Figure 11.

Foveal bias can mask inhibition of return (IOR) when the effect of eccentricity is neglected. IOR manifests as diminished odds of fixating a previously visited face relative to unfixated faces at the same eccentricity. Markers show a comparison of the previous fixation effect as estimated by two models; the first (model A, shown on the y-axis), includes only the intercepts for previous fixation, target and face regressors, and the second (model B, shown on the x-axis) includes, in addition, the main effect of foveal eccentricity as a 3^rd order polynomial. To ensure that effects in both models are related to transitions between faces rather than refixations to the most recent target, fixations following saccades of less than 3 deg. amplitude were excluded from model fitting. Model A’s failure to correct for foveal bias results in a positive displacement in the previous fixation effect, a consequence of the fact that previously fixated faces tend on average to be closer to the current point of fixation. This displacement decreases as the number of fixations per trial increases due to convergence towards ergodicity. With three fixations per trial, the minimum required to observe any return fixations, model B still reveals IOR, while model A shows an effect with reversed (positive) sign, an example of Simpson’s paradox.