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SUMMARY:What is the temporal resolution of categorical perception? - Prof 
 Leon Deouell\, Human Cognitive Neuroscience Lab\, Hebrew University of Jer
 usalem
DTSTART:20180309T163000Z
DTEND:20180309T173000Z
UID:TALK100264@talks.cam.ac.uk
CONTACT:Louise White
DESCRIPTION:Abstract\nWhat levels of neural processing correspond with sub
 jective perception? Numerous studies addressed this question but few if an
 y compared the temporal dynamics of neural activity to that of subjective 
 perception. Here we examined the neural response to sustained\, full contr
 ast\, supraliminal images\, and looked for neural responses which track th
 e presence of the stimulus with high fidelity for its entire duration. Int
 racranial EEG was recorded from the surface of the cortex in patients (> 1
 000 iEEG electrodes)\, while they viewed images presented for varying dura
 tions of 300-1500ms. The fidelity of sustained high-frequency broadband ac
 tivity gradually decreased across the ventral stream: single-trial stimulu
 s duration could be decoded with an accuracy of at least 150ms from early 
 visual cortex but unreliably in anterior\, category-selective regions. Thi
 s result presents an apparent dissociation between neural activity and per
 ception\, as the patients could clearly see and categorize the images whil
 e they were displayed.  Next\, fifteen healthy participants were tested us
 ing slow event-related fMRI with images lasting 9 or 15 seconds. In this c
 ase\, we found robust sustained BOLD responses across the entire ventral s
 tream hierarchy. The two sets of results can be reconciled by taking into 
 account the different temporal resolutions of BOLD signal and iEEG. Sporad
 ically-bursting neural activity\, which is not informative about the prese
 nce of the stimulus on a sub-second timescale\, can still be informative a
 bout the stimulus presence with a coarser resolution reflected in the hemo
 dynamic response. The combined findings raise new questions about which te
 mporal resolution is relevant for subjective perception.\n
LOCATION:Ground Floor Lecture Theatre\, Department of Psychology
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