In many theories of cognition, researchers propose that working memory and perception operate interactively. For example, in previous studies researchers have suggested that sensory inputs matching the contents of working memory will have an automatic advantage in the competition for processing resources. The authors tested this hypothesis by requiring observers to perform a visual search task while concurrently maintaining object representations in visual working memory. The hypothesis that working memory activation produces a simple but uncontrollable bias signal leads to the prediction that items matching the contents of working memory will automatically capture attention. However, no evidence for automatic attentional capture was obtained; instead, the participants avoided attending to these items. Thus, the contents of working memory can be used in a flexible manner for facilitation or inhibition of processing.
attention; working memory; visual search; capture
Many studies have found that representations in working memory (WM) can guide visual attention towards items that match the features of the WM contents. While some researchers contend that this occurs involuntarily, others suggest that the impact of WM content on attention can be strategically controlled. Here, we varied the probability that WM items would coincide with either targets or distracters in a visual search task to examine (i) whether participants could intentionally enhance or inhibit the influence of WM items on attention, and (ii) whether cognitive control over WM biases would also affect access to the memory content in a surprise recognition test. We found visual search to be faster when the WM item coincided with the search target, and this effect was enhanced when the memory item reliably predicted the location of the target. Conversely, visual search was slowed when the memory item coincided with a search distracter, and this effect was diminished, but not abolished, when the memory item was reliably associated with distracters. This strategic dampening of the influence of WM items on attention came at a price to memory, however, as participants were slowest to perform WM recognition tests on blocks when the WM content was consistently invalid. These results document that attentional capture by WM contents is partly, but not fully, malleable by top-down control, which appears to adjust the state of the WM content to optimize search behavior. These data illustrate the role of cognitive control in modulating the strength of WM biases of selection, and support a tight coupling between WM and attention.
The biased competition theory proposes that items matching the contents of visual working memory will automatically have an advantage in the competition for attention. However, evidence for an automatic effect has been mixed, perhaps because the memory-driven attentional bias can be overcome by top-down suppression. To test this hypothesis, the Pd component of the event-related potential waveform was used as a marker of attentional suppression. While observers maintained a color in working memory, task-irrelevant probe arrays were presented that contained an item matching the color being held in memory. We found that the memory-matching probe elicited a Pd component, indicating that it was being actively suppressed. This result suggests that sensory inputs matching the information being held in visual working memory are automatically detected and generate an “attend-to-me” signal, but this signal can be overridden by an active suppression mechanism to prevent the actual capture of attention.
visual working memory; attend-to-me signal; attentional suppression; event-related potential; Pd
Introspectively we experience a phenomenally rich world. In stark contrast, many studies show that we can only report on the few items that we happen to attend to. So what happens to the unattended objects? Are these consciously processed as our first person perspective would have us believe, or are they – in fact – entirely unconscious? Here, we attempt to resolve this question by investigating the perceptual characteristics of visual sensory memory. Sensory memory is a fleeting, high-capacity form of memory that precedes attentional selection and working memory. We found that memory capacity benefits from figural information induced by the Kanizsa illusion. Importantly, this benefit was larger for sensory memory than for working memory and depended critically on the illusion, not on the stimulus configuration. This shows that pre-attentive sensory memory contains representations that have a genuinely perceptual nature, suggesting that non-attended representations are phenomenally experienced rather than unconscious.
Information held in working memory (WM) can guide attention during visual search. The authors of recent studies have interpreted the effect of holding verbal labels in WM as guidance of visual attention by semantic information. In a series of experiments, we tested how attention is influenced by visual features versus category-level information about complex objects held in WM. Participants either memorized an object’s image or its category. While holding this information in memory, they searched for a target in a four-object search display. On exact-match trials, the memorized item reappeared as a distractor in the search display. On category-match trials, another exemplar of the memorized item appeared as a distractor. On neutral trials, none of the distractors were related to the memorized object. We found attentional guidance in visual search on both exact-match and category-match trials in Experiment 1, in which the exemplars were visually similar. When we controlled for visual similarity among the exemplars by using four possible exemplars (Exp. 2) or by using two exemplars rated as being visually dissimilar (Exp. 3), we found attentional guidance only on exact-match trials when participants memorized the object’s image. The same pattern of results held when the target was invariant (Exps. 2–3) and when the target was defined semantically and varied in visual features (Exp. 4). The findings of these experiments suggest that attentional guidance by WM requires active visual information.
