Signal Detection Theory Applied to Size Constancy in Virtual Environments

Abstract

Pictorial depth cues and instructional set are two factors that influence the degree to which size constancy maintains in static two-dimensional perspective displays. Signal detection theory (SDT) allows the determination of whether these factors influence observers' sensitivity to perceived size (d') versus their subjective criteria (bias) for making ”same” or ”different” discriminative responses. Two objects were presented at various perceived distances in static perspective displays that varied in number of available pictorial depth cues. Observers made comparative size judgments regarding the objects' apparent distal size (phenomenal instructions) or objective distal size (objective instructions). Observers showed greater sensitivity to distal size differences when responding to apparent, rather than objective size differences. The presence of more pictorial depth cues produced greater sensitivity than a reduced-cue condition, especially under objective instructions. Overall, results indicate that SDT reveals aspects of size perception in pictorial displays not assessed through more traditional analyses based solely on accuracy.