An item and order processing analysis of word length, generation and perceptual interference effects in human memory

When participants are presented with lists of items for immediate serial recall, tradition would suggest that a race begins - between the need to constantly refresh or recycle the memory trace of that list, and a tendency for the memory trace to decay. Standard models in the literature assumed a complex interaction of mental subsystems whereby a controlling attentional process strove to keep the memory of such a list alive for a sufficiently long period of time so it could be remembered and output in order, using a type of recirculating loop rehearsal and storage mechanism to offset the decay process. Evidence supporting such models stemmed from the observation that more short words could be remembered in order than long words (Baddeley, Thomson, & Buchanan, 1975). This word length effect, described in the second chapter, was a crucial piece of evidence for rehearsal and decay models, in the example given, the recirculating loop was seen as being time-based and extremely limited in capacity, such that memory was deemed equivalent to the amount of information which could be cycled through the rehearsal loop in about two seconds. A number of recent challenges to this model of remembering have cast doubt on the nature of the process as described in such models as that of Baddeley (1990; 1996). Chapter 1 began by providing an overview of the development of such models from their earliest form, and also introduced some alternative ideas about the structure and function of human memory. A processing view was described, in which the probability of recalling a list of items depended not upon a race between decay and rehearsal, but on differential processing of items based on their nature. As remembering a list in its original order involves not only remembering the items themselves, but also information about how they relate together in the list, an alternate theory was advanced that in some cases the processing of information about the items, and information about their serial order could dissociate, producing a processing tradeoff. As individual items were better remembered, information about their presentation order diminished. This observation (Nairne, Riegler, & Serra, 1991) was introduced as the item-order hypothesis. The item-order hypothesis suggested that under certain conditions increased item processing could lead to deficits in order processing, and that this produced a dissociation in performance between item and order memory tasks. The generation effect (Slamecka & Graf, 1978) was one such example, as was the perceptual interference effect (Mulligan, 2000), and these were discussed in Chapter 3. The word length effect was seen as another instance where this tradeoff might be observed. A design incorporating elements of item and order tasks based upon Nairne et al. (1991) was detailed in the fourth chapter, leading on to empirical testing of the word length effect (Chapter 5), the generation effect (Chapter 6) and the perceptual interference effect (Chapter 7). This series of experiments compared word length and generation effects under serial recall and single item recognition tasks, using a range of test conditions designed to allow replication and extension of existing data from these separate streams of research. Results did not appear as predicted for some aspects of generation and all aspects of perceptual interference, and further experiments in Chapter 8 attempted to address the current findings. For the experiments involving word length, short words were better recalled than long words on the serial recall task, but long words were better recognised in the recognition task. Following additional manipulations in Chapter 8, the generation effect began to produce a similar pattern, but the results for perceptual interference were inconclusive. Word length data, however, were consistent with the item-order approach and supported a novel explanation for the word length effect. Implications and conclusions were discussed in Chapter 9.