Compression of environmental representations following interactions with objects

Previous work reveals that interacting with all objects in an environment can compress spatial memory for the entire group of objects. To assess the scope and magnitude of this effect, we tested whether interacting with a subset of objects compresses spatial memory for all objects in an environment. Participants inspected objects in one or two unmarked regions of space, then recalled the distances between pairs of objects from memory. One group of participants picked up objects in both regions, a second group picked up objects in one region and passively viewed objects in the other region, and a third group passively viewed objects in both regions. When participants manually interacted with objects, they recalled shorter object-pair distances throughout the environment. The magnitude of this effect was the same, regardless of whether participants interacted with all objects in the environment or just a subset of them. Together, these findings suggest that interacting with objects can compress environmental representations in memory, even when observers interact with a relatively small subset of objects.     

Neural representations in human spatial memory

Ekstrom et al. report the responses of single neurons recorded from the brains of human subjects performing a spatial navigation task in virtual reality. They found cells encoding the subject's current location, view and destination. These data, and related findings in animals, directly reveal some of the representations underlying spatial cognition. They highlight the potential for cognitive psychology and systems neuroscience to combine to provide a neuronal-level understanding of human behaviour.     

Configural representations in spatial working memory

Two studies investigate the nature of representations in spatial working memory, directly addressing the question of whether people represent the configuration information above and beyond independent positional information when representing multiple sequentially presented locations. In Experiment 1, participants performed a location memory task in which they recalled the location of objects that were presented sequentially on a screen. Comparison of participants' data with simulated data modelled to represent independent positional representation of spatial locations revealed that participants represented the configural properties of shorter sequences (3 and 4 locations) but not of longer ones (5 and 7 locations). Experiment 2 employed a sequential recognition task in which participants were asked to judge whether two consequently presented spatial sequences were identical. These experiments confirmed sensitivity to configural properties of spatial sequences.     

Switching between environmental representations in memory

In everyday life we accomplish tasks that require the storage and access of mental representations of different environments that we are not currently perceiving. Past research has suggested that environments are encoded by a series of independent representations that are organized in memory. Three experiments tested this idea further by asking whether multiple representations of environments can be accessed simultaneously. Using a cued task-set switching paradigm, subjects judged spatial relationships between target locations in two familiar environments. Response times were longer when successive trials probed different environments, an effect not due to switching between semantic categories or semantic priming, suggesting that representations of environments are accessed sequentially. Implications for various hypotheses concerning the properties of environmental representations are discussed.     

Visual and proprioceptive representations in spatial memory

It has been shown that spatial information can be acquired from both visual and nonvisual modalities. The present study explored how spatial information from vision and proprioception was represented in memory, investigating orientation dependence of spatial memories acquired through visual and proprioceptive spatial learning. Experiment 1 examined whether visual learning alone and proprioceptive learning alone yielded orientation-dependent spatial memory. Results showed that spatial memories from both types of learning were orientation dependent. Experiment 2 explored how different orientations of the same environment were represented when they were learned visually and proprioceptively. Results showed that both visually and proprioceptively learned orientations were represented in spatial memory, suggesting that participants established two different reference systems based on each type of learning experience and interpreted the environment in terms of these two reference systems. The results provide some initial clues to how different modalities make unique contributions to spatial representations.     

Verbal cues flexibly transform spatial representations in human memory

ABSTRACT

Humans possess a unique ability to communicate spatially-relevant information, yet the intersection between language and navigation remains largely unexplored. One possibility is that verbal cues accentuate heuristics useful for coding spatial layouts, yet this idea remains largely untested. We test the idea that verbal cues flexibly accentuate the coding of heuristics to remember spatial layouts via spatial boundaries or landmarks. The alternative hypothesis instead conceives of encoding during navigation as a step-wise process involving binding lower-level features, and thus subsequently formed spatial representations should not be modified by verbal cues. Across three experiments, we found that verbal cues significantly affected pointing error patterns at axes that were aligned with the verbally cued heuristic, suggesting that verbal cues influenced the heuristics employed to remember object positions. Further analyses suggested evidence for a hybrid model, in which boundaries were encoded more obligatorily than landmarks, but both were accessed flexibly with verbal instruction. These findings could not be accounted for by a tendency to spend more time facing the instructed component during navigation, ruling out an attentional-encoding mechanism. Our findings argue that verbal cues influence the heuristics employed to code environments, suggesting a mechanism for how humans use language to communicate navigationally-relevant information.     

