Search Time with a Color Display: Analysis of Distribution Funcations

Color displays were used for a search task. The task involved locating a particular three-digit number in a background of other numbers, given the first two digits of the target and its color. The display variables were the number of display items of the same color as the target (TCS); the number of background items not of the target's color (NOB); and the color difference between the target and background items (ΔE). Search times obtained with each of 17 combinations of these conditions were discussed in terms of their cumulative distribution functions (CDFs). The observed CDFs were compared with some theoretical CDFs: normal, linear, and exponential. Search times were normally distributed when targets were immediately obvious to searchers (TCS and NOB small,ΔE large). The exponential CDF was best when the target was less conspicuous (TCS and NOB large, ΔE small) so that searchers had to scan the display to locate the target. The exponential model was improved by addition of a parameter to represent human response time. Furthermore, the parameters of the exponential model were shown to respond in a consistent and theoretically meaningful manner to changes of the display variables.