Encoding and representation of simultaneous and sequential arrays in visuospatial working memory

The effect of presentation type on organization in visuospatial working memory (VSWM) was examined. Stimuli were presented sequentially or simultaneously at study, and participants made same/different judgements at test. The test array varied in four different spatial configuration conditions: one featuring no changes from study, one in which two items switched, one in which the same array repeated but in a different location, and one in which a completely novel test stimulus appeared. Results indicated the use of a global configuration for both simultaneous and sequential presentations and showed increased impairment of item-level knowledge with sequential presentations. Overall, these results support the use of a global configuration organization as a fundamental aspect of VSWM processing.     

Redundancy effects in the perception and memory of visual objects

Is visual representation of an object affected by whether surrounding objects are identical to it, different from it, or absent? To address this question, we tested perceptual priming, visual short-term, and long-term memory for objects presented in isolation or with other objects. Experiment 1 used a priming procedure, where the prime display contained a single face, four identical faces, or four different faces. Subjects identified the gender of a subsequent probe face that either matched or mismatched with one of the prime faces. Priming was stronger when the prime was four identical faces than when it was a single face or four different faces. Experiments 2 and 3 asked subjects to encode four different objects presented on four displays. Holding memory load constant, visual memory was better when each of the four displays contained four duplicates of a single object, than when each display contained a single object. These results suggest that an object's perceptual and memory representations are enhanced when presented with identical objects, revealing redundancy effects in visual processing.     

Visual long-term memory and change blindness: Different effects of pre- and post-change information on one-shot change detection using meaningless geometric objects

To clarify the relationship between visual long-term memory (VLTM) and online visual processing, we investigated whether and how VLTM involuntarily affects the performance of a one-shot change detection task using images consisting of six meaningless geometric objects. In the study phase, participants observed pre-change (Experiment 1), post-change (Experiment 2), or both pre- and post-change (Experiment 3) images appearing in the subsequent change detection phase. In the change detection phase, one object always changed between pre- and post-change images and participants reported which object was changed. Results showed that VLTM of pre-change images enhanced the performance of change detection, while that of post-change images decreased accuracy. Prior exposure to both pre- and post-change images did not influence performance. These results indicate that pre-change information plays an important role in change detection, and that information in VLTM related to the current task does not always have a positive effect on performance.     

Scene structure enhances change detection

Theories of objects recognition, scene perception, and neural representation of scenes imply that jumbling a coherent scene should reduce change detection. However, evidence from the change detection literature questions whether jumbling affects change detection. The experiments reported here demonstrate that jumbling does, in fact, reduce change detection. In Experiments 1 and 2, change detection was better for normal scenes than for jumbled scenes. In Experiment 3, inversion failed to interfere with change detection, demonstrating that the disruption of surface and object continuity inherent to jumbling is responsible for reduced change detection. These findings provide a crucial commonality between change detection research and theories of scene perception and neural representation. We also discuss why previous research may have failed to find effects of jumbling.     

The capacity of visual short-term memory within and between hemifields

Visual short-term memory (VSTM) and attention are both thought to have a capacity limit of four items [e.g. Luck, S. J., & Vogel, E. K. (1997). The capacity of visual working memory for features and conjunctions. Nature, 309, 279-281; Pylyshyn, Z. W., & Storm, R. W. (1988). Tracking multiple independent targets: evidence for a parallel tracking mechanism. Spatial Vision, 3, 179-197.]. Using the multiple object visual tracking paradigm (MOT), it has recently been shown that twice as many items can be simultaneously attended when they are separated between two visual fields compared to when they are all presented within the same hemifield [Alvarez, G. A., & Cavanagh, P. (2004). Independent attention resources for the left and right visual hemifields (Abstract). Journal of Vision, 4(8), 29a.]. Does VSTM capacity also increase when the items to be remembered are distributed between the two visual fields? The current paper investigated this central issue in two different tasks, namely a color and spatial location change detection task, in which the items were displayed either in the two visual fields or in the same hemifield. The data revealed that only memory capacity for spatial locations and not colors increased when the items were separated between the two visual fields. These findings support the view of VSTM as a chain of capacity limited operations where the spatial selection of stimuli, which dominates in both spatial location VSTM and MOT, occupies the first place and shows independence between the two fields.     