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Working memory; Attentional capture; Visual search
Researchers use a variety of behavioral tasks to analyze the effect of biological manipulations on memory function. This research will benefit from a systematic mathematical method for analyzing memory demands in behavioral tasks. In the framework of reinforcement learning theory, these tasks can be mathematically described as partially-observable Markov decision processes. While a wealth of evidence collected over the past 15 years relates the basal ganglia to the reinforcement learning framework, only recently has much attention been paid to including psychological concepts such as working memory or episodic memory in these models. This paper presents an analysis that provides a quantitative description of memory states sufficient for correct choices at specific decision points. Using information from the mathematical structure of the task descriptions, we derive measures that indicate whether working memory (for one or more cues) or episodic memory can provide strategically useful information to an agent. In particular, the analysis determines which observed states must be maintained in or retrieved from memory to perform these specific tasks. We demonstrate the analysis on three simplified tasks as well as eight more complex memory tasks drawn from the animal and human literature (two alternation tasks, two sequence disambiguation tasks, two non-matching tasks, the 2-back task, and the 1-2-AX task). The results of these analyses agree with results from quantitative simulations of the task reported in previous publications and provide simple indications of the memory demands of the tasks which can require far less computation than a full simulation of the task. This may provide a basis for a quantitative behavioral stoichiometry of memory tasks.
Most theories of attention propose that we maintain attentional templates in visual working memory to control what information is selected. In the present study, we directly tested this proposal by measuring the contralateral-delay activity (CDA) of human event-related potentials (ERPs) during visual search tasks in which the target is cued on each trial. Here we show that the CDA can be used to measure the maintenance of attentional templates in visual working memory while processing complex visual scenes. In addition, this method allowed us to directly observe the shift from working memory to long-term memory representations controlling attention as learning occurred and experience accrued searching for the same target object. Our findings provide definitive support for several critical proposals made in theories of attention, learning, and automaticity.
HIV infection is often associated with frontal systems pathology and related deficits in the strategic encoding and retrieval aspects of episodic memory. However, no prior HIV studies have explicitly examined source memory, which refers to recall of information regarding the context in which a declarative memory was formed. Source memory is heavily reliant upon frontal systems and strategic cognitive processes and is singly dissociable from the content of the memory (i.e., item memory), which is more dependent upon medial temporal systems and automatic processes. The present study examined item and source memory in 60 individuals with HIV infection and 35 demographically similar seronegative participants. The primary finding of interest was a significant HIV effect on source (but not item) memory for complex visual stimuli. Follow-up correlational analyses showed a significant association between visual source memory errors and impairment on measures of executive functions, working memory, and higher-level list learning encoding strategies. These findings extend the hypothesized profile of strategic encoding and retrieval deficits in HIV to the construct of source memory, which may be differentially affected relative to item memory for complex visual stimuli.
Human immunodeficiency virus; neuropsychological assessment; encoding; episodic memory; frontal lobe
Exogenous covert attention improves discriminability and accelerates the rate of visual information processing (M. Carrasco & B. McElree, 2001). Here we investigated and compared the effects of both endogenous (sustained) and exogenous (transient) covert attention. Specifically, we directed attention via spatial cues and evaluated the automaticity and flexibility of exogenous and endogenous attention by manipulating cue validity in conjunction with a response-signal speed-accuracy trade-off (SAT) procedure, which provides conjoint measures of discriminability and information accrual. To investigate whether discriminability and rate of information processing differ as a function of cue validity (chance to 100%), we compared how both types of attention affect performance while keeping experimental conditions constant. With endogenous attention, both the observed benefits (valid-cue) and the costs (invalid-cue) increased with cue validity. However, with exogenous attention, the benefits and costs in both discriminability and processing speed were similar across cue validity conditions. These results provide compelling time-course evidence that whereas endogenous attention can be flexibly allocated according to cue validity, exogenous attention is automatic and unaffected by cue validity.
covert attention; exogenous; endogenous; automaticity; flexibility
Working memory representations play a key role in controlling attention, making it possible to shift attention to task relevant objects. Visual working memory has a capacity of 3–4 objects, but recent studies suggest that only one representation can guide attention at a given moment. We directly tested this proposal by monitoring eye movements while observers searched for one or two different colors in arrays containing two or four different colors. First, we identified behavioral signatures of template use: When observers implemented a single color template, they sequentially searched many consecutive items of a color (long run lengths), and they exhibited a delay prior to switching gaze from one color to another (switch cost). In contrast, when searching two colors simultaneously, observers exhibited short run lengths and no switch costs, consistent with the simultaneous guidance of attention by the two cued colors. Thus, multiple working memory representations can guide attention concurrently.
