Stable individual signatures in object localization

Abstract

Perceptual processes in human observers vary considerably across a number of domains, producing idiosyncratic biases in the appearance of ambiguous figures [1], faces [2], and a number of visual illusions [3-6]. This work has largely emphasized object and pattern recognition, which suggests that these are more likely to produce individual differences. However, the presence of substantial variation in the anatomy and physiology of the visual system [4,7,8] suggests that individual variations may be found in even more basic visual tasks. To support this idea, we demonstrate observer-specific biases in a fundamental visual task - object localization throughout the visual field. We show that localization judgments of briefly presented targets produce idiosyncratic signatures of perceptual distortions in each observer and suggest that even the most basic visual judgments, such as object location, can differ substantially between individuals.

Figure 1. Stimulus arrangement and localization errors

(A) On each trial, subjects were shown a brief (50 ms) noise patch at one of 48 randomly selected locations (the possible locations of the patch center, indicated by ‘x’s, and the markings shown in white were not visible to subjects). Subjects reported the patch location using one of four possible response methods (see Methods and panel C legend). The mean angular difference between the subject’s response and the true center of the noise patch was calculated for each location. (B) Mean response errors at each location for every subject (outward adjustment method, red: clockwise errors, blue: counterclockwise errors) reveal substantial individual variation in response error between subjects. (C) Response errors from a representative subject show a high degree of consistency across the four different response methods, shown in the legend (white dotted circles represent gaze location at time of response). Mean error is plotted as a function of angular location for each method, with positive values corresponding to clockwise errors, and negative values corresponding to counterclockwise errors. (D) To determine the degree of within-observer similarity, we correlated the errors for each response method (see legend in panel C) with the other three response methods within the same observer (solid bars). Between-observer similarity for each method was calculated by averaging all pairwise comparisons between subjects (hatched bars). Horizontal bars represent the upper bound of the central 95% of the permuted null distribution (see Supplemental Information). (E) To determine stability in subjects’ response errors over time, correlations between pairs of sessions within a subject were sorted into three bins based on their temporal separation (in weeks). Open circles represent individual correlations between pairs of sessions, and filled circles represent binned averages. Average correlations were calculated from individual Fisher z values and then transformed to Pearson’s r. Error bars represent bootstrapped 95% confidence intervals.