The effect of spatial organization of targets and distractors on the capacity to selectively memorize objects in visual short-term memory

We conducted a series of experiments to explore how the spatial configuration of objects influences the selection and the processing of these objects in a visual short-term memory task. We designed a new experiment in which participants had to memorize 4 targets presented among 4 distractors. Targets were cued during the presentation of distractor objects. Their locations varied according to 4 spatial configurations. From the first to the last configuration, the distance between targets’ locations was progressively increased. The results revealed a high capacity to select and memorize targets embedded among distractors even when targets were extremely distant from each other. This capacity is discussed in relation to the unitary conception of attention, models of split attention, and the competitive interaction model. Finally, we propose that the spatial dispersion of objects has different effects on attentional allocation and processing stages. Thus, when targets are extremely distant from each other, attentional allocation becomes more difficult while processing becomes easier. This finding implicates that these 2 aspects of attention need to be more clearly distinguished in future research.     

The right hemisphere advantage in visual change detection depends on temporal factors

What accounts for the Right Hemisphere (RH) functional superiority in visual change detection? An original task which combines one-shot and divided visual field paradigms allowed us to direct change information initially to the RH or the Left Hemisphere (LH) by deleting, respectively, an object included in the left or right half of a scene presented centrally. We manipulated the perceptual salience and semantic relevance of the change as well as the duration of the Inter-Stimulus Interval (ISI) between the scenes in order to clarify the role of the RH in memory and attention processes, and to explore whether lengthening the ISI would enhance the contribution of the LH. When analyzing data collapsed over the two levels (high vs. low) of salience and of relevance, changes were better detected in the left visual field (lvf) than in the right visual field (rvf) in the case of a short ISI, while no difference emerged in the case of a long ISI. Moreover, lengthening the ISI resulted in a performance decrement in the lvf, both for accuracy and response speed. The fact that the RH superiority was limited to short intervals indicates that stimulus-driven orienting contributes more than perceptual processing to this hemispheric asymmetry. When considering perceptual and semantic properties of the change, the effect of the ISI duration seemed to specifically emerge in the case of low relevance, with an enhancement of accuracy in the rvf when comparing the long with the short ISI. This suggests that the ISI influence on hemispheric performance operates on different levels.     

Mental imagery in a visuospatial working memory task and modulation of activation

Ability to process information during a mental imagery task relying on visuospatial working memory and the advantages offered by the possibility of focusing the activation on specific items were examined in younger and older adults. The mental imagery task used for the study required participants to mentally move on a two-dimensional (5×5) or three-dimensional (3×3×3) matrix, while having to hold in memory either the whole pathway (WP condition) or just the final position reached (FP condition). The results revealed age-related differences in ability to modulate activation of visuospatial information. In particular, older adults, unlike the younger counterparts, did not benefit when the task allowed just part of the presented material to be considered. In particular, they drew less advantage from the three-dimensional matrix than the younger group. The findings are discussed in terms of the importance of processes reducing visuospatial working memory activation of irrelevant information and of the difficulties encountered by older adults in the modulation of activation.     

Visual working memory and threat monitoring: Spider fearfuls show disorder-specific change detection

Previous studies of biased information processing in anxiety addressed biases of attention and memory, but little is known about the processes taking place between them: visual working memory (VWM) and monitoring of threat. We investigated these processes with a change detection paradigm. In Experiment 1, spider fearfuls (SF) and non-anxious controls (NAC) judged two subsequently presented displays as same or different. The displays consisted of several pictures, one of which could depict a spider. In Experiment 2, SF and NAC, both without snake fear, were tested with displays including either a spider or a snake image to determine the material-specificity of biased VWM. Both groups showed increased change detection for threat images. This effect was significantly stronger in SF, for spider images only, indicating a threat-specific VWM bias. Thus, contrary to the assumptions made by most cognitive models of anxiety, an explicit memory bias was found.     

Visual marking and change detection

The preview benefit from prior exposure of response-irrelevant (distracter) objects in visual search has been accounted for in terms of top-down inhibition (i.e. visual marking), bottom-up abrupt onset capture, or asynchrony-dependent perceptual segregation. We assess the relative contribution of abrupt onset and visual marking in a paradigm combining visual search with a visual working memory task. We investigated time-based selection of multiple objects for storage in visual working memory, using a change detection paradigm (Luck and Vogel in Nature 390:279–281, 1997) with distracter preview. We varied preview exposure (short vs. long), in a series of three experiments. The contribution of asynchrony-related perceptual segregation was assessed across experiments by varying the complexity of the stimuli (colored squares, oriented bars and oriented T-shapes) and the type of change detection (color or orientation), resulting in different levels of perceptual segregation between visual elements. The results suggest that bottom-up abrupt onset, visual marking and perceptual segregation factors co-operate in time-based selection for storage in visual working memory.     

