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Vance M. Zemon, Paige M. Weinger, Adeola Harewood, Valerie Nunez, Jean-Phillipe Michel, Sarvin Azizgolshani, Janet Izrailova, George Hu, Pamela Butler, James Gordon; A Short-Duration Visual Evoked Potential (VEP) Test Protocol. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5719.
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To develop a battery of short-duration visual evoked potential (VEP) conditions that yield automated, objective response measures with statistical verification that can characterize several distinct neural mechanisms in the human visual system.
In short-duration runs, each stimulus condition was presented for ~2 s and the EEG was recorded synchronized to the display’s frame rate. Each condition was run 10 times. Stimulus conditions (10-deg field) included a contrast-reversing checkerboard (100% contrast) to elicit a transient VEP (tVEP) to examine multiple frequency mechanisms, a pair of radial patterns (partial-windmill and windmill-dartboard) with elements contrast-reversed at ~4 Hz (32% contrast) to elicit steady-state VEPs (ssVEP) that quantify nonlinear lateral inhibitory interactions, and a dartboard with each element contrast-reversed by a sum of high frequency sinusoids (22.8 & 24.8 Hz, 32% contrast/sinusoid) to yield an intermodulation response at 2 Hz that reflects excitatory nonlinear interactions. In addition, contrast-sweep conditions (bright or dark isolated checks) in which contrast increased in octave steps from 2-64% elicited ssVEPs at 12 Hz to assess ON/OFF pathways. For the checkerboard condition, a comparison single 1-min run was conducted and the EEG was chopped into 10 6-s epochs to perform a similar analysis. Each epoch was Fourier analyzed and multivariate statistical measures were applied to determine the significance of each frequency component. All response measures and statistics were generated automatically upon completion of the test. The sample consisted of 16 adults (10 females, 6 males, 18-49 years old).
Analysis of the tVEP revealed that four lower frequency bands (ranging up to 48 Hz), identified previously, yielded significant responses under both the 2-s and 1-min conditions, with a similar pattern of signal strength. Morphology of the time-domain waveforms was also similar under both conditions. Each type of short-duration ssVEP replicated the phenomena reported previously for the respective 1-min condition.
It is possible to capture and quantify an individual’s VEP response in brief epochs of EEG. Each frequency-domain mechanism can be assessed reliably without extended fixation of the stimulus. This technique might provide sensitive measures of dysfunction in various states of disease or brain injury.
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