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Perception and attention

Perception and attention. Lecture 3 (Chapters 4, 5, and 6). Last week. We looked at the various methods and models used in cognitive neuroscience Structural methods, such as MRI and CT Functional methods, such as single-cell recording, PET, fMRI, and lesion studies. This week.

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Perception and attention

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  1. Perception and attention Lecture 3 (Chapters 4, 5, and 6)

  2. Last week • We looked at the various methods and models used in cognitive neuroscience • Structural methods, such as MRI and CT • Functional methods, such as single-cell recording, PET, fMRI, and lesion studies

  3. This week • We will look at • Some auditory and a lot of visual perception • Object recognition • Attention • We will also review some important disorders that result from lesions in the systems discussed • This covers chapters 4, 5, and 6 (ends at page 245)

  4. Middle and inner ear

  5. Auditory pathways in the brain

  6. Inner ear

  7. Uncoiled cochlea

  8. Auditory pathways

  9. Auditory cortex is hidden in the transverse temporal gyrus

  10. Vision

  11. Position of the eyes in the brain

  12. Section through the retina

  13. Rods are sensitive but cannot detect color

  14. Cones are for color vision

  15. Path of the optic nerves

  16. Axonal pathways from the retina to the occipital cortex

  17. Lateral geniculate nucleus

  18. Position of the LGN in the brain

  19. Axonal pathway to the LGN

  20. Lesions to the visual pathways Black parts of visual fields are blind Lesions to the optic nerve cause unilateral deficit in one of the visual fields Lesions to optic chiasma cause bitemporal hetronymous hemianopia Lesions to optic tract, LGN, and optic radiations cause homonymous hemianopia Lesions to optic radiations (Meyer’s loop) cause homonymous hemianopia (quandrantanopia) Lesions to rostral visual cortex cause homonymous hemianopia with macular sparing

  21. What and where pathways from the occipital cortex Where What

  22. A neuron in inferior temporal cortex (IT)

  23. PET study on what and where in humans

  24. Magnocellular pathway aka Dorsal pathway aka Parietal pathway aka Where pathway Summing up the what and where Parvocellular pathway aka Ventral pathway aka Temporal pathway aka What pathway

  25. The code of the brain • Extremely localized coding • 0000000000000000010000000000000000 • Semi-distributed or sparse coding • 0000100000100000010000000010000000 • Distributed coding • 1010111000101100110101000110111000

  26. Extremely localized coding leads to the grandmother cell

  27. Sparse coding • Forms a good middle ground between fully distributed and extremely localized coding • Is biologically plausible • Is computationally sound in that it allows very large numbers of representations with a small number of units

  28. Find the greenT...

  29. Conjunction search is much slower

  30. Ann Treisman’s model of feature perception and integration • The different maps are sparsely activated • Different maps are used, rather than a combined map • Co-activation is used to code for conjunction • Perceptual confusion may arise

  31. Press the button if you see the square...

  32. Reaction time increases with position uncertainty

  33. Desimone’s study of V4* neurons * V4 is visual cortex before inferotemporal cortex (IT)

  34. Neurons in IT show evidence of ‘short-term memory’ for events Human Monkey • Delayed matching-to-sample task • Many cells reduce their firing if they match the sample in memory • Several (up to five) stimuli may intervene • The more similar the current stimulus is to the stimulus in memory

  35. Neural population response to familiar stimulus first decreases, after presentation of ‘target’, then decreases during delay period, increases during early choice, and stabilizes about 100ms before the saccade

  36. Reduced IT response and memory • Priming causes a reduction of firing in IT • This may be a reduced competition • This results in a sharpening of the population response • This in turns leads to a sparser representation

  37. Novelty filtering • Desimone et al.: IT neurons function as ‘adaptive filters’. They give their best response to features to which they are sensistive but which they have not recently seen (cf. Barlow) • This is a combination of familiarity and recency • Reduction in firing occurs when the animal (or the neuron) becomes familiar with the stimulus • This can be an effect of reduced competition

  38. Bisect all the lines…, a test for hemineglect

  39. Different visual stimulus arrays

  40. Evidence for contralateral inhibition

  41. Evidence for ipsilateral exitation

  42. Neglect distributed in objects

  43. Neglect in imaging

  44. Next week... • Memory systems and amnesia • Executive functions • Chapters 7 and 11 (not continuous!)

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