The Effect of Stimulus Contrast and Spatial Position on Saccadic Eye Movement Parameters.

(1) Background: Saccadic eye movements are rapid eye movements aimed to position the object image on the central retina, ensuring high-resolution data sampling across the visual field. Although saccadic eye movements are studied extensively, different experimental settings applied across different studies have left an open question of whether and how stimulus parameters can affect the saccadic performance. The current study aims to explore the effect of stimulus contrast and spatial position on saccadic eye movement latency, peak velocity and accuracy measurements. (2) Methods: Saccadic eye movement targets of different contrast levels were presented at four different spatial positions. The eye movements were recorded with a Tobii Pro Fusion video-oculograph (250 Hz). (3) Results: The results demonstrate a significant effect of stimulus spatial position on the latency and peak velocity measurements at a medium grey background, 30 cd/m2 (negative and positive stimulus polarity), light grey background, 90 cd/m2 (negative polarity), and black background, 3 cd/m2 (positive polarity). A significant effect of the stimulus spatial position was observed on the accuracy measurements when the saccadic eye movement stimuli were presented on a medium grey background (negative polarity) and on a black background. No significant effect of stimulus contrast was observed on the peak velocity measurements under all conditions. A significant stimulus contrast effect on latency and accuracy was observed only on a light grey background. (4) Conclusions: The best saccadic eye movement performance (lowest latency, highest peak velocity and accuracy measurements) can be observed when the saccades are oriented to the right and left from the central fixation point. Furthermore, when presenting the stimulus on a light grey background, a very low contrast stimuli should be considered carefully.

Modeling D15 test sequences in red-green anomalous trichromacy.

Color arrangement tests such as the D15 test can be used to detect congenital and acquired color vision defects. However, the D15 test cannot be used as the only test to assess color vision because of its relatively low sensitivity in less severe cases of color vision deficiency. In this study, we attempted to determine D15 cap arrangements for red/green anomalous trichromats with varying degrees of severity of color vision deficiency. The color coordinates of D15 test caps corresponding to a particular type and severity of color vision deficiency were determined using the model proposed by Yaguchi et al. [J. Opt. Soc. Am. A35, B278 (2018)JOAOD60740-323210.1364/JOSAA.35.00B278]. The arrangement of the color caps was modeled by assuming that individuals with color vision deficiency would arrange the D15 test caps judging by color differences perceived by them. The proposed simulation correctly predicts the increase in severity of color vision deficiency with spectral reduction between the L- and M-cone photopigments. The type of color vision deficiency is correctly predicted with few exceptions in protanomalous trichromats.