Observers detecting a signal in two multiple observation tasks

Signal detection theory (SDT) is tested against a high threshold and a low threshold theory for two kinds of unusual tasks. In the first, the detection of the signal uses the central level of information processing; in the second, the lack of information originates in the stimulus itself rather than in the sensory organs' limitations. The observation is repeated a fixed number of times for the two tasks, and the observed integration of successive information is compared with predictions derived from the SDT and from threshold theories. All results strongly support the SDT which can thus be considered as a general model for risky binary decision-making insofar as these experiments are representative. This would be an argument to replace the classical analysis of the performance in terms of time and number of errors by a new analysis in terms of capability and strategy. The data show how the subjects are more selective for detecting the signal when the task is more difficult, and at the beginning and the end of a series of presentations. The organization of the decision-criteria of the rating-procedure varies with the difficulty of the condition, and with the number of observations in order to allow the subject to discriminate between likelihood ratios which become more precise.