David Nichols¹, Kiana Watt¹, Margaret McCray¹; ¹Roanoke College

Interocular suppression can render invisible an image shown to only one eye with the sudden onset or sustained presentation of a stimulus in the other eye. While the effect is strongest for overlapping images, interocular suppression extends to nearby areas. Prior research with distinct adaptation and testing phases found the onset of a contralateral surround resulted in a similar amount of suppression on a nonoverlapping monocular grating regardless of the presence or absence of an ipsilateral surround. With prolonged viewing, fusible surrounds with matching images in the two eyes suppressed less than rivalrous surrounds with nonmatching images, theoretically due to alternations in the strength of the contralateral surround. The current study used continuous perceptual monitoring of a monocular target grating for sixty seconds while the presence or absence of a surround in the ipsilateral and contralateral eye varied independently and randomly every two seconds. Data has been collected from over twenty participants across two experimental setups (mirror stereoscope and shutter glasses), with different presentation parameters (including varying the size of the monocular grating and contrast of the surrounds) to establish the consistency of the observed effects. A monocular target remained visible when there was only an ipsilateral surround, but would occasionally become invisible when there was a contralateral surround present, establishing interocular suppression. Novel findings were that suppression from visibility was substantially more likely when there was only a contralateral surround than when both the contralateral and ipsilateral surrounds were present in a fusible way, even at their time of onset. Furthermore, removing the ipsilateral surround when the contralateral surround was already present resulted in an increased amount of suppression. Therefore, while a contralateral surround is necessary for interocular suppression, its presence alone is not sufficient and its suppressive strength is impacted by the presence of a fusible ipsilateral surround.