The development of visual short-term memory for multifeature items during middle childhood

Visual short-term memory (VSTM) research suggests that the adult capacity is limited to three or four multifeature object representations. Despite evidence supporting a developmental increase in capacity, it remains unclear what the unit of capacity is in children. The current study employed the change detection paradigm to investigate both the capacity and nature of the representations of VSTM in 7-year-olds, 10-year-olds, and adults. Two experimental conditions were used to compare memory performance for single-feature objects with that for multifeature objects. Results provided further and more convincing evidence for a developmental increase in VSTM. Furthermore, the “loading up” of features in the multifeature condition was found to incur no significant performance deficit in all age groups. These findings are explained in terms of a developmental increase in the number of integrated multifeature object representations in VSTM.     

The change probability effect: incidental learning, adaptability, and shared visual working memory resources

Statistical properties in the visual environment can be used to improve performance on visual working memory (VWM) tasks. The current study examined the ability to incidentally learn that a change is more likely to occur to a particular feature dimension (shape, color, or location) and use this information to improve change detection performance for that dimension (the change probability effect). Participants completed a change detection task in which one change type was more probable than others. Change probability effects were found for color and shape changes, but not location changes, and intentional strategies did not improve the effect. Furthermore, the change probability effect developed and adapted to new probability information quickly. Finally, in some conditions, an improvement in change detection performance for a probable change led to an impairment in change detection for improbable changes.     

The consequence of a limited-capacity short-term memory on repeated visual search

ABSTRACT

When participants search the same letter display repeatedly for different targets we might expect performance to improve on each subsequent search as they memorize characteristics of the display. However, here we find that search performance improved from a first search to a second search but not for a third search of the same display. This is predicted by a simple model that supports search with only a limited capacity short-term memory for items in the display. To support this model we show that a short-term memory recency effect is present in both the second and the third search. The magnitude of these effects is the same in both searches and as a result there is no additional benefit from the second to the third search.     

Cross-modal and intra-modal binding between identity and location in spatial working memory: The identity of objects does not help recalling their locations

In this study we tested incidental feature-to-location binding in a spatial task, both in unimodal and cross-modal conditions. In Experiment 1 we administered a computerised version of the Corsi Block-Tapping Task (CBTT) in three different conditions: the first one analogous to the original CBTT test; the second one in which locations were associated with unfamiliar images; the third one in which locations were associated with non-verbal sounds. Results showed no effect on performance by the addition of identity information. In Experiment 2, locations on the screen were associated with pitched sounds in two different conditions: one in which different pitches were randomly associated with locations and the other in which pitches were assigned to match the vertical position of the CBTT squares congruently with their frequencies. In Experiment 2 we found marginal evidence of a pitch facilitation effect in the spatial memory task. We ran a third experiment to test the same conditions of Experiment 2 with a within-subject design. Results of Experiment 3 did not confirm the pitch–location facilitation effect. We concluded that the identity of objects does not affect recalling their locations. We discuss our results within the framework of the debate about the mechanisms of “what” and “where” feature binding in working memory.     

The role of convexity in perception of symmetry and in visual short-term memory

Visual perception of shape is affected by coding of local convexities and concavities. For instance, a recent study reported that deviations from symmetry carried by convexities were easier to detect than deviations carried by concavities. We removed some confounds and extended this work from a detection of reflection of a contour (i.e., bilateral symmetry), to a detection of repetition of a contour (i.e., translational symmetry). We tested whether any convexity advantage is specific to bilateral symmetry in a two-interval (Experiment 1) and a single-interval (Experiment 2) detection task. In both, we found a convexity advantage only for repetition. When we removed the need to choose which region of the contour to monitor (Experiment 3) the effect disappeared. In a second series of studies, we again used shapes with multiple convex or concave features. Participants performed a change detection task in which only one of the features could change. We did not find any evidence that convexities are special in visual short-term memory, when the to-be-remembered features only changed shape (Experiment 4), when they changed shape and changed from concave to convex and vice versa (Experiment 5), or when these conditions were mixed (Experiment 6). We did find a small advantage for coding convexity as well as concavity over an isolated (and thus ambiguous) contour. The latter is consistent with the known effect of closure on processing of shape. We conclude that convexity plays a role in many perceptual tasks but that it does not have a basic encoding advantage over concavity.     

