Unconscious processing of orientation and color without primary visual cortex

Jennifer L. Boyer; Stephenie Harrison; Tony Ro

doi:10.1073/pnas.0505332102

Edited by Lawrence Weiskrantz, University of Oxford, Oxford, United Kingdom, and approved September 15, 2005 (received for review June 27, 2005)

Abstract

In humans, the primary visual cortex (V1) is essential for conscious vision. However, even without V1 and in the absence of awareness, some preserved ability to accurately respond to visual inputs has been demonstrated, a phenomenon referred to as blindsight. We used transcranial magnetic stimulation (TMS) to deactivate V1, producing transient blindness for visual targets presented in a foveal, TMS-induced scotoma. Despite unawareness of these targets, performance on forced choice discrimination tasks for orientation (experiment 1) and color (experiment 2) were both significantly above chance. In addition to demonstrating that TMS can be successfully used to induce blindsight within a normal population, these results suggest a functioning geniculoextrastriate visual pathway that bypasses V1 and can process orientation and color in the absence of conscious awareness.

Footnotes

↵ * To whom correspondence should be addressed. E-mail: tro{at}rice.edu.
Author contributions: T.R. designed research; J.L.B., S.H., and T.R. performed research; J.L.B., S.H., and T.R. analyzed data; and J.L.B. and T.R. wrote the paper.
Conflict of interest statement: No conflicts declared.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: TMS, transcranial magnetic stimulation; SOA, stimulus onset asynchrony.
Copyright © 2005, The National Academy of Sciences