Hebb Repetition Effects in Complex and Simple Span Tasks Are Based on the Same Learning Mechanism

The Hebb repetition effect shows improvement in serial recall of repeated lists compared to random non-repeated lists. Previous research using simple span tasks found that the Hebb repetition effect is limited to constant uninterrupted lists, suggesting chunking as the mechanism of list learning. However, the Hebb repetition effect has been found in complex span tasks, which challenges the chunking explanation, as successive list items are separated by distractor processing, possibly interfering with the unified representations. We tested the possibility that Hebb repetition learning arises from chunking in simple span, but from position-item associations in complex span. In a series of five experiments, we found evidence that contradicts that hypothesis. Results show that (a) Hebb repetition learning in a complex span task can be transferred to a simple span task; (b) Hebb repetition learning from a complex span task cannot be transferred to a partially repeated simple span task; (c) partial repetition in a complex span task does not lead to learning; (d) Hebb repetition learning from a simple span task can be transferred to a complex span task; and (e) repeating the distractors in complex span has no impact on the Hebb repetition effect. These results suggest that the mechanism underlying the Hebb repetition effect in simple and complex span tasks is the same and points at the creation of chunks while excluding the distractors from the long-term memory representation.