The influence of crowding on eye movements: A preliminary study

Abstract

It is well known that nearby contours impair visual discrimination, a phenomenon, which is defined as crowding. We used letter targets with different surrounding features to investigate the influence of foveal crowding on fixation. Six participants, aged between 20-36 years, monocularly fixated on 6 different high-contrast targets presented at 0.1 logMAR above resolution threshold: a single letter H; a letter H surrounded by 4 flanking bars at either 1 or 2 stroke widths; a letter H surrounded by 4 flanking letters at either 1 or 2 stroke widths; and a line of 7 identical letter Hs. Participants sat 4m from the target display with head movements restrained by a forehead rest and bite-bar. The participants were instructed to keep their gaze directed at the center of the stimulus as stably as possible throughout each 15s trial. Each trial was shown 8 times and stimuli were presented in a random order.The horizontal and vertical position of the viewing eye was recorded using an Eyelink II at a sampling frequency of 250 Hz. The results indicate that fixation stability, expressed as log bivariate contour ellipse area, was generally poorer for the line of letters than when fixating on a single letter target. Fixation stability assessed using differently crowded letter targets appears relatively unaffected by surrounding crowding features except when the fixation letter is located in a line of similar targets. This result is consistent with the notion that observers can sometimes lose their place in a line acuity task.

Meeting abstract presented at VSS 2014