Encoding strategies in self-initiated visual working memory

During a typical day, visual working memory (VWM) is recruited to temporarily maintain visual information. Although individuals often memorize external visual information provided to them, on many other occasions they memorize information they have constructed themselves. The latter aspect of memory, which we term self-initiated WM, is prevalent in everyday behavior but has largely been overlooked in the research literature. In the present study we employed a modified change detection task in which participants constructed the displays they memorized, by selecting three or four abstract shapes or real-world objects and placing them at three or four locations in a circular display of eight locations. Half of the trials included identical targets that participants could select. The results demonstrated consistent strategies across participants. To enhance memory performance, participants reported selecting abstract shapes they could verbalize, but they preferred real-world objects with distinct visual features. Furthermore, participants constructed structured memory displays, most frequently based on the Gestalt organization cue of symmetry, and to a lesser extent on cues of proximity and similarity. When identical items were selected, participants mostly placed them in close proximity, demonstrating the construction of configurations based on the interaction between several Gestalt cues. The present results are consistent with recent findings in VWM, showing that memory for visual displays based on Gestalt organization cues can benefit VWM, suggesting that individuals have access to metacognitive knowledge on the benefit of structure in VWM. More generally, this study demonstrates how individuals interact with the world by actively structuring their surroundings to enhance performance.     

Quantity,not quality: the relationship between fluid intelligence and working memory capacity

A key motivation for understanding capacity in working memory (WM) is its relationship with fluid intelligence. Recent evidence has suggested a two-factor model that distinguishes between the number of representations that can be maintained in WM and the resolution of those representations. To determine how these factors relate to fluid intelligence, we conducted an exploratory factor analysis on multiple number-limited and resolution-limited measures of WM ability. The results strongly supported the two-factor model, with fully orthogonal factors accounting for performance in the number-limited and resolution-limited conditions. Furthermore, the reliable relationship between WM capacity and fluid intelligence was exclusively supported by the number factor (r=.66), whereas the resolution factor made no reliable contribution (r=−.05). Thus, the relationship between WM capacity and standard measures of fluid intelligence is mediated by the number of representations that can be simultaneously maintained in WM, rather than by the precision of those representations.     

Thought suppression,intelligence, and working memory capacity

The importance of individual differences in intelligence and working memory capacity in predicting the ability to intentionally suppress thoughts was investigated. Sixty participants completed a thought suppression task, and measures of working memory capacity (OSPAN), fluid intelligence (Raven's Matrices), and crystallised intelligence (the National Adult Reading Test). As predicted, the results indicated that more effective thought suppression was independently related to higher working memory capacity and greater fluid intelligence, but was unrelated to crystallised intelligence. The findings have theoretical implications for understanding the mechanisms underlying a failure to inhibit unwanted intrusions and clinical implications for disorders involving high levels of intrusive thoughts and memories.     

Validating running memory span: Measurement of working memory capacity and links with fluid intelligence

We manipulated running memory span tasks to examine effects on recall and relations with criterion measures of working memory capacity and general fluid intelligence. The goal of the manipulations was to limit or enhance opportunities for active input processing and response preparation in advance of test. We manipulated presentation rate in Experiment 1. Recall was higher at slow than at fast rates, but correlations with criterion measures were much the same across rate conditions. In Experiment 2, we manipulated the time at which the number of items to report was made known to the participants. They were given that information in advance (precue) or at test (postcue). Recall scores and correlations with criterion measures were much the same across cuing conditions. We conclude that running memory span provides valid measurement of working memory capacity that is predictive of higher order cognition across a wide range of conditions.     

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.     

