Overlapping mechanisms of attention and spatial working memory

Spatial selective attention and spatial working memory have largely been studied in isolation. Studies of spatial attention have provided clear evidence that observers can bias visual processing towards specific locations, enabling faster and better processing of information at those locations than at unattended locations. We present evidence supporting the view that this process of visual selection is a key component of rehearsal in spatial working memory. Thus, although working memory has sometimes been depicted as a storage system that emerges 'downstream' of early sensory processing, current evidence suggests that spatial rehearsal recruits top-down processes that modulate the earliest stages of visual analysis.     

Interference between object-based attention and object-based memory

Research has shown that there are at least two kinds of visual selective attention: location based and object based. In the present study, we sought to determine the locus of spatially invariant object-based selection using a dual-task paradigm. In four experiments, observers performed an attention task (object feature report or visual search) with a concurrent memory task (object memory or spatial memory). Object memory was interfered with more by a concurrent object-based attention task than by a concurrent location-based attention task. However, this interference pattern was reversed for spatial memory, with greater interference by a location-based attention task than by an object-based attention task. These findings suggest that object-based attention and locationbased attention are functionally dissociable and that some forms of object-based selection operate within visual short-term memory.     

Attention on our mind: The role of spatial attention in visual working memory

The current study shows that spatial visual attention is used to retrieve information from visual working memory. Participants had to keep four colored circles in visual working memory. While keeping this information in memory we asked whether one of the colors was present in the array. While retrieving this information, on some trials a probe dot was presented. When this probe dot was presented at the location of the color that had to be retrieved, participants responded faster than when it was presented at another location. Our findings further elaborate the role of visual attention in working memory: not only is attention the mechanism by which information is stored into working memory, it is also the mechanism by which information is retrieved from visual working memory.     

Cross-sensory transfer of reference frames in spatial memory

Two experiments investigated whether visual cues influence spatial reference frame selection for locations learned through touch. Participants experienced visual cues emphasizing specific environmental axes and later learned objects through touch. Visual cues were manipulated and haptic learning conditions were held constant. Imagined perspective taking when recalling touched objects was best from perspectives aligned with visually-defined axes, providing evidence for cross-sensory reference frame transfer. These findings advance spatial memory theory by demonstrating that multimodal spatial information can be integrated within a common spatial representation.     

Visual short-term memory always requires general attention

The role of attention in visual memory remains controversial; while some evidence has suggested that memory for binding between features demands no more attention than does memory for the same features, other evidence has indicated cognitive costs or mnemonic benefits for explicitly attending to bindings. We attempted to reconcile these findings by examining how memory for binding, for features, and for features during binding is affected by a concurrent attention-demanding task. We demonstrated that performing a concurrent task impairs memory for as few as two visual objects, regardless of whether each object includes one or more features. We argue that this pattern of results reflects an essential role for domain-general attention in visual memory, regardless of the simplicity of the to-be-remembered stimuli. We then discuss the implications of these findings for theories of visual working memory.     

Interference in immediate spatial memory

It has been suggested that maintenance in visuospatial immediate memory involves implicit motor processes that are analogous to the articulatory loop in verbal memory. An alternative account, which is explored here, is that maintenance is based on shifts of spatial attention. In four experiments, subjects recalled spatial memory span items after an interval, and in a fifth experiment, digit span was recalled after an interval. The tasks carried out during the interval included touching visual targets, repeating heard words, listening to tones from spatially sepa-rated locations, pointing to these tones, pointing to visual targets, and categorizing spatial tar-gets as being from the left or right. Spatial span recall was impaired if subjects saw visual tar-gets or heard tones, and this impairment was increased if either a motor response or a categorical response was made. Repeating words heard in different spatial locations did not impair recall, but reading visually presented words did interfere. For digit span only, the tasks involving a verbal response impaired recall. The results are interpreted within a framework in which active spatial attention is involved in maintaining spatial items in order in memory, and is interfered with by any task (visual, auditory, perceptual, motor) that also makes demands on spatial attention.     

