Red-Green Spatial Contrast Sensitivity Function: Comparison Between Steady State Visual Evoked Potential and Psychophysical Measurements

Abstract

 

Purpose:

 

To measure chromatic contrast sensitivity function (CSF) using steady state visual evoked potential (ssVEP) and to compare ssVEP and psychophysical CSF.

 

Methods:

 

Five normal trichromats (26.6 ± 1.7 years old) were monocularly tested. A red-green horizontal isoluminant grating (CIE 1976: u’= 0.288, v’= 0.480 and u’= 0.15, v’= 0.480) was presented at 5 Hz as a 5º diameter circle against a background of mean luminance (34.3 cd/m²) and mean chromaticity of the grating. Four spatial frequencies (0.4 - 2 cpd), were used. Heterochromatic Flicker Photometry protocol at 20 Hz was used to obtain the isoluminance. Psychophysical thresholds were measured with method of adjustments using the same spatio-temporal configuration as used in ssVEP as well as static presentation. ssVEP data were analyzed with a Fast Fourier Transform protocol. Second harmonic amplitude was plotted against the log pooled cone contrast and the data were fitted with a regression line. Contrast sensitivity was expressed as the reciprocal of the contrast value corresponding to the extrapolation of the fitted line to zero amplitude.

 

Results:

 

All CSFs were low-pass functions. The mean CSFs are shown in Table 1. The results of the dynamic psychophysical CSF agree with the electrophysiological CSF, while the static psychophysical CSF differed at all spatial frequencies (ANOVA p<0.05).

 

Conclusions:

 

The red-green CSF obtained using ssVEP was better correlated with the dynamic than with the static psychophysical CSF. Static thresholds were elevated in comparison to both dynamic CSFs. The results suggest that the second harmonic for the reversal pattern mode may reflect P pathway activity.  

 

Keywords: color vision • contrast sensitivity • pattern vision