The reliability and stability of visual working memory capacity

Because of the central role of working memory capacity in cognition, many studies have used short measures of working memory capacity to examine its relationship to other domains. Here, we measured the reliability and stability of visual working memory capacity, measured using a single-probe change detection task. In Experiment 1, the participants (N = 135) completed a large number of trials of a change detection task (540 in total, 180 each of set sizes 4, 6, and 8). With large numbers of both trials and participants, reliability estimates were high (α > .9). We then used an iterative down-sampling procedure to create a look-up table for expected reliability in experiments with small sample sizes. In Experiment 2, the participants (N = 79) completed 31 sessions of single-probe change detection. The first 30 sessions took place over 30 consecutive days, and the last session took place 30 days later. This unprecedented number of sessions allowed us to examine the effects of practice on stability and internal reliability. Even after much practice, individual differences were stable over time (average between-session r = .76).     

Self-rated autistic-like traits and capacity of visual working memory

The effect on the capacity of visual working memory of spatial complexity (as defined by Garner's principle) in rotation and reflection transformation was examined in persons differing along the Autism Spectrum Quotient (AQ), using a change-detection task. On each trial, nine line segments were arrayed in simple, medium, and complex configurations, which were presented in memory and test displays. 27 participants (8 men, 19 women; M age = 22.3 yr., SD = 2.7) were asked whether the orientations of stimuli between two displays were the same or different. On the basis of their AQ scores out of 50 (M AQ scores = 20.9, SD = 6.3), the participants were divided into groups with high (n = 13; M AQ scores = 26.2, SD = 4.1) and low (n = 12; M AQ scores = 15.3, SD = 2.7) self-reported autistic-like traits (High and Low AQ groups, 2 excluded for scores at the median). The results showed that spatial complexity affects the capacity of visual working memory for the Low AQ group but not for the High AQ group, suggesting the functional dissociation of spatial configuration and visual working memory in the High AQ group.     

Neuroanatomical correlates of processing in visual and visuospatial working memory

Working memory is traditionally seen as being organised in a modular way with a central executive orchestrating at least two slave systems (phonological loop and visuospatial sketch pad). Neuroanatomical correlates of the visual and visuospatial subsystems and the central executive are discussed in this article. A series of experiments are presented yielding evidence for a differentiation into active and passive processing in working memory as well as their neuroanatomical correlates in the prefrontal cortex. Data, yielding evidence for an interaction and separation of visual and visuospatial working memory are presented and discussed. Further results are presented which suggest a convergence of these two systems with increasing working memory demands. The discussed findings will give new insight in the organisation of visual and visuospatial working memory on the anatomical level.     

Motion tracking modulates capacity allocation of visual working memory

Previous studies on visual working memory (VWM) have primarily investigated memory for an array presented for a single moment. Here, we examined VWM for two arrays separated by a 1,100-msec interval. We focused on the allocation of VWM capacity to the two arrays as a function of dynamic events inserted between them. During the interval, irrelevant dots moved to form three types of motion: (1) coherent (apparent) motion that connected Arrays 1 and 2, (2) jumpy motion, or (3) coherent motion with two disconnected segments. Results showed that VWM for Array 2’s locations was better than for Array 1’s, especially when the arrays were connected by coherent motion. We suggest that coherent motion between two temporally disparate arrays connects the arrays into a single visual event VWM is then biased toward remembering the more recent state of the event.     

Expertise for upright faces improves the precision but not the capacity of visual working memory

Considerable research has focused on how basic visual features are maintained in working memory, but little is currently known about the precision or capacity of visual working memory for complex objects. How precisely can an object be remembered, and to what extent might familiarity or perceptual expertise contribute to working memory performance? To address these questions, we developed a set of computer-generated face stimuli that varied continuously along the dimensions of age and gender, and we probed participants’ memories using a method-of-adjustment reporting procedure. This paradigm allowed us to separately estimate the precision and capacity of working memory for individual faces, on the basis of the assumptions of a discrete capacity model, and to assess the impact of face inversion on memory performance. We found that observers could maintain up to four to five items on average, with equally good memory capacity for upright and upside-down faces. In contrast, memory precision was significantly impaired by face inversion at every set size tested. Our results demonstrate that the precision of visual working memory for a complex stimulus is not strictly fixed but, instead, can be modified by learning and experience. We find that perceptual expertise for upright faces leads to significant improvements in visual precision, without modifying the capacity of working memory.     

