June 2006
Volume 6, Issue 6
Free
Vision Sciences Society Annual Meeting Abstract  |   June 2006
Evidence for an early, direct visual input to V5/MT
Author Affiliations
  • Sheila Crewther
    School of Psychological Science, La Trobe University, Melbourne, Australia
  • Robin Laycock
    School of Psychological Science, La Trobe University, Melbourne, Australia, and Alfred Hospital, Monash University, Melbourne, Australia
  • Paul Fitzgerald
    Alfred Hospital, Monash University, Melbourne, Australia
  • David Crewther
    Brain Sciences Institute, Swinburne Univeristy of Technology, Melbourne, Australia
Journal of Vision June 2006, Vol.6, 571. doi:10.1167/6.6.571
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      Sheila Crewther, Robin Laycock, Paul Fitzgerald, David Crewther; Evidence for an early, direct visual input to V5/MT. Journal of Vision 2006;6(6):571. doi: 10.1167/6.6.571.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose: Human visual motion processing is usually considered to occur via feed-forward projections through V1 into dorsal extrastriate cortex (V5/MT), though evidence also exists for an early, direct midbrain or thalamic input to V5/MT which bypasses V1. Hence we used Transcranial Magnetic Stimulation (TMS) to investigate the sequence of temporal activation of V1 and V5/MT in motion processing.

Methods: Ten participants were exposed to TMS in the region of V1 and left V5/MT during performance on a 3AFCmotion direction detection task set at a 80% correct level. Stimulus was 80 dots moving coherently (2.2cm/sec) for duration 53–84ms. Double pulses were delivered with a stimulus-TMS onset asynchrony of between 0–220ms in 32ms intervals.

Results: Mean performance showed diminished accuracy during TMS to V1 and V5. Four participants showed a strong early inhibition of performance in V1 following TMS between 0–32ms while the other 6 showed a second smaller later inhibition effect at between 95–158ms post - stimulus onset. All participants showed diminished performance accuracy with TMS to V5 between 0ms and 32ms post stimulus onset only.

Discussion: This study demonstrates that accurate perception of direction of coherent motion requires activation of V5/MT within 30ms of stimulus onset suggesting that such early motion processing bypasses striate cortex.

Crewther, S. Laycock, R. Fitzgerald, P. Crewther, D. (2006). Evidence for an early, direct visual input to V5/MT [Abstract]. Journal of Vision, 6(6):571, 571a, http://journalofvision.org/6/6/571/, doi:10.1167/6.6.571. [CrossRef]
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