Visual memory -- does it even exist?

Researchers at Rochester recently reported that short-term memory for sign language words is more limited than for spoken words. In some sense, this is surprising. We've known for a long time now that sign languages recruit the same brain areas as spoken languages, so it stands to reason that many of the properties of sign languages would be similar to those of spoken languages, despite the obvious differences.

On the other hand, short-term visual memory is severely limited. If you give somebody a list of 7 spoken words, they can typically remember all of them. If you show somebody 7 objects, they cannot remember them. The textbooks say that you can only remember about 4 visual objects, but that turns out only to be true for very simple objects. In a series of experiments I ran (some of them online), the average person could remember only about 2 objects.

Even more striking is that visual short-term memory cannot be trained like verbal memory can be. A few people have learned to extend their verbal memory so that they could remember dozens of words at a time. However, nobody has been able to significantly improve their visual short-term memory (see a research report here).

Visual short-term memory is so incredibly limited that some vision scientists have wondered if it, in some sense, really exists. That is, they think that it may just be a biproduct of some other system (like our ability to imagine visual scenes), rather than a memory system in its own right. There is some sense to this. After all, what do you need short-term visual memory for? With verbal memory, it's obvious. You need to be able to remember the first part of a sentence while reading/hearing the rest of it. But why would you need to remember what you see over very short intervals?

Those who do not want to read a plug for my ongoing research should stop reading here.

I've been really fascinated by the limitations of short-term visual memory. I have run several experiments, one of which is still continuing. You can participate in it here.

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