What is spatial cognition? - Chapter 7

What does spatial cognition imply?

Spatial cognition is not just one domain: it includes focusing on various locations in space, integrating visual information, and manipulating objects in space, both perceptually and in memory.

Spatial perception

The dorsal, so called 'where' route is mainly specialized in spatial information, while the ventral 'what' route is mainly involved in processing the identity of objects. Milner and Goodale (1995) discovered that these routes both had a different purpose: the dorsal route is 'vision-for-action' (because the information flow would go directly to the motor system) while the ventral route is 'vision for perception'. Any similar dichotomy is actually a strong simplification of reality and should be used with caution.

Spatial attention

Spatial attention is the term given to the ability to direct attention to stimuli in space. In Posner's attention model spatial information processing holds an important place. He distinguishes between stimulus-driven "covert orienting" (our attention is automatically drawn by spatial stimuli) and top-down "overt orienting" (aspects of spatial attention that require executive control).

Spatial representations

A commonly used dichotomy of possible spatial representations is between egocentric and allocentric representations. When we take ourselves as a frame of reference, we use a self-centered representation. When there is a bird's eye view / mental map, we speak of an allocentric representation. Kosslyn (1994) states that our spatial representations are made through categorical information processing or through coordinated information processing. In categorical information processing, the left hemisphere is primarily involved and the relative spatial relationship between objects is central ("the glasses are in the drawer"). Coordinated information processing has a more metric character in which spatial relationships are expressed using coordinates. The right brain hemisphere specializes in the processing of fine-grained coordinates ("the glasses are 25 centimeters to the left of the book").

Spatial memory

Spatial memory covers three sub-domains: spatial working memory, object-location memory, and the learning and remembering of routes. When learning and remembering routes, a combination of egocentric and allocentric knowledge is of great importance (Burgess, 2006). Research into learning and remembering a route is often done by using a virtual maze in which objects serve as "landmarks". If a subject is placed in a maze, the allocentric knowledge can be tested by means of the landmarks because a field-dependent egocentric representation is no longer sufficient.

The visual-spatial sketchpad and mental rotation

Spatial working memory holds the spatial information for a short period and manipulates it. Dynamic spatial information would primarily rely on the spatial working memory, while static information is more concerned with the visual working memory. Within Baddeley's model, the visual-spatial sketchpad is responsible for this same function. Analogously to the number span, the block span measures the capacity of this sketchpad. An important function of the visual-spatial sketchpad is mental rotation. This means that people can manipulate a mental image in such a way that it can be presented in a different way.

Memory for objects and their locations

The memory for object locations is part of episodic memory. Research into brain injury patients has shown dissociations between different parts of the object-location memory.

How is a route learned?

Learning a route is another important part of spatial memory, and it involves all the above-mentioned spatial memory processes. Learning a route involves the use of landmarks, which relies on memory for object locations. Moreover, a combination of egocentric and allocentric knowledge is needed.

Visuospatial praxis

Visuospatial praxis and visuospatial planning are important parts of spatial cognition. Visuoconstructive praxis consists of skills that combine perception, memory, and planning with motor responses. These concepts are discussed further in later chapters.

What are consequences of impairments in spatial perception?

Simultanagnosia is a disorder whereby spatial perception is impaired. Patients suffering from this disorder do not have an overview of the world around them: they only see part of the visual scene at any given time. A distinction is made between ventral simultanagnosia and dorsal simultanagnosia (Farah, 1990). Ventral simultanagnosia is related to damage in the left inferior temporo-occipital or left occipital brain regions. Patients can observe multiple objects at the same time, but cannot recognize and / or interpret a scene as such. Another characteristic of this patient group is that they read letter-by-letter. Patients with dorsal simultanagnosia often have bilateral damage in the parietal-occipital or parietal areas of the brain. These patients use the identification of certain parts of an object to infer something about the whole object. They have difficulty locating the stimuli.

Which disorders can be distinguished within spatial attention?

Neglect

Unilateral neglect is a known attention disorder in which there is a delayed or even no response to stimuli on the contralateral side of the brain injury. Neglect can be a supramodal disorder, but in most cases it is limited to visual modality. Neglect occurs after both left and right hemispheric lesions, but is clearly more persistent after right hemispheric injury. In the acute phase, half of all patients have a forced position of the head and / or eyes to the right. The underlying mechanism of this is the exaggerated attention they have to stimuli in the ipsilateral side. Most patients also suffer from anosognosia while others suffer from anosodiaphoria (the latter group is aware of the disorder but is not concerned about it). Tasks to determine visual neglect are mostly cancellation tasks. There are various forms of neglect, and they almost always occur only after major brain injuries. Nevertheless, the critical lesion location for neglect is the right gyrus temporalis superior. There is no consensus on this. Account must be taken of the fact that neglect has many subtypes and it is a heterogeneous disorder that can manifest itself in multiple ways. Due to the size of the lesion, neglect often accompanies hemiparesis / hemiplegia and hemianopsia / visual field defects.

Extinction

The term extinction is used when neglect patients recover. They are often gradually able to detect and identify unilateral, visual, aural, or tactile stimuli on the neglected side, but they do not notice these stimuli in the case of simultaneous bilateral stimulation. The confrontation method is used to test this: the patient has to concentrate on the researcher's nose, while the researcher briefly moves one or two index fingers in the patient's left and right peripheral visual field.

