Decoupling of early V5 motion processing from visual awareness: a matter of velocity as revealed by transcranial magnetic stimulation evidence

Grasso, P. A., Làdavas, E., Bertini, C., Caltabiano, S., Thut, G. and Morand, S. (2018) Decoupling of early V5 motion processing from visual awareness: a matter of velocity as revealed by transcranial magnetic stimulation evidence. Journal of Cognitive Neuroscience, 30(10), pp. 1517-1531. (doi:10.1162/jocn_a_01298) (PMID:29916788)

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Abstract

Motion information can reach V5/MT through two parallel routes: one conveying information at early latencies through a direct subcortical route and the other reaching V5 later via recurrent projections through V1. Here, we tested the hypothesis that input via the faster direct pathway depends on motion characteristics. To this end, we presented motion stimuli to healthy human observers at different velocities (4.4°/sec vs. 23°/sec) with static stimuli as controls while applying transcranial magnetic stimulation (TMS) pulses over V5 or V1. We probed for TMS interference with objective (two-alternative forced choice [2AFC]) and subjective (awareness) measures of motion processing at six TMS delays from stimulus onset (poststimulus window covered: ∼27–160 msec). Our results for V5–TMS showed earlier interference with objective performance for fast motion (53.3 msec) than slow motion (80 msec) stimuli. Importantly, TMS-induced decreases in objective measures of motion processing did correlate with decreases in subjective measures for slow but not fast motion stimuli. Moreover, V1–TMS induced a temporally unspecific interference with visual processing as it impaired the processing of both motion and static stimuli at the same delays. These results are in accordance with fast moving stimuli reaching V5 through a different route than slow moving stimuli. The differential latencies and coupling to awareness suggest distinct involvement of a direct (i.e., colliculo-extrastriate) connection bypassing V1 depending on stimulus velocity (fast vs. slow). Implication of a direct pathway in the early processing of fast motion may have evolved through its behavioral relevance.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Thut, Professor Gregor and Morand, Dr Stephanie
Authors: Grasso, P. A., Làdavas, E., Bertini, C., Caltabiano, S., Thut, G., and Morand, S.
College/School:College of Medical Veterinary and Life Sciences > Institute of Neuroscience and Psychology
College of Medical Veterinary and Life Sciences > School of Life Sciences
Journal Name:Journal of Cognitive Neuroscience
Publisher:Massachusetts Institute of Technology
ISSN:0898-929X
ISSN (Online):1530-8898
Published Online:19 June 2018
Copyright Holders:Copyright © 2018 Massachusetts Institute of Technology
First Published:First published in Journal of Cognitive Neuroscience 30(10):1517-1531
Publisher Policy:Reproduced in accordance with the publisher copyright policy

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