Absolute judgments of size in a restricted visual environment.

Abstract

Sunzmary.-The number of categories of stimulation requisite to maximal information transmission in a size-judgment task was investigated. Absolute judgments were made of the size of visual stimuli in an otherwise stimulus-free visual field. The stimuli ranged from approximately 1 to 160' of visual angle. Three experimental phases of presentation were used: (1) pretest familiarization, no knowledge of resulrs; (2) pretest familiarization, knowledge of results after each presentation; and (3) no pretest familiarization, no knowledge of results. Performance level increased throughout Phases 1 and 2. Knowledge of results in Phase 2 gave noticeable increase in performance. Performance level dropped during the third or retention phase, although not below the highest level achieved in the first phase. The data suggest that 9 categories should be employed for maximal information transmission with no feedback, about 11 with feedback. This study is concerned with the ability of human Ss to make absolute judgments of physical size; the visual angle of a stimulus in an otherwise stimulus-free visual field was Ss only cue. Miller ( 1956) has reported the channel capacity%f h~lmans in an experimental situation to be approximately three bits. Said another way, Miller's proposition is that the span of absolute judgment of unidimensional stimuli is approximately seven categories. Similar figures are reported for all sensory modalities. The vis~ial research reported has been conducted in environments wherein secondary visual cues present may have influenced the judgments. In judgments of pitch and loudness, the aural environment was resuicted to stimilli alone. This study investigated the nanire of visual judgments in a restricted visual environment. METHOD The experiment was conducted in a light-tight room 15.24 X 4.88 m., with a 3.66 m. high ceiling. The walls and ceiling were black flocked to minimize reflected light. The floor was painted flat black. S sat in a black booth, head position fixed by a chin rest and head bar, and viewed the stimulus through a