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Doreen Wagner, Gunter Loffler, Velitchko Manahilov, Gael E. Gordon, Gordon N. Gordon, Peter Storch; Shape discrimination in migraineurs. Journal of Vision 2010;10(7):1373. doi: https://doi.org/10.1167/10.7.1373.
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© ARVO (1962-2015); The Authors (2016-present)
Migraine is a disabling condition for which the underlying neuronal mechanisms remain elusive. Patients with migraine often experience visual hallucinations (aura) and have been shown to exhibit subtle differences in visual processing compared to non-migraineurs interictally. Deficits have been reported under conditions including metacontrast masking and motion perception.
We compared masking effects in migraineurs and headache-free controls using a shape discrimination task, thought to involve processing in extrastriate cortical areas. Observers had to detect subtle deviations in circular contour shapes (radial-frequency patterns [RF]) in the presence of a larger contour mask. Thresholds - defined as the amount of radial amplitude (sharpness of the contours corners) required to discriminate perfect circles from pentagon-like shapes (RF 5) - were determined using a staircase procedure. The mask, a RF 5 pentagon shape with an amplitude 16 times its detection threshold, was presented at 5 stimulus onset asynchronies (SOA): 0ms (simultaneous), 66.7ms, 100ms, 133.3ms and 250ms. Tests (1-deg radius) and mask (1.5-deg radius) were shown for 25ms. The cross-sectional profile of the contours was given by a fourth derivative of a Gaussian with a peak spatial frequency of 8 cpd. Luminance contrast of all stimuli was 0.9. Nine migraineurs with aura, 9 migraineurs without aura and 10 headache-free controls participated.
Confirming typical masking effects, all subjects showed raised thresholds between SOA 66.7-100ms compared to simultaneous presentation of mask and test shape (SOA=0ms).
While migraineurs without aura performed almost as well as the control group, migraineurs with aura had higher thresholds for all backward masking conditions (SOA>0), with peak difference occurring at SOA 66.7ms (p=0.036). This finding could reflect a general difficulty for migraineurs with aura to detect shapes in a distractive environment which might be due to a hyperexcitability in migraineurs with aura.
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