Procedural Memory Preserved in Amnesia

They say you never forget how to ride a bicycle. Certainly motor skills tend to be very durable in normal people, but there is considerable evidence that learned skills are also preserved in organic amnesics.

Not only do amnesics tend to retain their old skills from before onset, they also retain the ability to learn new skills and procedures, even in patients who find most other forms of learning impossible.

Corkin (1968) reported that HM Opens in new window was able to learn a number of new motor skills such as mirror drawing.

Mirror drawing involves drawing a shape on a piece of paper viewed through a mirror, which is a very difficult skill to learn since all the normal visual feedback is reversed.

HM succeeded in learning this new skill to a reasonable level of competence, though significantly he remained unaware that he had learned it, and he did not recognize the apparatus when it was shown to him on a later occasion.

This ability to learn skills and procedures without being aware of having learned them seems to be a common finding in studies of amnesics. For example, Starr and Philips (1970) describe a patient known as PQ, who had been a concert pianist before becoming amnesic as a result of an HSE infection Opens in new window.

PQ not only retained his ability to play the piano, but proved to be quite capable of learning to play new pieces of music, though he remained quite unaware that he was able to play them.

Glisky et al. (1986) reported that amnesics had been successfully trained to carry out simple computer tasks, though the training had required a great deal of time and patience. It was also noted that although these patients had been able to learn the meanings of several computer commands, this learning was only demonstrated while operating the computer and showed no generalization to other contexts.

This suggests that skill learning in amnesics is highly inflexible, possibly because it does not take place at a conscious level. In view of the many studies showing intact skill learning in amnesics, Cohen and Squire (1980) have suggested a distinction between procedural memory Opens in new window, which can be demonstrated by performing some skilled procedure, and declarative memory Opens in new window, which can actually be stated in a deliberate and conscious way.

Cohen and Squire suggest that amnesics have an intact procedural memory, but an impaired declarative memory. This would explain the fact that they can learn new skills and procedures but reveal no conscious awareness of it.

The preservation of procedural memory in amnesics represents an example of learning which remains intact at an unconscious level, and in this respect it resembles implicit memory.