A1 Refereed original research article in a scientific journal
Early processing in primary visual cortex is necessary for conscious and unconscious vision while late processing is necessary only for conscious vision in neurologically healthy humans
Authors: Mikko Hurme, Mika Koivisto, Antti Revonsuo, Henry Railo
Publisher: ACADEMIC PRESS INC ELSEVIER SCIENCE
Publication year: 2017
Journal: NeuroImage
Journal name in source: NEUROIMAGE
Journal acronym: NEUROIMAGE
Volume: 150
First page : 230
Last page: 238
Number of pages: 9
ISSN: 1053-8119
eISSN: 1095-9572
DOI: https://doi.org/10.1016/j.neuroimage.2017.02.060
Abstract
The neural mechanisms underlying conscious and unconscious visual processes remain controversial. Blindsight patients may process visual stimuli unconsciously despite their VI lesion, promoting anatomical models, which suggest that pathways bypassing the VI support unconscious vision. On the other hand, physiological models argue that the major geniculostriate pathway via VI is involved in both unconscious and conscious vision, but in different time windows and in different types of neural activity. According to physiological models, feedforward activity via VI to higher areas mediates unconscious processes whereas feedback loops of recurrent activity from higher areas back to VI support conscious vision. With transcranial magnetic stimulation (TMS) it is possible to study the causal role of a brain region during specific time points in neurologically healthy participants. In the present study, we measured unconscious processing with redundant target effect, a phenomenon where participants respond faster to two stimuli than one even when one of the stimuli is not consciously perceived. We tested the physiological feedforward-feedback model of vision by suppressing conscious vision by interfering selectively either with early or later VI activity with TMS. Our results show that early VI activity (60 ms) is necessary for both unconscious and conscious vision. During later processing stages (90 ms), VI contributes selectively to conscious vision. These findings support the feedforward-feedback-model of consciousness.
The neural mechanisms underlying conscious and unconscious visual processes remain controversial. Blindsight patients may process visual stimuli unconsciously despite their VI lesion, promoting anatomical models, which suggest that pathways bypassing the VI support unconscious vision. On the other hand, physiological models argue that the major geniculostriate pathway via VI is involved in both unconscious and conscious vision, but in different time windows and in different types of neural activity. According to physiological models, feedforward activity via VI to higher areas mediates unconscious processes whereas feedback loops of recurrent activity from higher areas back to VI support conscious vision. With transcranial magnetic stimulation (TMS) it is possible to study the causal role of a brain region during specific time points in neurologically healthy participants. In the present study, we measured unconscious processing with redundant target effect, a phenomenon where participants respond faster to two stimuli than one even when one of the stimuli is not consciously perceived. We tested the physiological feedforward-feedback model of vision by suppressing conscious vision by interfering selectively either with early or later VI activity with TMS. Our results show that early VI activity (60 ms) is necessary for both unconscious and conscious vision. During later processing stages (90 ms), VI contributes selectively to conscious vision. These findings support the feedforward-feedback-model of consciousness.
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