Spatial memory
In cognitive psychology and neuroscience, spatial memory is a form of memory responsible for the recording and recovery of information needed to plan a course to a location and to recall the location of an object or the occurrence of an event.[1] Spatial memory is necessary for orientation in space.[2][3] Spatial memory can also be divided into egocentric and allocentric spatial memory.[4] A person's spatial memory is required to navigate around a familiar city. A rat's spatial memory is needed to learn the location of food at the end of a maze. In both humans and animals, spatial memories are summarized as a cognitive map.[5]
Spatial memory has representations within working, short-term memory and long-term memory. Research indicates that there are specific areas of the brain associated with spatial memory.[6] Many methods are used for measuring spatial memory in children, adults, and animals.[5]
Short-term spatial memory[edit]
Short-term memory (STM) can be described as a system allowing one to temporarily store and manage information that is necessary to complete complex cognitive tasks.[7] Tasks which employ short-term memory include learning, reasoning, and comprehension.[7] Spatial memory is a cognitive process that enables a person to remember different locations as well as spatial relations between objects.[7] This allows one to remember where an object is in relation to another object;[7] for instance, allowing someone to navigate through a familiar city. Spatial memories are said to form after a person has already gathered and processed sensory information about her or his environment.[7]
Long-term spatial memory[edit]
Spatial memory recall is built upon a hierarchical structure. People remember the general layout of a particular space and then "cue target locations" within that spatial set.[14] This paradigm includes an ordinal scale of features that an individual must attend to in order to inform his or her cognitive map.[15] Recollection of spatial details is a top-down procedure that requires an individual to recall the superordinate features of a cognitive map, followed by the ordinate and subordinate features. Two spatial features are prominent in navigating a path: general layout and landmark orienting (Kahana et al., 2006). People are not only capable of learning about the spatial layout of their surroundings, but they can also piece together novel routes and new spatial relations through inference.
A cognitive map is "a mental model of objects' spatial configuration that permits navigation along optimal path between arbitrary pairs of points."[16] This mental map is built upon two fundamental bedrocks: layout, also known as route knowledge, and landmark orientation. Layout is potentially the first method of navigation that people learn to utilize; its workings reflect our most basic understandings of the world.
Hermer and Spelke (1994) determined that when toddlers begin to walk, around eighteen months, they navigate by their sense of the world's layout. McNamara, Hardy and Hirtle identified region membership as a major building block of anyone's cognitive map (1989). Specifically, region membership is defined by any kind of boundary, whether physical, perceptual or subjective (McNamara et al., 1989). Boundaries are among the most basic and endemic qualities in the world around us. These boundaries are nothing more than axial lines which are a feature that people are biased towards when relating to space; for example, one axial line determinant is gravity (McNamara & Shelton, 2001; Kim & Penn, 2004). Axial lines aid everyone in apportioning our perceptions into regions. This parceled world idea is further supported by the finding that items that get recalled together are more likely than not to also be clustered within the same region of one's larger cognitive map.[15] Clustering shows that people tend to chunk information together according to smaller layouts within a larger cognitive map.
Boundaries are not the only determinants of layout. Clustering also demonstrates another important property of relation to spatial conceptions, which is that spatial recall is a hierarchical process. When someone recalls an environment or navigates terrain, that person implicitly recalls the overall layout at first. Then, due to the concept's "rich correlational structure", a series of associations become activated.[14] Eventually, the resulting cascade of activations will awaken the particular details that correspond with the region being recalled. This is how people encode many entities from varying ontological levels, such as the location of a stapler; in a desk; which is in the office.
One can recall from only one region at a time (a bottleneck). A bottleneck in a person's cognitive navigational system could be an issue. For instance, if there were a need for a sudden detour on a long road trip. Lack of experience in a locale, or simply sheer size, can disorient one's mental layout, especially in a large and unfamiliar place with many overwhelming stimuli. In these environments, people are still able to orient themselves, and find their way around using landmarks. This ability to "prioritize objects and regions in complex scenes for selection (and) recognition" was labeled by Chun and Jiang in 1998. Landmarks give people guidance by activating "learned associations between the global context and target locations."[14] Mallot and Gillner (2000) showed that subjects learned an association between a specific landmark and the direction of a turn, thereby furthering the relationship between associations and landmarks.[17] Shelton and McNamara (2001) succinctly summed up why landmarks, as markers, are so helpful: "location...cannot be described without making reference to the orientation of the observer."
