A two-stage search of visual working memory: investigating speed in the change-detection paradigm

A popular procedure for investigating working memory processes has been the visual change-detection procedure. Models of performance based on that procedure, however, tend to be based on performance accuracy and treat working memory search as a one-step process, in which memory representations are compared to a test probe to determine if a match is present. To gain a clearer understanding of how search of these representations operate in the change-detection task, we examined reaction time in two experiments, with a single-item probe either located centrally or at the location of an array item. Contrary to current models of visual working memory capacity, our data point to a two-stage search process: a fast first step to check for the novelty of the probe and, in the absence of such novelty, a second, slower step to search exhaustively for a match between the test probe and a memory representation. In addition to these results, we found that participants tended not to use location information provided by the probe that theoretically could have abbreviated the search process. We suggest some basic revisions of current models of processing in this type of visual working memory task.     

Organizing the properties of impossible figures

The empirical study of impossible figures requires that independent variables be well-specified. This paper provides an aid for such a task by developing a classification system which partitions cornered torus figures into meaningful subsets. These can be used to identify both formal and psychological properties of known as well as unknown possible and impossible figures in much the same manner as with the periodic table of chemical elements. The classification is polytopic (for demensional) and is formally, not empirically, derived. Coherent three-dimensional and two-dimensional forms of the system are possible without loss of information.     

Capacity limits in list item recognition: Evidence from proactive interference

Capacity limits in short‐term recall were investigated using proactive interference (PI) from previous lists in a speeded‐recognition task. PI was taken to indicate that the target list length surpassed working memory capacity. Unlike previous studies, words were presented either concurrently or sequentially and a new method was introduced to increase the amount of PI. On average, participants retrieved about four items without PI. We suggest an activation‐based account of capacity limits.     

Just lying there,remembering: Improving recall of prose in amnesic patients with mild cognitive impairment by minimising interference

The hallmark of amnesia is poor explicit long‐term memory along with normal short‐term memory. It is often stated that information encountered by amnesic patients is forgotten within 1 minute of presentation. However, previous work has not distinguished between forgetting as a function of time versus the interfering material occupying that time. We show that there is a marked benefit of reduced interference in amnesic patients with mild cognitive impairment (MCI), a condition that is characterised by anterograde amnesia in the absence of other neuropsychological deficits and carries an increased risk for Alzheimer's disease. The result suggests that long‐term memory is encoded in these patients to a greater extent than had been realised but that their memory is highly vulnerable to interference.     

Age differences in visual working memory capacity: not based on encoding limitations

Why does visual working memory performance increase with age in childhood? One recent study ( Cowan et al., 2010b ) ruled out the possibility that the basic cause is a tendency in young children to clutter working memory with less‐relevant items (within a concurrent array, colored items presented in one of two shapes). The age differences in memory performance, however, theoretically could result from inadequate encoding of the briefly presented array items by younger children. We replicated the key part of the procedure in children 6–8 and 11–13 years old and college students (total N = 90), but with a much slower, sequential presentation of the items to ensure adequate encoding. We also required verbal responses during encoding to encourage or discourage labeling of item information. Although verbal labeling affected performance, age differences persisted across labeling conditions, further supporting the existence of a basic growth in capacity.     

On the capacity of attention: its estimation and its role in working memory and cognitive aptitudes

Working memory (WM) is the set of mental processes holding limited information in a temporarily accessible state in service of cognition. We provide a theoretical framework to understand the relation between WM and aptitude measures. The WM measures that have yielded high correlations with aptitudes include separate storage-and-processing task components, on the assumption that WM involves both storage and processing. We argue that the critical aspect of successful WM measures is that rehearsal and grouping processes are prevented, allowing a clearer estimate of how many separate chunks of information the focus of attention circumscribes at once. Storage-and-processing tasks correlate with aptitudes, according to this view, largely because the processing task prevents rehearsal and grouping of items to be recalled. In a developmental study, we document that several scope-of-attention measures that do not include a separate processing component, but nevertheless prevent efficient rehearsal or grouping, also correlate well with aptitudes and with storage-and-processing measures. So does digit span in children too young to rehearse.     

Chunk limits and length limits in immediate recall: a reconciliation

Whereas some research on immediate recall of verbal lists has suggested that it is limited by the number of chunks that can be recalled (e.g., N. Cowan, Z. Chen, & J. N. Rouder, 2004; E. Tulving & J. E. Patkau, 1962), other research has suggested that it is limited by the length of the material to be recalled (e.g., A. D. Baddeley, N. Thomson, & M. Buchanan, 1975). The authors investigated this question by teaching new paired associations between words to create 2-word chunks. The results suggest that both chunk capacity limits and length limits come into play. For the free recall of 12-word lists, 6 pre-learned pairs could be recalled about as well as 6 pre-exposed singletons, suggesting a chunk limit. However, for the serially ordered recall of 8-word lists, 4 pre-learned pairs could be recalled about as well as 8 pre-exposed singletons, suggesting a length limit. Other conditions yielded intermediate results suggesting that sometimes both limits may operate together.     

Learning in a unidimensional absolute identification task

We tested whether there is long-term learning in the absolute identification of line lengths. Line lengths are unidimensional stimuli, and there is a common belief that learning of these stimuli quickly reaches a low-level asymptote of about seven items and progresses no more. We show that this is not the case. Our participants served in a 1.5-h session each day for over a week. Although they did not achieve perfect performance, they continued to improve day by day throughout the week and eventually learned to distinguish between 12 and 20 line lengths. These results are in contrast to common characterizations of learning in absolute identification tasks with unidimensional stimuli. We suggest that this learning reflects improvement in short-term processing.