Behavioral assessment of motion parallax and stereopsis as depth cues in rhesus monkeys.

Although human psychophysical results show that motion parallax and stereopsis are both effective depth cues, it is not clear whether the same is true for non-human primates. As an initial step, we assessed the extent to which rhesus monkeys are capable of processing depth information based solely on motion parallax as compared with stereopsis. We constructed a unique display that enabled us to provide depth cues by either stereopsis or motion parallax or both. Our results show that monkeys can process depth information conveyed both by motion parallax and stereopsis. As in humans, motion parallax was somewhat less effective for depth discrimination than was stereopsis. These findings prepare efforts for assessing how motion parallax and stereopsis are co-processed in the visual system.