Dunlap, K. (1915). A new measure of visual discrimination. Psychological Review, 22(1), 28-35.
http://dx.doi.org/10.1037/h0073278
Linear method was used to test the visual acuity of four Ss with the help of an instrument called the duoscope. Three factors involved in visual acuity were (i) the physical distribution of the light-flux of the retina, determined by the resolving power of the eye, (ii) the distribution of energy or activity in the physiological image of the retina, determined by the distribution in the physical image and by irradiation and (iii) the difference-sensibility for brightness differences. Results showed that the daylight adaptation gave greater acuity and there was no uniform influence of brightness between the limits of the conditions obtained. Results of the lowest brightness differed from that of higher brightness. The duoscope method was considered to be a useful instrument for practical testing of eyes. (PsycINFO Database Record (c) 2016 APA, all rights reserved)