Using selective interference to investigate spatial memory representations

Two experiments used a selective interference procedure in an attempt to determine whether nonverbal visual stimuli were represented in memory in a verbal or spatial format. A spatial representation was clearly implicated. In both experiments, Ss were required to remember either the positions or the identities of seven target items in a 25-item array. During the retention interval for that information, Ss attempted to recognize schematic face or airplane photograph stimuli in a same-different memory task. Memory performance on one or both tasks was greatly impaired when the recall task involved position or spatial information, but was either much less or not at all affected by an identity or verbal information recall task. Because of the selective nature of the interference and on the basis of certain correlational evidence, the experimental results were also interpreted as providing support for the notion that verbal and spatial information are stored and processed in separate information-processing systems.     

Semantic and spatial factors in environmental memory

Reaction time (RT) in simple categorization tasks was predicted to vary as a function of the relatedness among environmental items. Differences in RT were interpreted as reflecting differences in proximity or strength of associations in environmental memory. In Experiment 1, subjects sorted names of familiar local buildings according to which seemed to go together. Hierarchical cluster analysis revealed major clusters whose members were related in function and, within these, smaller clusters of buildings related by spatial proximity. In Experiment 2, subjects responded “Yes” if two items on a trial were both local buildings and “No” if one item was local and one nonlocal. Subjects responded significantly faster to pairs taken from the cluster analysis that were related by both spatial proximity and function than they did to unrelated pairs or pairs related in function only. In Experiment 3, a free-associaton task identified related pairs of spatially proximate, functionally dissimilar environmental items. In Experiment 4, RTs to these pairs did not differ from RTs to pairs of spatially proximate, functionally dissimilar items or from RTs to pairs unrelated functionally and spatially. Spatial proximity and functional similarity together contribute to the organization in memory of buildings in the physical environment.     

Determinants of spatial priming in environmental memory

Spatial priming in recognizing objects in experimentally learned environments has been proposed as strong evidence for spatial organization of environmental memory. However, in all studies showing recognition priming effects, encoding and rehearsal contiguity may have coincided with spatial proximity, and thus priming may have been due to temporal associations formed during rehearsal, not encoded spatial relations per se. We investigated this question in four experiments, using a trip trial learning method in which temporal contiguity and spatial relations were independent. In Experiment 1, no spatial priming in recognition was found, even though indirect evidence suggested that subjects had encoded spatial relations. In Experiment 2, the trip trial method was compared with the free study procedure commonly used in previous priming studies. Spatial priming occurred only for free study subjects, even though the two groups were equivalent on direct measures of encoding accuracy. In Experiment 3, spatial priming in recognition was obtained with a modification of the trip trial method in which temporal and spatial contiguity were deliberately confounded. In Experiment 4, the unmodified trip trial method produced spatial priming in a location-decision task. Taken together, our results suggest that environmental memory may be spatially organized, but retrieval of object identities does not necessarily activate encoded spatial relations.     

Cognitive representations of functional interactions with objects

Two studies addressed people’s knowledge about the movements underlying functional interactions with objects, when the interactions were described by simple verbal labels expressing environmental goals. In Experiment 1, subjects rated each action with respect to six dimensions: which portion of the limb moved, distance moved, forcefulness, effectors involved, size of the contact surface, and resemblance to grasp. Ratings were systematic and fell on two distinct underlying factors related to limb movement and effector (usually the hand) configuration. In Experiment 2, subjects sorted a subset of the actions by similarity of movement. Clustering and multidimensional scaling solutions indicated that the six initial dimensions contributed to similarity judgments, along with additional parameters. The results support the existence of cognitively accessible, but still relatively specific, representations of functional actions, with potential implications for motor and memory performance.     

The CA3 network as a memory store for spatial representations

Comparative neuroanatomy suggests that the CA3 region of the mammalian hippocampus is directly homologous with the medio-dorsal pallium in birds and reptiles, with which it largely shares the basic organization of primitive cortex. Autoassociative memory models, which are generically applicable to cortical networks, then help assess how well CA3 may process information and what the crucial hurdles are that it may face. The analysis of such models points at spatial memories as posing a special challenge, both in terms of the attractor dynamics they can induce and how they may be established. Addressing such a challenge may have favored the evolution of elements of hippocampal organization observed only in mammals.     

