Visual temporal frequency characteristics determined by pseudorandom stimuli.

Abstract

PURPOSE: To investigate whether a rapid and practical determination of the temporal frequency characteristic (TFC) of the visual system can be obtained by using the visually evoked potentials (VEPs) elicited by pseudorandom binary sequence (PRBS) stimulation. METHODS: VEPs were recorded from eight volunteers. For the conventional steady state VEPs (S-VEP), the eye was stimulated with five stimulus frequencies. To acquire the PRBS-VEPs, the eye was stimulated with a PRBS stimulus for 40 seconds. The TFC for the S-VEP was calculated from the root mean squared amplitude for each frequency using Fourier transform. For the PRBS stimulus, a cross-correlation function between PRBS (x[t]) and PRBS-VEP (y[t]) was calculated to obtain the TFC. RESULTS: The TFCs obtained by the PRBS and S-VEP methods were highly correlated (P < 0.05), and the TFC curves resembled those in the literature. Most important, the data necessary to determine the TFCs using the PRBS stimulus could be obtained in 4 minutes, whereas that for the S-VEP required 60 minutes for the two eyes. CONCLUSIONS: The high correlation between the TFCs obtained by the two methods indicated that the PRBS technique gives a good measure of the TFC of the human visual system. The significantly shorter time required for this method demonstrated that it is a practical method for determining the linear (and nonlinear) property of the visual system and that it may be useful in clinical applications.