Display quality and the speed of visual letter search

Previously it has been suggested that visual search tasks can be used to ev aluate the perceptual quality of display devices with respect to their abil ity to convey alphanumeric information. The purpose of the present study wa s to examine how character size and contrast used in a visual search test a ffects its sensitivity to differences in the quality of display devices. Th e task of the observer was to search for, and identify, an uppercase letter from a rectangular array of characters in which the other items were numer als. Threshold search time, that is, the duration of stimulus presentation required for search that is successful with a given probability, was determ ined by using a multiple-alternative staircase method, Eye movements were r ecorded simultaneously by using a fast video eye tracker. Threshold search times were measured as a function of character size at two contrast levels using a CRT and an LCD display. For all experimental conditions, threshold search time decreased with increasing letter size. This was accompanied wit h a decrease in the number of eye fixations per search as well as a decreas e of fixation duration. At high contrast (C-Michelson approximate to 1), no statistically significant difference was found between the two displays. H owever, at the lower contrast used (C-Michelson approximate to 0.2) and at small character sizes, threshold search times for the CRT display were clea rly longer and the number of fixations per search was higher than for the L CD display. In conclusion, visual letter search is a more sensitive method for display evaluation at small contrasts and with small character sizes. ( C) 2001 Elsevier Science BN. All rights reserved.