Neuropsychology · Simplified
What Each Profile Can Decide
The useful question about a case is not what it shows but which claims it is able to speak to at all.
The evidence
Three profiles
All three are fictional. Each was tested on the same two things: learning new facts, and learning a new manual skill over several days.
Two claims
For each claim, decide what each profile does to it. There are three answers and the third one matters most.
What this shows
Two impairments together decide nothing
Key idea: A profile speaks to a claim when it shows one thing preserved while another is lost, because that is difficult to reconcile with the two abilities depending on exactly the same resources in exactly the same way. A profile in which everything is impaired is compatible with that account and with several others, so it decides nothing, however severe it is and however carefully it was measured. That is why the third answer is the important one: recognising that a case cannot settle a question is a finding about the evidence, not a failure to reach a conclusion. A single dissociation always leaves the alternative that the lost task was simply harder; a reversal defeats that reply, but it still does not prove two completely separate biological systems, and it does not rule out every possible single-system or overlapping-network account.
Three fictional profiles, described in a sentence each. Real cases are never this clean: impairments are partial, tasks differ in difficulty in ways that are hard to equate, and a person who looks intact on one measure may be impaired on a more sensitive one. Absence of evidence in a single testing session is weak evidence of absence. Nothing here names a syndrome, and no real patient is described.
The longer version adds a third claim, further profiles, and the step from a single dissociation to a double one worked through explicitly. It is at Memory Systems Detective in the main collection.