Double-judgment psychophysics: problems and solutions.

Many paradigms for comparing identification thresholds with detection thresholds require the observer to make double judgments. We show that these paradigms can produce misleading results because of response biases and attentional shifts. For example, the subject's response bias plus correlated noise can mimic inhibition between channels. Some of these same problems can affect single-judgment paradigms. A detailed analysis of the double-judgment forced-choice paradigm reveals that there are a multiplicity of optimal strategies, some of which enhance identification over detection. Several improved analysis techniques for minimizing the effects of cognitive factors are proposed for both the double-judgment forced-choice paradigm and the double-judgment rating-scale paradigm. A classification scheme for distinguishing different types of interactions and correlations is developed. When the new rating-scale algorithm is applied to the detection of well-separated spatial frequencies, substantial masking but negligible inhibition is found. The rating-scale paradigm is shown to be useful in revealing not only the sensitivity and the interactions of the underlying mechanisms but also the observer's information-processing strategies.