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Sheila Crewther, Robin Laycock, Paul Fitzgerald, David Crewther; TMS stimulation of V5 interferes with single word reading. Journal of Vision 2007;7(9):515. doi: 10.1167/7.9.515.
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© ARVO (1962-2015); The Authors (2016-present)
Word reading is a skill commonly associated with parvocellular and ventral pathway processing rather than magnocellular dorsal stream processing. However there is considerable evidence for a magnocellular/dorsal impairment in developmental dyslexia. Such controversial views can be viewed in terms of the hypothesis of Bullier and colleagues (2001) which suggested that the magnocellular latency advantage underlying the earliest feedforward signals from primary visual cortex V1 into the dorsal stream play a significant role in the initial global analysis of the scene and early activation of transient attention prior to retroactive feedback to (V1) and the ventral stream. Such a dorsal feedback loop could be expected to be important for fast and accurate automated reading so we investigated the necessity of of V1 and dorsal area V5 in word recognition using transcranial magnetic stimulation (TMS).
Eleven healthy young adults viewed brief presentations of single words followed by a mask of white noise, with stimuli duration adjusted such that word detection was at least 80% correct (mean duration = 56ms), in a three-alternate-forced-choice paradigm. On each trial a paired-pulse of TMS was delivered to either V1 or V5 at randomly selected onset asynchronies between 0 and 221ms post word onset. Preliminary analyses suggest that TMS stimulation of V1, either early at or before 32ms, or later at approximately 95ms inhibited word recognition. TMS induced disruption over V5 showed greater variability between participants, with accuracy primarily disrupted with stimulation between 60ms and 160ms. These findings suggest that the dorsal stream plays a functional role in single word reading.
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