|Ranxiao Frances Wang (2007), Scholarpedia, 2(10):3839.||doi:10.4249/scholarpedia.3839||revision #47716 [link to/cite this article]|
What is spatial updating?
When an animal moves from one place to another and turns from one direction to another, the spatial relationship between the animal and its environment changes constantly. Spatial updating refers to the cognitive process that computes the spatial relationship between an animal and its surrounding environment as it moves based on perceptual information about its own movements. Vector summation is usually considered to be the underlining mechanism. Spatial updating is a very common process found in almost all species tested, including insects, birds, rodents, and primates including humans. Precision of spatial updating varies across species and individuals, and errors can accumulate over time. Spatial updating is one of the fundamental forms of navigation that occurs automatically and continuously whenever an animal moves (Schmidt, et al., 1992), and it contributes to object and scene recognition by predicting the appearance of objects or scenes from new vantage points so that the animal can recognize them easily as it moves (Simons & Wang, 1998). Spatial updating also has profound impact on spatial reasoning and spatial imagery. Physical movements consistent with spatial imaginations can facilitate performance, while inconsistent physical movements can lead to impairment (Presson & Montello, 1994).
Different forms of spatial updating
The basic form of spatial updating is path integration (sometimes called dead reckoning). The path integration process computes the location of an origin relative to the navigator’s current position and orientation. Path integration has been studied extensively, especially in insects. The advanced form of spatial updating keeps track of multiple targets in the environment and estimates their new relationship to the animal as it moves around (instead of just the origin alone). Studies on multi-target spatial updating have been conducted primarily with humans. A few studies have shown that non-human animals, including insects, are capable of updating more than one target as well (Collett, Collett & Wehner, 1999).
Extensions of spatial updating
There are several cognitive processes that are closely related to spatial updating, and sometimes treated as a special form of spatial updating.
With the development of virtual reality technology, visual and other perceptual stimulations can be presented to the sensory system to simulate real movements while the observer physically remains stationary. Judgments of the new spatial relationships after simulated movements often resemble the pattern with real movements, but with reduced efficiency (Wraga, Creem-Regehr, & Proffitt, 2004).
Spatial reasoning and imagined perspective change
These tasks involve judgments of spatial relationships after imagined movements (e.g., imagine oneself turning, translating, imagine an object rotating, etc.), with no sensory information about the movements. These tasks are generally very difficult and young children often fail in these tasks. The cognitive process involved in spatial reasoning tasks are different from the spatial updating system, and usually needs to compete with and overcome the spatial updating system to generate a correct answer (May, 2004; Wang, 2007).
How to measure spatial updating
Spatial updating is usually studied using a target-localization test after some movements. In a typical spatial updating task, subjects learn the location of some targets at a starting place facing a particular direction. Then they make some movements, such as turning or traveling along a path. At the end of the movement, they report the location of these targets, which are now invisible and in new relationships to themselves. Accuracy and reaction time of these target localization responses are taken as measurements of their spatial updating performance. A special case of this test is known as the novel shortcut task. Although it is traditionally used as a test for cognitive maps, it is actually a spatial updating test (Wang, 2003). In this task, subjects are led along an outbound trip, sometimes with multiple segments. At the end of the trip, they are released and required to travel to the origin in a straight line. The accuracy of their homeward direction and distance can indicate their spatial updating ability.
Perceptual factors influencing spatial updating
It is generally believed that the accuracy of path integration is determined by the accuracy of self-motion estimation. Due to the nature of the process, path integration is always subject to cumulative errors. Thus it has constraints in its ability to provide accurate guidance for long-range navigation. Some studies suggest that path integration is reset every once in a while. For example, studies show that animals can reset the homing vector to zero when they return to their nest, or recalibrate the vector by familiar targets (Müller & Wehner, 1994). Different animals may rely on different perceptual cues for estimating their self-motion, such as optical flow, magnetic fields, and internal cues such as energy expenditure (effort to move), efferent copy of the motor command, and vestibular and proprioceptive information. Usually multiple sources of perceptual information are combined to provide more accurate estimation of self motion. When the cues are in conflict, some cues have stronger influence than others. It has been shown that animals are more likely to use visual cues (i.e., visual dominance) when other cues (such as the internal senses) are in conflict with them. For example, bees flying through a patterned tunnel with wind can correctly estimate the distance traveled, suggesting that optical flow information overrides the energy expenditure measure (Srinivasan et al., 1996).
Cognitive factors influencing spatial updating
The accuracy of spatial updating can be influenced by whether people are instructed to focus their attention on the target objects or on their own movements during the trip. Attention to the target objects can improve their judgment performance, but seems to slow down their movements en route (Amorim et al., 1997).