An influential conception of visual working memory is of a small number of discrete memory “slots”, each storing an integrated representation of a single visual object, including all its component features. When a scene contains more objects than there are slots, visual attention controls which objects gain access to memory.
A key prediction of such a model is that the absolute error in recalling multiple features of the same object will be correlated, because features belonging to an attended object are all stored, bound together. Here, we tested participants’ ability to reproduce from memory both the color and orientation of an object indicated by a location cue. We observed strong independence of errors between feature dimensions even for large (6 item) memory arrays, inconsistent with an upper limit on the number of objects held in memory.
Examining the pattern of responses in each dimension revealed a gaussian distribution of error centered on the target value that increased in width under higher memory loads. For large arrays, a subset of responses were not centered on the target but instead predominantly corresponded to mistakenly reproducing one of the other features held in memory. These misreporting responses again occurred independently in each feature dimension, consistent with ‘misbinding’ due to errors in maintaining the binding information that assigns features to objects.
The results support a shared-resource model of working memory, in which increasing memory load incrementally degrades storage of visual information, reducing the fidelity with which both object features and feature bindings are maintained.
Working memory (WM) selectively maintains a limited amount of currently relevant information in an active state to influence future perceptual processing, thought, and behavior. The representation of the information held in WM is unknown, particularly the degree of separation between the representation of an object’s identity and its location. The current experiments examined the flexibility of object and location WM representations by measuring reaction times on a visual discrimination task during the delay period of a WM recognition task for object identities, locations, or both. Results demonstrate that during WM delay periods attention is biased toward information that matches the current contents of WM. Attention is not biased toward information that was present in the encoded memory sample but not relevant for the memory recognition test. This specificity of the interaction between WM and attention applies to both the identity and the location of the remembered stimulus and to the relationship between an object and its location. The results suggest that when this relationship is necessary for task performance, WM represents an object and its identity in an integrated manner. However, if this relationship is not task relevant, the object and location information are represented in WM separately.
Previous studies indicate 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 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 5 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 is compromised. The efficiency of attention cannot be the sole explanation for the capacity difference.
Prior studies have shown that spatial attention modulates early visual cortex retinotopically, resulting in enhanced processing of external perceptual representations. However, it is not clear whether the same visual areas are modulated when attention is focused on, and shifted within a working memory representation. In the current fMRI study participants were asked to memorize an array containing four stimuli. After a delay, participants were presented with a verbal cue instructing them to actively maintain the location of one of the stimuli in working memory. Additionally, on a number of trials a second verbal cue instructed participants to switch attention to the location of another stimulus within the memorized representation. Results of the study showed that changes in the BOLD pattern closely followed the locus of attention within the working memory representation. A decrease in BOLD-activity (V1–V3) was observed at ROIs coding a memory location when participants switched away from this location, whereas an increase was observed when participants switched towards this location. Continuous increased activity was obtained at the memorized location when participants did not switch. This study shows that shifting attention within memory representations activates the earliest parts of visual cortex (including V1) in a retinotopic fashion. We conclude that even in the absence of visual stimulation, early visual areas support shifting of attention within memorized representations, similar to when attention is shifted in the outside world. The relationship between visual working memory and visual mental imagery is discussed in light of the current findings.
Visual short-term memory (VSTM) is limited in the quantity and quality of items that can be retained over time. Importantly, these two mnemonic parameters interact: increasing the number of items in VSTM reduces the quality with which they are represented. Here, we ask whether this trade-off is under top-down control. Specifically, we test whether participants can strategically optimise the trade-off between quality and quantity for VSTM according to task demands. We manipulated strategic trade-off by varying expectations about the number of to-be-remembered items (Experiments 1–2) or the precision required for the memory-based judgement (Experiment 3). In a final experiment, we manipulated both variables in a complementary way to maximise the motivation to strategically control the balance between number and the quality of items encoded into VSTM. In different blocks, performance would benefit most either by encoding a large number of items with low precision or by encoding a small number of items with high precision (Experiment 4). In all experiments, we compared VSTM performance on trials matched for mnemonic demand, but within contexts emphasising the quality or quantity of VSTM representations. Across all four experiments, we found no evidence to suggest that participants use this contextual information to bias the balance between the number and precision of items in VSTM. Rather, our data suggest that the trade-off may be determined primarily by stimulus-driven factors at encoding.