What disorders are distinguishable within spatial memory?

Many types of neurological damage can lead to an impaired spatial working memory. There is functional functionalization within the working memory: a patient with a right parietal lobe lesion performs worse on the Corsi Blocks Test than a patient with a left parietal lobe lesion. Even after a frontal dysfunction (schizophrenia) or a frontal lesion, a disturbance can occur in the spatial working memory due to the involvement of the executive functions. The problems mainly manifest themselves on tasks where object and location information must be combined. Most tasks that only use spatial memory, such as mental rotation tasks, mainly involve the parietal cortex. Cognitive aging also has a major influence on the deterioration of the spatial working memory.

What disorders are there within the object-location memory?

If the medial temporal lobe or structures in the diencephalon are impaired, there is a disorder specific to the object location memory: patients with a right hippocampal lesion in particular perform significantly worse on tasks where the location of an object has to be remembered. If the damage is positioned in the right hemisphere, the patient performs worse when the "coordinated" positional information has to be withheld; if the damage is in the left hemisphere, the categorical object information is worse associated with the position (this is a double dissociation).

Topographical disorientation?

A disorder that often occurs in patients with a neurodegenerative disorder is topographic disorientation: these patients have difficulty navigating, learning a route or finding their way back after a right or left hemispheric lesion (the latter is rarer). It is not a unitary disorder, so several sub-processes can be selectively disturbed (Farah, 2003).

• Egocentric disorientation: This disorder is the result of a lesion in which the junction of the posterior parietal lobe and the occipital lobe is damaged. Patients have difficulty estimating the relative location of objects relative to themselves.

• Disorientation in direction / ‘Heading disorientation’: This specific disorder is the result of a damaged posterior gyrus cinguli. Patients have difficulty observing and remembering "landmarks" and their relative orientation.

• ‘Landmark’ agnosia: In this specific disorder, the patient has difficulty recognizing "landmarks".

• Anterograde disorientation: The critical lesion location is the right gyrus parahippocampalis. New routes cannot be learned.

• Left-Right Confusion: This specific spatial orientation disorder mainly occurs in Alzheimer's patients and is also the fourth characteristic of the Gerstmann syndrome (in addition to finger diagnosis, acalculia and agraphy) in the case of left-hemispheric parietal lobe damage.

Learning a route is measured within a clinic with maze tasks or a virtual-reality computer task; outside the clinic, patients are asked to actually walk a specific route and walk back.

Which disorders are distinguishable within spatial praxis?

Constructive apraxia

Simple drawing tasks such as drawing or copying a three-dimensional cube may be greatly affected by the lack of education of healthy elderly people, and are therefore not suitable for establishing constructive impairments within the frame of Alzheimer's disease. A patient with a constructive apraxia simplifies a drawing, extends certain parts and draws the copy very close or even on top of the original (the latter being the phenomenon called "closing in"). Patients often have a left or right posterior parietal and / or occipital cortex lesion. A patient with a lesion in the left hemisphere may be able to make a symmetrical drawing (this patient does have an overview), but has much more trouble filling in the details. A patient with a lesion in the right hemisphere has difficulty drawing symmetrical and often loses the overview of the task.

Optical ataxia and Bálint's syndrome

If a patient has difficulty reaching and grasping visual objects in the peripheral visual field, this person suffers from a pure optic ataxia. This disorder is the result of unilateral or bilateral damage to the parietal cortex (and in particular the superior parietal lobe and the intracietal sulcus). After unilateral injury, the patient often has a contralateral visual field defect in addition to the pure optical ataxia that manifests itself in the field contralateral to the lesion. The simplest way to detect optic ataxia is by comparing grasping conditions inside and outside of the central field of vision with each other while the patient is focusing on the researcher's face. These grasping and reaching problems are modality specific: for example, patients can experience difficulty in grasping at visual targets, they usually have no difficulty in reaching for the location of aural or somatosensory stimuli when they are blindfolded. Patients with Bálint-Holmes syndrome (or Bálint syndrome) have three disorders: dorsal simultan agnosia, optic ataxia, and oculomotor apraxia. Patients appear to be blind because they bump into everything, and are often unaware of objects unless these are centrally positioned in their field of vision. Their perceptual experience is a chaotic succession of single objects (they cannot process more than one stimulus at a time). The Bálint syndrome is the result of bilateral damage to the occipito-parietal area in the dorsal route, but each of the syndromes has a separate pathophysiological substrate (demonstrated by double dissociations for each of the disorders).

What does spatial cognition look like?

Spatial cognitive functions use several systems, each of which has a different neural subsystem for processing a specific aspect of spatial cognition. In a global model, the following brain systems with associated spatial cognitive functions can be distinguished:

The frontal lobe plays a major role in spatial working memory, integrating information and spatial-temporal learning

The posterior temporal lobe is involved in the 'where' route, the egocentric coding, the categorical relationships (left hemisphere) and coordinated relationships (right hemisphere) and in spatial localization and attention

The temporal lobe is related to the 'what' route, and shape and object recognition

The hippocampus is involved in allocentric coding, and linking the object and the location (object-location binding)