Midterm 1

1. Midterm 1 Oct. 6 in class Review Session after class on Monday – Location TBA

2. Read this article for Friday Oct 8th!

3. Cognitive Operations • What does the brain actually do? • Some possible answers: • “The mind” • Information processing… • Transforms of mental representations • Execution of mental representations of actions

4. First Principles • “cognitive operations are processes that generate, elaborate upon, or manipulate representations” • As patterns of activity in one or more neurons • We often lack conscious access to these representations • Neuroscientists still know very little about how information is represented in the brain

5. Mental Representations • Mental representations can start with sensory input and progress to more abstract forms • Local features such as colors, line orientation, brightness, motion are represented at low levels How might a neuron “represent” the presence of this line?

6. Mental Representations • Mental representations can start with sensory input and progress to more abstract forms • Local features such as colors, line orientation, brightness, motion are represented at low levels • A “labeled line” • Activity on this unit “means” that a line is present • Does the line actually have to be present?

7. Mental Representations • Mental representations can start with sensory input and progress to more abstract forms • texture defined boundaries are representations arrived at by synthesizing the local texture features

8. Mental Representations • Mental representations can be “embellished” - Kaniza Triangle is represented in a way that is quite different from the actual stimulus -the representation is embellished and extended

9. Mental Representations • Mental Representations can be transformed • Rubin Vase, Necker Cube are examples of mental representations that are dynamic

10. Mental Representations can be transformed Shepard & Metzlar (1971) mental rotation is an example of transforming a mental representation in a continuous process Mental Representations Mentally rotate the images to determine whether they are identical or mirror-reversed SAME MIRROR-REVERSED

11. Mental Representations can be transformed Shepard & Metzlar (1971) mental rotation is an example of transforming a mental representation in a continuous process Mental Representations

12. Mental Representations can be transformed Shepard & Metzlar (1971) mental rotation is an example of transforming a mental representation in a continuous process Mental Representations

13. Mental Representations can be transformed Shepard & Metzlar (1971) mental rotation is an example of transforming a mental representation in a continuous process The time it takes to respond is linearly determined by the number of degrees one has to rotate Somehow the brain must perform a set of operations on these representations - where? how? Mental Representations

14. Mental Representations • Mental Representations can be transformed into abstract information representations • Posner letter matching task • Are these letters from the same category (vowels or consonants) or are they different?

15. Mental Representations • Mental Representations can be transformed into abstract information representations • Posner letter matching task • Are these letters from the same category (vowels or consonants) or are they different? • Are they physically the same or are they the same in an abstract way - they are in the same category? A A A a SAME A U S C A S DIFFERENT

16. Mental Representations • Mental Representations can be transformed into abstract information representations • Posner letter matching task • Participants are fastest when the response doesn’t require transforming the representation from a direct manifestation of the stimulus into something more abstract

17. Mental Representations • Mental Representations can interfere • Stroop task: name the colour in which the word is printed (I.e. don’t read the word, just say the colour

18. Mental Representations • Mental Representations can interfere • Stroop task: name the colour in which the word is printed (I.e. don’t read the word, just say the colour RED

19. Mental Representations • Mental Representations can interfere • Stroop task: name the colour in which the word is printed (I.e. don’t read the word, just say the colour BLUE

20. Mental Representations • Mental Representations can interfere • Stroop task: name the colour in which the word is printed (I.e. don’t read the word, just say the colour GREEN

21. Mental Representations • Mental Representations can interfere • Stroop task: name the colour in which the word is printed (I.e. don’t read the word, just say the colour RED

22. Mental Representations • Mental Representations can interfere • Stroop task: name the colour in which the word is printed (I.e. don’t read the word, just say the colour BLUE

23. Mental Representations • Mental Representations can interfere • Stroop task: name the colour in which the word is printed (I.e. don’t read the word, just say the colour GREEN

24. Mental Representations • Mental Representations can interfere • Stroop task: name the colour in which the word is printed (I.e. don’t read the word, just say the colour • The mental representation of the colour and the representation of the text are incongruent and interfere • one representation must be selected and the other suppressed • This is one conceptualization of attention

25. Mental Representations • These are some examples of how a cognitive psychologist might investigate mental representations • The cognitive neuroscientists asks: • where are these representations formed? • What is the neural mechanism? What is the code for a representation? • What is the neural process by which representations are transformed?

