SEEING WHAT YOU DON'T SEE?

Following certain kinds of brain lesions, patients report an inability to see objects, but if pressed to guess at their location they display a capacity to point at them with reasonable accuracy. The phenomenon, called "blindsight", is one of the more dramatic of a number of lines of evidence suggesting that being aware of doing something is distinguishable from doing something, that areas of the brain underlying the experience of doing at least some things are distinct from those needed to actually do those things.

Such a dissociation has a number of interesting implications. In a general sense, it provides evidence for the existence and significance of an "unconscious" as a contributor to human behavior (and hence for consciousness as distinctive part rather than synomous with the totality of brain function). Blindsight also provides a possible explanation for some experiences of "magical" or "transcendent" abilities, at least insofar as these relate to performance characteristics of individuals for which the individuals themselves cannot account. A dissociation between unconscious and conscious processing is also of significance in an educational context, since the two sorts of processing may acquire, process, and make use of experiences in different ways.

Blindsight - the ability to respond appropriately to visual inputs while lacking the feeling of having seen them - might be something which only occurs in cases of brain damage, but seems much more likely to be a significant phenomenon of intact brain function as well. Indeed, it seems likely that blindsight (and similar phenomena in other spheres) is an important ingredient of of a variety of activities where one wants to move quickly and appropriately, without "thinking about it".

The display below is designed to allow you to try and experience blindsight yourself, in a simple and controllable situation. First you will need to set some parameters. Stare at the cross in the middle of the screen and click the Try button. A target will briefly appear above and to the left of the cross in the center of the screen. Sliders control the duration of the target, as well as its size and how much lighter or darker the target is in comparison to the grey background. Move the speed slider to find the shortest duration target which you can reliably see on every trial (this will vary somewhat depending on your equipment). Then reduce size and/or contrast to yield a target which you can just detect (this can be done with a number of different combinations).

Click on the Play button to initiate a series of trails during which you should keep your eyes on the cross in the center of the display. Position one hand on your keyboard so as to give easy access to the space bar, and the Z, X, and C or the <, >, and ? keys. You will need to move and click your mouse with your other hand. The target will appear randomly at one of four locations around the cross when you press the spacebar. With as little thought as possible, move your mouse so the location of the target is within the cursor circle (which appears when you hit the spacebar) and click. Then press the Z(<) key if you are sure you saw the target, the X (>) key if you think you saw it but aren't sure, and the C (?) key if you're pretty sure you didn't see the target. Repeat the sequence of space bar, mouse click, and keyboard press at least twenty times, and then click Stop (which was the Play button). The summary window that appears when you click the Stop button shows a plot of the normalized locations of each of your mouse clicks relative to target location for all four target locations. Plotted points within the circle correspond to trials when you successfully put the target within the cursor circle. This would be expected to occur about twenty five percent of the time if you clicked randomly at the four target locations.
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