Fixation stability

Fixation stability was measured at the beginning of each block (as described in the Experimental design section) as the bivariate contour ellipse area (BCEA) (Steinman, 1965) that included 1 standard deviation (68%) of the fixation points after removing saccades and data more than 3.3 standard deviations (0.1%) from the mean of the raw data after removing points that were more than 10° farther from fixation than the scotoma border (presumably a data collection error). Although not ideal (Castet & Crossland, 2012), the BCEA has been previously used to measure the spread of fixation data. To examine the effect of training on fixation stability (BCEA), we used a linear mixed model of the logarithm of BCEA with phase as a fixed effect and subject as a random effect. Post-estimation Wald tests were used for simple linear paired comparisons (i.e., for comparisons not inherent in the linear mixed model). To examine the effect of scotoma size on fixation stability, we used a linear mixed model of the logarithm of BCEA with scotoma size as a fixed effect and block number as a random effect within subject (i.e., allowed each subject to have a different learning–effect slope).