People use both the layout of a particular space and the presence of orienting landmarks in order to navigate. Psychologists have yet to explain whether layout affects landmarks or if landmarks determine the boundaries of a layout. Because of this, the concept suffers from a chicken and the egg paradox. McNamara has found that subjects use "clusters of landmarks as intrinsic frames of reference," which only confuses the issue further.[16]
People perceive objects in their environment relative to other objects in that same environment. Landmarks and layout are complementary systems for spatial recall, but it is unknown how these two systems interact when both types of information are available. As a result, people have to make certain assumptions about the interaction between the two systems. For example, cognitive maps are not "absolute" but rather, as anyone can attest, are "used to provide a default...(which) modulated according to...task demands."[14] Psychologists also think that cognitive maps are instance based, which accounts for "discriminative matching to past experience."[14]
This field has traditionally been hampered by confounding variables, such as cost and the potential for previous exposure to an experimental environment. Technological advancements, including those in virtual reality technology, have made findings more accessible. Virtual reality affords experimenters the luxury of extreme control over their test environment. Any variable can be manipulated, including things that would not be possible in reality.
Visual–spatial distinction[edit]
Logie (1995) proposed that the visuo-spatial sketchpad is broken down into two subcomponents, one visual and one spatial.[11] These are the visual cache and the inner scribe, respectively.[11] The visual cache is a temporary visual store including such dimensions as color and shape.[11] Conversely, the inner scribe is a rehearsal mechanism for visual information and is responsible for information concerning movement sequences.[11] Although a general lack of consensus regarding this distinction has been noted in the literature,[10][21][22] there is a growing amount of evidence that the two components are separate and serve different functions.
Visual memory is responsible for retaining visual shapes and colors (i.e., what), whereas spatial memory is responsible for information about locations and movement (i.e., where). This distinction is not always straightforward since part of visual memory involves spatial information and vice versa. For example, memory for object shapes usually involves maintaining information about the spatial arrangement of the features which define the object in question.[21]
In practice, the two systems work together in some capacity but different tasks have been developed to highlight the unique abilities involved in either visual or spatial memory. For example, the visual patterns test (VPT) measures visual span whereas the Corsi Blocks Task measures spatial span. Correlational studies of the two measures suggest a separation between visual and spatial abilities, due to a lack of correlation found between them in both healthy and brain damaged patients.[10]
Support for the division of visual and spatial memory components is found through experiments using the dual-task paradigm. A number of studies have shown that the retention of visual shapes or colors (i.e., visual information) is disrupted by the presentation of irrelevant pictures or dynamic visual noise. Conversely, the retention of location (i.e., spatial information) is disrupted only by spatial tracking tasks, spatial tapping tasks, and eye movements.[21][22] For example, participants completed both the VPT and the Corsi Blocks Task in a selective interference experiment. During the retention interval of the VPT, the subject viewed irrelevant pictures (e.g., avant-garde paintings). The spatial interference task required participants to follow, by touching the stimuli, an arrangement of small wooden pegs which were concealed behind a screen. Both the visual and spatial spans were shortened by their respective interference tasks, confirming that the Corsi Blocks Task relates primarily to spatial working memory.[10]
Learning difficulties[edit]
Nonverbal learning disability (NVLD) is characterized by normal verbal abilities but impaired visuospatial abilities. Problem areas for children with nonverbal learning disability include arithmetic, geometry, and science. Impairments in spatial memory are linked to nonverbal learning disorder and other learning difficulties.[95]
Arithmetic word problems involve written text containing a set of data followed by one or more questions and require the use of the four basic arithmetic operations (addition, subtraction, multiplication, or division).[22] Researchers suggest that successful completion of arithmetic word problems involves spatial working memory (involved in building schematic representations) which facilitates the creation of spatial relationships between objects. Creating spatial relationships between objects is an important part of solving word problems because mental operations and transformations are required.[22]
Researchers investigated the role of spatial memory and visual memory in the ability to complete arithmetic word problems. Children in the study completed the Corsi block task (forward and backward series) and a spatial matrix task, as well as a visual memory task called the house recognition test. Poor problem-solvers were impaired on the Corsi block tasks and the spatial matrix task, but performed normally on the house recognition test when compared to normally achieving children. The experiment demonstrated that poor problem solving is related specifically to deficient processing of spatial information.[22]
Sleep[edit]
