Amanda L. Gilchrist

Seven-year-olds allocate attention like adults unless working memory is overloaded

Previous studies have indicated that visual working memory performance increases with age in childhood, but it is not clear why. One main hypothesis has been that younger children are less efficient in their attention; specifically, they are less able to exclude irrelevant items from working memory to make room for relevant items. We examined this hypothesis by measuring visual working memory capacity under a continuum of five attention conditions. A recognition advantage was found for items to be attended as opposed to ignored. The size of this attention-related effect was adult-like in young children with small arrays, suggesting that their attention processes are efficient even though their working memory capacity is smaller than that of older children and adults. With a larger working memory load, this efficiency in young children was compromised. The efficiency of attention cannot be the sole explanation for the capacity difference.

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.

Investigating the childhood development of working memory using sentences: New evidence for the growth of chunk capacity

Child development is accompanied by a robust increase in immediate memory. This may be due to either an increase in the number of items (chunks) that can be maintained in working memory or an increase in the size of those chunks. We tested these hypotheses by presenting younger and older children (7 and 12 years of age) and adults with different types of lists of auditory sentences: four short sentences, eight short sentences, four long sentences, and four random word lists, each read with a sentence-like intonation. Young children accessed (recalled words from) fewer clauses than did older children or adults, but no age differences were found in the proportion of words recalled from accessed clauses. We argue that the developmental increase in memory span was due to a growing number of chunks present in working memory with little role of chunk size.

Can the focus of attention accommodate multiple, separate items?

Researchers of working memory currently debate capacity limits of the focus of attention, the proposed mental faculty in which items are most easily accessed. Cowan (1999) suggested that its capacity is about 4 chunks, whereas others have suggested that its capacity is only 1 chunk. Recently, Oberauer and Bialkova (2009) found evidence that 2 items could reside in the focus of attention, but only because they were combined into a single chunk. We modified their experimental procedure, which depends on a pattern of switch costs, to obtain a situation in which chunking was not likely to occur (i.e., each item remained a separate chunk) and still obtained results consistent with a capacity of at least 2 items. Therefore, either the focus of attention can hold multiple chunks or the switch cost logic must be reconsidered.

THEORY AND MEASUREMENT OF WORKING MEMORY CAPACITY LIMITS

Abstract We review the evidence for various kinds of limit in the capability of working memory, the small amount of information that can be held in mind at once. To distinguish between types of limit in working memory, we invoke metaphors of space (capacity), time (decay and speed), and energy (control of attention). The review focuses primarily on recent evidence on a limit in how many chunks can be held in working memory, how this kind of limit can be measured, and how it can be distinguished from other types of limits. We explore the theoretical and practical importance of different working memory limits in research that is nomothetic (referring to general laws) and ideographic (referring to individual and group differences). The appropriate measure of working memory depends on ones holistic or analytic scientific interest.

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.

Retrospective cues based on object features improve visual working memory performance in older adults.

Abstract Research with younger adults has shown that retrospective cues can be used to orient top-down attention toward relevant items in working memory. We examined whether older adults could take advantage of these cues to improve memory performance. Younger and older adults were presented with visual arrays of five colored shapes; during maintenance, participants were presented either with an informative cue based on an object feature (here, object shape or color) that would be probed, or with an uninformative, neutral cue. Although older adults were less accurate overall, both age groups benefited from the presentation of an informative, feature-based cue relative to a neutral cue. Surprisingly, we also observed differences in the effectiveness of shape versus color cues and their effects upon post-cue memory load. These results suggest that older adults can use top-down attention to remove irrelevant items from visual working memory, provided that task-relevant features function as cues.

How should we measure chunks? a continuing issue in chunking research and a way forward.

Generally defined, chunking is a process through which one reorganizes or groups presented information to compress information; it is one of the best-known methods of increasing the amount of information stored in memory. Chunking can occur by two different means: either through strategic reorganization based on familiarity or prior knowledge, or through grouping based on perceptual characteristics. An example of the former is using knowledge of acronyms to break a string of letters (e.g., AWOLNASAMIA) into smaller, separate groups (i.e., AWOL, NASA, MIA). In the case of the latter, more common with visual stimuli, one can form groups on the basis of similarity or proximity. Although both methods are considered part of the general phenomenon of chunking, it is the goal-directed, strategic chunking that is the focus of this piece. Although the process of chunking has been discussed as a mnemonic strategy in William Jamess Principles of Psychology (1890), it is most widely known through George Millers paper, “The Magical Number Seven, Plus or Minus Two.” Miller (1956) primarily reviewed several studies that examined capacity limits in immediate recall; across various types of stimuli, a consistent recall limit of between five and nine items was observed. As a secondary emphasis, Miller also discussed recoding and subsequent implications on estimates of immediate memory capacity. Miller observed that if information was recoded into meaningful units (called chunks), this increased the amount of information that could be recalled, and thereby increased immediate memory span. This occurs because increased meaning through chunking or recoding increases the size of each respective chunk (e.g., Tulving and Patkau, 1962; Chase and Simon, 1973; Simon, 1974), but the number of chunks that can be stored in short-term memory remains constant, typically limited to four or fewer items (e.g., Cowan, 2001; Gobet and Clarkson, 2004; Mathy and Feldman, 2012). Despite the fact that Miller published his paper nearly 60 years prior, our understanding of chunking remains incomplete. In particular, though many chunking papers use a variety of methods to measure how chunks are formed and retrieved, it is unclear whether the majority of these methods of measuring chunks accurately reflect the internal cognitive processes that are involved in chunk formation. Before discussing this problem in further detail, I will briefly review well-known methods of measuring chunks and how these methods have been used in previous research (see Gilchrist and Cowan, 2012, for a detailed discussion of chunking and these measurement methods). For present purposes, I will be restricting these measurement methods to those involved in deliberate and goal-directed chunking of verbal materials, as these typically require more effortful processing.

New insights into an old problem: Distinguishing storage from processing in the development of working memory

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