Effect of image contrast and sharpness on visual search for computer icons

The purpose of the study was to determine the effect of image blur and contrast on the speed of visual search for user interface icons and investigate how the effect is reflected in eye movement parameters. The task of the observer was to search for a target icon from among a rectangular array of distracter icons. A staircase algorithm was used to determine the stimulus presentation time, threshold search time, for which the probability of correct responses was 0.79. Simultaneously, eye-movements were recorded with a video eye-tracker with a sampling rate of 250 Hz. Image sharpness was varied by filtering the stimulus images with a Gaussian low-pass filter. The results showed that with increasing contrast or sharpness search time, number of fixations per search, and fixation duration first decreased, and then became constant at medium levels of contrast or sharpness. These effects were somewhat more pronounced for contrast than for sharpness. Saccade amplitudes were not affected by contrast or sharpness. The results suggest that the perception of user interface icons is quite resistant to small or moderate deterioration of image quality. (C) 2003 Elsevier B.V. All rights reserved.