Search in an unstructured visual field is an independent random process under the conditions described in this paper. The basic data for this report are 3072 search trials for each of four practiced observers. The four targets were circular and intercepted angles of 4.8′, 13′, 24′, and 46′. Four search areas which measured 0.011, 0.084, 0.26, and 0.48 sterad, and four values of background luminance 0.01, 0.1, 1.0, and 12.4 ft-L were employed. Four contrasts were used for each of the 16 target size and background luminance conditions. These contrasts were generally at least twice the 95% threshold contrast.
The data for the four subjects were combined, and since a one-parameter distribution was an adequate description, the mean time to detection has been tabulated for the 64 different experimental conditions to summarize these findings.
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