Nonmetric scaling of line lengths using latencies,similarity, and same-different judgments

An experiment investigating the relation between various ways of deriving psychophysical functions for line length is reported. A two-phase computer-controlled experiment in which the stimuli were pairs of lines was performed. In the first phase, the pair was presented for several seconds and the S was required to make a category judgment of the similarity of the lines. In the second phase, the pair was presented for a very brief period of time and the S decided whether the lines were the same or of different lengths. Three sets of data were analyzed: (1) the similarity judgments, (2) the proportion of correct different judgments, and (3) the latency of the correct different judgments. An individual differences analysis indicated that there were individual differences in the similarity and latency data. This analysis was not applicable to the proportion data. Nonmetric scaling revealed that the psychophysical functions based on all three sets of data were essentially identical