Visuo-Motor Relationships: Plasticity and Development

1. Visuo-Motor Relationships:Plasticity and Development

2. Problem of sensory-motor coordination: How do we relate the visual and motor worlds? For reaching, a visual signal about location must be transformed into a command to the arm and hand muscles. This is not innate, but must be learnt during development.

3. Development of reaching Within first 2 weeks, already directing arm towards objects. Some crude control of reach direction. Improves by the 5th month; consistently touch targets. Won’t reach for targets beyond arm’s length. Catching and anticipating target motion at 6 months. Distance accuracy develops more slowly, improving by 7 months.

4. Increased use of visual feedback between 5 and 11 months

5. More evidence that visuo-motor coordination must be learnt during development. Evidence: kittens given visual experience without opportunity for movement, and motor experience without vision, don’t learn how to control their movements using vision. Correlating the two is necessary (Held & Hein study).

6. Role of Experience in Development of Visuo-motor coordination Held & Hein 1 2 Both kittens get visual experience and motor experience Visual experience correlated with motor commands/proprioceptive feedback/vision of limbs Gets both, but uncorrelated. Kitten 2 -abnormal visuo-motor coordination.

7. Also maintain ability to adapt to new relationships.

8. Adaptation to different relation between visual and movement. George Stratton • Wore inverting lens for 8 days • Believed that we learn visual directions by associating visual experiences with other forms of sensory feedback (e.g. proprioceptive). • Alternatively… Adaptation results from learning correlation betweeen vision and actively generated motor commands (Held, 1965). Also - prism adaptation

9. Why do we need to retain plasticity for new visuo-motor relationships? 1. Need to adjust to changes in body size during development. 2. Need to adjust to damage/aging. 3. Need to adjust to environmental changes eg ice, loads etc. 4. Need to learn arbitrary mappings for tool use etc. 5. Need to acquire new motor skills. 6. Visuo-motor coordination is a computationally difficult problem for the brain. Need flexibility to correct errors.

10. Experimental question: . 1. How much plasticity is there? Can we adapt to an arbitrary visuo-motor relationship? 2. What are the properties of this adaptation? Eg how fast, how complete? Does it generalize from one region of space to another? Does it generalize from one hand to another?

11. Method Virtual environment: head mounted display with virtual objects. Phantom device monitors finger position and provides force feedback. Visual scene rotated around the Y-axis by 90 degrees, interchanging horizontal and vertical dimensions. Task: Procedure: 2 baseline, 20 reaches in rotated environment, recovery, transfer (hands or locations) Adapt to reaching objects in one part of the display. Is there transfer to another part? Data recorded: XYZ position and forces every few msec.

12. Results How do we measure adaptation? Trajectories: X vs Y and Z vs Y Velocity profiles Duration of movement. How do these change with practice? Smoother, more direct trajectories? Smoother velocity profiles? Higher peak velocities? Faster reaches? How complete is the adaptation? (compare last adaptation trial with baseline) Is there any after effect? (compare recovery trials with baseline) Compare adaptation of the two hands. Does the second hand adapt faster? Complete transfer would be indicated by perfect performance on first trial. Partial transfer indicated by a faster learning rate. Similarly, is there transfer to another location?

13. Discussion Review findings. Evaluate extent of adaptation. Was plasticity demonstrated? Are subjects really learning a new set of relationships of just learning to ignore the visual feedback? How could we distinguish these possibilities?

14. Neural basis of adaptation? Possible sites: Posterior parietal cortex (AIP, MIP), supplementary motor area, pre-motor, motor cortex, cerebellum, basal ganglia …

15. Ability to adapt to new relationships requires cerebellum

16. Neural control of Reaching & Grasping

17. Neural control of Grasping Both vPM and AIP neurons fire for specific hand actions/objects. For example, this neuron prefers a precision grip. Precision grip Power grip

18. Neural control of Grasping vPM neurons fire for grasping movements made in the light and dark. In contrast, AIP neurons fire far less when moving in the dark, and in general, AIP has more visual neurons than vPM.

19. Neural control of Grasping

20. Neural control of Grasping Neurons in the vPM also fires when perceiving, as well, as producing grasping movements!