Perceptual and mnemonic matching-to-sample in humans: contributions of thehippocampus, perirhinal and other medial temporal lobe cortices

Two questions were addressed by the present study. The first was whether th e previously reported item recognition deficit which is shown by amnesic pa tients may be due to a perceptual rather than a memory deficit. To address this question a group of amnesic patients were tested on a 14-choice forced -choice visual item recognition test which included a "simultaneous" condit ion in which the sample remained visible during the matching decision and a zero second delay. Eacott, Gaffan and Murray (1994) have reported an impai rment in simultaneous matching-to-sample following perirhinal damage in mon keys. In our amnesic patients, a deficit was found only after filled delays of 10 seconds or longer and this was also the case for a subgroup of patie nts whose damage included the perirhinal cortex. The second question, which arose from the model of Aggleton and Brown (1999), was whether performance on the DMS task would remain intact following selective damage to the hipp ocampus. We tested a patient with bilateral damage to the hippocampus on th e 14-choice DMS task and found that her performance was not significantly i mpaired at delays of up to 30 seconds.