had seen and the choice stimuli selected by each of the two hands
Gazzaniga Experiment II
- presenting two stories simultaneously, one to each hemisphere of the split-brain subject P.S.
- left hemisphere quickly reported its whole story, then right hemisphere reported its story in fragments
- left hemisphere combined the responses into a single coherent story
–> the final report from the left hemisphere told the whole story, making use of what it saw and what it heard the right hemisphere say
Hallmark 1: Response x Visual Field Interaction
= when a stimulus is presented to the left visual field, the patient can only respond adequately with his/her left hand, and vice versa for the right field and hand
Hallmark 2: Hemispheric Specialization
= each of the two hemispheres is better at certain tasks
Left Hemisphere: language, maths, self-recognition
Right Hemisphere: visuospatial tasks, inference, time, object and face recognition, regularities
Hallmark 3: Post Hoc Confabulation
= happens after actions with the left hand
–> an explanation is given by a conscious agent (LH) who did not initiate or execute the action (RH)
Hallmark 4: Split Attention
= each hemisphere may have its own independent focus of attention
Hallmark 5: Inability to Compare Stimuli across the Midline
–> each hemisphere independently perceives the contralateral visual field (the right hemisphere possibly perceiving the left visual field unconsciously)
Partial Consciousness Model
= only the left hemisphere gives rise to consciousness, while the right hemisphere only processes information in an unconscious manner
–> the right hemisphere may prime the left hemisphere toward certain behavior
Split Consciousness Model
= in a split-brain patient, each hemisphere has its own consciousness, independent of the other hemisphere
–> two independent conscious agents
New Model: One Conscious Agent with Unintegrated Visual Perception
- consciousness is unified in split-brain patients
- unintegrated perception –> in split-brain patients visual perception is unintegrated across visual fields
Visual information and cognition might be split across the midline BUT each visual field and cognition module can be monitored by a single central agent, which simultaneously controls both hands and speech (as in normal people)
Functional Unity as the Basis of Unified Consciousness
Functional unity: different parts of a system operate mostly in conjunction, rather than independently
- subcortical areas are still unified in split-brain patients
- if the different cortical systems in a split-brain patient are driven by common input and produce conjoined output, then functional unity could still arise in the cortex, even without direct links between both cerebral hemispheres
