Levels of Analysis

1. Cortical Lobes Vision, Audition, Language “What vs. Where” Pathways/Networks Cortical Areas Motion, Color , Faces Directions of motion, orientation Cortical Column Computations Lateral inhibition Neural Circuit Neuron Code Levels of Analysis Anatomical Functional

3. Organizational principles of the visual system • Retinotopy • Anatomical organization • “Hierarchical” organization • Functional organization based on neural response properties

4. Retinotopy • Retinotopy = a spatial map of the visual field with retina-based coordinates • Implication = a spot of light in the visual field will activate a ‘spot’ of cortex based on eye position

6. Retinotopy sets the stage • Retinotopy = a spatial map of the visual field with retina-based coordinates • Implication = a spot of light in the visual field will activate a ‘spot’ of cortex based on eye position • Retinotopicmaps define multiple visual areas (i.e., each “area” has its own map of the visual field)

7. Macaque Retinotopy Source: Tootell et al., 1982

9. V2d LVM V2v UVM Polar angle UVM Eccentricity HM LVM V1 F

10. V2d LVM V2v UVM LVM V1 UVM F HM

11. V2d LVM V2v UVM LVM V1 UVM F HM

12. 8 Hz flicker (checks reverse contrast 8X/sec) • good stimulus for driving visual areas • subjects must maintain fixation (on center dot) EXPANDING RINGS ROTATING WEDGES

14. Spatial Maps Beyond Visual Cortex • Hagler, D. and M.I. Sereno (2005) Spatial maps in frontal and prefrontal cortex. Neuroimage29:567-577 • Sereno, M.I., S. Pitzalis, and A. Martinez (2001) Mapping of contralateral space in retinotopic coordinates by a parietal cortical area in humans. Science294:1350-1354.

15. MIDTERM • Worth 99% of final grade

16. Retinotopy: a powerful tool for studying the mind • Retinotopy & Mental Imagery • Retinotopy & Attention • Retinotopy & Spatial Memory

17. Visual Imagery (old days) • Does visual imagery rely on symbolic (“language-like”) processing or depictive (picture-like) representations? (Pylyshyn vs. Kosslyn) • Use RT in standard cognitive psychology paradigm to infer “visual-like” behavior.

18. Visual Imagery (old days) RT depends on position of probe Imagery a ‘sequential’, ‘depictive’ operation x f

19. Retinotopy & Visual Imagery • Slotnick SD, Thompson WL, Kosslyn SM. Visual mental imagery induces retinotopically organized activation of early visual areas. Cereb Cortex. 2005 Oct;15(10):1570-83. • Does imagery evoke cortical activity with precise visual field topography?

21. Perception Imagery Attention

22. Organizational principles of the visual system • Retinotopy • Anatomical Organization • “Hierarchical” organization • Functional Organization based on neural response properties

23. Functional “Hierarchy” Properties of lower areas (lower = anatomically closer to the retina) form the building blocks of higher areas. • The visual feature(s) that elicit an increase in spike rate becomes progressively more complex. • “Selectivity” • “Tuning” • The area of visual space that elicits an increase in spike rate in a neuron becomes progressively larger. • “Receptive field”

24. Input Image Early visual cortex Higher visual cortex Small & Simple Large & Complex

25. Functional “Hierarchy” Properties of lower areas (lower = anatomically closer to the retina) form the building blocks of higher areas. • The visual feature(s) that elicit an increase in spike rate becomes progressively more complex. • “Selectivity” • “Tuning” • The area of visual space that elicits an increase in spike rate in a neuron becomes progressively larger. • “Receptive field”

26. LGN  V1 Connections • More “complex” tuning/selectivity • Larger receptive fields

27. LGN Response Properties • Selectivity = light/dark spots of light • Receptive fields = are extremely small. Fovea approximately few minutes (60 minutes = 1 degree)

28. LGN Response Properties

29. p.156 LGN  V1

30. Functional “Hierarchy” • The visual feature(s) that elicit an increase in spike rate becomes progressively more complex. • “Selectivity” • “Tuning” • The area of visual space that elicits an increase in spike rate in a neuron becomes progressively larger. • “Receptive field”

31. Movie Time On-center Off-center Direction Cell Simple Cell

32. Functional “Hierarchy” • The visual feature(s) that elicit an increase in spike rate becomes progressively more complex. • “Selectivity” • “Tuning” • “Selective” = the type of stimulus that a neuron responds to • “Tuning” = a continuous stimulus dimension • A neuron can be “selective” (e.g., a “face cell”) but that doesn’t necessarily imply “tuning”

33. Orientation tuning in V1

34. 2 3 10 4 Can “Tuning” be measured with fMRI? 0 1

35. ~1-2 mm

36. Other forms of “tuning” • Other visual examples • Other auditory examples • …

37. Beyond V1 • Assumption that the Hubel & Wiesel approach will extend to other visual areas • “Simple” feature selectivity combines to form more “complex” feature selectivity • “Hierarchical Feedforward Model” • Observations in extra-striate areas • Selectivity becomes more complex • Receptive fields are larger

38. Next week Thursday