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Psy 345 > Lectures 11 & 12 > Flashcards

Lectures 11 & 12 Flashcards

1
Q

Reference frame

A

System for representing locations relative to some real or arbitrary standard
Neglect can affect multiple reference frames

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2
Q

2 Main Classes of Reference Frames

A
  1. Egocentric Space- locations defined relative to the observer (retina, head, body midline)
  2. Allocentric Space- locations defined independently of observer (but in relation to gravity, or other objects)
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3
Q

3 types of egocentric reference frames

A
  1. Hemispatial- defined relative to body midline
    ( right of the body means right hemispace)
  2. Somatotopic- defined in relation to parts of the body
    ( this can move dependent to the hemispace, both arms can be in same hemispace)
  3. Retinotopic- defined in relation to the retina
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4
Q

2 types of allocentric reference frames

A
  1. Environmental/gravitational- relative to the environment
    Have rubber duck in environmental left and environmental right. Patient will ignore whole duck in the left. We know it is not a problem with egocentric left because we have patient lie down and they still ignore left duck (disentangles the reference frames by having them lie down)
  2. Stimulus-centered- relative to the middle of the object
    Patient may ignore the left side of the object despite its orientation. Think of rubber duck being turned sideways and upside down. Will still neglect original left side of it
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5
Q

Implications of reference frames

A
  • Spatial relations (left vs. right) are represented in a variety of reference frames
  • Different frames are used for different spatial processes
  • Parietal cortex is where the different spatial maps are represented in the brain
  • Neglect may affect multiple reference frames
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6
Q

Representation of external space experiment done by Bisiach and Luzzatti

A

Neglect patients who lived in town for most of their lives told to imagine themselves at Point A facing Point B and to describe what they saw
Then vice versa
Result: neglect of the left image is also in imagination
Patients with unilateral neglect:
When they faced north would ignore features on left. When faced south, once again ignore features on the right that they had just named previously
Left parietal represents the right side of space; right parietal represents the left side of space
Neglect is due to a problem forming visual representations including memory by the hemisphere that is damaged

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7
Q

Attention as acts a mental spotlight

Experiment by Hemholtz

A

Attention selects information for conscious processing
Attention can be dissociated from overt direction of gaze
Overt- where your attention is focused
Covert- can tend your attention to place where eyes are not looking (peripheral)
Covert attention is disturbed in neglect

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8
Q

Posner Task

A

Valid Cue: directs attention to target location
Invalid Cue: directs attention to wrong location (20% of cues are invalid)
Results: For normally intact people reaction time is slower for invalid cues on both-sides of space
For people with neglect from right parietal lesions they were slower overall, performance asymmetry, and left target detection was severely impaired after an invalid right cue
This pattern is called “extinction-like reaction time pattern”

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9
Q

Improve performance in neglect

A

Ask patients to report cues before line bisection task actually improves their performance
( have them read a number on each side of the line)

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10
Q

Why is left neglect more common than right neglect

A

Could be that the right hemisphere can pay attention to both right and left hemispace, while the left hemisphere can only look at right hemispace

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11
Q

Kinsbourne’s attentional orienting model of left neglect

A

Orienting- the process that “directs” overt or covert attention to regions in space
-Kinsbourne said that each hemisphere directs orienting contralaterally
-They compete for control
-When one hemisphere is damaged, the other one dominates orienting
-It over-attends in its preferred direction
-Left hemisphere has a stronger bias than right hemisphere in right-handed individuals
(left hemisphere is the base of language)
This all results in left neglect being more common

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12
Q

Compatibility of the 3 theories

A

They are all complementary of each other

  1. The left hemisphere has a stronger orienting bias, and that leads to a predominance of left neglect
  2. Attention can be directed within multiple mental representations:
    - images in our head with eyes closes
    - external world
    - our own bodies
  3. If neglect involves a rightward attentional bias, the same bias will be shown despite the frame of reference we are using
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13
Q

