1. Attention and neglect

2. Neurophysiology of Attention
The Superior Colliculus
MT, MST and PPC
V2, V4 and IT

3. Neurophysiology of Attention
The Superior Colliculus
MT, MST and PPC
V2, V4 and IT

4. The Superior Colliculus
Receptive Field

5. The Superior Colliculus
Receptive Field
Saccadic Enhancement

6. The Superior Colliculus
Receptive Field

7. Is the saccadic enhancement in the superior colliculus due to attention or to a motor intent?

8. The Superior Colliculus
Receptive Field
Attention alone can increase the firing rate

9. Receptive Field

11. Response enhancement could correspond to the selection of the attended target
This enhancement seems to be independent of the behavior

12. Physiology of Attention
The Superior Colliculus
MT, MST and PPC (the posterior parietal cortex)
V4 and IT (the infero temporal cortex)

13. Treue and Maunsell, MST

16. Response to the attended stimulus is enhanced
Enhancement is stronger when the distractor and the target are in the same receptive field
The response to the distractor is decreased

17. PPC: Gottlieb and Goldberg, 1998
Cue: Triangle *
1st Saccade
2nd Saccade
Firing Rate
Cue +
Time
Cue: Circle * +
2nd Saccade
Firing Rate
1st Saccade
Time

18. Cells in MT and PPC:
Attention boosts the gain of the response to the attended stimulus while reducing the response to the unattended stimulus.

19. Physiology of Attention
The Superior Colliculus
MT and PPC (the posterior parietal cortex)
V2, V4 and IT

20. Reynolds et al, 1999 Monkey attends preferred stimulus of the cell

21. Reynolds et al, 1999 Monkey attends null stimulus for the cell

22. McAdams and Maunsell, 1999
Colored Gaussian

23. McAdams and Maunsell, 1999

24. McAdams and Maunsell, 1999

25. What’s going on? Maunsell: Desimone: Gain modulation No baseline shift
Seen everywhere although strongest when the distractor and the target are in the same receptive field
Desimone:
Not gain: normalization
Baseline shift
Seen only when the distractor and the target are in the same receptive field

26. Neglect

28. Line Cancellation

29. Line Bisection

30. Patient: Frederico Fellini

31. Patients: Right Parietal Task: Shape Identification
Karnath et al., 1993
Patients: Right Parietal
Task: Shape Identification
Condition Condition 2

32. Retinocentric Neglect
Right Target
Left Target
% Correct
Prediction for
Retinocentric Neglect
Condition Condition2

33. Trunk-centered Neglect
Right Target
Left Target
% Correct
Prediction for
Trunk-centered Neglect
Condition Condition2

34. Patients
% Correct
% Correct
Patient 1
Patient 2
C C2
C C2

35. Frames of reference for neglect:
Trunk-centered?

36. Left hand is still neglected even though it is now on the right
Left hand is neglected

37. Can neglect be object-centered?

38. Object-centered or relative neglect?

39. Object-centered or relative neglect?
Draw the white half
Draw the black half

40. Driver et al, Neuropsychologia, 1994
Axis-centered neglect
Main axis
Hard Easy
Driver et al, Neuropsychologia, 1994

41. Frames of Reference of Neglect
Neglect always affects a mixture of egocentric frames of reference for all behaviors
Neglect is always relative
In some patients, it can also be axis-centered (object-centered).

42. Can we relate the behavior of hemineglect patients to the response of neurons involved in spatial representations?
What do we know of the response properties of neurons involved in spatial representations?

43. Retinal Location (deg)
Eye Position
ex = -20
ex = 0
ex = 20
Activity –
Retinal Location (deg)
(Andersen et al., 1985)

45. Motor commands, M, are non linear functions of sensory inputs, S, and posture signals, P:
M = f(S,P)
Such functions can be approximated by linear combinations of basis functions, Bi(S,P):
M = S ci Bi(S,P)
Claim: parietal neurons compute basis functions

46. Retinal Location (deg)
Activity
Retinal Location (deg)
Eye Position (deg)
Eye Position
ex = -20
ex = 0
ex = 20
Activity –
Retinal Location (deg)

47. Eye Movements Reaching Premotor Cortex Head-Centered Map
Superior Colliculus
Retinotopic Map
Eye Movements
Reaching
Eye
Position
Basis Function
Layer
(Parietal Cortex)
Retinal Location
Eye Position
Units
Retinotopic Map
Visual Cortex

48. Can we generalize the basis function theory of spatial representations to object-centered representations?

49. Neuronal Activity
Trials
Left of the object Right of the object

50. Saccades Direction (deg)
Left of the object
Right of the object
Saccades Direction (deg)
Neuronal Activity
Activity
Trials

51. Explicit object-centered neurons or gain modulated neurons?

52. Saccades Direction (deg)
Left of the object
Right of the object
Saccades Direction (deg)
Neuronal Activity
Activity
Trials

53. It appears that the parietal cortex uses basis functions for spatial representations in:
Egocentric coordinates (eye-, head-, body-centered)
Object-centered coordinates

54. Eye Movements Reaching Premotor Cortex Head-Centered Map
Superior Colliculus
Retinotopic Map
Eye Movements
Reaching
Eye
Position
Basis Function
Layer
(Parietal Cortex)
Retinal Location
Eye Position
Units
Retinotopic Map
Visual Cortex

55. Left Retinal Position Right Left Retinal Position Right
Premotor Cortex
Head-Centered Map
Superior Colliculus
Retinotopic Map
Right
Right
Basis Function
Layer
Eye Position
Eye Position
Left Retinal Position Right
Left Retinal Position Right
Left Map
Right Map
Eye Position
Units
Retinotopic Map
Visual Cortex

56. Main assumptions of the hemineglect model:
Parietal neurons compute basis functions
Basis function units are distributed across hemispheres according to contralateral gradients

57. Left Retinal Position Right Left Retinal Position Right
Premotor Cortex
Head-Centered Map
Superior Colliculus
Retinotopic Map
Right
Right
Basis Function
Layer
Eye Position
Eye Position
Left Retinal Position Right
Left Retinal Position Right
Left Map
Right Map
Eye Position
Units
Retinotopic Map
Visual Cortex

58. Saliency: summed activity in the basis function layer
Right
Eye Position
Left
Left
Right
Retinal Location

59. Model Patients Error Error Error Error Patients Line Orientation
Line Length
Line Length
Error
Error
Patients
Model
Line Orientation
Line Orientation

60. Patients: Right Parietal Task: Shape Identification
Karnath et al., 1993
Patients: Right Parietal
Task: Shape Identification
Condition Condition 2

61. Right Target
Left Target
Model
Condition Condition 2

62. Left Stimulus Right Stimulus C2 C1 Head Position Retinal Location

63. Left hand is still neglected even though it is now on the right
Left hand is neglected

64. General principle: any change of posture toward the ipsilesional side results in an improvement in performance (extreme case: vestibular recovery)

65. Relative neglect

66. Draw the black half
Draw the white half

70. Object-centered neglect

72. Activity in the Basis Function Layer
Main axis
Hard Easy

73. Conclusions
Parietal neurons compute basis functions of their inputs. As a result, they encode the location of objects in multiple frames of reference simultaneously
A lesion of a basis function representation leads to a syndrome similar to hemineglect if the basis functions are distributed across hemispheres according to contralateral gradients
This approach can be generalized to object-centered representations