Sleep has been found to benefit spatial memory, by enhancing hippocampal-dependent memory consolidation,[96] elevating different pathways which are responsible for synaptic strength, control plasticity-related gene transcription and protein translation (Dominique Piber, 2021).[97] Hippocampal areas activated in route-learning are reactivated during subsequent sleep (NREM sleep in particular). One study demonstrated that the actual extent of reactivation during sleep correlated with the improvement in route retrieval and therefore memory performance the following day.[98] The study established the idea that sleep enhances the systems-level process of consolidation that consequently enhances/improves behavioral performance. A period of wakefulness has no effect on stabilizing memory traces, in comparison to a period of sleep. Sleep after the first post-training night, i.e., on the second night, does not benefit spatial memory consolidation further. Therefore, sleeping in the first post-training night e.g. after learning a route, is most important.[96]
Further, it has been illustrated that early and late nocturnal sleep have different effects on spatial memory. N3 of the NREM sleep, also referred to as slow wave sleep (SWS), is supposed to have a salient role for the sleep-dependent creation of spatial memory in humans. Particularly in the study conducted by Plihal and Born (1999),[99] the performance on mental rotation tasks was higher among participants who had early sleep intervals (23.00–02.00 am) after learning the task compared to the ones who had late sleep intervals (03.00–06.00 am). These results suggest that early sleep, which is rich in SWS, has certain benefits for the formation of spatial memory. When researchers examined whether early sleep would have such an impact on word stem priming task (verbal task), the results were the opposite. This was not surprising for researchers as priming tasks mostly rely on procedural memory, and thus, it benefits more late retention sleep (dominated by REM sleep) rather than early.[99]
Sleep deprivation and sleep has also been a researched association. Sleep deprivation hinders memory performance improvement due to an active disruption of spatial memory consolidation.[96] As a result, spatial memory is enhanced by a period of sleep. Similar results were confirmed by another study examining the impact of total sleep deprivation (TSD) on rats' spatial memory (Guan et al., 2004).[100] In the first experiment conducted, the rats were trained in Morris water maze for 12 trials in 6 hours to find a hidden platform (transparent and not visible in the water) by using spatial cues in the environment. In each trial, they started from a different point and were allowed to swim for a maximum of 120 s to reach the platform. After the learning phase, they gave a probe trial to test spatial memory (after 24 h). In this trial, the hidden platform was removed from the maze and the time animals spent in the target area (which was occupied by hidden platform before) was a measure of spatial memory persistence. The control rats, who had spontaneous sleep, spent significantly more time in the target quadrant compared to ones who had total sleep deprivation. In terms of spatial learning, which is indicated by the latency to find the hidden platform, there were no differences. For both control and sleep deprived rats, the time required to find a platform was decreasing with every new trial.[100]
In the second experiment, the rats were trained to swim to a visible platform whose location was changed in each trial. For every new trial, the rats started from the opposite side of the platform. After the training in a single trial, their memory was tested after 24 h. Platform was still in the maze. The distance and the time they needed to swim to the visible platform were considered as non-spatial memory measures. No significant difference has been found between sleep deprived rats and control rats. Similarly, in terms of spatial learning, which is indicated by latency to reach the visible platform, there were no significant differences. TSD does not affect non-spatial learning and non-spatial memory.[100]
In reference to the effects of sleep deprivation on humans, Dominique Piber (2021)[97] featured in his literature review the clinical observations which shows that people with severe sleep disorders frequently have abnormalities in spatial memory. As visible in the studies of both, insomnia patients who suffer from a sleep disorder which features interrupted, non-restorative sleep and deficits in cognitive performance during the day, are documented to have a negative performance in a spatial task, in comparison with the healthy participants (Li et al., 2016;[101] Chen et al., 2016;[102] Khassawneh et al., 2018;[103] He et al., 2021[104]).
Likewise, dreaming has an important role in spatial memory. A study conducted by Wamsley and Stickgold (2019)[105] proved that participants, who incorporate a recent learning experience into their overnight dream content, show an increased overnight performance improvement. Thus, supporting the hypothesis that dreaming reflects memory processing in the sleeping brain. Moreover, according to the authors, one of the explanations is that maze‐related dreams are indicators that performance‐relevant components of task memory are being reactivated in the sleeping brain. Additionally, the study supports the idea that dream reports can include an experimental learning task during all stages of sleep, including REM and NREM.[105]
Virtual reality (VR) has also been used to study the connection between dreams and spatial memory. Ribeiro, Gounden, and Quaglino (2021)[106] proposed spatialized elements in a VR context and found that after a full night of sleep in a home setting, when the material studied was incorporated into the dream content, the recall performance of these elements was better than the performance obtained after a comparable wake period.[106]