Module 3 Flashcards
Define efference.
Motor output.
Define afference.
The inflow of information from sensory receptors.
Define reafference.
Sensory information occurring as a consequence of self-produced movements.
Define ex-afference.
Sensory information coming from the outside world, independent from motor impulses.
Explain Von Holst’s fly experiments. What did he conclude?
Experiment 1: When a fly is placed within a moving environment, the fly rotates along with it. The moving environment creates a visual flow, and triggers the fly’s following reflex. When the fly moves on its own, the following reflex is not triggered. The first hypothesis is that the following reflex is inhibited with self-produced movements.
Experiment 2: the fly’s neck is now rotated, so the retinal images are shifted (things look like they are moving in the opposite direction). When placed in a moving environment, the fly still follows the visual flow, just in the opposite direction. When moving on its own, it also follows the visual flow (like chasing its own tail). This disproves the initial hypothesis.
Explain the reafference principle.
We generate expectations of sensory feedback (efference copies), and we compare it to our actual sensory feedback. If the actual and predicted feedback match, we interpret it as reafferent, and the nervous system is not activated. When they don’t match, we interpret it as ex-afferent, and the nervous system is activated.
Why is it important to actively produce your own movements (Held kitten study)?
The kitten that was moving passively had impaired visual-motor development. Visual-motor development depends on the ability to experience the consequences of your own self-produced movements.
How is an error signal produced, and where is it corrected?
An error signal is produced when the predicted and actual sensorimotor outcome do not match. It is corrected by the control mechanism.
In the Held prism study, why did only the ‘active’ group adapt to the novel conditions? What is necessary for adaptation?
Adaptation requires an integration of efference and reafference. In other words, it requires an association between visual and kinesthetic feedback based on self-produced movements.
How is GL able to adapt similarly to the control group (cursor task)?
Through visual feedback - a conflict between where the cursor went vs. where it was supposed to go.
What is the inverse model?
Part of the controller mechanism. It takes information about the current and desired state, and prepares a motor command in advance based on the desired outcome.
i.e. touchpad sensitivity, gas pedal sensitivity.
What is the forward model?
Part of the predictor mechanism. It predicts how the effector will act, and simulates a response based on the efference copy.
i.e. how much acceleration would I expect if I pressed on the gas pedal?
What is the problem with closed loop control? How do we overcome this?
It takes time to receive feedback. Behavioral oscillations occur, with waiting for feedback and overcorrecting.
We overcome this using the forward model. We create predictions of how the movement should occur.
How is GL able to make corrections (similar to controls) to her reaching task, when she cannot see her hand, and has no proprioception?
She sees the target location, and has a preplanned prediction of how the movement should occur.
In the reaching task study by Miall, how did they disrupt the forward model? What explains the missing of the target?
They probed the cerebellum with TMS during the RT interval. This disrupts proprioception, and leaves people to rely on feedback.
With the forward model disrupted, people are relying on outdated feedback. They think that their hand started closer to the starting point than it actually did. There is no predictive control to correct them if their hand moves too far.
