Reaction time (RT) for detection of gratings of different spatial frequencies (SF, 0.87-13.87 c/d) and contrast (2-32 times above the detection threshold) was measured. It was found that at low stimulus contrast, 2 and 4 times above the detection threshold, the dependence of mean RT on SF is an "S"-type function with the two plateaus 50-60 ms apart. The standard deviation (SD) increases significantly for SFs within the range 2.60-6.93 c/deg and this coincides with the transition of mean RT from one plateau to another. At higher contrast the dependence of RT on the SF is a monotonically increasing function without any plateau and SD does not demonstrate any extrema within the entire SF-range. The results suggest that RT is determined by two mechanisms (transient and sustained) at low contrast, and by one (transient) mechanism at higher contrasts.

There is evidence in the literature that hypofunction of the thyroid gland (hypothyroidism) affects color vision in rodents by influencing the production of visual pigment opsin. The effect of hypothyroidism on color vision in humans has not been examined in any great detail. In this cross-sectional study we evaluated color discrimination using the Farnsworth-Munsell 100 hue test (FM-100) in 25 individuals with pre-treatment hypothyroidism (mean age 38±9.2 Yrs), and a control euthyroid group, n=26 (mean age 39.6±8.4 Yrs). There were no statistically significant difference in the total error score (TES) between the groups, but the hypothyroid group had a significantly greater partial error scores (PES) along the blue-yellow (B-Y) axis compared to the red-green (R-G) axis. No statistically significant differences in B-Y and R-G PES were observed in the control group. This study shows that hypothyroidism affects color vision in humans, with impairment being more pronounced in the blue-yellow color subsystem.

Contradictory results have been obtained in the studies that compare contour integration abilities in Autism Spectrum Disorders (ASDs) and typically developing individuals. The present study aimed to explore the limiting factors of contour integration ability in ASD and verify the role of the external visual noise by a combination of psychophysical and eye-tracking approaches. To this aim, 24 children and adolescents with ASD and 32 age-matched participants with typical development had to detect the presence of contour embedded among similar Gabor elements in a Yes/No procedure. The results obtained showed that the responses in the group with ASD were not only less accurate but also were significantly slower compared to the control group at all noise levels. The detection performance depended on the group differences in addition to the effect of the intellectual functioning of the participants from both groups. The comparison of the agreement and accuracy of the responses in the double-pass experiment showed that the results of the participants with ASD are more affected by the increase of the external noise. It turned out that the internal noise depends on the level of the added external noise: the difference between the two groups was non-significant at the low external noise and significant at the high external noise. In accordance with the psychophysical results, the eye-tracking data indicated a larger gaze allocation area in the group with autism. These findings may imply higher positional uncertainty in ASD due to the inability to maintain the information of the contour location from previous presentations and interference from noise elements in the contour vicinity. Psychophysical and eye-tracking data suggest lower efficiency in using stimulus information in the ASD group that could be caused by fixation instability and noisy and unstable perceptual template that affects noise filtering.

Our previous study has shown that individuals with untreated hypothyroidism display significantly higher partial error scores ( P E S ) along the blue–yellow axis compared to the red–green axis than normal individuals using the Farnsworth–Munsell 100 hue test [J. Opt. Soc. Am. A 37, A18 (2020)JOAOD60740-323210.1364/JOSAA.382390]. We wished to determine how color discrimination may change when hypothyroidism has been treated to the point of euthyroidism. Color discrimination was reassessed for 17 female individuals who had undergone treatment for hypothyroidism, and the results were compared with 22 female individuals without thyroid dysfunction. No statistically significant difference was found in the total error score ( T E S ) for the first and second measurements for both groups ( p > 0.45 ). The P E S for the hypothyroid group improved significantly in the previously impaired color regions after the treatment. Color discrimination defects found in untreated hypothyroidism can be negated with treatment of the condition over an appropriate time period.