지각판단 중 인간 1차시각피질의 역할 규명을 위한 뇌영상연구

학위논문 (박사)-- 서울대학교 대학원 : 뇌인지과학과, 2015. 8. 이상훈.Primary visual cortex (V1) forms the initial cortical representation of objects and events in our visual environment, and it distributes information about that representation to higher cortical areas within the visual hierarchy. Decades of work have established tight linkages between neural activity occurring in V1 and features comprising the retinal image, but it remains debatable how that activity relates to perceptual decisions. An actively debated question is the extent to which V1 responses determine, on a trial-by-trial basis, perceptual choices made by observers. By inspecting the population activity of V1 from human observers engaged in a difficult visual discrimination task, we tested one essential prediction of the deterministic view: choice-related activity, if it exists in V1, and stimulus-related activity should occur in the same neural ensemble of neurons at the same time. Our findings do not support this prediction: while cortical activity signifying the variability in choice behavior was indeed found in V1, that activity was dissociated from activity representing stimulus differences relevant to the task, being advanced in time and carried by a different neural ensemble. Moreover, realizing that small deviations in fixational eye movements could affect our fMRI measurements, we tested and confirmed that this pattern of results cannot be attributed to fixational eye movements. The spatiotemporal dynamics of population responses suggest that short-term priors, perhaps formed in higher cortical areas involved in perceptual inference, act to modulate V1 activity prior to stimulus onset without modifying subsequent activity that actually represents stimulus features within V1.1. INTRODUCTION 1 2. EXPERIMENT 1: NEURAL SIGNATURES OF STIMULUS AND CHOICE ARE DISSOCIATED IN POPULATION ACTIVITY OF HUMAN V1 DURING PERCEPTUAL DECISION-MAKING 4 2.1. FINE RING-SIZE CLASSIFICATION TASK 4 2.2. DEFINITION OF ECCENTRICITY-TUNING FOR INDIVIDUAL VOXELS 8 2.3. DEFINITION OF TRIAL-RELATED MATRICES OF POPULATION RESPONSES 11 2.4. NEITHER STIMULI NOR CHOICES SIGNIFICANTLY CORRELATED WITH RAW RESPONSES 13 2.5. DISSOCIATED SIGNATURES OF STIMULUS AND CHOICE IN TUNED RESPONSES 18 2.6. DECODING STIMULUS AND CHOICE INFORMATION FROM RAW RESPONSES WITH POPULATION READ-OUT WEIGHTS 23 3. EXPERIMENT 2: PUPIL SIZE DYNAMICS DURING FIXATION IMPACT THE ACCURACY AND PRECISION OF VIDEO-BASED GAZE ESTIMATION 29 3.1. SPURIOUS EYE MOVEMENT SIGNALS IN VIDEO-BASED GAZE ESTIMATION 30 3.2. PUPIL SIZE VARIATION AND GAZE POSITION ESTIMATES DURING FIXATION 32 3.3. CORRECTION OF GAZE POSITION MEASUREMENTS FOR PUPIL SIZE ARTIFACT 37 3.4. COMPARISON BETWEEN PUPIL CENTER ESTIMATION METHODS 44 4. EXPERIMENT 3: CHOICE SIGNATURES IN V1 CANNOT BE ATTRIBUTED TO FIXATIONAL EYE MOVEMENTS 47 4.1. CORRECTION OF GAZE POSITION MEASUREMENTS DURING THE FINE RING-SIZE CLASSIFICATION TASK FOR PUPIL SIZE ARTIFACT 49 4.2. LACK OF CHOICE SIGNATURE IN FIXATIONAL EYE MOVEMENTS 54 5. DISCUSSIONS 59 5.1. THE ROLE OF V1 IN PERCEPTUAL DECISION-MAKING 59 5.2. POTENTIAL ORIGIN OF THE CHOICE SIGNATURE IN V1 64 5.3. PUPIL SIZE DYNAMICS DURING FIXATION 67 5.4. PUPIL SIZE ARTIFACT IN VIDEO-BASED GAZE ESTIMATION 70 6. EXPERIMENTAL PROCEDURES 74 6.1. OBSERVERS 74 6.2. FMRI EXPERIMENTAL SETUP 74 6.3. FMRI BEHAVIORAL PROTOCOL (EXPERIMENT 1) 75 6.4. ACQUISITION AND PREPROCESSING OF MRI DATA 77 6.5. ECCENTRICITY-TUNING MAPPING IN V1 VOXELS 79 6.6. DEFINITION OF ECCENTRICITY BINS 83 6.7. COMPUTATION OF STIMULUS AND CHOICE PROBABILITIES 84 6.8. PREDICTION OF V1 POPULATION RESPONSES TO RING STIMULI 87 6.9. DECOMPOSITION OF FMRI POPULATION RESPONSES INTO TUNED AND UNTUNED COMPONENTS 88 6.10. POPULATION DECODING OF STIMULUS AND CHOICE INFORMATION 89 6.11. EYE-TRACKING EXPERIMENTAL SETUP 90 6.12. EYE-TRACKING BEHAVIORAL PROTOCOL (EXPERIMENT 2 AND 3) 93 6.13. EYE-TRACKING DATA PREPROCESSING 94 6.14. CORRECTION OF GAZE POSITION MEASUREMENTS FOR PUPIL SIZE ARTIFACT 97 6.15. ACCURACY AND PRECISION ANALYSIS OF GAZE POSITION SIGNAL 98 6.16. STATISTICAL POWER ANALYSIS OF GAZE POSITION SIGNAL 100 6.17. MICROSACCADES ANALYSIS 101 6.18. PUPIL SIZE ANALYSIS 102 6.19. ANALYSIS OF GAZE POSITION AND VERGENCE ANGLE 103 BIBLIOGRAPHY 104 국문초록 116Docto