During the last decade one of the most contentious and heavily studied topics in the attention literature has been the role that working memory representations play in controlling perceptual selection. The hypothesis has been advanced that to have attention select a certain perceptual input from the environment, we only need to represent that item in working memory. Here we summarize the work indicating that the relationship between what representations are maintained in working memory and what perceptual inputs are selected is not so simple. First, it appears that attentional selection is also determined by high-level task goals that mediate the relationship between working memory storage and attentional selection. Second, much of the recent work from our laboratory has focused on the role of long-term memory in controlling attentional selection. We review recent evidence supporting the proposal that working memory representations are critical during the initial configuration of attentional control settings, but that after those settings are established long-term memory representations play an important role in controlling which perceptual inputs are selected by mechanisms of attention.
visual attention; visual working memory; long-term memory; event-related potentials
Although phonological representations have been a primary focus of verbal working memory research, lexical-semantic manipulations also influence performance. In the present study, the authors investigated whether a classic phenomenon in verbal working memory, the phonological similarity effect (PSE), is modulated by a lexical-semantic variable, word concreteness. Phonological overlap and concreteness were factorially manipulated in each of four experiments across which presentation modality (Experiments 1 and 2: visual presentation; Experiments 3 and 4: auditory presentation) and concurrent articulation (present in Experiments 2 and 4) were manipulated. In addition to main effects of each variable, results show a Phonological Overlap × Concreteness interaction whereby the magnitude of the PSE is greater for concrete word lists relative to abstract word lists. This effect is driven by superior item memory for nonoverlapping, concrete lists and is robust to the modality of presentation and concurrent articulation. These results demonstrate that in verbal working memory tasks, there are multiple routes to the phonological form of a word and that maintenance and retrieval occur over more than just a phonological level.
working memory; language production; serial recall; phonological similarity; concrete
A cued, visuospatial attention task and a working memory task were administered to 89 healthy adults genotyped for a T-to-C polymorphism in CHRNA4, a nicotinic receptor subunit gene. Increasing gene dose of the C allele of the CHRNA4 gene (i.e., no C alleles, one C allele, two C alleles) was associated with increased reaction time (RT) benefits of valid attentional cuing and reduced RT costs of invalid cues, but was not associated with working memory performance. In a second experiment, 103 healthy persons were genotyped for a G-to-A polymorphism of the dopamine beta-hydroxylase (DBH) gene. Increasing gene dose of the G allele of the DBH gene was associated with increased working memory accuracy at a high memory load. However, there was no consistent association between the DBH gene and visuospatial attention. Thus, a double dissociation was observed, with visuospatial attention associated with CHRNA4 but not the DBH gene and, conversely, working memory associated with the DBH gene but not CHRNA4. The results show that normal allelic variations in single neurotransmitter genes modulate individual differences in processing components of cognitive functions in healthy individuals.
We investigated the relation between the two systems of visuospatial attention and working memory by examining the effect of normal variation in cholinergic and noradrenergic genes on working memory performance under attentional manipulation. We previously reported that working memory for location was impaired following large location precues, indicating the scale of visuospatial attention has a role in forming the mental representation of the target. In one of the first studies to compare effects of two single nucleotide polymorphisms (SNPs) on the same cognitive task, we investigated the neurotransmission systems underlying interactions between attention and memory. Based on our previous report that the CHRNA4 rs#1044396 C/T nicotinic receptor SNP affected visuospatial attention, but not working memory, and the DBH rs#1108580 G/A noradrenergic enzyme SNP affected working memory, but not attention, we predicted that both SNPs would modulate performance when the two systems interacted and working memory was manipulated by attention. We found the scale of visuospatial attention deployed around a target affected memory for location of that target. Memory performance was modulated by the two SNPs. CHRNA4 C/C homozygotes and DBH G allele carriers showed the best memory performance but also the greatest benefit of visuospatial attention on memory. Overall, however, the CHRNA4 SNP exerted a stronger effect than the DBH SNP on memory performance when visuospatial attention was manipulated. This evidence of an integrated cholinergic influence on working memory performance under attentional manipulation is consistent with the view that working memory and visuospatial attention are separate systems which can interact.
Three experiments were conducted to investigate the effects of working memory content on temporal attention in a rapid serial visual presentation attentional blink paradigm. It was shown that categorical similarity between working memory content and the target stimuli pertaining to the attentional task (both digits) increased attentional blink magnitude compared to a condition in which this similarity was absent (colors and digits, respectively). This effect was only observed when the items in working memory were not presented as conjunctions of the involved categories (i.e., colored digits). This suggested that storage and retrieval from working memory was at least preferentially conjunctive in this case. It was furthermore shown that the content of working memory enhanced the identification rate of the second target, by means of repetition priming, when inter-target lag was short and the attentional blink was in effect. The results are incompatible with theories of temporal attention that assume working memory has no causal role in the attentional blink and support theories that do.
