The Non-Uniformity of the Orientation Space in Ensemble Perception

Ensemble summary statistics if a relatively new field of study. The visual system extracts information of a set of items in a compressed form of summary statistics (mean, variance, range, numerosity). However, the uniformity of the orientation space has not been yet confirmed. Performance in visual discrimination of orientation is superior for stimuli around cardinal axes (0° and 90°) compared to oblique orientations (45°). This effect has previously been shown for individual line orientations. This study aims to identify the influence of the oblique effect and segmentation on ensemble perception of the average orientation of multiple lines. The method of constant stimuli and the two-alternative forced choice (2-AFC) paradigm are used to measure the performance in the task of averaging. The standard deviation of the psychometric functions are analyzed and the oblique and cardinal allocations are compared. Results of the experiment can not be properly interpreted and a conclusion about the uniformity or non-uniformity of the orientation space can not be made because of the limitations of knowledge about the effects and ommisions in the experimental procedure.