No evidence of binding items to spatial configuration representations in visual working memory

When detecting changes in visual features (e.g., colour or shape), object locations, represented as points within a configuration, might also be automatically represented in working memory. If the configuration of a scene is represented automatically, the locations of individual items might form part of this representation, irrespective of their relevance to the task. Participants took part in a change-detection task in which they studied displays containing different sets of items (shapes, letters, objects), which varied in their task relevance. Specifically, they were asked to remember the features of two sets, and ignore the third set. During the retention interval, an audio cue indicated which of the to-be-remembered sets would become the target set (having a 50% probability of containing a new feature). At test, they were asked to indicate whether a new feature was present amongst the target set. We measured binding of individual items to the configuration by manipulating the locations of the different sets so that their position in the test display either matched or mismatched their original location in the study display. If items are automatically bound to the configuration, location changes should disrupt performance, even if they were explicitly instructed not to remember the features of that particular set of items. There was no effect on performance of changing the locations of any of the sets between study and test displays, indicating that the configural representation did not enter their decision stage, and therefore that individual item representations are not necessarily bound to the configuration.     

No functional role of attention-based rehearsal in maintenance of spatial working memory representations

The present study systematically examined the role of attention in maintenance of spatial representations in working memory as proposed by the attention-based rehearsal hypothesis [Awh, E., Jonides, J., & Reuter-Lorenz, P. A. (1998). Rehearsal in spatial working memory. Journal of Experimental Psychology - Human Perception and Performance, 24(3), 780-790]. Three main issues were examined. First, Experiments 1-3 demonstrated that inhibition and not facilitation of visual processing is often observed at the memorized location during the retention interval. This inhibition was caused by keeping a location in memory and not by the exogenous nature of the memory cue. Second, Experiment 4 showed that inhibition of the memorized location does not lead to any significant impairment in memory accuracy. Finally, Experiment 5 connected current results to the previous findings and demonstrated facilitation of processing at the memorized location. Importantly, facilitation of processing did not lead to more accurate memory performance. The present results challenge the functional role of attention in maintenance of spatial working memory representations.     

Reference directions and reference objects in spatial memory of a briefly viewed layout

Two experiments investigated participants' spatial memory of a briefly viewed layout. Participants saw an array of five objects on a table and, after a short delay, indicated whether the target object indicated by the experimenter had been moved. Experiment 1 showed that change detection was more accurate when non-target objects were stationary than when non-target objects were moved. This context effect was observed when participants were tested both at the original learning perspective and at a novel perspective. In Experiment 2, the arrays of five objects were presented on a rectangular table and two of the non-target objects were aligned with the longer axis of the table. Change detection was more accurate when the target object was presented with the two objects that were aligned with the longer axis of the table during learning than when the target object was presented with the two objects that were not aligned with the longer axis of the table during learning. These results indicated that the spatial memory of a briefly viewed layout has interobject spatial relations represented and utilizes an allocentric reference direction.     

Configural representations in spatial working memory: modulation by perceptual segregation and voluntary attention

In what form are multiple spatial locations represented in working memory? The present study revealed that people often maintain the configural properties (interitem relationships) of visuospatial stimuli even when this information is explicitly task-irrelevant. However, the results also indicated that the voluntary allocation of selective attention prior to stimulus presentation, as well as feature-based perceptual segregation of relevant from irrelevant stimuli, can eliminate the influence of stimulus configuration on location-change detection performance. In contrast, voluntary attention cued to the relevant target location following presentation of the stimulus array failed to attenuate these influences. Thus, whereas voluntary selective attention can isolate or prevent the encoding of irrelevant stimulus locations and configural properties, people, perhaps due to limitations in attentional resources, reliably fail to isolate or suppress configural representations that have been encoded into working memory.     

Binding serial order to representations in working memory: a spatial/verbal dissociation

Verbal information is coded naturally as ordered representations in working memory (WM). However, this may not be true for spatial information. Accordingly, we used memory span tasks to test the hypothesis that serial order is more readily bound to verbal than to spatial representations. Removing serial-order requirements improved performance more for spatial locations than for digits. Furthermore, serial order was freely reproduced twice as frequently for digits as for locations. When participants reordered spatial sequences, they minimized the mean distance between items. Participants also failed to detect changes in serial order more frequently for spatial than for verbal sequences. These results provide converging evidence for a dissociation in the binding of serial order to spatial versus verbal representations. There may be separable domain-specific control processes responsible for this binding. Alternatively, there may be fundamental differences in how effectively temporal information can be bound to different types of stimulus features in WM.     

