Foveal xenon flash disruption of steady-state visual evoked potentials

The effects of foveal exposure to near maximum permissible levels of broad-band light from lamps of differing flash durations and visual angle subtense on steady-state visual evoked potentials ( SSVEP 's) were measured in four human volunteers. SSVEP 's in response to a counterphasing checkerboard pattern were recorded with a two-phase vector voltmeter used as an analog fourier analyzer and were averaged across repeated presentation of the flash from each lamp. Two microsecond flashes of approximately 0.4 degrees have minimal, although significant effects on early visual processing of a 2.77 degrees diameter 6/24 (20/80) target. Five hundred microsecond flashes of equivalent size have greater effects; larger flashes (11.3, degrees 500 mus) produced afterimages that totally obscured the target for approximately 3.4 s and also reduced the SSVEP to near zero. Recovery of the SSVEP was subjectively correlated with afterimage duration rather than target obscuration . Therefore, single short small retinal image flashes may have minimal transient effects on photopic suprathreshold vision.