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Banich & Compton (2011) Cognitive Neuroscience, 3

Rd

Jamie Ward (2010)
...
Wadsworth Cengage
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Psychology Press
nd
Ed
...
researchers often distinguish between the superior parietal lobule
and the inferior parietal lobule, which are separated by the intraparietal sulcus
...


•

The parietal regions of the dorsal stream are also closely connected with frontal lobe
regions that control the body’s movement

•

Unlike cells in the ventral processing stream, cells in parietal areas are not particularly
sensitive to form or color, making them ill suited for detecting the visual properties
from which shape can be derived

•

Cells in the posterior parietal cortex are most responsive to attributes of visual
information that are useful for processing spatial relations
...


•

Developmentally, children often confuse left and right long after they have a clear
understanding of up and down
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•

The amount of binocular disparity, or discrepancy between the images seen by the
two eyes, is a cue to depth
...


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Evidence from humans suggests that although dam- age to the parietal cortex in
humans can impair depth perception, there does not seem to be any syndrome in
which perception of spatial depth is disrupted but all other spatial functions are intact
...


•

studies of brain-damaged patients indicate that reference frames can be independently

disrupted by brain damage
...


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The parietal region also plays a role in localizing information in auditory as well as
visual space, as lesions of the parietal lobe disrupt the ability to localize sounds

•

Initial evidence confirming the important role of the right hemisphere in localization
of position in space came from studies of perceptual asymmetries

Relations between Points in Space
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categorical spatial relations = specifies the position of one location relative to
another in dichotomous categorical terms (e
...
, above vs
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Evidence suggests that the left hemisphere is specialized

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for computing categorical spatial relations and that the right hemisphere is specialized
for metric spatial relationships

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metric and categorical spatial relations are considered to be independent of one
another

Constructional abilities
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the ability to motorically produce or manipulate items so that they have a particular
spatial relationship, often referred to as constructional praxis

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Although deficits in spatial-constructional skills are typically associated with righthemisphere damage, such deficits can also occur following left hemisphere damage

•

Deficits following left-hemisphere damage probably occur for one of two reasons:

•

Firstly, performance may be disrupted as a result of damage to additional regions

besides the one critical for the constructional component of the task
•

Second, it is likely that many of these tasks can be performed using verbal strategies

•

One way to perform this task is to analyze the spatial relationships in a given
template
...
g: strolling through our
neighbourhoods or driving our cars around them)

•

therefore, our motion-perception systems must have a way of taking into account the
whole body’s movement through space to accurately perceive whether objects around
us are moving or stationary
the vestibular system provides sensory information from the inner ear about the
body’s movement

•
•

Area MST may then integrate information about the body’s movement through space
together with retinal-image information to infer the movement speed and direction of
external objects

Rotation
•

rotation is movement of an object around an axis

•

In humans, the ability to rotate objects mentally has been studied extensively by
Shepard and colleagues (Shepard, 1988), who found that the greater the degree of
mental rotation required to align two 3-D objects, the greater the time required to
decide whether they are identical

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studies suggest that the parietal regions are responsible for rotational abilities

•

disruption of the right parietal region by TMS in neurologically intact people led to
impaired performance on a mental rotation task

•

Researchers reasoned that the brain region specifically involved in rotation should
show a specific relationship between the degree of activity and the degree of rotation

•

activity in right parietal cortex that increases with the degree of rotation suggests that
mental rotation is supported by a continuous transformation of a spatial representation

•

mental rotation can be performed by thinking about the actions that would be required
to manipulate the object to rotate it in a particular direction

Space and action

•

one important function of the dorsal stream is to participate in sensory-motor
translation—transforming sensory representations into action patterns
...


•

Other research has also found, somewhat counterintuitively, that the poor reaching
performance of optic ataxics improves if there is a delay between the presentation of
the target and the reaching movement

•

a double dissociation in human brain- damaged patients suggests the independence of
the dorsal “how” system from the “what” system in the ventral stream

•

Different subareas within the parietal cortex appear to contribute to the sensory-motor
transformations necessary for different kinds of movements

•

studies of both monkeys and humans indicate that the spatial representations coded by
the parietal cortex play an important role in guiding limb and eye movements to
specific spatial locations

Spatial navigation
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a crucial spatial skill is the ability to navigate around an environment

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People seem to invoke two basic strategies for spatial navigation, referred to as routebased versus cognitive map strategies

•

n route-based strategies, the person’s understanding is represented as a sequence of
steps, often specified in terms of particular landmarks

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This kind of spatial navigation does not require a map-like understanding of how the
neighbourhood is laid out

•

Rather it just involves being able to follow directions, by responding to a particular
cue (stop sign) with the correct action (turn left)

•

It is also egocentrically oriented, in the sense that the instruction “turn left” means
“left” in relationship to you

•

In contrast, a map-based strategy involves having an allocentric understanding of how
all of the different parts of the landscape relate to one another
...


•

Both the stylus maze and locomotor maze tasks are performed poorly by patients with
damage to the parietal lobe

•

research with brain-damaged patients illustrates that spatial navigation can be
disrupted in several different ways

•

The syndrome most closely tied to the dorsal stream pathways is egocentric
disorientation, which involves the inability to represent the location of objects in
relationship to the self
...


•

Although the posterior parietal cortex, hippocampus, and parahippocampal gyrus have
been most studied with respect to their roles in spatial navigation, another region
called the retrosplenial cortex also appears to be implicated in navigation

•

this region is on the medial surface of the parietal cortex, posterior to the splenium of
the corpus callosum

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studies in other species have found that spatial navigation is disrupted when the
retrosplenial cortex is experimentally damaged

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In sum, the ability to find one’s way around a complex, large-scale environment
depends on several component skills that appear to be carried out by several different
brain regions

Challenges to the dorsal-ventral stream dichotomy
•

it is important to recognize that spatial functions are not completely segregated to the
parietal region of the brain

•

Although the parietal lobes (particularly in the right hemisphere) are extremely
important in spatial cognition, they are not the only brain regions involved

•

the parietal lobe is not solely dedicated to spatial functions

•

It also plays an important role in attention and vigilance

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cells in the ventral stream represent an object’s shape in a size- and position-invariant
manner, which is useful for recognizing the object’s identity

•

Depth and movement cues are also important for both ventral and dorsal stream
processes

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