The effect of spatial attention on invisible stimuli

The influence of selective attention on visual processing is widespread. Recent studies have demonstrated that spatial attention can affect processing of invisible stimuli. However, it has been suggested that this effect is limited to low-level features, such as line orientations. The present experiments investigated whether spatial attention can influence both low-level (contrast threshold) and high-level (gender discrimination) adaptation, using the same method of attentional modulation for both types of stimuli. We found that spatial attention was able to increase the amount of adaptation to low- as well as to high-level invisible stimuli. These results suggest that attention can influence perceptual processes independent of visual awareness.     

Readout from iconic memory and selective spatial attention involve similar neural processes

Iconic memory and spatial attention are often considered separately, but they may have functional similarities. Here we provide functional magnetic resonance imaging evidence for some common underlying neural effects. Subjects judged three visual stimuli in one hemifield of a bilateral array comprising six stimuli. The relevant hemifield for partial report was indicated by an auditory cue, administered either before the visual array (precue, spatial attention) or shortly after the array (postcue, iconic memory). Pre- and postcues led to similar activity modulations in lateral occipital cortex contralateral to the cued side. This finding indicates that readout from iconic memory can have some neural effects similar to those of spatial attention. We also found common bilateral activation of a fronto-parietal network for postcue and precue trials. These neuroimaging data suggest that some common neural mechanisms underlie selective spatial attention and readout from iconic memory. Some differences were also found; compared with precues, postcues led to higher activity in the right middle frontal gyrus.     

Going the distance: Extra-symbolic contributions to the symbolic control of spatial attention

Over the past 30 years, researchers have used symbolic cues such as spatial words and arrows to direct observers' attention to the location of target objects that appear at a single, fixed distance in simple visual environments; however, they have done so by using symbolic cues that provide only partial—directional—information about the spatial location of target objects. Thus, it remains unclear whether observers can only shift their attention broadly in the cued direction in response to these cues or whether they can shift their attention to the specific location of the target by combining an expectation about direction (derived from apprehension of the directional cue) with an expectation about distance (derived from some extra-symbolic cue). The results of two experiments showed that observers do shift their attention to relatively coarse spatial locations by combining expectancies about direction and distance, and that the extent to which observers do so is modulated by the presence of visible markers and the expected distance of the target. These findings are important because they provide the first evidence that extra-symbolic information about distance contributes to the symbolic control of spatial attention.     

The effect of spatial and nonspatial contextual information on visual object memory

Recent research has found visual object memory can be stored as part of a larger scene representation rather than independently of scene context. The present study examined how spatial and nonspatial contextual information modulate visual object memory. Two experiments tested participants’ visual memory by using a change detection task in which a target object's orientation was either the same as it appeared during initial viewing or changed. In addition, we examined the effect of spatial and nonspatial contextual manipulations on change detection performance. The results revealed that visual object representations can be maintained reliably after viewing arrays of objects. Moreover, change detection performance was significantly higher when either spatial or nonspatial contextual information remained the same in the test image. We concluded that while processing complex visual stimuli such as object arrays, visual object memory can be stored as part of a comprehensive scene representation, and both spatial and nonspatial contextual changes modulate visual memory retrieval and comparison.     

Interference with spatial working memory: An eye movement is more than a shift of attention

In the present experiments, we examined whether shifts of attention selectively interfere with the maintenance of both verbal and spatial information in working memory and whether the interference produced by eye movements is due to the attention shifts that accompany them. In Experiment 1, subjects performed either a spatial or a verbal working memory task, along with a secondary task requiring fixation or a secondary task requiring shifts of attention. The results indicated that attention shifts interfered with spatial, butnot with verbal, working memory, suggesting that the interference is specific to processes within the visuospatial sketchpad. In Experiment 2, subjects performed a primary spatial working memory task, along with a secondary task requiring fixation, an eye movement, or an attention shift executed in the absence of an eye movement. The results indicated that both eye movements and attention shifts interfered with spatial working memory. Eye movements interfered to a much greater extent than shifts of attention, however, suggesting that eye movements may contribute a unique source of interference, over and above the interference produced by the attention shifts that accompany them.     

