S-Space College of Natural Sciences (자연과학대학) Brain and Cognitive Sciences (뇌인지과학과) Theses (Ph.D. / Sc.D._뇌인지과학과)
Neuroimaging studies on the role of human primary visual cortex during perceptual decision-making
지각판단 중 인간 1차시각피질의 역할 규명을 위한 뇌영상연구
- 자연과학대학 뇌인지과학과
- Issue Date
- 서울대학교 대학원
- visual perception; perceptual decision; primary visual cortex; fMRI; eye-tracking; choice probability
- 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.