Purchase this article with an account.
A. Jue, J.N. Nam, S.C. Barbarino, J.M. Gallardo, K. Holopigian, R.E. Carr, W. Seiple; Contrast Response Functions of the Multifocal VEP as a Function of Eccentricity . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5373.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
The amplitude versus contrast response function of the traditional full–field visual evoked response (VEP) has been previously examined. However, 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. This mfVEP stimulus configuration has many spatial and temporal differences relative to the traditional VEP stimulus. In this study, we examined the contrast response characteristics of the mfVEP as a function of eccentricity.
mfVEPs were recorded in response to a square pattern of elements each having the same number and size of checks. The spatial frequency of the checks was set to produce the maximum mfVEP amplitude for each eccentricity ring. The luminance of the black checks was 12 cd/m2 and that of the white checks was 150 cd/m2. On separate trials, contrast ranged from 85% to 10%. 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. Amplitudes for all rings initially increased with increasing contrast; however at higher contrasts, amplitude saturation was observed. For the inner ring (38 minarc checks), amplitudes saturated at a contrast of approximately 30%. For the second ring (53 minarc checks), amplitudes saturated at approximately 50% contrast. Likewise, for the third and fourth rings (101 minarc checks), saturation was observed above 50% contrast.
The contrast at which mfVEP amplitude saturation occurred increased with increasing eccentricity.
This PDF is available to Subscribers Only