Direct estimation considered within a comparative judgment framework.

Two experiments that employed the dimension of line length were conducted to support an interpretation of direct estimation within the framework of comparative judgment. It was reasoned that because memorial and processing demands increased, decreasing amounts of transmitted information should be found in discrimination, categorization, and estimation tasks when considered in that order. The data of the first experiment supported the prediction. However, external anchors provided to reduce demand in estimation had no apparent effect. A second study did indicate a marginal effect of anchors when subjects were instructed to employ them but, more strikingly, demonstrated that the shape of the psychophysical function was sensitive to the differential labels that accompanied the anchors. Labels derived from a Fechnerian assumption about psychophysical relations produced a Fechnerian function, whereas labels derived from the actual ratio of the stimulus line to the largest line produced a function consistent with Stevens's power law. It was concluded that the evidence favored a view of direct estimation consonant with cognitive interpretations rather than with the idea of a universal psychophysical function.