===== In Preparation === Modelling the Relative Recency Discrimination Task: Evaluation of Two Neural Coding Approaches Guido Bugmann(1) and Raju S.Bapi(2) (1)Center for Neural and Adaptive Systems School of Computing, University of Plymouth, Plymouth, PL4 8AA, United Kingdom email: gbugmann@soc.plym.ac.uk (2)Computational Neurobiology Group Kawato Dynamic Brain Project, ERATO, JST 2-2 Hikaridai, Seika, Soraku, Kyoto 619-0288, Japan email: rajubapi@erato.atr.co.jp} Keywords: Serial Order, Short-term memory, Priming, Prefrontal Cortex, Relative Recency Discrimination, Neural Code. Abstract Relative recency discrimination task is typically used to assess the temporal organisation function of the prefrontal cortex (PFC). Subjects look at a series of cards (with words or drawings on them) and on seeing a test card determine which of the two items was seen more recently. Results show that patients with damage to the prefrontal cortex are severely impaired on this task. We propose a memory trace--priming mechanism, based on automatic time-marking process hypothesis (Schacter, 1987), to offer a computational account of the results. We contend that successive words seen by subjects leave decaying memory traces in PFC which subsequently prime the representations in higher sensory areas such as Inferotemporal Cortex (IT) during discrimination judgements. Two possible neural coding approaches (deterministic and probabilistic) are explored for the implmentation of the proposed trace mechanism. A timer circuit with a decay-time constant of approximately one minute successfully replicates human experimental results and prefrontal damage is modelled as disruption (noise) in the memory process.