Effects of semantic and temporal grouping on serial order processing

Introduction: Temporal grouping is a benchmark effect for our understanding of serial order processing in verbal short-term memory (VSTM). However, whether other types of grouping effect also impact serial order processing in VSTM is largely unknown. In this study, we compared temporal and semantic grouping effects in immediate serial recall (ISR) and reconstruction tasks to assess whether semantic knowledge can also interacts with serial order processing. Method: Through 4 experiments, participants performed a VSTM task in which they were invited to listen and recall in the correct serial order lists composed of 6 words. Verbal lists of unrelated words were directly compared with lists that were semantically related by triplets of 3 (e.g. three, leaf, branch, cloud, sky, rain) or were interleaved (e.g. three, cloud, leaf, sky, branch, rain). These semantic conditions were manipulated along with two different temporal grouping effects, with verbal lists being temporally grouped with 2 groups of 3 words, or 3 groups of 2 words. In a 5th experiment, we used a visually presented order reconstruction task to further investigate the effect of interleaved semantically related lists. Results: We observed that both temporal and semantic grouping effects independently increased within-group transpositions and decreased inter-group transpositions in the grouped conditions. Interleaved semantically related lists however, did increased within-category transpositions (e.g. recalling leaf, cloud, tree, sky instead of three, cloud, leaf, sky) only in the order reconstruction task. Conclusion: These results provide evidence that semantic knowledge can also influence the pattern of transposition in serial order processing of VSTM. In addition, we show that this result can be attributed to the influence of top-down, controlled attention.