Infants' representations of three-dimensional occluded objects

Infants' ability to represent objects has received significant attention from the developmental research community. With the advent of eye-tracking technology, detailed analysis of infants' looking patterns during object occlusion have revealed much about the nature of infants' representations. The current study continues this research by analyzing infants' looking patterns in a novel manner and by comparing infants' looking at a simple display in which a single three-dimensional (3D) object moves along a continuous trajectory to a more complex display in which two 3D objects undergo trajectories that are interrupted behind an occluder. Six-month-old infants saw an occlusion sequence in which a ball moved along a linear path, disappeared behind a rectangular screen, and then a ball (ball-ball event) or a box (ball-box event) emerged at the other edge. An eye-tracking system recorded infants' eye-movements during the event sequence. Results from examination of infants' attention to the occluder indicate that during the occlusion interval infants looked longer to the side of the occluder behind which the moving occluded object was located, shifting gaze from one side of the occluder to the other as the object(s) moved behind the screen. Furthermore, when events included two objects, infants attended to the spatiotemporal coordinates of the objects longer than when a single object was involved. These results provide clear evidence that infants' visual tracking is different in response to a one-object display than to a two-object display. Furthermore, this finding suggests that infants may require more focused attention to the hidden position of objects in more complex multiple-object displays and provides additional evidence that infants represent the spatial location of moving occluded objects.     

Egocentric metric representations in peripersonal space: A bridge between motor resources and spatial memory

Research on visuospatial memory has shown that egocentric (subject-to-object) and allocentric (object-to-object) reference frames are connected to categorical (non-metric) and coordinate (metric) spatial relations, and that motor resources are recruited especially when processing spatial information in peripersonal (within arm reaching) than extrapersonal (outside arm reaching) space. In order to perform our daily-life activities, these spatial components cooperate along a continuum from recognition-related (e.g., recognizing stimuli) to action-related (e.g., reaching stimuli) purposes. Therefore, it is possible that some types of spatial representations rely more on action/motor processes than others. Here, we explored the role of motor resources in the combinations of these visuospatial memory components. A motor interference paradigm was adopted in which participants had their arms bent behind their back or free during a spatial memory task. This task consisted in memorizing triads of objects and then verbally judging what was the object: (1) closest to/farthest from the participant (egocentric coordinate); (2) to the right/left of the participant (egocentric categorical); (3) closest to/farthest from a target object (allocentric coordinate); and (4) on the right/left of a target object (allocentric categorical). The triads appeared in participants' peripersonal (Experiment 1) or extrapersonal (Experiment 2) space. The results of Experiment 1 showed that motor interference selectively damaged egocentric-coordinate judgements but not the other spatial combinations. The results of Experiment 2 showed that the interference effect disappeared when the objects were in the extrapersonal space. A third follow-up study using a within-subject design confirmed the overall pattern of results. Our findings provide evidence that motor resources play an important role in the combination of coordinate spatial relations and egocentric representations in peripersonal space.     

Effects of environmental enrichment on spatial memory and neurochemistry in middle-aged mice

The present study compared the effects of environmental enrichment on spatial memory, glutamic acid decarboxylase (GAD) activity, and synaptophysin levels in middle-aged male and female mice. Prior to testing, a subset of 18-month-old male and female C57BL/6 mice was housed with two to three toys and a running wheel in the home cage for up to 29 d. Adult mice (7 mo) of both sexes and the remaining middle-aged mice were group (social) housed, but not exposed to enriching objects. After the enrichment period, all mice were tested in a 1-day version of the Morris water maze, in which both spatial and nonspatial memory were assessed. Immediately after testing, the hippocampus and frontoparietal cortex were dissected, and GAD activity and synaptophysin levels were measured. Environmental enrichment reduced the age-related impairment in spatial acquisition and retention; relative to adult social controls, middle-aged enriched mice were unimpaired, whereas middle-aged social controls were impaired. This reduction was similar in middle-aged males and females. Enrichment did not affect cued memory in either sex. Although hippocampal GAD activity was increased by enrichment in males, all other neurochemical measurements were unaffected by enrichment or aging in either sex. These data suggest that environmental enrichment initiated at middle age can reduce age-related impairments in spatial memory in males and females, although the underlying neurobiological mechanisms of this effect remain unknown.