What is attention directed to?………………………………………….……28
- Space-based attention ……………………………………………….28
- Feature-based attention………………………………………………28
- Object-based attention…………………………………..…..….……29
- Sources and targets of attention in the brain…………………………….…31
Attention modulates different response properties…………………..……..31
Firing rate modulation………………….……………………………32
- Response enhancement.……………………….…………..…….32
- Response suppression…………………………………………33
- Baseline enhancement………………………………..………34
- Reliability increase……………………………………….………….36
- Response sensitivity increase……………………………….……….37
- Response selectivity modulation…………………………….………38
- Synchronization, oscillation and correlated responses across cell population…………………………………………………………….39
Objectives……………………………………………………………………..….42
Method……………………………………………………………………………43
- Subjects………………………………………………………….…………43
- Stereotactic MRI……………………………………………….…………..43
- Head-post implantation surgery.……………………….…………………..44
- Stimuli…………………………………………………….………………..46
Tasks…………………………………………………………………………47
- Passive task…………………………………………………………..47
- Active task (two-alternative forced-choice body/object categorization)……………………………………………………….47
- Training…………………………………………………….………………50
- Eye monitoring………………………………………………….………….52
- Craniotomy surgery …………………………………………….………….52
Recording………………………………………………………….……….53
- Recoded area…………………………………………………….…..54
- Recording room…………………………………………….………..54
- Data acquisition setup…………………………………………….…54
- Noise reduction………………………………………………….…..55
- Electrode insertion ………………………………………………….56
- Signal amplification and frequency filtering ……………………….57
Data analysis……………………………………………………..…………59
- Category selectivity index…………………………………….……..60
- High and low baseline trials………………………………….………60
- RMI (rate modulation index)……………………………………..…61
- FF (fano factor)………………………………………………….…..61
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- CP (choice probability)………………………………………………62
- RMI onset……………………………………………………………65
- Neural/behavioral score……………………………………………..66
- Peristimulus time histograms (PSTH), normalizing and smoothing ……………………………………………………………………….67
Results…………………………………………………………………………….68
Conclusion………………………………………………………………………..88
Figures……………………………………………………………………………90
- Stimulus set …………………………………….……………..….90
- Figure 2. Different noise levels of an exemplar stimulus ……………….…91
- Figure 3. Passive task……………………………………………………….92
- Figure 4. Active task (two-alternative forced-choice body/object categorization…………………………………………………………….…93
- Figure 5. Monkeys’ performance in body/object categorization task. …….95
- Figure 6. The pattern of performance decline as a function of noise level was reverse for bodies and objects …………………………………………….. 96
- Figure 7. Monkeys’ performance in body/object categorization task for subcategories …………………………………………………………..…..97
- Figure 8 .Performance decline between adjacent signal levels in subcategories of bodies and objects ……………………………….………98
- Figure 9. Behavioral d́ (d́ = Z “hit rate” – Z “false alarm”) in different visual signals ……………………………………………………………….…….. 99
- Figure 10. Cumulative d́ in signal level of 90 ……………………….……100
- Figure 11. Reaction time in different signal conditions in correct and wrong trials……………………………………………………………………….101
- Figure 12. Reaction time in subcategory level……………………………102
- Figure 13. Relation between reaction time and performance in different signal levels…………………………………………………………….…103
- Figure 14. Mean number of microsaccades in different noise levels……..104
- Figure 15. Mean number of microsaccades in correct and wrong trials of different signal levels……………………………………………………..105
- Figure 16. Reaction time in trials with and without microsaccades in different signal levels…………………………………………………..…106
- Figure 17. Normalized mean firing rate of body cells across different visual signals and behavioral conditions…………………………………….…..107
- Figure 18. Normalized mean firing rate of non-body cells across different visual signals and behavioral conditions…………………………………..109
- Figure 19.Response modulation index (RMI) as a function of task difficulty……………………………………………………………….….111
- Figure 20. Mean response modulation onset across body image signal levels in body cells’ correct trials…………………………………………….….112
- Figure 21. Attentional enhancement of IT cells’ body-object discriminability (d’) was observed only in correct trials and degree of enhancement depended on task difficulty………………………………………………………..…114
- Figure 22. Mean d’ modulation in correct (blue) and wrong (black) compared to passive condition in body cells…………………………………………116
- Figure 23. Mean d’ modulation in correct (blue) and wrong (black) compared to passive condition in non-body cells……………………………………117
