Final answer:
Fusion is the threshold phenomenon that shows binocular summation when both eyes view the same images, facilitating depth perception and three-dimensional structure from two-dimensional signals.
Step-by-step explanation:
The threshold phenomena that show binocular summation when images are the same is C) Fusion. Binocular summation refers to the improved perception of visual information when both eyes are used together. This process allows for a clearer and more detailed perception than what either eye could achieve on its own. The fusion phenomenon involves combining the slightly different images from each eye into a single coherent image. When the brain fuses these images properly, it can perceive depth and three-dimensional structure from the two-dimensional retinal signals, a process also related to stereopsis. This binocular cue differs from that of stereopsis, which specifically refers to the ability to perceive depth based on the differences, or binocular disparity, between the images seen by the two eyes. Suppression refers to the brain's ability to ignore input from one eye to prevent double vision, rather than combining the inputs from both eyes. Rivalry occurs when different images are presented to each eye, leading to a visual competition between the two images rather than their combination.