1. Binding problems and feature integration theory

2. Feature detectors Neurons that fire to specific features of a stimulus Pathway away from retina shows neurons that fire to more complex stimuli Cells that are feature detectors: –Simple cortical cell –Complex cortical cell –End-stopped cortical cell

3. Single cell recording of neurons in the temporal lobe An electrode is inserted in this area, and measure neural responses when stimuli are changed gradually

5. Neurons in this area respond to complex stimuli like those shown on the left.

6. Selective adaptation

8. Selective adaptation to size

11. 1 2 3 4 5 6 7 8 9 10 11 12

13. 1 2 3 4 5 6 7 8 9 10 11 12

17. Figure 3.30 How neurons that respond best to narrow (N), medium (M), and wide (W) bars respond to the medium-bar grating on the right of Figure 3.28. (a-b): Response before adaptation. (c) Response after adaptation to the wide-bar grating at the top left. (d) Response after adaptation to the narrow-bar grating on the bottom left.

18. After Image

21. After images: Red  Green Green  Red Blue  Yellow Yellow  Blue RGBY Color perception

22. R G BY adaptation After image

23. Binding problem

24. Two visual pathways (what & where/how systems) Image from Neuroscience, 2 nd Ed. (2000).

25. Columnar organization Neurons that respond to the same orientation are packed in the same column Image courtesy of Dr. Paul Wellman and Neuroscience, 2 nd Ed. (2000).

26. Distributed coding; then what do you need?  Combining input

27. Feature integration theory by Treisman & Gelade –Attention plays a central role in solving the binding problem. –Attention helps organize information.

28. Attention and Figure-ground segregation Depending on where you look at, the figure and the ground switch rapidly.  Attention plays some role in determining the figure and the ground.

29. Attention and 3D structure Depending on where to look at, you get different 3D structures.

33. Damage to the parietal lobe creates binding errors.

36. Copies of the black (A) and the white (B) vertical contour. Copies of the black (A) and the white (B) diagonal contour.

37. Copies of the left sub- figure (A) The right subfigure (B) And the central sub- figure (C)

38. Feature integration theory Attention is the “glue” that combines the information from the what and where systems.

39. What can you predict from this theory? If you can’t attend, you can’t combine information.  Illusionary conjunction

40. Demonstration I will show you a scene quickly. Report first the black numbers. Report what you see at each of the 4 locations. +++ Mask

42. +++++

45. Report first the black numbers. Report what you saw at each of the 4 locations.

46. Illusionary conjunctions We tend to put different features from different objects together. Some brain damaged patients (parietal lobe) show illusionary conjunctions even when the patients were allowed to view the stimuli for 10 seconds.

47. Visual search experiments Feature search –This is easy because you find the target by looking for a single feature. –  you don’t need attention Conjunction search –For this you need to combine two or more features (color and orientation) –  you need attention Looking for the target

48. Conjunction search –For this you need to combine two or more features (color and orientation) –  you need attention –Because you can attend an item one at a time, the difficulty in the conjunction search increases proportional to the number of items in the stimulus frame. –This is not the case in the feature search.

49. Find Which is more difficult?

50. Find Which is more difficult?

51. Feature binding and attention (Treisman, 1988) Experiments: Task Given a stimulus frame containing visual items, subjects were asked to indicate whether or not a target item was present in the frame.

52. Target:

56. Feature search vs. conjunction search Feature search –The target item has a unique feature. Conjunction search –You need to combine features to find the target. –You need attention. –Because you can attend only one item at a time, the conjunction search becomes more difficult when more items are in the stimulus frame.

57. Generality of the results: Feature search Conjunction search

58. Experiments: Measure accuracy and response times (conjunction cases vs. non-conjunction cases)

60. Response time # of distractors 1000 ms 500ms

61. Response time # of distractors 1000 ms 500ms

62. The physiology of attention How do you combine features? Synchrony hypothesis When neurons in different parts of the cortex are firing to the same object, the pattern of firing is synchronized (they fire at the same time, and in the same manner). So when neurons are firing in synchrony, the corresponding features are bound together.

63. Separate neurons respond to color (green, blue, white), contours (orientations), textures, so on. Synchrony hypothesis: –When the features come from the same object (i.e., the woman), these neurons fire at the same time in the same manner. –When the neurons fire at the same time and in the same manner, we perceive “binding” of features. Attention is likely to increase synchrony

64. Attention Selecting information Enhancing information Combining information