Interhemispheric pathways

A

Commissures:
projection fibers that connect structures on the left & right sides of the brain
Corpus Callosum:
largest commissure; 225 million commissural fibers

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14
Q

Region-Specific connections of the corpus callosum

A
  1. Rostrum: orbital frontal cortex
  2. Genu: prefrontal cortex
  3. Rostral body: superior frontal and motor cortex
  4. Caudal body: parietal/somatosensory and temporal/auditory
  5. Splenium: occipital cortices-not V1
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15
Q

Types of callosal connections

A

Interhemispheric connections
1. Homotopic: connects with same regions (left V2 to right V2)
2. Heterotopic: connects different regions (left V2 to right V3)
Interhemispheric connections are contralateral
Intrahemispheric connections are ipsilateral

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16
Q

Basics of Epilepsy

A

Seizure: abnormally excessive or synchronous neural activity in the brain
Epilepsy (chronic): a chronic seizure disorder typically controlled with medicine
Occurs in less than 1% of population
Many people will have one or 2 seizures in lifetimes
-high fever
-metabolic disturbance

17
Q

Intractable Epilepsy

A

unresponsive to medicine, often requires surgery

18
Q

Seizures of a focal origin

A

Treated by focal surgery: removal of seizure focus, lobectomy, or hemispherectomy

19
Q

Generalized intractable seizure disorder

A

Commissurotomy: surgical cutting of the commissures
There was experiments on monkeys in the 1930s which showed
-reduced spread of the seizure activity
-reduced response of mirror focus
few obvious behavioral effects

20
Q

Roger Sperry Experiments

A

Blind fold on the right eye
Intact animal: sensory and callosal transfer of information from left to right hemisphere
Then,
optic chasm was cut. Information from left eye did not cross, however, intact corpus callosum allowed share information just at later stages
Then,
chasm and callosum was cut resulting in information being completely isolated to its respective hemispheres.

21
Q

How was the disconnection syndrome revealed

A

Surgeons Vogel and Bogen used hemispheric separation to relieve 24 human patient of intractable epilepsy
Sperry, Gazzaniga, Bogen uncover dual brain reality
-is there 2 minds in 1 cranium
-hemisphere function differences
-chiasm cannot be cut in humans

22
Q

What gets cut during surgery?

A

ALWAYS: corpus callosum; connects parietal, occipital, frontal and parts of temporal cortices
SOMETIMES: anterior commissure; connects temporal and limbic structures
SOMETIMES (INADVERTENTLY): Hippocampal commissure (part of fornix)
USUALLY NOT: posterior commissure
NEVER: collicular commissure; connects superior colliculi

23
Q

Commissurotomy

A

corpus callosum and anterior commissures are surgically severed

24
Q

Callosotomy

A

only the corpus callosum is severed

25
Q

Staged callosotomy section

A

First stage: only anterior or posterior portion of corpus callosum is cut
Second stage: another surgery to complete the callosotomy if needed

26
Q

Who gets callosal surgery

A

Most effective forAtonic seizures (drop attacks),
tonic-clonic (grand mal) seizures
When seizures are severe and frequent enough to ruin life quality, medicine doesn’t work
Surgery works by interrupting the seizure spreading activity from each hemisphere

27
Q

Surgery facts

A

frequency reduced about 70-80% by partial callostomy

80-90% by complete callostomy, medication effectiveness actually improves

28
Q

Tachistoscopic Hemifield Presentation (fast)

A 
Fixate centrally
Brief exposure (less than 150 ms) which is too short for a saccade
Uni-manual response to select what the eye saw
  1. word presented to left visual field
  2. word processed by right visual cortex
  3. left hand reaches for apple
29
Q

The Z lens

A

Developed by Iran Zaidel
One eye patched
Lens on other eye allows image to project to one hemiretina only
This experiment can use extended images or videos

Psy 345 (2 decks)

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