Effects of Uniocular and Binocular Excitation of the Peripheral Retina with Test Fields of Various Shapes on Binocular Summation*

Square test fields subtending a visual angle of 1° on a side were presented at 28 positions in the field of vision on a circle with a radius of 10° around fixation. Visual thresholds for the right eye, the left eye, and for both eyes were determined on two observers. In the lateral periphery the binocular thresholds are lower than the monocular thresholds (binocular summation); near the vertical meridian above and below fixation, however, binocular sensitivity is not greater than monocular sensitivity. When, instead of squares, rectangular test fields of 12°×2° and 14°×4° are presented in horizontal or vertical position, it is found that on the median line no binocular summation occurs when the test fields are presented vertically, but summation prevails when the test fields are presented horizontally. It appears that the amount of overlap of a test field into the lateral periphery and the conveying of impulses from both retinas to the same cerebral hemisphere is important for binocular summation.