1. ¹Department of Psychology, University College London, London, UK
2. ²Institute of Neurology, University College London, London, UK

Correspondence: Professor DR Shanks, Department of Psychology, University College London, Gower Street, London WC1E 6BY, UK. Tel: +44 20 7679 7588; Fax: +44 20 7436 4276; E-mail: d.shanks@ucl.ac.uk

Received 6 May 2005; Revised 1 August 2005; Accepted 8 September 2005; Published online 12 October 2005.

Abstract

We examined learning and expression of contextual implicit learning of a sequence of targets in a speeded target-detection task in amnesic and control participants. Amnesia was of organic origin in one participant group and induced psychopharmacologically (diazepam 7.5 or 15 mg) in another. Although the amnesic groups were able to learn the target sequence normally, their expression of sequence knowledge (priming) was attenuated when contextual support was limited. This was evaluated by studying response latencies for targets primed by between 0 and 5 preceding context locations. Whereas control participants showed priming when the current target location was primed by only two previous locations, priming was eliminated with two (but not four) previous locations by a low dose of diazepam and was eliminated even with four elements of context under a high dose of diazepam and in amnesia of organic origin. The results suggest that a function of the hippocampal memory system is to support contextual learning and performance, even when that learning is nondeclarative.