26. First Principles • What are some ways that information might be represented by neurons?

27. First Principles • What are some ways that information might be represented by neurons? • Magnitude might be represented by firing rate (e.g. brightness) • Presence or absence of a feature or piece of information might be represented by whether certain neurons are active or not – the “labeled line” (e.g. color, orientation, pitch) • Conjunctions of features might be represented by coordinated activity between two such labeled lines • Binding of component features might be represented by synchronization of units in a network

28. V I S I O N S C I E N C E

29. Visual Pathways • Themes to notice: • Contralateral nature of visual system • Information is organized: • According to spatial location • According to features and kinds of information

30. Visual Pathways • Image is focused on the retina • Fovea is the centre of visual field • highest acuity • Peripheral retina receives periphery of visual field • lower acuity • sensitive under low light

31. Visual Pathways • Retina has distinct layers

32. Visual Pathways • Retina has distinct layers • Photoreceptors • Rods and cones respond to different wavelengths

33. Visual Pathways • Retina has distinct layers • Amacrine and bipolar cells perform “early” processing • converging / diverging input from receptors • lateral inhibition leads to centre/surround receptive fields - first step in shaping “tuning properties” of higher-level neurons

34. Visual Pathways • Retina has distinct layers • signals converge onto ganglion cells which send action potentials to the Lateral Geniculate Nucleus (LGN) • two kinds of ganglion cells: Magnocellular and Parvocellular • visual information is already being shunted through functionally distinct pathways as it is sent by ganglion cells

35. Visual Pathways • visual hemifields project contralaterally • exception: bilateral representation of fovea! • Optic nerve splits at optic chiasm • about 90 % of fibers project to cortex via LGN • about 10 % project through superior colliculus and pulvinar • but that’s still a lot of fibers! Note: this will be important when we talk about visuospatial attention

36. Visual Pathways • Lateral Geniculate Nucleus maintains segregation: • of M and P cells (mango and parvo) • of left and right eyes P cells project to layers 3 - 6 M cells project to layers 1 and 2

37. Visual Pathways • Primary visual cortex receives input from LGN • also known as “striate” because it appears striped when labeled with some dyes • also known as V1 • also known as Brodmann Area 17

38. Visual Pathways • Primary cortex maintains distinct pathways – functional segregation • M and P pathways synapse in different layers W. W. Norton

39. The Role of “Extrastriate” Areas • Consider two plausible models: • System is hierarchical: • each area performs some elaboration on the input it is given and then passes on that elaboration as input to the next “higher” area • System is analytic and parallel: • different areas elaborate on different features of the input

40. The Role of “Extrastriate” Areas • Different visual cortex regions contain cells with different tuning properties

41. The Role of “Extrastriate” Areas • Functional imaging (PET) investigations of motion and colour selective visual cortical areas • Zeki et al. • Subtractive Logic • stimulus alternates between two scenes that differ only in the feature of interest (i.e. colour, motion, etc.)

42. The Role of “Extrastriate” Areas • Identifying colour sensitive regions Subtract Voxel intensities during these scans… …from voxel intensities during these scans …etc. Time ->

43. The Role of “Extrastriate” Areas • result • voxels are identified that are preferentially selective for colour • these tend to cluster in anterior/inferior occipital lobe

44. The Role of “Extrastriate” Areas • similar logic was used to find motion-selective areas Subtract Voxel intensities during these scans… …from voxel intensities during these scans …etc. STATIONARY STATIONARY MOVING MOVING Time ->

45. The Role of “Extrastriate” Areas • result • voxels are identified that are preferentially selective for motion • these tend to cluster in superior/dorsal occipital lobe near TemporoParietal Junction • Akin to Human V5

46. The Role of “Extrastriate” Areas • Thus PET studies doubly-dissociate colour and motion sensitive regions

47. The Role of “Extrastriate” Areas • Electrical response (EEG) to direction reversals of moving dots generated in (or near) V5 • This activity is absent when dots are isoluminant with background

48. The Role of “Extrastriate” Areas • V4 and V5 are doubly-dissociated in lesion literature:

49. The Role of “Extrastriate” Areas • V4 and V5 are doubly-dissociated in lesion literature: • achromatopsia (color blindness): • there are many forms of color blindness • cortical achromatopsia arises from lesions in the area of V4 • singly dissociable from motion perception deficit - patients with V4 lesions have other visual problems, but motion perception is substantially spared

50. The Role of “Extrastriate” Areas • V4 and V5 are doubly-dissociated in lesion literature: • akinetopsia (motion blindness): • bilateral lesions to area V5 (extremely rare) • severe impairment in judging direction and velocity of motion - especially with fast-moving stimuli • visual world appeared to progress in still frames • similar effects occur when M-cell layers in LGN are lesioned in monkeys