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A.C. James, T. Maddess, X.L. Goh, N. Winkles; Spatially Sparse Pattern–Pulse Stimulation Enhances Multifocal Visual Evoked Potential Analysis . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3602.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The pattern–pulse multifocal visual evoked potential (James, 2003 IOVS) is a method for the rapid concurrent testing of multiple visual field locations by presentation of temporally sparse pulses of pattern contrast. Compared to the more commonly used rapid contrast reversal, it maintains the visual system in a high contrast–gain state, producing significantly larger response amplitudes. The lower presentation rates also mean that simultaneous stimulation of neighbouring regions occurs less often, which may enhance response amplitude due to the avoidance of lateral suppression effects. Methods: Stimuli were presented monocularly in 56 regions of a cortically–scaled dartboard of total diameter 48o at 75Hz frame rate, with 4x4 checkerboard patterns pulsed in contrast independently in each region at mean rate 4 or 9 pulses/s. At each mean rate, stimulus variants were used which either allowed or avoided the simultaneous presentation of stimuli in neighbouring regions. Evoked potentials were recorded from 10 subjects, for 6 runs of 55s for each stimulus condition. Elementary response waveforms were estimated for each region by multiple linear regression, with noise quantified by mean square from 400–800ms, beyond the presumed response window. The multiplicative effects of stimulus parameters were estimated by multiple linear regression of decibel signal, noise and SNR power on stimulus and subject factors. Results: The spatially sparse variant which avoids simultaneous stimulation of neighbouring regions gave a significant (p<.05) response signal to noise power increase by a factor of 1.32 (+/–0.1SE), due primarily to increased signal power. The faster mean rate of 9 presentations/s relative to 4 presentations/s gave a signal power decreased by the factor 0.29 (+/–0.02SE) (p<.001), but with variance reduced by the greater number of presentations leading to a change in signal to noise power ratio by a factor of 0.40 (+/–0.07SE) (p<.001). Conclusions: The use of a spatially sparse design of stimulus can increase the efficiency of a multifocal analysis by 32%, equivalent to a decrease in recording time of 25% to achieve a criterion signal to noise ratio. This improvement is on top of the benefit gained by the temporally sparse presentation, which is in line with our previous reports, and further improves the prospects for a practical clinical application of multifocal VEP analysis.
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