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 to the left 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.

Now click on the Play button to initiate a series of trails.

The summary window that appears when you click the Stop button shows a plot, for all four target locations, of the locations of each of your mouse clicks relative to a normalized target location, 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. It should be (of course) be well above twenty-five percent on trials where you know you saw the target (green dots in the summary window).

What's interesting is whether your score is substantially above twenty-five percent on trials where you're less certain whether you saw the target (blue dots) and trials where you're certain you didn't (red dots). Values in the vicinity of fifty percent and above for the last case are pretty good evidence of blindsight.

Try the game, see how you do, and let us know. Our own experience is that some people do better than others, and that people who do less well frequently get better after playing the game for a while. The tough part seems to be getting oneself to stop worrying about whether you actually saw the target and just click. Which, of course, raises some interesting questions about the relation between conscious and unconscious processing.


Blindsight by L. Weiskrantz (Oxford, 1986) is a valuable monograph by one of the pioneer investigators of the phenomenon. "Varieties of vision: from blind responses to conscious recognition" (P. Stoerig, Trends in Neuroscience 19: 401-406, 1996) provides a more recent discussion of blindsight as one of several demonstrable dissociations in human visual processing.

The general "problem" of consciousness, what it is and what it is (and is not) useful for, is increasingly being treated as a serious scientific issue. The Brain Project provides extensive background and a good entry point into current activity in this area.

Continuing conversation
(to contribute your own observations/thoughts , write Serendip)


10/09/2005, from a Reader on the Web

I was playing the blindsight game, and indeed getting significantly more than 25% of the spots that I didn't see. But I would say i was mostly guessing by which area I didn't feel I had been looking at as closely enough to have seen the dot. Not saying that it doesn't work by blindsight, just that there may be another way to beat the expectation without cheating (pay attention to say only two segments, and if you don't see it then choose randomly from the other two)


11/15/2005, from a Reader on the Web

I scored 57% when I thought I saw it, and 0% when I wasa sure I didn't it. There were some other things going on as well, e.g. some times the dot would wizz around, not just appear in one place. Must have been "eyes playing tricks", but after thinking about this, I wonder if that saying holds true anymore :)


01/10/2006, from a Reader on the Web

Hello, I found your blindsight applet interesting. I have been looking into blindsight as I became interested after playing with some poker cards recently. Specifically, I found that I could "guess" what card I had seen 20-35 times in each 52 card deck when they were flashed really quickly from a distance of 4 feet or more. Each time I guessed and was right I was really shocked because the card was not legible to my conscious mind. If I was lucky I could tell the color,, but that was it. It was not luck because I have seen these same results many times now. One time three cards were flashed at me,,,and I got all three right the first time! I am not sure what is going on,, but it is real and quatifiable/repeatable. Best regards, Paul


02/01/2006, from a Reader on the Web

The prompt is so important. I.e., The fact that the subject doesn't know the answer until someone else ASKS him to guess the answer. I wonder if there is a difference between being prompted by a live human being or by a machine. Another common example of blindsight (I wonder) is the experience of racking one's brain all day long for an answer to a simple question, only to have the answer pop into your head the moment you finish dialing a friend's number on the telephone and he hasn't even picked up the phone! P.S. It's good to see you have a discussion board. I have linked to this site for some time from my own site at http://www.clydeburger.com/articles/essay.htm

Exhibit by Paul Grobstein and Bogdan Butoi. Java applet by Bogdan Butoi.


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