Implicit memory influences the allocation of attention in visual cortex

The visual environment is highly regular, with particular objects frequently appearing in specific locations. Previous studies of visual search have shown that people take advantage of such regularities, detecting targets more quickly when they appear at a predictable location within a given spatial configuration. Moreover, this effect depends on implicit rather than explicit memory for the configurations. These studies have suggested that implicit long-term memory for contextual information influences the allocation of attention, modulating the flow of information through visual cortex. The present study used event-related potentials to provide the first direct support for this proposal. We suggest that this guidance of attention by implicit memory is important in the natural environment because it allows environmental regularities to influence perception without the intervention of limited-capacity conscious processes.     

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.     

Statistical regularities guide the spatial scale of attention

Visual scenes contain information on both a local scale (e.g., a tree) and a global scale (e.g., a forest). The question of whether the visual system prioritizes local or global elements has been debated for over a century. Given that visual scenes often contain distinct individual objects, here we examine how regularities between individual objects prioritize local or global processing. Participants viewed Navon-like figures consisting of small local objects making up a global object, and were asked to identify either the shape of the local objects or the shape of the global object, as fast and accurately as possible. Unbeknown to the participants, local regularities (i.e., triplets) or global regularities (i.e., quadruples) were embedded among the objects. We found that the identification of the local shape was faster when individual objects reliably co-occurred immediately next to each other as triplets (local regularities, Experiment 1). This result suggested that local regularities draw attention to the local scale. Moreover, the identification of the global shape was faster when objects co-occurred at the global scale as quadruples (global regularities, Experiment 2). This result suggested that global regularities draw attention to the global scale. No participant was explicitly aware of the regularities in the experiments. The results suggest that statistical regularities can determine whether attention is directed to the individual objects or to the entire scene. The findings provide evidence that regularities guide the spatial scale of attention in the absence of explicit awareness.     

The role of overt attention in emotion-modulated memory

The presence of emotional stimuli results in a central/peripheral tradeoff effect in memory: memory for central details is enhanced at the cost of peripheral items. It has been assumed that emotion-modulated differences in memory are the result of differences in attention, but this has not been tested directly. The present experiment used eye movement monitoring as an index of overt attention allocation and mediation analysis to determine whether differences in attention were related to subsequent memory. Participants viewed negative and neutral scenes surrounded by three neutral objects and were then given a recognition memory test. The results revealed evidence in support of a central/peripheral tradeoff in both attention and memory. However, contrary with previous assumptions, whereas attention partially mediated emotion-enhanced memory for central pictures, it did not explain the entire relationship. Further, although centrally presented emotional stimuli led to decreased number of eye fixations toward the periphery, these differences in viewing did not contribute to emotion-impaired memory for specific details pertaining to the periphery. These findings suggest that the differential influence of negative emotion on central versus peripheral memory may result from other cognitive influences in addition to overt visual attention or on postencoding processes.     

Feature-based memory-driven attentional capture: visual working memory content affects visual attention

In 7 experiments, the authors explored whether visual attention (the ability to select relevant visual information) and visual working memory (the ability to retain relevant visual information) share the same content representations. The presence of singleton distractors interfered more strongly with a visual search task when it was accompanied by an additional memory task. Singleton distractors interfered even more when they were identical or related to the object held in memory, but only when it was difficult to verbalize the memory content. Furthermore, this content-specific interaction occurred for features that were relevant to the memory task but not for irrelevant features of the same object or for once-remembered objects that could be forgotten. Finally, memory-related distractors attracted more eye movements but did not result in longer fixations. The results demonstrate memory-driven attentional capture on the basis of content-specific representations.     