Spatial updating is also subject to memory decay when the relevant perceptual information is eliminated. For example, when desert ants are captured during their foraging journey and placed in a container, their ability to follow a particular vector course vanished after a few days, suggesting their memory of the homing vector may be lost over time (Ziegler & Wehner, 1997).
Recent studies have shown that spatial updating has capacity limitations and the updating performance depends on the number of objects to be updated (i.e., the set-size effect). In these studies, people were asked to locate varying numbers of objects either after spatial updating or without spatial updating. Increasing the number of target objects impairs people’s localization performance when they need to do updating, but has little effect when people remained stationary and no updating is needed. This set-size effect suggests that spatial updating has a capacity limitation and cannot update large number of targets without losing efficiency (Wang, 2007). Because of the limitation in the number of targets a spatial updating system can keep track of effectively, humans have been shown to switch targets when they move from one environment to another. For example, studies have shown that spatial updating in nested environments (e.g., a room inside a building, a building inside a city, etc.) does not occur for all environments at the same time. While navigating between nested environments, people seem to switch representations at particular spatial regions to maintain online those environments they are approaching, and this process is accompanied by losing track of one’s relation to the old environments. As a consequence, humans readily form new spatial representations during navigation, but often do not incorporate them into the existing system of spatial knowledge (Wang, 2003).
Is spatial updating automatic?
Spatial updating is said to be automatic with three levels of meanings. First, spatial updating is sometimes spontaneous, namely it occurs without explicit instruction or intention. For example, path integration in most animals occurs automatically. Spontaneous spatial updating has also been demonstrated in humans. For example, people are often unaware of the fact that they are keeping track of their relationship with the surrounding objects almost all the time. Second, spatial updating is often obligatory and very difficult to suppress. That is, spatial updating can occur involuntarily and people have difficulty in preventing it from happening. For example, studies have shown that when people are asked to turn their body with eyes closed and then point to objects “as if you did not move” (namely to suppress or undo the spatial updating process), people have great difficulty performing the task (Farrell & Robertson, 1998). These data suggest that spatial updating is difficult to suppress when observers move, and therefore is obligatory. Third, spatial updating is automatic in the sense that it is quick, easy, and requires little resource or attention. There has been little evidence for this type of automatic updating, and most empirical data suggest that spatial updating is not resource/attention free. For example, instructions of attentional focus can influence spatial updating (Amorim et al., 1997). The capacity limits of spatial updating also suggest that updating is resource-demanding and its efficiency depends on the number of targets been processed.
Type of environment
Spatial updating also depends on the target type. It has been shown that the scale of the environment and perceptual experience of the targets can also influence the updating process. For example, a study on spatial updating in multiple, nested environments asked blindfolded human subjects to turn either relative to the small, immediate environment, or to the larger, more remote environment, and then point to targets in both the environment in which they turned (updated environment) and the other environment (non-updated background environment). People automatically kept track of their relationship to targets in their immediate surroundings, but they did not update the more remote environment unless they were explicitly instructed to, suggesting that the spatial updating process depends on the nature of the environment (Wang & Brockmole, 2003). Similar studies have shown that perceptual experience of the targets also plays a role in the spatial updating process. Directly perceived target objects (for example, objects learned visually, by touch, etc.) are updated automatically, while targets learned through verbal description alone without direct perceptual experience are not updated automatically (Wang, 2004). Moreover, objects learned in virtual reality are also updated automatically, suggesting that perceptual experience of the objects is a important factor for spatial updating.
Models of spatial updating
Allocentric modelsThe most prevalent model of spatial updating is the allocentric model, usually in conjunction with a cognitive map (Gallistel, 1990; O'Keefe & Nadel, 1978). Allocentric representations encode object locations in an external reference frame and therefore remains relatively stable and unchanging as the observer moves. The position and orientation of the observer is encoded relative to this external reference frame, just as another “object”. Consequently, the spatial updating process involves computing changes in the observer’s position and orientation with respect to a constant external reference frame (see Figure 1).
Egocentric updating modelIt was recently proposed that spatial updating is primarily an egocentric system (Wang & Spelke, 2002). According to this model, each target location is encoded with respect to the observer rather than to an external reference frame. Spatial updating is the process that accounts for changes in the relationship between the observer and each target in the environment and maintains a dynamic representation of these egocentric vectors (see Figure 2).
Dual systems models
Some researchers proposed dual-system models which contain both egocentric and allocentric components. The long-term memory component is thought to be more allocentric, while the working memory component is considered to be more egocentric in nature (Mou et al., 2004).
Physiological model of path integration
The physiological mechanism of spatial updating is not well understood at present. Some researchers proposed that the hippocampal place cell and head-direction cell system may serve as the “path integrator” for rodents (McNaughton et al, 1996).
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