The roles of the central executive and visuospatial storage in mental arithmetic: A comparison across strategies

Previous research has demonstrated that working memory plays an important role in arithmetic. Different arithmetical strategies rely on working memory to different extents—for example, verbal working memory has been found to be more important for procedural strategies, such as counting and decomposition, than for retrieval strategies. Surprisingly, given the close connection between spatial and mathematical skills, the role of visuospatial working memory has received less attention and is poorly understood. This study used a dual-task methodology to investigate the impact of a dynamic spatial n-back task (Experiment 1) and tasks loading the visuospatial sketchpad and central executive (Experiment 2) on adults' use of counting, decomposition, and direct retrieval strategies for addition. While Experiment 1 suggested that visuospatial working memory plays an important role in arithmetic, especially when counting, the results of Experiment 2 suggested this was primarily due to the domain-general executive demands of the n-back task. Taken together, these results suggest that maintaining visuospatial information in mind is required when adults solve addition arithmetic problems by any strategy but the role of domain-general executive resources is much greater than that of the visuospatial sketchpad.     

Relations between vocabulary development and verbal short-term memory: The relative importance of short-term memory for serial order and item information

Although many studies have shown an association between verbal short-term memory (STM) and vocabulary development, the precise nature of this association is not yet clear. The current study reexamined this relation in 4- to 6-year-olds by designing verbal STM tasks that maximized memory for either item or serial order information. Although empirical data suggest that distinct STM processes determine item and serial order recall, these were generally confounded in previous developmental studies. We observed that item and order memory tasks were independently related to vocabulary development. Furthermore, vocabulary development was more strongly associated with STM for order information in 4- and 6-year-olds and with STM for item information in 5-year-olds. These data highlight the specificity of verbal STM for serial order and item information and suggest a causal association between order STM processes and vocabulary development, at least in 4- and 6-year-olds.     

The impact of aging and hearing status on verbal short-term memory

The aim of this study is to assess the impact of hearing status on age-related decrease in verbal short-term memory (STM) performance. This was done by administering a battery of verbal STM tasks to elderly and young adult participants matched for hearing thresholds, as well as to young normal-hearing control participants. The matching procedure allowed us to assess the importance of hearing loss as an explanatory factor of age-related STM decline. We observed that elderly participants and hearing-matched young participants showed equal levels of performance in all verbal STM tasks, and performed overall lower than the normal-hearing young control participants. This study provides evidence for recent theoretical accounts considering reduced hearing level as an important explanatory factor of poor auditory-verbal STM performance in older adults.     

Dynamic binding of identity and location information: a serial model of multiple identity tracking

Tracking of multiple moving objects is commonly assumed to be carried out by a fixed-capacity parallel mechanism. The present study proposes a serial model (MOMIT) to explain performance accuracy in the maintenance of multiple moving objects with distinct identities. A serial refresh mechanism is postulated, which makes recourse to continuous attention switching, a capacity-limited episodic buffer for identity-location bindings, indexed location information stored in the visuospatial short-term memory, and an active role of long-term memory. As identity-location bindings are refreshed serially, a location error is inherent for all other targets except the focally attended one. The magnitude of this location error is a key factor in predicting tracking accuracy. MOMIT’s predictions were supported by the data of five experiments: performance accuracy decreased as a function of target set-size, speed, and familiarity. A mathematical version of MOMIT fitted nicely to the observed data with plausible parameter estimates for the binding capacity and refresh time.     

The effect of cueing on change blindness and same blindness

We used the change blindness paradigm of Landman, Spekreijse, and Lamme (2003) to measure the effect of cues on the ability to detect changes between two presentations of an array of eight rectangles separated by an interstimulus interval (ISI). Next, we measured the ability to detect sameness as the target rectangle remained the same when all of the others changed orientation. We were surprised to find no difference between change-detection and same-detection performance. These results (1) are consistent with the notion that some kind of internal representation was cued during the ISI, (2) mitigate against the recruitment of grouping strategies and/or forming a Gestalt, and (3) imply that under conditions facilitated by cues same-detection performance can be as good as change-detection performance.