The development of visual working memory capacity during early childhood

The change detection task has been used in dozens of studies with adults to measure visual working memory capacity. Two studies have recently tested children in this task, suggesting a gradual increase in capacity from 5 years to adulthood. These results contrast with findings from an infant looking paradigm suggesting that capacity reaches adult-like levels within the first year. The current study adapted the change detection task for use with children younger than 5 years to test whether the standard version of the task was too difficult and may have underestimated children's capacity. Results showed that 3- and 4-year-olds could successfully complete this modified task and that capacity increased roughly linearly, from 2 or 3 items during this period to 3 or 4 items between 5 and 7 years. Furthermore, performance did not differ significantly between the modified version and a replication of the standard version with 5- and 7-year-olds. Thus, there is no evidence that previous research with the change detection task underestimated children's capacity. Further research is needed to understand how performance relates across the infant looking task and change detection to provide a more complete picture of visual working memory capacity over development.     

Individual differences in working memory capacity predict visual attention allocation

To the extent that individual differences in working memory capacity (WMC) reflect differences in attention (Baddeley, 1993; Engle, Kane, & Tuholski, 1999), differences in WMC should predict performance on visual attention tasks. Individuals who scored in the upper and lower quartiles on the OSPAN working memory test performed a modification of Egly and Homa’s (1984) selective attention task. In this task, the participants identified a central letter and localized a displaced letter flashed somewhere on one of three concentric rings. When the displaced letter occurred closer to fixation than the cue implied, high-WMC, but not low-WMC, individuals showed a cost in the letter localization task. This suggests that low-WMC participants allocated attention as a spotlight, whereas those with high WMC showed flexible allocation.     

Distinct capacity limits for attention and working memory: Evidence from attentive tracking and visual working memory paradigms

A hallmark of both visual attention and working memory is their severe capacity limit: People can attentively track only about four objects in a multiple object tracking (MOT) task and can hold only up to four objects in visual working memory (VWM). It has been proposed that attention underlies the capacity limit of VWM. We tested this hypothesis by determining the effect of varying the load of a MOT task performed during the retention interval of a VWM task and comparing the resulting dual-task costs with those observed when a VWM task was performed concurrently with another VWM task or with a verbal working memory task. Instead of supporting the view that the capacity limit of VWM is solely attention based, the results indicate that VWM capacity is set by the interaction of visuospatial attentional, central amodal, and local task-specific sources of processing.     

The influence of temporal resolution power and working memory capacity on psychometric intelligence

According to the temporal resolution power (TRP) hypothesis, higher TRP as reflected by better performance on psychophysical timing tasks accounts for faster speed of information processing and increased efficiency of information processing leading to better performance on tests of psychometric intelligence. An alternative explanation of individual differences in psychometric intelligence highlights individual differences in working memory (WM) capacity which has been found to be closely associated with psychometric intelligence. A latent variable approach was applied on the data of 200 participants ranging in age from 18 to 30 years and spanning a large range of levels of psychometric intelligence. Functional relationships were examined among TRP, WM capacity, as well as reasoning and speed of processing as two important aspects of psychometric intelligence. As predicted by the TRP hypothesis, the relation between TRP and psychometric intelligence was mediated by WM capacity supporting the view that higher TRP leads to better coordinated mental operations which, in turn, result in higher psychometric intelligence. The results are discussed against the background that WM capacity and psychometric reasoning are hardly dissociable from each other and that the specific factors limiting WM capacity and accounting for the mediation effect need to be identified in future research.     

