Binocular summation in scotopic vision.

Abstract

Investigations of different aspects of visual perception frequently raise the question of whether or not stimuli appear brighter when seen with both eyes than when they are seen with only one eye. Summation, denned as an additive effect occurring within the central nervous system which is mediated by binocular perception and characterized by an increase in the apparent brightness of a given field, is a factor which may influence measurements of visual sensitivity under conditions of dark adaptation. The semi-decussation of the optic tracts, homolateral parts of the retinae being represented on corresponding cortical hemispheres, is a fact which has led to the formation of various theories concerning the interaction of the two retinal fields, which, after neural elaboration, are united to form a single perceptual field.Although the problem of summation has been primary in a number of studies, there has been such variation in the methods of experiment, combined many times with insufficient * This study is condensed from a dissertation prepared under the direction of Dr. H. Helson and accepted by Bryn Mawr College in partial fulfillment of the requirements for the degree of Doctor of Philosophy. Copies of the dissertation are on file at the Bryn Mawr College Library. The writer is indebted to Dr. Helson for generous assistance in the experimental work and constructive criticism in the preparation of the thesis.

Two Eyes Are Better Than One—Binocular Summation of Dark Vision in Healthy Individuals and Patients with Chronic Respiratory Disease

“…Several investigators have found that binocular summation increases when corresponding retinal areas are stimulated as compared with stimulation of non-corresponding areas; this also implies the existence of neural summation. 4,9,35 Furthermore, the existence of neural enhancement is supported by the finding that some visual cortical neurons are binocularly activated, 36,37 which is further evidence that the two eyes are not completely independent receptors. Legge,5,11 who proposed the quadratic summation rule to describe binocular summation for contrast, also found summation in excess of what the probability summation model would predict.…”

“…Studies that did not confirm the existence of binocular summation at absolute threshold had often not observed the importance of certain factors such as the size of the stimuli and that the same corresponding retinal loci should be exposed and ideally at the same time. 3,9 Furthermore, there had been large interindividual differences in several studies and the authors concluded that binocular summation occurred in some subjects but not in others. The heterogeneity of previous studies and their different conclusions raises questions about the phenomenon of binocular summation at absolute threshold, its magnitude, and its dependence on experimental conditions.…”

The psychophysical inquiry into binocular summation

“…But simply providing a clear fixation point is not sufficient. The fixation point and the test target should be on the same horopter in order to insure proper accommodation and to promote proper convergence for the stimulation of corresponding retinal points, a condition apparently necessary for the operation of summation (Shaad, 1935).…”

Binocular summation in the perception of form at brief durations

“…The superiority of binocular viewing in a detection situation seems well established (Collier, 1954;Matin, 1962;Pirenne, 1943;Shaad, 1935;Wolf & Zigler, 1963) although the basis for this superiority is still a matter of controversy. Some view binocular vision as essentially two monocular systems working together.…”