Readings 5-7

Question 1

In the study by Sarlegna et. al, what was the objective? What were the testing conditions?

Answer 1

The objective was to observe any adaptation differences between a control group and a deafferented patient (GL) in a reaching task. They wanted to see if proprioception was necessary for adaptation, or if GL could adapt using visual information.

Pre-rotation - baseline measurements.
Per-rotation - introducing the rotation to the reaching task.
Post-rotation - rotation was taken away to observe after-effects.

Question 2

What were the results of the Sarlegna et. al study?

Answer 2

• At baseline, GL’s responses were impaired and more variable than the controls.
• Adaptation and de-adaptation were similar between GL and the controls. However, GL could not restore her baseline performance.
• In conclusion, GL is able to adapt to novel conditions based on visual feedback in a similar way to the controls with proprioception. The key is that everybody is able to make kinematic predictions based on actual and desired states (sensory prediction error).

Question 3

In the study by Williams et. al, what was the objective? What were the testing conditions?

Answer 3

The objective was to compare size weight illusion (SWI) effects between controls and schizophrenia (SP) patients. The hypothesis was that SP patients have a reduced SWI response due to an impaired forward model.

Weight comparison tasks - asked to judge the weight of 2 disks (could be of the same size, or have 1 of each size in each hand).

SWI trials - a 90g small disk was compared to a heavier large disk that gradually increased in weight. Again, they were asked to judge which one was heavier.

Question 4

What were the results of the Williams et. al study?

Answer 4

• No differences in weight discrimination between SP patients and controls.
• In the SWI tasks, SP patients had a point of subjective equality at a lower weight than the controls.
• Proves that the difference is due to impaired internal models, not due to an issue with weight discrimination.

Question 5

In the study by Cullen and Brooks, what was the objective?

Answer 5

The objective was to differentiate cerebellar sensory signals that come from active movements (reafference), from signals that come from passive movements (ex-afference). In addition, they found 2 different processing streams for unexpected head movements and unexpected body movements.

Question 6

In the study by Cullen and Brooks, what did they measure? In what conditions did they measure?

Answer 6

They measured sensory signals from unimodal neurons and bimodal neurons.

They measured monkey’s active head and body movements and passive head and body movements in isolation. Then they measured the signals when the monkey moved its head actively, but the body was moved passively.

Question 7

What are the conclusions of the Brooks and Cullen study?

Answer 7

• Unimodal neurons respond to passive head motion. Bimodal neurons respond to passive body motion.
• similar signals were found when active and passive motion happened concurrently, so active motion does not interfere with passive motion.
• Neither of the neurons picked up much during active movement. That means there is some attenuation of the signals during active motion (in the nuclei).