Cerebral Lateralization and Specialization

1
Cerebral Lateralization and Specialization

• Split-brain patients transection of corpus
  callosum

2
Cerebral Lateralization and Specialization

• Split-brain patients
• Wada test amobarbital injection to one carotid
  artery

3
Cerebral Lateralization and Specialization

• Hemispheric communication
• Corpus callosum
• Anterior commissure
• Posterior commissure

4
Cerebral Lateralization and Specialization

• Corpus callosum connections
• Homotopic projections to the same location in LH
  and RH (majority of projections)
• Heterotopic projections to different locations
  in LH and RH
• Head (genu) anterior frontal lobes
• Body posterior frontal and parietal lobes
• Tail (splenium) temporal and occipital lobes

5
Cerebral Lateralization and Specialization

• Sectioning of corpus callosom in humans
• Performed on severe epileptics whose seizures do
  not respond to medication
• Often have neurological problems secondary to the
  epilepsy
• May be incomplete
• Sometimes partially sectioned
• When complete LH and RH are functionally
  independent

6
Cerebral Lateralization and Specialization

• Hemispheric specialization
• LH specialization for language and speech in most
• Word superiority effect in RVF-LH, but not in
  LVF-RH

7
Cerebral Lateralization and Specialization

• Hemispheric specialization
• LH specialization for language and speech in most
• Word superiority effect in RVF-LH, but not in
  LVF-RH
• RH can recognize words, but not syntax

8
Cerebral Lateralization and Specialization

• Hemispheric specialization
• LH specialization for language and speech in most
• RH specialization for visuospatial processing in
  most
• Block-design
• Face recognition

9
Cerebral Lateralization and Specialization

• Hemispheric specialization
• LH specialization for language and speech in most
• RH specialization for visuospatial processing in
  most
• Attention seems to be a unitary process
• Split-brain patients can't attend to different
  locations in LVF and RVF simultaneously
• Spatial priming crosses visual fields

10
Cerebral Lateralization and Specialization

• Hemispheric specialization
• LH specialization for language and speech in most
• RH specialization for visuospatial processing in
  most
• Attention seems to be a unitary process
• Split-brain patients can't attend to different
  locations in LVF and RVF simultaneously
• Spatial priming crosses visual fields
• Perceptual priming crosses visual fields

11
Cerebral Lateralization and Specialization

• Hemispheric specialization
• LH specialization for language and speech in most
• RH specialization for visuospatial processing in
  most
• Attention seems to be a unitary process
• Split-brain patients can't attend to different
  locations in LVF and RVF simultaneously
• Spatial priming crosses visual fields
• Perceptual priming crosses visual fields
• Single pool of attentional resources

12
Cerebral Lateralization and Specialization

• Converging evidence of hemispheric specialization
• Patients with brain damage
• Double dissociation method
• Navon's hierarchical letter stimuli local vs
  global structure

T T T T T T T T T T T
13
Cerebral Lateralization and Specialization

• Converging evidence of hemispheric specialization
• Patients with brain damage
• Double dissociation method
• Navon's hierarchical letter stimuli local vs
  global structure
• LH patients have deficit in processing local
  structure
• RH patients have deficit in processing global
  structure

14
Cerebral Lateralization and Specialization

• Converging evidence of hemispheric specialization
• Patients with brain damage
• Research with normal subjects
• Dichotic listening
• Visual half-field presentation
• Sergent (1982) choice RT - "Yes" if H or L, "No"
  if F or T

15
Cerebral Lateralization and Specialization

• Converging evidence of hemispheric specialization
• Patients with brain damage
• Research with normal subjects
• Dichotic listening
• Visual half-field presentation
• Limitations
• Effects are small and inconsistent
• Publication bias for positive results
• Not clear what a visual field or ear advantage
  means research may say more about the task than
  about information processing

16
Cerebral Lateralization and Specialization

• What is lateralized?
• LH and RH more similar than different
• Size
• Shape
• Neuron density and interconnections
• Asymmetry may convey evolutionary advantage
• More efficient use of limited cortical space
• Reduce redundancy - expand capability
• Hemispheres work together using multiple
  representations and computational processing
  styles

17
Cerebral Lateralization and Specialization

• What is lateralized?
• Processing style / differences in processing
  efficiency
• LH
• Verbal
• Analytical
• Sequential
• RH
• Spatial
• Holistic
• Parallel

18
Cerebral Lateralization and Specialization

• What is lateralized?
• A computational basis for global/local perceptual
  asymmetry the spatial frequency hypothesis
• Striate neuron receptive fields
• Tuned to contrast
• Vary in size
• Spatial frequency filters

19
Cerebral Lateralization and Specialization

• What is lateralized?
• A computational basis for global/local perceptual
  asymmetry the spatial frequency hypothesis
• Striate neuron receptive fields
• Fourier's theorem complex frequency patterns can
  be decomposed in a sum of sinusoids

20
Cerebral Lateralization and Specialization

• What is lateralized?
• A computational basis for global/local perceptual
  asymmetry the spatial frequency hypothesis
• Striate neuron receptive fields
• Fourier's theorem
• Global information conveyed by low spatial
  frequencies
• Local information conveyed by high spatial
  frequencies

21
Cerebral Lateralization and Specialization

• What is lateralized?
• A computational basis for global/local perceptual
  asymmetry the spatial frequency hypothesis
• Striate neuron receptive fields
• Fourier's theorem
• Kitterle et al. (1990)
• LH advantage for processing high spatial
  frequencies (local)
• RH advantage for processing low spatial
  frequencies (global)

22
Cerebral Lateralization and Specialization

• What is lateralized?
• Categorical and coordinate representations
• Categorical (LH)
• General properties of objects that define
  equivalence in abstract terms
• Use spatial information to classify objects
• Coordinate (RH)
• Metrical
• Specify exact locations with respect to other
  objects or the observer

23
Cerebral Lateralization and Specialization

• What is lateralized?
• Prototype vs exemplar memory systems
• Prototype (LH)
• Composite or average member of class
• Exemplar (RH)
• Specific members of class

24
Cerebral Lateralization and Specialization

• What is lateralized?
• Problem solving
• LH analytical, complex processing strategies
• Frequency matching strategy for random events
• Schema generation strategy falsely classifies new
  items as old when similar to old
• Elaborative forms illusory correlations (detects
  patterns when none exist)
• RH simple processing strategies
• Frequency maximizing strategy for random events
• Perceptual matching strategy rejects new items as
  old when similar to old
• Veridical