Sight without Light


Originally uploaded by Pete Mandik.

Eric Schwitzgebel’s got a cool question: ” With Your Eyes Closed, Can You See Your Hand in Front of Your Face?

At one point, Eric describes something apparently oft discussed amongst spelunkers:

But on the other hand, most people, deep in a cave where there isn’t a single photon to pierce the darkness, will report being able to see their hands moving in front of their faces. That this isn’t a matter of picking up on visual stimulus is made clearer by our inability in such situations to detect another person’s hand waved before our faces. It seems that our knowledge of the movement of our hand is somehow affecting our visual experience, or at least our judgments about our visual experience, without actually causing any visual input.

Such a phenomenon is a pretty extreme case of what I call “Underdetermined Perception” of the “Active Perception” variety in my paper “Action-Oriented Representation“.

The perception of illusory contours is just one kind of underdetermined perception. The focus of this chapter is another kind of underdetermined perception: what I shall call “active perception”. Active perception occurs in cases in which the percept, while underdetermined by sensation, is determined by a combination of sensation and action.

An …example of …active perception is reported by Lenay et al. (1997) and Hanneton et al. (1999). Subjects use a tactile based device to identify simple 2-dimensional forms such as broken lines and curves. The subjects wear a single tactile stimulator on a fingertip. The stimulator is driven by a magnetic pen used in conjunction with a graphic tablet. A virtual image in black and white pixels is displayed on a screen that only the experimenter is allowed to see. The subject scans the pen across the tablet and thus controls a cursor that moves across the virtual image. A stimulus is delivered to the fingertip only when the cursor is on pixels that make up the figure and not on background pixels. Subjects with control over the pen are able to identify the images. Subjects that merely passively receive the tactile information cannot.

Hanneton S., Gapenne O., Genouel C., Lenay C., Marque C. (1999). “Dynamics of shape recognition through a minimal visuo-tactile sensory substitution interface.” Third Int. Conf. On Cognitive and Neural Systems. pp. 26-29.

Lenay C., Cannu S., Villon P. (1997). “Technology and perception : the contribution of sensory substitution systems.” In Second International Conference on Cognitive Technology, Aizu, Japan , Los Alamitos: IEEE, pp. 44-53.

7 Responses to “Sight without Light”

  1. This sounds like a fascinating research program. As the ex-caver from Eric’s blog I can say this: Between the two kinds of phantom hands–the waving one and the still one–I have usually felt more visceral confidence in the waving one. But there are plenty of visual phantoms of the unmoving kind as well.

  2. Pete Mandik says:

    Thanks for the report, Justin. Would you happen to be aware of a literature on this phenomenon?

  3. Sorry, Pete. I’m not aware of any formal studies. You might get in touch with the National Speleological Society.

    Unfortunately, any data you might find on this phenomenon could well be conflated with data on total darkness hallucinations in general. Give anyone an hour or two in total darkness and she will experience a great many hallucinations, both visual and auditory. Some have suggested to me that young people are less likely to “see” the phantom waving hand than adults. But that’s purely anecdotal.

  4. The moving hand being more vivid than the still hand makes sense, since proprioceptive input — and plausibly efferent output — is livelier when you’re in motion.

    But actually that raises the issue: Is it really knowledge of the output doing the work? Or is it proprioceptive input? Those might be pretty hard to disentangle, unless you have a friend move your hand for you!

  5. Paul Patton says:

    Here is a very interesting paper relevant to the question of active perception:

    R. P. N. Rao (1999) An optimal estimation approach to visual perception and learning. Vision Research 39: 1963-1989

    Rao postulates that visual perception involves an interaction of top-down expectations derived from previous experience and current noisy visual sensory input. After training a Kalman filter computer model with a series of images, he shows that when the model is presented with noisy and incomplete input based on one of the training images it can generate an accurate recreation of the appropriate image. He thinks that feedback projections in the visual system carry top down predictions which influence processing at earlier levels in such a fashion. Rao’s model suggests a way to account for the spelunker’s hallucination, provided that we additionally postulate that non-visual senses might affect visual expectations. If high levels of the visual system ‘expect’ to see a hand based on past experiences in which certain proprioceptive inputs were accompanied by the sight of a moving hand, then perhaps these ‘expectations’ bias earlier stages of the visual system, resulting in an illusory moving hand.

  6. Pete Mandik says:

    Thanks, Paul.

    Kalman filter models would indeed be useful for modelling the spelunker hallucination. Does Rao explicitly mention spelunkers?

    Also, why do you think we need to “additionally postulate that non-visual senses might affect visual expectations”? I’ll grant that is one possibility, but not the only possibility. Another possible thing that could affect visual expectations is efference copies of motor command signals.

  7. Paul Patton says:

    Rao has several papers on generative models of perception, but I don’t think any of them mention the spelunker hallucination. I agree with you that the illusion might be based on efference copy rather than proprioceptive feedback. Or, as is often the case in the nervous system, it could be based on multiple sources of input (eg. efference copy and proprioception).