Is three greater than five: the relation between physical and semantic size in comparison tasks.

Abstract

In this study, subjects were asked to judge which of two digits (e.g., 3 5) was larger either in physical or in numerical size. Reaction times were facilitated when the irrelevant dimension was congruent with the relevant dimension and were inhibited when the two were incongruent (size congruity effect). Although judgments based on physical size were faster, their speed was affected by the numerical distance between the members of the digit pair, indicating that numerical distance is automatically computed even when it is irrelevant to the comparative judgment being required by the task. This finding argues for parallel processing of physical and semantic information in this task. When two multidimensional stimuli are compared along one dimension, irrelevant aspects of the stimuli may intrude and influence the decision. This suggests an inability to ignore or filter information even when it is irrelevant. It is important to know how the filtering of an irrelevant dimension depends upon the similarity of its processing to that required for the relevant dimen­ sion. Some dimensions are physical (e.g., size, color); others are based on stored semantic information (e.g., numerical value). Mental comparisons often involve both physical and semantic dimensions. Manipulation of both physical and semantic dimensions as relevant or irrelevant to the comparison should help define how they interact. Furthermore, when a dimension such as size or value is being processed, the information extracted can be crude (e.g., large or small) or fine­ grained. We wish to find out how detailed the processing of the irrelevant dimension is. In order to study these questions, we manipulated both the numerical and physical size of digits in comparative judgment tasks. The stimuli in our study were pairs of Arabic numerals. We manipulated the physical size (i.e., height) and the semantic magnitude (i.e., numerical value) of the stimuli. Each pair of digits could be characterized as congruent, incongruent, or neutral. In a congruent pair, the physically larger digit was also numerically larger (e.g., 53). In an incongruent pair, the physically larger digit was numerically smaller (e.g., 5 3). Neutral stimuli were those in which the two digits were the same on the irrelevant dimension (e.g., the pair 53 can be