Camille Morvan
The visual acuity decreases with the eccentricity, the foveal region has a high resolution and the periphery has a low resolution. This information would be useful for planning saccades that maximize information gain. We designed a task that subjects could perform optimally if they had some knowledge of their own visual acuity. The observer was provided with two locations where the target could appear. S/he was instructed to saccade to either of them or to a point midway between them and to report the identity of the target. The independent variable was the separation between the target possible locations. For the shorter separations, the ideal strategy was to saccade to a point midway between the two positions, for the larger separations, the optimal strategy was to saccade to either the right or left item. We found that observers were largely suboptimal at this task, and their performance did not show any knowledge of their own visual acuity.
We then implemented an easier version of the task where the subjects had to compare the visibility of 2 targets at different
eccentricities and with different contrasts. Relying on one cue alone (brighter is better; closer is better) is not enough to perform the task, instead, the subject needed to combine both cues and estimate which combination was easier to see. We first mapped each subject’s acuity for the target presented at different eccentricities and different contrasts. In a following probability-comparison task, the subject was given 2 familiar targets and asked to choose the one that he could perceived with the higher accuracy. Using a staircase procedure we obtained the probability equivalence points for particular eccentricities between three contrasts. We compared the subjective mappings with the true ones and tested their transitivity. We found that observers have imprecise and even incoherent knowledge of the relative uncertainties of different targets. Those results contrast with several models of visual search and visual exploration and indicate that although knowledge about one’s acuity is available to the visual system, it is not accessible to the observer’s judgment.