Classic work on visual short-term memory (VSTM) suggests that people store a limited amount of items for subsequent report. However, when human observers are cued to shift attention to one item in VSTM during retention, it seems as if there is a much larger representation, which keeps additional items in a more fragile VSTM store. Thus far, it is not clear whether the capacity of this fragile VSTM store indeed exceeds the traditional capacity limits of VSTM. The current experiments address this issue and explore the capacity, stability, and duration of fragile VSTM representations.
We presented cues in a change-detection task either just after off-set of the memory array (iconic-cue), 1,000 ms after off-set of the memory array (retro-cue) or after on-set of the probe array (post-cue). We observed three stages in visual information processing 1) iconic memory with unlimited capacity, 2) a four seconds lasting fragile VSTM store with a capacity that is at least a factor of two higher than 3) the robust and capacity-limited form of VSTM. Iconic memory seemed to depend on the strength of the positive after-image resulting from the memory display and was virtually absent under conditions of isoluminance or when intervening light masks were presented. This suggests that iconic memory is driven by prolonged retinal activation beyond stimulus duration. Fragile VSTM representations were not affected by light masks, but were completely overwritten by irrelevant pattern masks that spatially overlapped the memory array.
We find that immediately after a stimulus has disappeared from view, subjects can still access information from iconic memory because they can see an after-image of the display. After that period, human observers can still access a substantial, but somewhat more limited amount of information from a high-capacity, but fragile VSTM that is overwritten when new items are presented to the eyes. What is left after that is the traditional VSTM store, with a limit of about four objects. We conclude that human observers store more sustained representations than is evident from standard change detection tasks and that these representations can be accessed at will.
Interactions between visual attention and visual short-term memory (VSTM) play a central role in cognitive processing. For example, attention can assist in selectively encoding items into visual memory. Attention appears to be able to influence items already stored in visual memory as well; cues that appear long after the presentation of an array of objects can affect memory for those objects (Griffin & Nobre, 2003). In five experiments, we distinguished two possible mechanisms for the effects of cues on items currently stored in VSTM. A protection account proposes that attention protects the cued item from becoming degraded during the retention interval. By contrast, a prioritization account suggests that attention increases a cued item’s priority during the comparison process that occurs when memory is tested. The results of the experiments were consistent with the first of these possibilities, suggesting that attention can serve to protect VSTM representations while they are being maintained.
It is commonly hypothesized that external representations serve as memory aids and improve task performance by means of expanding the limited capacity of working memory. However, very few studies have directly examined this memory aid hypothesis. By systematically manipulating how information is available externally versus internally in a sequential number comparison task, three experiments were designed to investigate the relation between external representations and working memory. The experimental results show that when the task requires information from both external representations and working memory, it is the interaction of information from the two sources that determines task performance. In particular, when information from the two sources does not match well, external representations hinder instead of enhance task performance. The study highlights the important role the coordination among different representations plays in distributed cognition. The general relations between external representations and working memory are discussed.
Quantity or numerosity is one of the basic properties of our environment. Humans and animals both have the neural representation of quantity or “number sense”. The ability to extract and to manipulate numbers is closely related to our various cognitive functions such as the capacity of working memory, mathematical achievement, and texture perception. Evidence shows that the sense of number is not a unitary mechanism but rather a composition of two distinct processes; enumeration and estimation. The review examines how numerosity is represented in the visual domain and its relation to different modes of attention. Enumeration or counting permits an exact representation of a distinct number of objects, with an awareness of each object achieved through focal deployment of attention to each object serially. On the other hand, estimation involves an approximation of the number of different items or a sense of ensemble statistics, achieved through fast deployment of distributed attention over a set of objects as a whole. In this overview we suggest that a focused attention mode is more suitable for enumeration, whereas a distributed attention mode is better for estimation.
A prevalent view of working memory (WM) considers it to be capacity-limited, fixed to a set number of items. However, recent shared resource models of WM have challenged this “quantized” account using measures of recall precision. Although this conceptual framework can account for several features of visual WM, it remains to be established whether it also applies to auditory WM.
We used a novel pitch-matching paradigm to probe participants’ memory of pure tones in sequences of varying length, and measured their precision of recall. Crucially, this provides an index of the variability of memory representation around its true value, rather than a binary “yes/no” recall measure typically used in change detection paradigms. We show that precision of auditory WM varies with both memory load and serial order. Moreover, auditory WM resources can be prioritized to cued items, improving precision of recall, but with a concomitant cost to other items, consistent with a resource model account.
Working memory; Precision; Auditory perception; Resource model; Memory capacity; Pitch-matching