Visibilia and Perceptibilia

Perhaps the best way to introduce visibilia is through a novel but commonplace example. When we view someone in profile, we see a person who appears to have only one eye. If we were to produce an observational drawing of what we see, it would be inaccurate to render them with two eyes where only one is visible. So perhaps in this sense we might be forgiven if, on consideration, we became a little confused about how best to describe what we actually perceive.

Essentially visibilia are appearances in which things of one kind look-like things of another kind. A question that plagues contemporary philosophy of perception and perceptual psychology is whether there might be any truth to the claim that we actually perceive visibilia, whether they have any causal influence on us or whether, on the contrary, they are non existent figments. Several other questions arise. If visibilia are non-existent, then how did we ever come to conceive of them in the first place or to mistake whatever it is that we do perceive for them? And don’t photographs categorically prove the existence of visibilia? Aren’t visibilia out there in the world in a measurable quantifiable sense and if so then surely we perceive them? Surely visibilia have influence upon us?

Michael Martin (2010) argues that mirror images, rainbows, holograms and even the sky should be included in the class of visibilia. We might even say these things are more visibilia than perceptibilia – the contrast will turn out to be informative.

Many keyboards have been tapped into oblivion over the questions of visibilia yet there seems to be no easy resolution to the problem. However, perhaps rather than focusing on examples like mirrors and rainbows etc. it might be more revealing to dwell a little on the more absurd example I gave at the outset. If it is true that we do indeed perceive a one-eyed person when viewed in profile, then this sight should surely be a little surprising. If we could conduct a brain scan of someone as they watch another person rotating, there should be peaks of arousal when the observer sees only one eye and perhaps yet more arousal when they see no eyes at all—as the figure turns to face away from the viewer.

I would be willing to wager a considerable sum that there wouldn’t be any appreciable arousal at all. In fact I suspect that the level of arousal might actually diminish as any face is turned away from us.

I’m not at all convinced that we perceive visibilia, and the reason I’m not convinced is because perception is in no way an impoverished snapshot of the world. Perception, at every moment, is interlaced with knowledge about the things that we see. We have a confidence bordering on certainty that the person moving before us is a three dimensional being. And in the instant that we see them we are host to a profusion of latent expectations about what we would be likely to see as they move around etc. These expectations do not suddenly come into being in the moment of encounter. They are merely part of our repertoire of possible responses to the world: our knowledge. As someone spins around before us the perceptible properties constantly update and confirm what we already know and, whenever they do not confirm what we know, it is then that we should expect to register some form of surprise because we now see something unexpected.