COORDINATE SYSTEMS Flashcards
How do you specify position?
Position is only meaningful with reference to known point(s)
What is a reference frame?
A coordinate system used to represent the position of an object, etc
The origin of the coordinate system is a particular reference point
Egocentric
Position relative to our self
Allocentric
Position relative to something external to us
Different types of egocentric reference frames
Eye-centered (retinotopic): eye as origin of coordinate system
Head-centered: head as origin of coordinate system
Body-centered: body (or body part) as origin of coordinate system
Different types of allocentric reference frames
Object-centered: Particular object as origin of coordinate system
World-centered: Like a street map
Pathway between parietal cortex and hippocampus
Hippocampus in medial temporal lobe uses allocentric reference frame
Parietal cortex predominantly uses egocentric reference frame
Retrosplenial cortex (located between hippocampus and parietal cortex) contains both allocentric and egocentric cells
Retrosplenial cortex involved in spatial transformations
Transformations between allocentric and egocentric information likely requires head-direction information
Head-direction information can be combined with egocentric information to produce an orientation-invariant (allocentric) spatial representation
Head-direction cells found in several brain areas, especially anterior thalamus
– Head-direction cells respond to our directional heading in the horizontal plane
– E.g., cell might respond whenever head is pointing north-west
– Response not dependent on body position or orientation of head relative to body
Retrosplenial cortex is connected with anterior thalamus and has access to head-direction information
Pathway between parietal cortex and hippocampus likely used for transformations between egocentric and allocentric coordinates during navigation
Parietal cortex, retrosplenial cortex and hippocampus likely work in concert
Parietal cortex may provide egocentric information to the hippocampus to integrate with existing hippocampal allocentric representations
for a dynamic representation of our current location in the environment
Parietal cortex may use the output of the hippocampus to support locomotion through the environment
planning the next movement in a navigational sequence
Hand-centered position of target (T-H)
1) Compute T-H by directly subtracting eye-centered hand position (H) from eye-centered target position (T)
2) Compute T-H by transforming the position of the target in steps, from eye-centered to body-centered coordinates (then subtracting the body-centered position of the hand)
