Is There a Magnocellular Advantage? A TMS Study of Early Visual Cortex
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1
La Trobe University Melbourne, Australia
An important aspect of the ‘magnocellular advantage’ model of visual processing, whereby rapid magnocellular activation of parietal attention mechanisms are initiated prior to ventral stream processing, is the timing advantage of magnocellular (M) over parvocellular (P) inputs to early visual cortex. To test this, the critical timing of processing of stimuli preferentially targeting M and P pathways in early visual cortex (EVC) was investigated with Transcranial Magnetic Stimulation (TMS). Tasks consisted of orientation discrimination of separate grating patterns presented in either contralateral or ipsilateral visual fields. Single-pulse TMS was delivered to left EVC at randomised onset asynchronies 0-120ms post-stimulus onset. In the M task, the gratings were achromatic, with high temporal and low spatial frequencies, whilst the P task was isoluminant with low temporal and high spatial frequencies. The novel finding of TMS-induced effects in the ipsilateral visual field indicated that it could not be used as a reliable control comparison. Performance on the M task showed reduced performance following TMS administered in both an early period (30-60ms post-stimulus onset) and a later period (75-105ms post-stimulus onset), however only the latter was significant. Performance on the P task also showed a non-significant reduction in performance in the later period. Whilst both M- and P-biased stimuli required later critical processing in early visual cortex, TMS demonstrated differences in the necessity of early visual processing between M- and P-stimuli. This indicates support for a critical involvement of early M processing prior to later M and P processing in early visual cortex.
Keywords:
Transcranial magnetic stimulation (TMS),
Magnocellular Advantage,
magnocellular pathway,
Parvocellular pathway,
Early Visual Cortex
Conference:
ACNS-2012 Australasian Cognitive Neuroscience Conference, Brisbane, Australia, 29 Nov - 2 Dec, 2012.
Presentation Type:
Poster Presentation
Topic:
Sensation and Perception
Citation:
Shilton
AL,
Laycock
R,
Hoysted
CL and
Crewther
S
(2012). Is There a Magnocellular Advantage? A TMS Study of Early Visual Cortex.
Conference Abstract:
ACNS-2012 Australasian Cognitive Neuroscience Conference.
doi: 10.3389/conf.fnhum.2012.208.00083
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Received:
12 Oct 2012;
Published Online:
07 Nov 2012.
*
Correspondence:
Miss. Alexandra L Shilton, La Trobe University Melbourne, Melbourne, Australia, alshilton@students.latrobe.edu.au