Abstract
We investigated human performance in speed and precision of detecting a deviating visual target embedded in one of two otherwise identical non-figurative Perlin-noise images (i.e. a spot-the-difference task). The image-pairs were presented in four different presentation formats: spatially separated in horizontal or vertical direction while simultaneously presented, or sequentially separated on the same location with a brief delay or without any delay. In the two spatial conditions failure to detect the target within 30 sec (change blindness) occurred in about 6-7% of the trials, and with the brief delay 2.4% of the trials. Fast error-free detection (i.e. pop out) was obtained using the sequential format with no delay. Average detection time when target was detected was about 9 sec for the two spatial formats. Detection time was faster, about 6 sec, for the brief delay condition. In trials where detection was reported, the precision of locating the target was equal in the horizontal and brief delay conditions, and better than in the vertical condition. Misses obtained in the horizontal and brief delay conditions were also more strongly correlated than correlations between misses in the vertical and horizontal, and between the vertical and brief delay conditions. Some individuals' performances when comparing images in the vertical direction were at chance level. This suggests influences of known poorer precision when making saccades in the vertical compared to horizontal direction. The results may have applications for radiologists since the stimuli and task is similar to radiologists' task when detecting deviations between radiological images.