Serial position effects and duration of memory for nonspatial stimuli in rats

Recognition memory for lists of nonspatial items was tested in rats using a nonmatching-to-sample task. The recency effect at short retention intervals disappeared as the interval increased, but primacy did not develop although responding was still above chance up to 2 hr after 10-s sample times. Neither proactive nor retroactive interference was apparent. Rats transferred the nonmatching-to-sample rule to completely novel stimuli. The study failed to replicate the prominent U-shaped serial position curve found in a similar study by P. Reed, T. Chih-Ta, J.P. Aggleton, and J.N.P. Rawlins (1991), for which E.A. Gaffan and D. Gaffan (1992) had found the data less variable than expected. Evidence of primacy in this procedure remains insubstantial.