Exploring interactions between long-term and working memory using the Hebbian repetition effect

1. Exploring interactions between long-term and working memory using the Hebbian repetition effect Kathryn L. Gigler & Paul J. Reber, Department of Psychology, Northwestern University, Evanston, IL Introduction Experimental results • However, in Exp 3, the repetition effect is observed only in participants able to recognize the repeated sequence during a post-training recognition task, F(19)=4.86, p <.05 • WM is often referred to as a gateway for LTM, though the systems also interact in the opposite direction • This can be seen in the ability of experts to maintain large quantities of domain-specific information in mind, as LTM supports expanded WM capacity for this information1 • The Hebbrepetition effect can be seen as an in-lab demonstration of this; participants perform better on material that was presented repeatedly than on material that was not in a WM task2 • Whether this effect can be observed when the repeated material is presented in fragments, and whether the effect occurs with or without explicit awareness, remain controversial3 • Can the Hebbrepetition effect be observed in a novel task where the repeated sequence is presented in fragments? • What is the relationship between LTM, awareness, and WM under these conditions? Exp 1: Same starting point for repeated sequence * * • Effect of LTM/awareness: • In Exp 2, no participants were aware of the repeated sequence, as measured on a post-training test of recognition • In Exp 3, a subset of participants identified the repeated sequence, and these participants only demonstrated the repetition effect, F(19)=4.86, p <.05 • Additionally, higher initial WM span seems to lead to greater LTM awareness, as higher-span participants recognized the repeated sequence at post-training, t (10)=2.73, p <.03 • Hebbrepetition effect: • In Exp 1, where the repeated sequence was obvious to participants, the effect can be observed at adaptive sequence lengths in all participants, F(39)=10.61, p<.01 • In Exp 2 and 3, where the repeated sequence was not obvious to participants, the effect is not observed across all participants SeVi task and methods Conclusions • The repetition effect was observed (in some participants) at a presentation rate of 40% repeated/80% random, but not at 20% repeated/80% random • Suggests that sequences must be of a certain length in order to learn statistical regularities between items when sequence is fragmented • As measured by the repetition effect and recognition test, advantage for repeated material occurred only if participants were aware of the repeated sequence • This advantage was enhanced for higher-span participants, indicating a “rich get richer” effect • Sequential visuospatial working memory task (SeVi-WM)4,5 • Presentation Phase (A) • Sequence of cues scroll vertically down to targets at bottom of screen • Response Phase (B) • Participants reproduce the sequence using D/F/J/K keys • Length of presented sequence is adaptive via staircase method • 2 correct or incorrect leads to +1/-1 length for next sequence Higher WM span Hebb repetition effect (supported by LTM) Enhanced WM on task 12-item repeating sequence • Experiment 1 (A): • Presented fragments always start from the same point within the repeated sequence • Two 50-minute training sessions; 20% repeated/80% random (N=40) D J F K J K D F J D K F A 4-item fragment D J F K J K D F J D K F Enhanced task performance D J F K J K D F J D K F 5-item fragment D J F K J K D F J D K F 6-item fragment • Experiments 2 and 3 (B): • Presented fragments start from randomized points within the repeated sequence • Exp 2: Two 50-minute training sessions20% repeated and 80% random (N=26) • Exp 3: Two 50-minute training sessions40% repeated and 60% random (N=21) References B Ericsson, K.A. & Kintsch, W. (1995). Long-term working memory. Psychol Rev, 102(2):211-45. Hebb, D.O. (1961). Distinctive features of learning in the higher animal. In J.F. Delafresnaye (Ed.), Brain mechanisms and learning, 37-46. Oxford: Blackwell. Couture, M. & Tremblay, S. (2006). Exploring the characterisitcs of the visuospatial Hebb repetition effect. Memory & Cognition, 34(8), 1720-9. Sanchez, D.J., Gobel, E.W. & Reber, P.J. (2010). Performing the unexplainable: Implicit task performance reveals individually reliable sequence learning without explicit knowledge. Psych Bull & Review, 17(6), 790-6. Gigler, K.L. & Reber, P.J. Sequence-specific and non-specific gains in working memory. Under revision. Acknowledgements: Funding for this work was provided by the Department of Psychology and the Family Institute of Northwestern University. 4-item fragment D J F K J K D F J D K F D J F K J K D F J D K F 5-item fragment 6-item fragment D J F K J K D F J D K F