Influence of target size and eccentricity on binocular summation of reaction time in kinetic perimetry

To assess how target size and eccentricity affect binocular summation (BS) of reaction time (RT) at suprathreshold level, we measured RT using targets of 0.108° and 0.216° at four eccentricities (0°, 5°, 15°, 25°) in six normal volunteers. The difference between the monocular/binocular RT differentials for both sizes significantly increased in the periphery (P < 0.05). The smaller target required significantly longer monocular RT at 25° (P < 0.01) and generated greater neural summation than the larger target (P < 0.01). This suggests that when monocular function has reached its limit in visual processing in the periphery, BS increases, facilitates visual processing, and shortens binocular RT.

Research highlights
► Binocular RTs were significantly shorter than monocular RTs for both target sizes.
► The smaller target showed larger monocular/binocular RT differential in the periphery.
► The smaller target generated greater neural summation than the larger target.
► Only the monocular RT was significantly prolonged at 25° with the smaller target.
► Monocular/binocular RTs for the larger target did not increase with eccentricity.