Representation of dynamic spatial configurations in visual short-term memory

Locations of multiple stationary objects are represented on the basis of their global spatial configuration in visual short-term memory (VSTM). Once objects move individually, they form a global spatial configuration with varying spatial inter-object relations over time. The representation of such dynamic spatial configurations in VSTM was investigated in six experiments. Participants memorized a scene with six moving and/or stationary objects and performed a location change detection task for one object specified during the probing phase. The spatial configuration of the objects was manipulated between memory phase and probing phase. Full spatial configurations showing all objects caused higher change detection performance than did no or partial spatial configurations for static and dynamic scenes. The representation of dynamic scenes in VSTM is therefore also based on their global spatial configuration. The variation of the spatiotemporal features of the objects demonstrated that spatiotemporal features of dynamic spatial configurations are represented in VSTM. The presentation of conflicting spatiotemporal cues interfered with memory retrieval. However, missing or conforming spatiotemporal cues triggered memory retrieval of dynamic spatial configurations. The configurational representation of stationary and moving objects was based on a single spatial configuration, indicating that static spatial configurations are a special case of dynamic spatial configurations.     

The role of spatial working memory in inhibition of return: evidence from divided attention tasks

Inhibition of return (IOR) refers to a bias against returning attention to a location that has been recently attended. In the present experiments, we examined the role of working memory in IOR by introducing secondary tasks (in the temporal interval between the cue and the target) that involved a working memory component. When the secondary task was nonspatial in nature (monitoring odd digits or adding digits), IOR was present, although overall reaction times were greater in the presence of the secondary task. When the task involved a spatial working memory load (remembering the directionality of arrows or the orientation of objects), IOR was eliminated. However, when the participants had incentive to process the directionality of an arrow but did not have to use any memory system, IOR persisted at peripheral locations. Overall, the results suggest that IOR is partially mediated by a spatial working memory system.     

Object detection in natural scenes: Independent effects of spatial and category-based attention

Humans are remarkably efficient in detecting highly familiar object categories in natural scenes, with evidence suggesting that such object detection can be performed in the (near) absence of attention. Here we systematically explored the influences of both spatial attention and category-based attention on the accuracy of object detection in natural scenes. Manipulating both types of attention additionally allowed for addressing how these factors interact: whether the requirement for spatial attention depends on the extent to which observers are prepared to detect a specific object category—that is, on category-based attention. The results showed that the detection of targets from one category (animals or vehicles) was better than the detection of targets from two categories (animals and vehicles), demonstrating the beneficial effect of category-based attention. This effect did not depend on the semantic congruency of the target object and the background scene, indicating that observers attended to visual features diagnostic of the foreground target objects from the cued category. Importantly, in three experiments the detection of objects in scenes presented in the periphery was significantly impaired when observers simultaneously performed an attentionally demanding task at fixation, showing that spatial attention affects natural scene perception. In all experiments, the effects of category-based attention and spatial attention on object detection performance were additive rather than interactive. Finally, neither spatial nor category-based attention influenced metacognitive ability for object detection performance. These findings demonstrate that efficient object detection in natural scenes is independently facilitated by spatial and category-based attention.     

Orientation dependence of spatial memory acquired from auditory experience

The present study investigated whether memory for a room-sized spatial layout learned through auditory localization of sounds exhibits orientation dependence similar to that observed for spatial memory acquired from stationary viewing of the environment. Participants learned spatial layouts by viewing objects or localizing sounds and then performed judgments of relative direction among remembered locations. The results showed that direction judgments following auditory learning were performed most accurately at a particular orientation in the same way as were those following visual learning, indicating that auditorily encoded spatial memory is orientation dependent. In combination with previous findings that spatial memories derived from haptic and proprioceptive experiences are also orientation dependent, the present finding suggests that orientation dependence is a general functional property of human spatial memory independent of learning modality.