Viewing distance affects reaction time to discriminate letters of a constant, small size

Abstract

Continuous physiological fluctuations in visual accommodation may affect the ability to sustain resolution of small-letter stimuli. To investigate this possibility, the experimenter had subjects view a small letter that was subtly transformed into another letter at a random time during a 12-sec viewing interval. Reaction time (RT) to detect the letter change was measured for stimuli of a constant size and brightness viewed at different distances. RTs were shortest at and around an individually determined optical distance and rose to over 1 sec as the difference between the viewing distance and this point increased, for both far and near optical distances. The data suggest that the ability to sustain an accommodative response during a 12-sec interval varies as a function of the optical distance of the stimuli and that transient accommodative inaccuracies are sufficient to impair letter recognition. © 1986 Psychonomic Society, Inc.