- Figure 24. Temporal pattern of baseline firing rate modulation in active compared to passive condition…………………………………………….118
- Figure 25. Temporal pattern of p-values of t-tests measuring significant increase of baseline rate in active compared to passive condition……..…119
- Figure 26. Frequency distribution of proportion of HBTs in body (top) and non-body (bottom) cells during active task…………………………….…120
- Figure 27. Baseline dependent enhancement of body and suppression of non-body cells’ responses to presentation of body images in correct condition……………………………………………………………….….121
- Figure 28. Baseline dependent enhancement of body and suppression of non-body cells’ responses to presentation of body images in wrong condition………………………………………………………………..…122
- Figure 29. Temporal dynamic of body and non-body cells’ RMI to presentation of body images in correct and wrong conditions for HBTs………………………………………………………………………123
- Figure 30. Temporal dynamic of body and non-body cells’ RMI to presentation of body images in correct and wrong conditions for LBTs…124
- Figure 31. P-values of t-tests measuring significant enhancement of body and suppression of non-body cells’ responses in HBTs as time window to define high baseline activity varied over time…………………………….125
- Figure 32. P-values of t-tests measuring significantly larger RMI values of body and smaller RMI values of non-body cells’ in HBTs vs. LBTs as time window to define high vs. low baseline activity varied over time…….….126
- Figure 33. Body cells’ RMI values of high and low baseline trials across body stimulus signal levels…………………………………………….…127
- Figure 34. Baseline dependent modulation of body and non-body cells’ responses to presentation of object images…………………………….…129
- Figure 35. Baseline dependent modulation of body and non-body cells’ responses to presentation of object images…………………………….…130
- Figure 36. Temporal dynamics of body and non-body cells’ RMI to presentation of object images in correct and wrong conditions for HBTs………………………………………………………………………131
- Figure 37. Temporal dynamics of body and non-body cells’ RMI to presentation of object images in correct and wrong conditions for LBTs………………………………………………………………………132
- Figure 38. Frequency distribution of adjusted RMI values for body and non-body cells in HBTs and LBTs………………………………………….…133
- Figure 39. Rate-matched fano factor modulation index (FFMI) of body and non-body cells to presentation of body images in correct condition for HBTs vs. LBTs………………………………………………………………..…134
- Figure 40. Rate-matched fano factor modulation (FFMI) of body and non-body cells to presentation of object images in correct conditions for HBTs and LBTs. …………………………………………………………………135
- Figure 41a. Frequency distribution of normalized d’ modulation difference in LBTs vs. HBTs for body and non-body cells…………………………..136
- Figure 41b. The impact of task specific attentional modulation on firing rate depends on cells’ category selectivity……………………………………..137
- Figure 42. The impact of task specific attentional modulation on firing rate depends on cells’ category selectivity………………………………….…138
- Figure 43. Comparison of RMI values of correct vs. wrong trials of LBTs and HBTs……………………………………………………………….…139
- Figure 44. Comparison of rate modulation in body and non-body cells population across trials of body images with different baseline spike counts……………………………………………………………………..140
- Figure 45. Comparison of rate modulation in body and non-body cells population across trials of object images with different baseline spike counts………………………………………………………………….….142
- Figure 46. Baseline dependent correlation of neural activity and behavioral choice…………………………………………………………………..…143
- Figure 47. Correlation between CP and cells’ body/object discrimination power………………………………………………………………………144
- Figure 48. CP values of body cells plotted against the HBTs proportion in active task………………………………………………………………….145
- Figure 49. RMI values of body cells plotted against the HBTs proportion in active task…………………………………………………………………146
- Figure 50. Attentional modulation of baseline and evoked response in 30 low baseline cells…………………………………………………………147
- Figure 51. Attentional modulation of baseline and evoked response in 30 low baseline cells…………………………………………………………148
- Figure 52. Percent of HBT in active is plotted vs. percent of HBT in passive for 14 body and 16 non-body cells………………………………………..149
- Figure 53. RMI of low baseline body and non-body cells in different stimulus and choice conditions……………………………………………150
[سه شنبه 1399-10-09] [ 08:24:00 ق.ظ ]
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