This article reports evidence of two kinds of serial position effects in immediate serial recall: One involves interresponse pauses, and the other response durations. In forward and backward recall, responding was faster at initial and final positions than at center positions, exhibiting a bow-shaped function relative to serial position. These data were obtained in a spoken recall study in which ungrouped lists of four to six words and postcuing of recall direction were used. The pause pattern is consistent with several models of serial memory, including a distinctiveness model (Brown, Neath, & Chater, 2002) and a version of the ACT-R model augmented with a spontaneous grouping strategy (Maybery, Parmentier, & Jones, 2002). The duration pattern suggests that response articulation depends on the processing context, rather than being modular.
Response time (RT) measures have recently gained popularity in serial recall research because they are thought to reveal aspects of retrieval not detected by accuracy measures. One goal of this study was to examine patterns of interresponse pauses as a function of serial position in spoken recall, both forward and backward, and in doing so, to illuminate differences in RT patterns between a previous study from our lab (Thomas, Milner, & Haberlandt, 2003) and a study conducted by Maybery, Parmentier, and Jones (2002). The other goal was to determine whether spoken word durations are influenced by the output context in which the words are articulated.
In the Maybery et al. (2002) and the Thomas et al. (2003) studies, ungrouped lists of up to six items were used, with typed recall as a response mode. Maybery and colleagues used standard forward recall, with consonants as stimuli. We used forward and backward recall, with words as stimuli. In forward recall, both sets of studies showed an RT peak at output position 1, consistent with the idea that subjects prepare the entire list for output before emitting the first item (Sternberg, Monsell, Knoll, & Wright, 1978). The RT patterns for positions 2-N differed across the two studies. We reported flat RTs for these positions, whereas Maybery et al. found a bow-shaped function.
RTs in our previous study (Thomas et al., 2003) were longer in backward recall than in forward recall. They exhibited a bow-shaped function with a slowdown from initial toward center positions, followed by a continuous speedup. We attributed this pattern to a scan-and-drop strategy (Conrad, 1965). Using this strategy, subjects first emit the most recent item and then repeatedly scan to the beginning of the list, advance to the target item, and emit and drop the target item.
In the present study, we used spoken recall, rather than typed recall, and we recorded interresponse pauses and word durations separately. Because speaking is faster than typing, it is considered a more sensitive measure of the temporal dynamics of recall. The dependent variable in our previous study was the aggregate RT for each item. It was not possible to distinguish between the interresponse pause and the duration of typing a word. Thus, the aggregate measure masked the pause between responses, the interval of theoretical interest. Nevertheless, by adding pauses and durations in the present study, we can compare spoken recall times with the typed recall times in our previous study (Thomas et al., 2003).
Examining the pause function in serial recall is important because it advances our knowledge of the processes that occur during the silent interval between responses. The pause is thought to be the locus of retrieval operations in serial recall, including memory search (Cowan, 1992) and lexical access (Hulme, Newton, Cowan, Stuart, & Brown, 1999).
A flat RT function relative to position is predicted by models that assume a serial search involving an equal load per item, including the ACT-R model (Anderson, Bothell, Lebiere, & Matessa, 1998). …