Improvement in working memory is not related to increased intelligence scores

The acknowledged high relationship between working memory and intelligence suggests common underlying cognitive mechanisms and, perhaps, shared biological substrates. If this is the case, improvement in working memory by repeated exposure to challenging span tasks might be reflected in increased intelligence scores. Here we report a study in which 288 university undergraduates completed the odd numbered items of four intelligence tests on time 1 and the even numbered items of the same tests one month later (time 2). In between, 173 participants completed three sessions, separated by exactly one week, comprising verbal, numerical, and spatial short-term memory (STM) and working memory (WMC) tasks imposing high processing demands (STM–WMC group). 115 participants also completed three sessions, separated by exactly one week, but comprising verbal, numerical, and spatial simple speed tasks (processing speed, PS, and attention, ATT) with very low processing demands (PS-ATT group). The main finding reveals increased scores from the pre-test to the post-test intelligence session (more than half a standard deviation on average). However, there was no differential improvement on intelligence between the STM-WMC and PS-ATT groups.     

Choking under pressure and working memory capacity: When performance pressure reduces fluid intelligence

Recent findings (Beilock & Carr, 2005) have demonstrated that only individuals with a high working memory capacity (WMC) “choke under pressure” on math problems with high working memory demands. This suggests that performance pressure hinders those who are the most qualified to succeed, because it consumes the WMC they usually rely on to achieve superior performance. This puts into question the use of performance in high-pressure situations as a means of distinguishing individuals with lesser or greater WMC potentials. While addressing several limitations of past research, we offer evidence that such choking (1) occurs only in individuals with high WMC, because of their anxiety-ridden perceptions of high-stakes situations, and (2) is not confined to tasks involving acquired skills and knowledge, but encompasses fluid reasoning abilities or intelligence (Gf). These findings have strong implications for assessments of people’s intellectual capacities in academic, clinical, work, and research settings.     

Electrophysiological correlates of encoding processes in a full-report visual working memory paradigm

Why are some visual stimuli remembered, whereas others are forgotten? A limitation of recognition paradigms is that they measure aggregate behavioral performance and/or neural responses to all stimuli presented in a visual working memory (VWM) array. To address this limitation, we paired an electroencephalography (EEG) frequency-tagging technique with two full-report VWM paradigms. This permitted the tracking of individual stimuli as well as the aggregate response. We recorded high-density EEG (256 channel) while participants viewed four shape stimuli, each flickering at a different frequency. At retrieval, participants either recalled the location of all stimuli in any order (simultaneous full report) or were cued to report the item in a particular location over multiple screen displays (sequential full report). The individual frequency tag amplitudes evoked for correctly recalled items were significantly larger than the amplitudes of subsequently forgotten stimuli, regardless of retrieval task. An induced-power analysis examined the aggregate neural correlates of VWM encoding as a function of items correctly recalled. We found increased induced power across a large number of electrodes in the theta, alpha, and beta frequency bands when more items were successfully recalled. This effect was more robust for sequential full report, suggesting that retrieval demands can influence encoding processes. These data are consistent with a model in which encoding-related resources are directed to a subset of items, rather than a model in which resources are allocated evenly across the array. These data extend previous work using recognition paradigms and stress the importance of encoding in determining later VWM retrieval success.     

Dual-task interference in visual working memory: A limitation in storage capacity but not in encoding or retrieval

The concurrent maintenance of two visual working memory (VWM) arrays can lead to profound interference. It is unclear, however, whether these costs arise from limitations in VWM storage capacity (Fougnie & Maro is, 2006) or from interference between the storage of one visual array and encoding or retrieval of another visual array (Cowan & Morey, 2007). Here, we show that encoding a VWM array does not interfere with maintenance of another VWM array unless the two displays exceed maintenance capacity (Experiments 1 and 2). Moreover, manipulating the extent to which encoding and maintenance can interfere with one another had no discernable effect on dual-task performance (Experiment 2). Finally, maintenance of a VWM array was not affected by retrieval of information from another VWM array (Experiment 3). Taken together, these findings demonstrate that dual-task interference between two concurrent VWM tasks is due to a capacity-limited store that is independent from encoding and retrieval processes.