Octopuses are therfore able to distinguish size irrespective of distance, which implies that they are able to tell the range of things they see. It is not known how they do this. Unlike Sepia and the other decapods studied, octopuses use only one eye at a time to direct attacks, and there can be no question of binocular assessment of distance. It is possible that the raising and lowering of the head by attentive octopuses is a means of ranging by parallax, and it is also possible that the widening of the pupil associated with movement of objects near the octopus reduces the depth of focus to permit more accurate ranging.

why do people do this.

close one eye! look around! amazingly, you’re not transported into the painted world! what could cause this. are you a wizard? who knows. it’s a god damned mystery.

i could kind of understand if they at least mentioned monocular cues, something like “this may imply that octopuses have convergently evolved monocular depth perception, similar to many vertebrates” but it’s like not even a mentioned possibility? why does this keep happening.