Quantification and statistical analysis of the transient visual evoked potential to a contrast-reversing pattern: A frequency-domain approach.

Visual function is often assessed by recording transient visual evoked potentials to contrast reversal of spatial patterns (tVEP-CR). This technique relies on measurements of amplitudes and peak times of a few points in the time-domain waveform, which require subjective selection of appropriate time points in a possibly noisy waveform and ignores much of the informational content in the response. Here, we introduce a set of frequency-domain measures that capture the full content of the response. Magnitude-squared coherence is used to determine the significance and reliability of magnitude measures; estimates of time delay are based on frequency-domain phase measures. In Study 1, extensive testing of a small number of observers revealed response details, and in Study 2, testing of a larger sample verified the novel frequency-domain measures and demonstrated the validity of a short-duration technique to produce reliable tVEP-CRs. In addition, Study 2 revealed adaptation effects present under prolonged stimulation conditions. Principal component analyses provided evidence for six distinct frequency mechanisms, and comparisons with time-domain measures indicated that power in high-frequency bands may be used as objective measures of excitatory input to visual cortex. A middle-frequency band captures the major peaks in the tVEP-CR waveform, and its power is highly correlated with the standard peak-to-trough amplitude measure. These novel frequency-domain indices may serve as more precise and powerful tools to assess visual function in healthy and diseased states.