Attention: the big picture

1. Attention: the big picture • Strongly intuitive concept • “Everybody knows what attention is. It is the taking possession by the mind in clear and vivid form of one, out of what seem several, simultaneously possible objects or trains of thought… It implies withdrawal from some things in order to deal effectively with others.” • “Selective”, “limited capacity” • Tied to “awareness”, “consciousness”, “alertness”, “vigilance”

2. Attention: the big picture • Control/Direction (Executive Function) • What determines our focus of attention? • Effects of attention • Once attention is focused (in space or on an object) what is the neural consequence?

3. Effects of attention • At what processing stage does attention act? • Early vs. Late Selection • Specificity of Attention • Task, Space, and Features • Biased Competition Model

4. Attention • Selective attention: a process that allows us to more fully process some information (sensory, memories, etc.) while ignoring other information. • Voluntary (“endogenous”) • Under our control • Reflexive (“exogenous”) • In response to sensory input

5. Covert attention (visual): we can attend to spatial locations that are different than where our eyes are pointed. + T L Fovea

6. Attention: Outline • At what processing stage does attention act? • Early vs. Late Selection • Specificity of Attention • Task, Space, and Features • Biased Competition Model

7. Early vs. Late Selection • Early selection: only very rudimentary processing is performed pre-attentively (before the filter) • Predicts object recognition, word recognition, etc. require attention • Late selection: information gets “fully processed” and attention selects a subset of this highly processed information • Predicts object recognition, word recognition, etc. do not require attention

8. (1) At what processing stage does attention act? • Selective Auditory Attention • What can the listener report about the unattended information? • Very little

9. (1) At what processing stage does attention act? • Broadbent (1958) early selection gating theory

10. (1) At what processing stage does attention act? • Revised version based on: intrusion of the unattended inputs • Your name, for example, would likely be detected.

12. ERP Evidence

13. ERP Evidence C1  originates in V1 N1/P1  originate in extra-striate cortex

14. ERP evidence • Attention affects activity in retinotopic visual cortex. • Source modeling and characteristics of the signal suggest not V1.

16. Electrophysiology Evidence • Attention effects easily measured in extrastriate areas • Very small (or nonexistent) in V1 V4

17. ERP & electrophysiology evidence • Attention affects activity in retinotopic visual cortex. • Source modeling and characteristics of the signal suggest not V1. • Single-neuron measurements show strong extra-striate effects but suggest only very weak or nonexistent effects in V1.

18. Early vs. Late Selection INTERMEDIATE

19. The fMRI challenge • Strong, reliable modulations of V1 with attention • Gandhi, Heeger, & Boynton (1999, PNAS) • Brefcynski & DeYoe (1999, Nat Neurosci) • Somers et al. (1999, PNAS)

20. fMRI: a new story ~25% V1: Left hemisphere

21. fMRI: a new story

22. Early vs. Late Selection INTERMEDIATE EARLY

23. Early Results Revised • “The classical notion concerning attention effects in visual cortex has held that the strongest effects are seen at the highest levels of the visual pathway, and that in primary visual cortex there is no effect of attention. (… these recent fMRI results) illustrate the change that has taken place in recent years.” Mike Posner & Charles Gilbert, PNAS, 1999.

24. Why is there the discrepancy between electrophysiology and fMRI measures of attention? • Species difference? • Physiological difference? • Non-spiking “activity” • Timing differences • Does attention = blood flow? • Something else?

25. Reconciliation: ERP’s • ERP’s: no effect in V1 • fMRI: strong effect in V1 • Proposal: C1 reflects feedforward activity in V1. The change measured with fMRI (no temporal resolution) represents the effect of feedback. • Prediction: Electrophysiology experiments might show changes in V1 with attention at later durations.

26. Reconciliation: electrophysiology • Attention effects appear later in V1 than sensory effects.

27. Why is there the discrepancy between electrophysiology and fMRI measures of attention? • Species difference? • Physiological difference? • Non-spiking “activity” • Timing differences • Does attention = blood flow? • Something else?

28. Early vs. Late Selection • Have we provided an answer? • Shown convincingly that there is an attention effect at early stages of visual processing. • What happens to unattended stimuli? • Early selection: only very rudimentary processing is performed pre-attentively (before the filter) • Predicts object recognition, word recognition, etc. require attention • Late selection: information gets “fully processed” and attention selects a subset of this highly processed information • Predicts object recognition, word recognition, etc. do not require attention

29. “gate” Selective attention: a process that allows us to more fully process some information while ignoring other information. V2 V3 V1 Attended Sensory Surface Unattended Unattended

30. Early vs. Late Selection • More recent theories: • early vs. late depends on attentional load • High load  early selection • Low load  late selection Paper for Thursday • Yi DJ, Woodman GF, Widders D, Marois R, Chun MM. Neural fate of ignored stimuli: dissociable effects of perceptual and working memory load. Nat Neurosci. 2004 Sep;7(9):992-6.

31. Attention: Outline • At what processing stage does attention act? • Early vs. Late Selection • Specificity of Attention • Features and Space • Biased Competition

32. Behavioral Goals • Use neurons with tuning best-matched to the behavioral goal. • Goals (vision): • Find the red book. (feature) • Look for danger coming from the left. (space) • Look for stop sign. (feature + space)

33. Feature 20 s 20 s 20 s 20 s Attend:color Attend:motion Attend:color Attend:motion

35. Task 20 s 20 s 20 s 20 s Attend:color Attend:motion Attend:color Attend:motion MT V4

37. Behavioral Goals • Use neurons with tuning best-matched to the behavioral goal. • Goals (vision): • Find the red book. (feature) • Look for danger coming from the left. (space) • Look for stop sign. (feature + space)

39. Behavioral Goals • Use neurons with tuning best-matched to the behavioral goal. • Goals (vision): • Find the red book. (feature) • Look for danger coming from the left. (space) • Look for stop sign. (feature + space)

40. “Attend Vertical”

41. 2 3 10 4 0 1

42. Gain effects • Carrie J. McAdams and John H. R. Maunsell. Effects of Attention on Orientation-Tuning Functions of Single Neurons in Macaque Cortical Area V4. The Journal of Neuroscience, January 1, 1999, 19(1):431-441 V4

43. “Attend Vertical”

44. Attention: Outline • At what processing stage does attention act? • Early vs. Late Selection • Specificity of Attention • Task, Space, and Features • Biased Competition

45. “Biased Competition”

46. “Biased Competition” • “Enhancements” of attention are in a context of multiple stimuli competing for access to behavior. • Single neurons: • Competition will be greatest when there are multiple items in a neuron’s receptive field.

47. “Biased Competition” V4 Neuron Neuron’s receptive Field Attention Response ‘Good’

48. “Biased Competition” V4 Neuron Neuron’s receptive Field Attention Response ‘Bad’ ‘Good’

49. “Biased Competition” V4 Neuron Neuron’s receptive Field Attention Response ‘Bad’ ‘Both’ ‘Good’

50. “Biased Competition” V4 Neuron Neuron’s receptive Field Attention Response ‘Bad’ ‘Both’ ‘Good’