Spatio-chromatic sensitivity explained by post-receptoral contrast.

We measured and modeled visibility thresholds of spatial chromatic sine-wave gratings at isoluminance. In two experiments we manipulated the base color, direction of chromatic modulation, spatial frequency, the number of cycles in the grating, and grating orientation. In Experiment 1 (18 participants) we studied four chromatic modulation directions around three base colors, for spatial frequencies 0.15-5 cycles/deg. Results show that the location, size and orientation of fitted ellipses through the observer-averaged thresholds varied with spatial frequency and base color. As expected, visibility threshold decreased with decreasing spatial frequency, except for the lowest spatial frequency, for which the number of cycles was only three. In Experiment 2 (27 participants) we investigated the effect of the number of cycles at spatial frequencies down to 0.025 cycles/deg. This showed that the threshold elevation at 0.15 cycles/deg in Experiment 1 was at least partly explained by the small number of cycles. We developed two types of chromatic detection models and fitted these to the threshold data. Both models incorporate probability summation across spatially weighted chromatic contrast signals, but differ in the stage at which the contrast signal is calculated. In one, chromatic contrast is determined at the cone receptor level, the dominant procedure in literature. In the other model, it is determined at a postreceptoral level, that is, after cone signals have been transformed into chromatic-opponent channels. We applied Akaike's Information Criterion to compare the performance of the models and calculated their relative probabilities and evidence ratios. We found evidence in favor of the second model and conclude that postreceptoral contrast is the most accurate determinant for chromatic contrast sensitivity.

An exploration of the initial effects of stereoscopic displays on optometric parameters.

PURPOSE: To compare the effect on optometric variables of reading text presented in 2-D and 3-D on two types of stereoscopic display. METHODS: This study measured changes in binocular visual acuity, fixation disparity, aligning prism, heterophoria, horizontal fusional reserves, prism facility and accommodation responses for near of subjects after completing ten consecutive reading tasks of 1 minute each. The tasks consisted of reading words on a polarized two-view (n = 39) and an auto-stereoscopic lenticular nine-view display (n = 19) with the text presented without or with stereoscopic disparity at 3 m. Performance was assessed by measuring reading speed and symptoms were rated by the Convergence Insufficiency Symptom Survey (CISS) questionnaire. RESULTS: With both types of display, CISS scores at least doubled immediately after subjects viewed the 3-D text image in an extreme stereoscopic condition compared to the 2-D condition (p < 0.001), while the mean reading speed slowed (p < 0.001). Mean changes in optometric test variables were not clinically or statistically significant (p values > 0.05). After the 3-D task one participant showed consistent clinically meaningful decreases in convergent fusional break and recovery points for both displays. CONCLUSION: When healthy adult subjects with normal binocular vision viewed text images at 3 m in extreme 3-D display settings for a short period of time there were no clinically significant mean changes in optometric test variables compared with 2-D viewing.