Determination of the chromatic contrast responses using wavelet analysis of visual evoked potentials

In order to test the human color vision objectively, we have developed the technique using the sweep parameter VEP technique (Norcia and Tyler, 1985) with an iso-luminant chromatic grating is effective to detect the defective color vision (Momose and Saito, EMBC2002). In this study, the wavelet transform using complex Morlet wavelet was examined to detect the dynamical spectrum of VEP in color vision defectives. Vertical sinusoidal iso-luminant chromatic gratings (6 Hz, 2 c/deg) presented on a color monitor were used as stimuli. The two colors for the gratings were selected from the colors on the dichromatic iso-chromatic lines. Steady-state VEPs were recorded during a continuous decrease of chromatic contrast at 10%/s. VEP components at 12 Hz and 16 Hz were evaluated as the response signal and background EEG (noise), respectively. For deuteranopic iso-chromatic colors, the signal to noise ratio (SNR) of deuteranope and deteranomalia were significantly lower than those of normals (P<0.01), indicating that this technique is effective for objectively detecting of the color vision defectives.