Analysis of Time Required for Distinct Imaging Using Improved Type of Tachistoscope

Abstract

The purpose of this study is to clarify the process of distinct imaging by normal eyes. The device used in the experiment was the improved Harvard Type Tachistoscope, re-modelled by the author to enable free setting of distances. Time till distinct imaging was measured at 5m under 350 lux; Landolt targets were exposed in 100 msec steps (by limiting methods) against each other, from 0.1 to 1.0 (decimal notation) subjects comprised 75 students, 17～21 years of age (naked eyes, 5m distance, all subjects 1.0+ in right and left visual acuity test of school). Eyes below 1.0 visual acuity and the eyes showing exceptional (abnormal) times in the distinct image experiment were excluded from analysis. The following results were obtained:

(1) Required time for distinct imaging was 200～300 msec, including all blurred or relatively distinct images.

(2) Distinct vision increases as object size decreases relative to visual targets of Landolt, requiring 1,000～1,500 msec in Landolt 1.0 (visual angle 1.0’). This seems to correspond with times of accommodation and fluctuations of accommodateon in daily life vision.