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J.N. Nam, A.T. Jue, J.M. Gallardo, K. Holopigian, R.E. Carr, W. Seiple; Spatial Frequency Tuning of the Multifocal VEP as a Function of Eccentricity . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5371.
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© ARVO (1962-2015); The Authors (2016-present)
The spatial frequency tuning of the traditional full–field visual evoked potential (VEP) has been examined in many studies. Recently, the use of the multifocal VEP (mfVEP) has become widespread. The most commonly used stimulus configuration consists of a dartboard arrangement of elements and the check size in these elements increases with increasing eccentricity. However, there are differences in the spatial and temporal configurations of the mfVEP stimulus versus the traditional VEP stimulus. Therefore, in this study we examined the spatial frequency tuning characteristic of the mfVEP as a function of eccentricity.
mfVEPs were recorded in response to a pattern of square elements each having the same number and size of checks. Spatial frequency was manipulated by changing check size and/or viewing distance. On separate trials, check size ranged from 404 minarc to 10 minarc. The luminance of the dark checks was 12 cd/m2 and that of the bright checks was 150 cd/m2. Checks were counterphase reversed according to an m–sequence determined by VERIS. mfVEPs were recorded using an active electrode 2.5 cm above the inion, referenced to the inion and grounded to the forehead. The first slice of the second–order response was analyzed.
The data were collapsed into four eccentricity rings: 0 to 3, 3 to 6, 6 to 10, and >10 degrees. Peak–to–peak amplitudes were measured for the positive peak (approximately 100 msec) and for the subsequent negative peak. For the inner ring, the largest amplitudes were found for check sizes of approximately 40 minarc. Amplitude decreased steeply for larger and smaller checks. For the second ring, amplitude was also tuned, but at a larger check size (approximately 50 minarc). The amplitude function was high–pass for the outer two rings, with little amplitude increase above a check size of 100 minarc.
In agreement with previous traditional full–field VEP reports, the check size producing maximum mfVEP responses increased with eccentricity.
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