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). â€œDynamics of shape recognition through a minimal visuo-tactile sensory substitution interface.â€ Third Int. Conf. On Cognitive and Neural Systems. pp. 26-29.
Lenay C., Cannu S., Villon P. (1997). â€œTechnology and perception : the contribution of sensory substitution systems.â€ In Second International Conference on Cognitive Technology, Aizu, Japan , Los Alamitos: IEEE, pp. 44-53.