Properties of receptive field on binocular fusion stimulation in the central visual field

Visual information projected onto corresponding points on the right and left retinas converges on the binocular cells in the visual cortex. The aim of this study is to investigative the characteristics of the receptive field for binocular stimulation in the central visual field of normal-sighted human subjects.

We investigated the receptive field for binocular stimulation under fusion conditions by combining the Octopus 201 with the space synoptophore. We measured binocular and monocular sensitivities while the fusion patterns were projected onto the Octopus 201 cupola, using the space synoptophore. We designed a new program to test 37 points in the central 6 degrees visual field. Six target sizes were tested: the white-spot targets of 0.054 degrees, 0.108 degrees, 0.216 degrees, 0.431 degrees, 0.862 degrees and 1.724 degrees projected diameters.

The threshold energy necessary for binocular stimulation was lower than that for the monocular stimulation in all subjects. This difference was more obvious on the test points that were more distant from the fovea when target sizes of 0.054 degrees and 0.108 degrees were used. The amount of binocular summation ratio was highest for target size 0.054 degrees in each stimulus area in the central 6 degrees of the visual field. When we measured binocular summation using target sizes larger than 0.108 degrees, the result was the constant summation.

The size of the receptive field for binocular stimulation is smaller than monocular stimulation under the same fusion condition. The amount of binocular summation varies as a function of target size.