Evaluating models of verbal serial short-term memory using temporal grouping phenomena

Li Ng

Research output: ThesisDoctoral Thesis

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[Truncated abstract] Various capabilities such as the ability to read or conduct a conversation rely on our ability to maintain and recall information in the correct order. Research spanning more than a century has been devoted to understanding how units of information are retained in order in short-term memory. The nature of the mechanisms that code the positions of items in serial short-term verbal recall can be investigated by examining a set of phenomena that can be termed temporal grouping effects. Inserting extended pauses to break a list of verbal items into sub-lists (e.g. SHD-QNR-BJF, where the dashes represents the pauses) improves the accuracy of serial recall relative to performance observed without this temporal grouping. In addition, two other effects are linked to temporal grouping. One of these effects is a shift in the shape of the serial position function, which changes from a single bowed function to a multiple-bowed function. That is, the serial position curve for ungrouped sequences is typically characterized by better performance for the beginning and ending items compared to the mid-list items. For grouped lists, the multiple-bowed function comprises better recall for the beginning and ending items within each group. Another effect associated with temporal grouping is a change in the patterns of order errors. For ungrouped sequences (e.g. SHDQNRBJF), order errors often involve the swapping of items in neighbouring positions, such as exchanging D for Q or R for B. By contrast, grouped sequences (such as SHD-QNR-BJF) show a reduction in order errors that cross group boundaries such as exchanging items D and Q or R and B; instead, there tend to be an increased incidence of exchanging items that share similar within-group positions such as swapping H and N or Q and B. According to several current models of short-term memory, items are retained by associating them with extra-list information such as contextual information. ... This was done by unconfounding temporal position (time from group onset) and ordinal position (number of items from group onset) for certain key items in sequences comprising two groups of four consonants. The critical manipulation was to vary the SOAs within and across the two groups. Errors that involve items migrating across groups should preserve within-group temporal position according to oscillator models, but should preserve within-group ordinal position according to non-oscillator models. Results from the intergroup errors strongly favored preservation of ordinal rather than temporal position. Finally, the Appendix reports an unpublished experiment that examined patterns of errors in recalling sequences of nine visually presented letters, where the letters were grouped into threes using temporal gaps. A critical manipulation was the insertion of a tobe- ignored item (an asterisk) between the first and second letters of selected groups. Inclusion of this item failed to alter the patterns of errors observed, indicating that the coding of serial position is based on only those events represented for recall. The central conclusion based on all the studies is that serial order for verbal items is retained using contextual positional codes that change with each presentation of a tobe- remembered item, are influenced by large temporal gaps that lead to grouping, but otherwise are not dependent on the timing of events.
Original languageEnglish
QualificationDoctor of Philosophy
Publication statusUnpublished - 2007


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