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Cerebral Lateralization and Specialization

Cerebral Lateralization and Specialization. Split-brain patients: transection of corpus callosum. Cerebral Lateralization and Specialization. Split-brain patients Wada test: amobarbital injection to one carotid artery. Cerebral Lateralization and Specialization. Hemispheric communication

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Cerebral Lateralization and Specialization

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  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

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