Spatial Cognition

Question 1

Dorsal Visual System

Answer 1

Spatial information- where
Key components are in the parietal cortex, which has subdivisions
* The anterior parietal lobe = somatosensory representations (not
considered part of the dorsal stream proper).
* The posterior parietal cortex (PPC) = multisensory and crucial in many
aspects of spatial cognition.

Question 2

Anatomy of the Dorsal Stream

Answer 2

• Within the PPC, the superior and inferior parietal
  lobules are separated by the intraparietal sulcus.
• The middle temporal (MT) and medial superior
  temporal (MST) areas contribute to motion.
• The dorsal stream receives visual information from
  primary visual cortex, also input from somatosensory
  cortex and vestibular system (information about
  position of the body in space)

Question 3

3 pathways of the dorsal stream

Answer 3

1. Connects Parietal cortex w/ prefrontal
   - spatial working memory
2. Parietal cortex + premotor cortex
   - visually guided actions like grasping and reaching
3. connects the parietal lobe with medial temporal cortex
   - supports spatial navigation

Question 4

Cells of the Dorsal stream

Answer 4

respond to attributes of visual information that are useful for processing spatial relations
Do not play a role in object recognition
not sensitive to form or colour

Question 5

Distinguishing Left from Right

Answer 5

The visual world is mapped in a retinotopic manner onto visual cortex, with the map reverse in relation to the visual world in respect to left-right AND up-down
Cortex of the left parietal lobe may be involved in left-right discriminations

Question 6

Coding for the three dimensions of space

Answer 6

The brain is able to code for the vertical (right-left), the horizontal (up-down), and depth (near-far) dimensions
Depth is computed in the cortex, retinal images received are initially two-dimensional

Question 7

Depth perception (binocular disparity)

Answer 7

Helps to localize items in the near-far plane
Depth is determined by the amount of binocular disparity
Cells in V1 are sensitive to different amounts of binocular disparity, and provide important information about depth for use by the dorsal stream regions
–cells in various regions of the dorsal stream have been shown to be
sensitive to binocular disparity.

Question 8

Motion Parallax

Answer 8

Objects that are close to you move more than objects that are further away
- a monocular depth cue (still works without binocular depth)
-Cells in area MT appear to integrate different types of cues to code for depth

Question 9

Spatial Frames of Reference

Answer 9

People can understand the spatial location of an object with egocentric and allocentric spatial frames of reference

Question 10

Egocentric Frames of Reference

Answer 10

The location of an object in relation to (some aspect of) oneself
Egocentric neglect is associated with right parietal lobe damage

Question 11

Allocentric Frames of reference

Answer 11

The location of an object in relation to other objects, independent of one’s own location
Object-centred neglect associated with right hemisphere middle and inferior temporal lobe damage

Question 12

Motion Perception

Answer 12

Inherently tied to spatial perception
- we must be able to represent our own motion in order to understand where we are located

Question 13

Neural Regions for Motion Perception

Answer 13

Area MT (AKA V5) critically important for perceiving motion
Area MST is involved with more complex motion, such as optic flow

Question 14

Optic Flow

Answer 14

the pattern of movement
of images on your retina as you move actively through an
environment
The movement of the retinal image for each aspect of the scene will depend on the speed and direction as well as the spatial relation of the of each scene in relation to the body

Question 15

Akinetopsia

Answer 15

Selective deficits in motion perception

Question 16

How can the brain tell if an object moved or the eye moved?

Answer 16

There are sources that provide the visual system with information on eye movement
- Motor regions of the brain send information if they are planning to move eyes
- Sensory receptors within the eye muscles provide ongoing feedback about changes in the position of the eye

Question 17

How does the brain account for the body moving with spatial awareness?

Answer 17

The body’s motion is taken into account to understand whether external objects are moving
- Researchers are still studying how the brain constructs stable visual representation throughout continuous body movement through space
- Parietal lobe regions receive input from the vestibular system and areas controlling + sensing eye movements

Question 18

Optic Ataxia

Answer 18

Disorder of visually guided reaching
Damage to the parietal lobe
— Most pronounced in the peripheral rather than central visual field
Most profound for real-time integration of vision and motion
May result from an inability to integrate cues involving eye-gaze direction and reaching direction

Question 19

Coding for Intended Movements towards targets (subregions that support sensorimotor translation)

Answer 19

Sensory-Motor integration within subsections of the parietal cortex
- Cells in the lateral intraparietal cortex code the location of stimulus then shift to the location of the planned movement
- coding of space for intended eye moements takes place in the lateral intraparietal region (LIP)
- Distrupting activity in the Parietal Reach Region (PRR) causes issues similar to optical ataxia

Question 20

2 basic strategies for spatial navigation

Answer 20

1. Route based strategies
   »» the person’s understanding is represented as a sequence of steps, often in terms of particular landmarks (egocentric)
2. Map-based strategies
   »» involves having an allocentric understanding of a space that allows one to know how different parts of the area relate to one another

Question 21

Egocentric Disorientation

Answer 21

The inability to represent the location of objects in relation to myself
associated with damage to the posterior parietal region
Patients have difficulties with navigation (both route-based and
map-based) because they are unable to represent spatial
relations

Question 22

Landmark Agnosia

Answer 22

Loses the ability to recognize certain landmarks that are used for navigation
Ventral stream area damage- what something is
Impacts route-based navigation

Question 23

3 Areas for Coding for Spatial Navigation

Answer 23

1. PPA (Parahippocampal place area)- landmarks relevant for navigation
2. Retrosplenial Complex (RSC)- determines egocentric location within a familiar spatial environment
3. Medial Temporal Lobe (MTL)- contains allocentric representaion of familar environments

Question 24

Anterograde Disorientation

Answer 24

Trouble constructing new environmental representations
Related to PPA damage
Can still navigate learned environments

Question 25

Heading disorientation

Answer 25

Issues with understanding own orientation in an environment but can recognize landmarks and locations