monkeys’ choice, particularly in trials with high baseline activity. We suggest that attentional enhancement of IT cells’ baseline firing rate is correlated with improved neural response reliability and category selectivity. These effects are dependent on the cells’ category selectivity, attentional load and the exact time of baseline activity increase.

 

Keywords: object recognition, neural baseline activity, visual attention, decision making

 

 

Table of Contents

Introduction…………………………………………………………………..….10

  1. The crucial role of “visual object categorization: in everyday life…………10
  2. Where in the brain is category information represented? ……………………11
  3. Anatomy of inferior temporal cortex…………………………….…………23
  4. Attention improves categorization performance, especially in difficult condition…………………………………………………………………….25
  5. Bottom-up vs. top-down attention………………………………….………26

  6. What is attention directed to?………………………………………….……28

    1. Space-based attention ……………………………………………….28
    2. Feature-based attention………………………………………………28
    3. Object-based attention…………………………………..…..….……29

  7. Sources and targets of attention in the brain…………………………….…31

  8. Attention modulates different response properties…………………..……..31

    1. Firing rate modulation………………….……………………………32

      1. Response enhancement.……………………….…………..…….32
      2. Response suppression…………………………………………33




  • Baseline enhancement………………………………..………34
  1. Reliability increase……………………………………….………….36
  2. Response sensitivity increase……………………………….……….37
  3. Response selectivity modulation…………………………….………38
  4. Synchronization, oscillation and correlated responses across cell population…………………………………………………………….39

Objectives……………………………………………………………………..….42

Method……………………………………………………………………………43

  1. Subjects………………………………………………………….…………43
  2. Stereotactic MRI……………………………………………….…………..43
  3. Head-post implantation surgery.……………………….…………………..44
  4. Stimuli…………………………………………………….………………..46

  5. Tasks…………………………………………………………………………47

    1. Passive task…………………………………………………………..47
    1. Active task (two-alternative forced-choice body/object categorization)……………………………………………………….47

  6. Training…………………………………………………….………………50
  7. Eye monitoring………………………………………………….………….52
  8. Craniotomy surgery …………………………………………….………….52

  9. Recording………………………………………………………….……….53

    1. Recoded area…………………………………………………….…..54
    2. Recording room…………………………………………….………..54
    3. Data acquisition setup…………………………………………….…54
    4. Noise reduction………………………………………………….…..55
    5. Electrode insertion ………………………………………………….56
    6. Signal amplification and frequency filtering ……………………….57

  10. Data analysis……………………………………………………..…………59

    1. Category selectivity index…………………………………….……..60
    2. High and low baseline trials………………………………….………60
    3. RMI (rate modulation index)……………………………………..…61
    4. FF (fano factor)………………………………………………….…..61
    5. FFMI (fano factor modulation index)…………………………….…61
    6. CP (choice probability)………………………………………………62
    7. این مطلب را هم بخوانید :
    8. ۱۰ راه برای گردش در اطراف پراکنده ترافیک وب سایت
    9. RMI onset……………………………………………………………65
    10. Neural/behavioral score……………………………………………..66
    11. Peristimulus time histograms (PSTH), normalizing and smoothing ……………………………………………………………………….67


 

Results…………………………………………………………………………….68

Conclusion………………………………………………………………………..88

Figures……………………………………………………………………………90

  5. Stimulus set …………………………………….……………..….90
  6. Figure 2. Different noise levels of an exemplar stimulus ……………….…91
  7. Figure 3. Passive task……………………………………………………….92
  8. Figure 4. Active task (two-alternative forced-choice body/object categorization…………………………………………………………….…93
  9. Figure 5. Monkeys’ performance in body/object categorization task. …….95
  10. Figure 6. The pattern of performance decline as a function of noise level was reverse for bodies and objects …………………………………………….. 96
  11. Figure 7. Monkeys’ performance in body/object categorization task for subcategories …………………………………………………………..…..97
  12. Figure 8 .Performance decline between adjacent signal levels in subcategories of bodies and objects ……………………………….………98
  13. Figure 9. Behavioral d́ (d́ = Z “hit rate” – Z “false alarm”) in different visual signals ……………………………………………………………….…….. 99
  14. Figure 10. Cumulative d́ in signal level of 90 ……………………….……100
  15. Figure 11. Reaction time in different signal conditions in correct and wrong trials……………………………………………………………………….101

 

 

 

 

 

 

 

 

 

 

 

  1. Figure 12. Reaction time in subcategory level……………………………102
  2. Figure 13. Relation between reaction time and performance in different signal levels…………………………………………………………….…103
  3. Figure 14. Mean number of microsaccades in different noise levels……..104
  4. Figure 15. Mean number of microsaccades in correct and wrong trials of different signal levels……………………………………………………..105
  5. Figure 16. Reaction time in trials with and without microsaccades in different signal levels…………………………………………………..…106
  6. Figure 17. Normalized mean firing rate of body cells across different visual signals and behavioral conditions…………………………………….…..107
  7. Figure 18. Normalized mean firing rate of non-body cells across different visual signals and behavioral conditions…………………………………..109
  8. Figure 19.Response modulation index (RMI) as a function of task difficulty……………………………………………………………….….111
  9. Figure 20. Mean response modulation onset across body image signal levels in body cells’ correct trials…………………………………………….….112
  10. 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
  11. Figure 22. Mean d’ modulation in correct (blue) and wrong (black) compared to passive condition in body cells…………………………………………116
  12. Figure 23. Mean d’ modulation in correct (blue) and wrong (black) compared to passive condition in non-body cells……………………………………117
  13. Figure 24. Temporal pattern of baseline firing rate modulation in active compared to passive condition…………………………………………….118
  14. Figure 25. Temporal pattern of p-values of t-tests measuring significant increase of baseline rate in active compared to passive condition……..…119
  15. Figure 26. Frequency distribution of proportion of HBTs in body (top) and non-body (bottom) cells during active task…………………………….…
موضوعات: بدون موضوع  لینک ثابت


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