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Hemisphere Asymmetries

Hemisphere Asymmetries. Can asymmetries be explained in terms of general dichotomy?. Hemisphere Asymmetries. Spatial Frequency Hypothesis. Sergent (1982) Left hemisphere more adept at processing high spatial frequency information

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Hemisphere Asymmetries

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  1. Hemisphere Asymmetries • Can asymmetries be explained in terms of general dichotomy?

  2. Hemisphere Asymmetries

  3. Spatial Frequency Hypothesis • Sergent (1982) • Left hemisphere more adept at processing high spatial frequency information • Right hemisphere more adept at processing low spatialfrequency information

  4. Spatial Frequencies Low Medium High

  5. Spatial Frequency Hypothesis • Sergent (1982) • Left hemisphere more adept at processing high spatial frequency information • Right hemisphere more adept at processing low spatialfrequency information • Receptive field size • Small in left hemisphere • Large in right hemisphere

  6. Retinotopic Organization

  7. Retinotopic Organization

  8. Small Receptive Field

  9. Large Receptive Field

  10. Visual Receptive Fields • On center / off surround • Accentuates edges

  11. Visual Receptive Fields

  12. Spatial Frequency Hypothesis • Kitterle et al. (1990) • Present sinusoidal gratings to left and right hemisphere using divided-visual field • Decide whether grating is wide or narrow Wide Narrow

  13. Spatial Frequency Hypothesis

  14. Spatial Frequency Hypothesis • Kitterle et al. (1990) Response time (ms) Hemisphere

  15. Spatial Frequency Hypothesis • Kitterle et al. (1990) • Present sinusoidal gratings to left and right hemisphere using divided-visual field • Decide whether grating is wide or narrow • Faster at narrow than wide in left hemisphere

  16. But Wait… • Does this mean that hemispheres are more or less adept depending on the size of the stimulus? • In early visual areas, yes • In later visual areas, no • Size information is processed separately from shape information in high-level vision areas • Receptive fields receive information from other neurons

  17. Receptive Fields

  18. Receptive Fields

  19. Hemisphere Asymmetries • Split-brain patients • Language in left • Spatial in right • Asymmetric brain damage • Associative agnosias (Farah, 1991) • Abstract/parts in left • Specific/wholes in right • Divided-visual field with normal subjects • Categorical vs. coordinate (Kosslyn et al., 1989) • Local vs. global (Van Kleeck, 1989) • Abstract vs. specific (Marsolek, 1995, 1999)

  20. Local vs. Global Unfiltered Low-pass filtered (No high frequencies) High-pass filtered (No low frequencies)

  21. Spatial Relationships

  22. Spatial Relationships

  23. Spatial Relationships

  24. Spatial Relationships • Low frequency information may be insufficient for above-below decision when dot is close to line • Left hemisphere better at categorical judgments than right because high frequency information is needed in the close condition

  25. Receptive Field Size • Large receptive fields can overlap with each other • Allows coding of very specific information • Allows effective coding of wholes

  26. Large Receptive Fields

  27. Small Receptive Fields

  28. Receptive Field Size • Large receptive fields can overlap with each other • Allows coding of very specific information • Allows effective coding of wholes • Small receptive fields cannot overlap as much • Does not allow coding of very specific information • Allows effective coding of parts

  29. Wait…What About Faces?

  30. Wait…What About Faces?

  31. Wait…What About Faces? • Pascalis et al. (1995) • 4-day old infants look longer at mother’s face than at stranger • Can recognize face • Infants cannot resolve high spatial frequencies

  32. Wait…What About Faces?

  33. Postnatal Vision: < 1 Month

  34. Postnatal Vision: 3 Months

  35. Postnatal Vision: 6 Months

  36. Wait…What About Faces? • Pascalis et al. (1995) • 4-day old infants look longer at mother’s face than at stranger • Can recognize face • Infants cannot resolve high spatial frequencies • Low spatial frequencies suffice for face recognition

  37. Speech Comprehension • Understanding streams of spoken words requires processing high-temporal frequencies • Left hemisphere adept with high-temporal frequencies • Left hemisphere better than right at spoken word comprehension • Comprehending prosody requires processing low-temporal frequencies • Right hemisphere adept with low-temporal frequencies • Right hemisphere better than left at prosodic comprehension

  38. Hemisphere Asymmetries • Split-brain patients • Language in left • Spatial in right • Asymmetric brain damage • Associative agnosias (Farah, 1991) • Abstract/parts in left • Specific/wholes in right • Divided-visual field with normal subjects • Categorical vs. coordinate (Kosslyn et al., 1989) • Local vs. global (Van Kleeck, 1989) • Abstract vs. specific (Marsolek, 1995, 1999) ✓ ✓ ✓ ✓ ✓ ✓

  39. Many, Many More… • Emotion • Expressing, perceiving • RH > LH • Valence • RH = negative; LH = positive • Action • RH = withdraw; LH = approach • Stereotyping • LH > RH • Music • RH > LH

  40. Asymmetries in Non-Humans • Chickens and pigeons • Left hemisphere advantage for categorizing food vs. non-food items • Right hemisphere advantage for learning exact location of food source • Macaque monkey • Left hemisphere lesions impair comprehension of vocalizations by other macaques • Right hemisphere lesions impair face discrimination

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