Word length and phonological similarity effects in simple, complex, and delayed serial recall tasks: implications for working memory.

Some current models of working memory argue that a passive short-term store is not involved in more dynamic working memory tasks. Other models argue that standard short-term memory and working memory tasks rely on common storage facilities. We examine these issues by exploring two signature effects of passive short-term storage in simple span, complex span, and Brown-Peterson tasks. The finding that all three tasks show word length and phonological similarity effects suggests that common processes or storage mechanisms are involved in all tasks. The implications for models of working memory are discussed.

Individual differences in memory span: the contribution of rehearsal, access to lexical memory, and output speed.

Rehearsal speed has traditionally been seen to be the prime determinant of individual differences in memory span. Recent studies, in the main using young children as the subject population, have suggested other contributors to span performance, notably contributions from long-term memory and forgetting and retrieval processes occurring during recall. In the current research we explore individual differences in span with respect to measures of rehearsal, output time, and access to lexical memory. We replicate standard short-term phenomena; we show that the variables that influence children's span performance influence adult performance in the same way; and we show that lexical memory access appears to be a more potent source of individual differences in span than either rehearsal speed or output factors.

Target similarity effects: support for the parallel distributed processing assumptions.

Recent research has begun to provide support for the assumptions that memories are stored as a composite and are accessed in parallel (Tehan & Humphreys, 1998). New predictions derived from these assumptions and from the Chappell and Humphreys (1994) implementation of these assumptions were tested. In three experiments, subjects studied relatively short lists of words. Some of the lists contained two similar targets (thief and theft) or two dissimilar targets (thief and steal) associated with the same cue (robbery). As predicted, target similarity affected performance in cued recall but not free association. Contrary to predictions, two spaced presentations of a target did not improve performance in free association. Two additional experiments confirmed and extended this finding. Several alternative explanations for the target similarity effect, which incorporate assumptions about separate representations and sequential search, are rejected. The importance of the finding that, in at least one implicit memory paradigm, repetition does not improve performance is also discussed.

Creating proactive interference in immediate recall: building a dog from a dart, a mop, and a fig.

Phonemic codes are accorded a privileged role in most current models of immediate serial recall, although their effects are apparent in short-term proactive interference (PI) effects as well. The present research looks at how assumptions concerning distributed representation and distributed storage involving both semantic and phonemic codes might be operationalized to produce PI in a short-term cued recall task. The four experiments reported here attempted to generate the phonemic characteristics of a nonrhyming, interfering foil from unrelated filler items in the same list. PI was observed when a rhyme of the foil was studied or when the three phonemes of the foil were distributed across three studied filler items. The results suggest that items in short-term memory are stored in terms of feature bundles and that all items are simultaneously available at retrieval.

The effect of item and relational processing on incidental long-term memory for order.

Although stimulus similarity and levels of processing are often manipulated in long-term episodic tasks that test item memory, little attention has been paid to how these variable affect long-term memory for temporal order. The effects of these variables on order memory was tested using a task that required the reconstruction of the initial presentation order of short lists after a filled delay. Initial learning of the lists always involved incidental processing procedures ranging from low-level item processes to high-level relational processes. In all experiments, changes in stimulus similarity and processing tasks had similar effects on order memory to the effects found in tasks involving long-term item memory. An interpretation of the data is proposed, based on the joint contribution of distinctive item and relation processing, and poor encoding of order information with shallow processing. It is concluded that item information must play a significant role in the long-term order reconstruction task.

Cuing effects in short-term recall.

Past research indicates that short-term memory can be immune to the effects of proactive interference (PI). Past research also indicates that immunity to PI is found only in those circumstances where phonemic representations of to-be-remembered items are present and provide discriminative information. The first three experiments demonstrate the existence of a further boundary condition. PI is observed only if interfering and target items are subsumed by the same cue. This finding suggests that short-term recall, like long-term recall, is cue dependent. Cuing effects are further explored in two experiments that manipulate category dominance. The finding that category dominance effects parallel PI effects strongly suggests that retrieval cues play a critical role in short-term recall.

Transient phonemic codes and immunity to proactive interference.

Empirical data indicate that when memory for subspan lists of taxonomically related material is tested immediately after study, prior experience with lists involving the same material has no effect upon recall or recognition. In six experiments, we explored the possibility that immunity to proactive interference (PI) is related to discriminative information that is provided by transient phonemic codes. In these experiments, we manipulated the strength of phonemic codes as well as their presence or absence. Immunity to PI was found only when it was presumed that a phonemic representation of the target items existed and that information provided discriminative information. In all other cases, PI was observed. The finding that PI effects correspond with the manipulation of phonemic information in a principled fashion provides strong evidence for the role of phonemic codes in producing short-term PI effects.

Associative priming in perceptual identification: effects of prime-processing requirements.

Three experiments assessed the effects of prime-processing instructions on associative priming in word identification and episodic memory for primes. In Experiment 1, groups instructed to read the prime silently or generate silently an associate of the prime showed a larger accuracy benefit for related over unrelated targets than did a group that decided whether an asterisk was to the right or left of the prime. The asterisk-search group showed a weaker repetition effect on a subsequent identification test of primes, indicating that the weaker priming in this group was a result of poorer perceptual processing. On a cued-recall test for primes, the generate group was superior to the other groups. In Experiment 2, we found that with weak prime-target associations, priming was comparable for read and generate groups and stronger than estimated for a guessing strategy, on the basis of single predictions made from each prime by an additional group. In Experiment 3, we demonstrated that the read and generate instructions produced similar mispriming and inhibitory effects. The results suggest that the depths of prime-processing manipulations do not have parallel effects on priming and episodic memory, and that associative priming in word identification, as in other tasks, may involve an expectancy process.

Retrieval plus scanning: does it occur?

In the two experiments reported here, we tested the retrieval-plus-scan model of delayed probe recognition by adding a second probe 2 sec after subjects had responded to the first probe. According to this model, the list items should still be in consciousness from the first probe at the time of the second probe. Consequently, on tests in which the first probe had been tested immediately, we expected to find the same pattern of performance on both first and second probes. On tests in which the first probe came after a filled delay, we expected the first-probe data to show the effects of retrieval and proactive interference. These effects should not be present on the second probe. The results of the first-probe data in both experiments were consistent with the retrieval-plus-scan model. The second-probe data did not fit the model, however. In the first experiment, the second probe on what had been delayed first-probe trials still produced intercept differences, indicating the presence of retrieval. In the second experiment, the effects of proactive interference were still present on the second probe. It is suggested that these results not only invalidate the retrieval-plus-scan model for delayed probe recognition but that they, along with other results, cast doubt on a scanning operation in immediate probe recognition.