REMERGE: A new approach to the neural basis of generalization and memory-based inference

1. REMERGE: A new approach to the neural basis of generalization andmemory-based inference DharshanKumaran, UCL Jay McClelland, Stanford University

2. Medial Temporal Lobe Proposed Architecture for the Organization of Semantic MemoryMcClelland, McNaughton & O’Reilly, 1995 name action motion Temporal pole color valance form

3. Two Questions • If extraction of generalizations depends on gradual learning, how do we form generalizations and inferences shortly after initial learning? • Why do some studies find evidence consistent with the view that an intact MTL facilitates certain types of generalization in memory?

4. Relational Theory of Memory (Eichenbaum & Cohen) • Proposes that elements of related memories become linked within the same memory trace, and that the formation of such linkages is a critical function of the MTL.

5. REMERGE: Recurrence and Episodic Memory Results in Generalization • Holds that several MTL based item representations may work together through recurrent activation • Draws on classic exemplar models (Medin & Shaffer, 1978; Nosofsky, 1984) • Extends these models by allowing similarity between stored items to influence performance, independent of direct activation by the probe (McClelland, 1981) • Demonstrates the strong dependence of some forms of generalization and inference on the strength of learning for trained items

6. Phenomena Considered • Benchmark Simulations • Categorization • Recognition memory • Acquired Equivalence • Associative Chaining • In paired associate learning • In hippocampal reactivation during sleep • Transitive Inference • Effects of increasing study • Effects of sleep

7. Acquired Equivalence(Shohamy & Wagner, 2008) • Study: • F1-S1; • F3-S3; • F2-S1; • F2-S2; • F4-S3; • F4-S4 • Test: • Premise: F1: S1 or S3? • Inference: F1: S2 or S4?

8. Acquired Equivalence(Shohamy & Wagner, 2008) • Study: • F1-S1; • F3-S3; • F2-S1; • F2-S2; • F4-S3; • F4-S4 • Test: • Premise: F1: S1 or S3? • Inference: F1: S2 or S4? F1 S1 F2 S2 F3 S3 F4 S4

9. Acquired Equivalence(Shohamy & Wagner, 2008) S1 S2 S3 S4 • Study: • F1-S1; • F3-S3; • F2-S1; • F2-S2; • F4-S3; • F4-S4 • Test: • Premise: F1: S1 or S3? • Inference: F1: S2 or S4? F1 S1 F2 S2 F3 S3 F4 S4

10. Acquired Equivalence(Shohamy & Wagner, 2008) S1 S2 S3 S4 • Study: • F1-S1; • F3-S3; • F2-S1; • F2-S2; • F4-S3; • F4-S4 • Test: • Premise: F1: S1 or S3? • Inference: F1: S2 or S4? F1 S1 F2 S2 F3 S3 F4 S4

11. Acquired Equivalence(Shohamy & Wagner, 2008) • Study: • F1-S1; • F3-S3; • F2-S1; • F2-S2; • F4-S3; • F4-S4 • Test: • Premise: F1: S1 or S3? • Inference: F1: S2 or S4?

12. Associative Chaining • Study: • AB, XY • BC, YZ • Test: • A: B or Y • A: C or Z A B C X Y Z

13. Hippocampal Reactivation After Maze Exploration Replays in Remerge: Forward: 51% Backward: 31% Crossed: 18% Disjoint: <1%

14. Growth in Generalization with Increasing Premise Strength

15. Discussion • As we’ve known for quite some time • Generalization and Inference can be supported by exemplar models • Should we, then, simply abandon the complementary learning theory, and just make it exemplars all the way down? • I think not – • Cortical learning supports changes in the ‘features’ that serve as the basis for exemplar learning • And clearly, retrograde amnesia studies support = an MTL basis for recent memory= a neocortical basis for remote memory • A future challenge is to develop an fully integrated neuro-computational theory of memory integrating MTL and neocortical influences