Effect of Target Size, Luminance, and Color on Monocular Fixation*

A contact-lens technique was used to record eye movements made by two subjects attempting to maintain fixation at the center of concentric round targets of several sizes (1.9′–87.2′ diam) and luminances (2.8, 7.8, and 21.5 mL). Fixation of red, blue, and white 1.9′-diam targets was also examined. Analysis-of-variance designs were employed to remove variability arising from sources other than these stimulus variables. Statistically reliable differences in mean fixation position were found with targets of different size, luminance, and color. The largest difference observed was less than 4′ and under most conditions was less than 2′. The bivariate dispersion of the eye about its mean position varied in a complex manner with the size and luminance of the target object. No statistically reliable effects of stimulus variables were found on drifts. Saccade frequency was considerably reduced with the largest targets. Results are discussed in terms of a “fixed error-signal system” for the control of eye position.