What are the main features of the Allocentric frame of reference?
- Centred on external objects
- Includes knowledge of our position in space; 'mental maps'
- Is represented in the HPC, with single neurons representing our position in the world
- Taxi drivers will use more allocentric FoR, and thus the longer they have been driving for, the higher the vol. of their posterior HPC grey matter (Maguire et al, 2001 [probably])
What are the main features of the egocentric frame of reference, and what are its subdivisions?
- Centred on the body
- Eyecentric: objects are coded relative to the centre of gaze.
- Left intraparietal (IP) area maintains a constant representation of space as the eyes move.
- Head-centred: hearing.
- Ventral IP is where headcentred FoR are located
- Joint-centred: e.g. grasp. Coded in terms of set of joint angles needed to perform movement.
- Grasp is located in anterior IP, reach in medial IP.
What is spatial neglect?
- Happens most frequently following stroke damage to the right side of one's brain
- In these cases, people are unable to become aware of items to their left
In neglect, why is it wrong to say that people cannot see things on their left?
- They CAN see things, their photoreceptors work fine, they just lack the cortical representation for what they're seeing
- This means it is not retinotopic (i.e. it has brain origin, not eye origin)
- Eg. someone with spatial neglect will see a whole Navon figure, but will only be able to cross out the non-neglected side of it.
- They can see it, they just can't act on this
What is the difference between egocentric and allocentric neglect?
- Allocentric neglect: neglected region is 1 side of an object, regardless of position relative to person
- Egocentric neglect: neglected region depends on position of object relative to person
What does spatial neglect tell us about internal representation?
- That we use multiple FoR!
- Each FoR has separate neural representation (hence why damage doesn't affect all FoR)
- That FoR are deployed when it is most task-relevant.
What brain region is associated with allocentric neglect when damaged?
The parietal cortex
Give an example of how different frames of reference are given preference in a day to day task
- Pick up teapot: Body FOR
- Pour the tea: Teapot FOR
- Remember which cup is yours from a different angle: Table FOR
- FOR are given priority when they are most relevant to the task at hand
How do the main two frames of reference differ for day to day life?
- Allocentric frames of reference are more efficient descriptions of the stable properties of the world
- Egocentric frames of reference are useful for representing the world on a moment to moment basis