Abstract
The effect of depth on the reaction time of size comparison was experimentally investigated. Subjects made “same” or “different” judgments on the objective size of two luminous rectangles presented in a dark room. The significant finding was that correct reaction times increased linearly with increase in depth between the two rectangles. Possible sources that might yield such a result were theoretically examined. Consequently, the result was explained by means of the time for the operations of accommodation and vergence eye movement necessary for fixating the eyes at the appropriate point in space. The reason was that these operations require more time as the depth between two objects increases. The present result is clearly different from that of the similar experiment carried out in a lighted room by other investigators. The difference seems to stem from the unusual formation of cues to distance in the dark.
