A novel swept-parameter transient visual evoked potential technique

Abstract

The visual evoked potential (VEP) is a noninvasive electrophysiological measure of the visual system's response to deliberate visual stimulation. Conventional methods of recording transient evoked responses are impractical for use with infant populations due to the repetitiveness of the procedure. The purpose of this study was to demonstrate the effectiveness and clinical usefulness of a novel swept-parameter transient VEP technique in characterizing a range of visual functions for assessment in early infancy in a fraction of the time necessitated by conventional techniques. The swept-transient stimulus was presented ten times and consisted of five different checkerboard patterns contrast-reversed by a 1 Hz square-wave temporal signal. Each pattern was presented at 100% contrast for two seconds in descending octave steps of spatial element size. For comparison purposes, conventional transient VEPs were obtained using 1-minute runs under identical spatial conditions as the swept-transient technique. Transient VEPs were extracted from the EEG by averaging responses from independent bins and were further processed using a discrete Fourier transform technique that removed all odd harmonic frequencies as well as frequencies above 50 Hz. In addition to the swept-transient technique, a recently developed steady-state VEP technique for deriving estimates of visual acuity was utilized to replicate earlier findings and to validate the usefulness of the statistical interpolation procedure used in calculating the estimates. Three participant age groups consisted of 27 four-month-old infants, 29 adults, and 10 children. Response measures included: latencies of peaks in the waveform, peak-to-peak amplitudes, and estimates of visual acuity. The results indicated that the swept-transient technique yielded reliable VEP waveforms in 1/6{dollar}\rm\sp{lcub}th{rcub}{dollar} the time required for conventional methods, with no loss of information. Functional relations between each response measure and spatial condition were nearly identical for the two VEP techniques under all conditions. The proficiency of the swept-transient technique along with its relevance for testing infant populations was demonstrated over conventional methods of recording transient VEPs. Furthermore, the acuity estimates derived through the interpolation procedure effectively replicated results of a previous study, and further demonstrated the precision of this technique with a much larger sample. Developmental implications were discussed for all findings.