COMPARISON OF ROC AND AFC METHODS IN A VISUAL DETECTION TASK

The visual observer performance for detecting low-contrast patterns by employing both the receiver operating characteristic (ROC) and the 9- alternative forced choice (9-AFC) method is investigated. For each obs erver and each experimental technique, the results were reproducible w ith respect to a repeated observation. When the results of different o bservers for each method are compared, a strong variation of values is found. From the ROC data obtained, the expected percentages of correc t detection in a 9-A.FC experiment is calculated and compared with the corresponding values of the actual 9-AFC experiment. For some observe rs, the latter values were significantly higher than the computed ones , whereas for others the results showed good agreement with prediction s from theory.