Midterm 2 Flashcards
Describe the components of the closed-loop control system.
The closed-loop system involves a comparison between the desired state and the actual state, generating an error signal. This signal is processed by the executive system, leading to adjustments by the effector, and feedback updates the actual state.
What is the role of efference copy in closed-loop motor control, and what is its main limitation?
Efference copy carries information about the desired state. However, its main limitation is its slow processing speed, as evidenced in studies of online control.
What is a reflex?
stereotyped, involuntary, automatic, and typically rapid responses to stimuli.
Describe the “loops within loops” concept in movement control.
The M1 and M2 reflexes operate as closed loops within the larger framework of movement control, contributing to dynamic adjustments and feedback integration.
How does movement time influence the involvement of M1, M2, and M3 responses?
Shorter movements primarily rely on M1 and M2, while longer movements incorporate M3 responses for more deliberate control.
Distinguish between the dorsal and ventral visual streams.
- The dorsal stream specializes in movement control, processing information from the entire visual field for non-conscious guidance of movements.
- The ventral stream handles conscious object identification, primarily in the central visual field.
Define optic flow and its significance in movement control.
Optic flow refers to the patterns of light ray movement over the retina, enabling the perception of motion, position, and timing.
crucial for the dorsal stream’s role in guiding movement.
Explain the concept of time-to-contact (Tau) in optic flow.
Tau is a measure of time-to-contact derived from optic flow. It’s calculated as the ratio of retinal image size to the rate of change of retinal image size and is proportional to the time remaining before contact with an object.
How does the ventral stream contribute to movement control?
The ventral stream provides crucial information about object properties, aiding in movement planning by integrating object knowledge with action goals.
also plays a role in long-latency feedback control.
What is a motor program?
A set of motor commands that is prestructured at the executive level and that defines the essentials of a skilled action.
What is open loop control?
Centrally determined, prestructured commands that are sent to the effector system and executed without feedback.
Anything operated without feedback.
What are degrees of freedom?
- The components of a control system that can vary independently and that are controlled to produce effective action.
- They relate to how many ways a thing can move and how many things can change. For example, a finger has four degrees of freedom
How do open loop models function?
- Preplanned instructions specify function, sequence, and timing.
- Once the program starts the system continues to completion without modification.
- There is no ability to detect and correct errors (reflexes).
When are open loop models used?
- For rapid, discrete movements.
- In predictable and stable environments.
- To initiate movements.
- Eventually to control long strings of learned/rehearsed movements.
How do open loop models initiate movements?
Movements are initiated as open-loop motor programs and progress unchanged if:
1. They are too fast for feedback to register.
2. There is no error and/or no change in the environment.
What is the evidence for motor programs?
5 main evidence:
1. Reaction time and movement complexity
2. Deafferentation experiments
3. Central pattern generators (CPGs)
4. Effects of blocking a limb
5. Inhibiting actions (Slater-Hammel expirement)
What did Polit & Bizzi (1978) find in their deafferentation experiments?
A monkey’s performance did not significantly deteriorate with deafferentation.
What is deafferentation experiments
experiments that show that sensory feedback is not necessary for movement production. This supports the theory that motor programs can be organized and performed in an open-loop framework.
What is a central pattern generator (CPG)?
A centrally located control mechanism that produces mainly genetically defined, repetitive actions such as locomotion or chewing. For example, a single simple input can result in a complex, repetitive behavior. CPGs are similar to a motor program, but they refer to inherited rather than learned skills.
What did the limb blocking experiemnt reveal?
Even when a limb was blocked during the experiment, the participant started to brake the movement. This suggests that aspects of the program cannot be stopped even if they are useless (or detrimental).
What is the Slater-Hammel experiment?
This experiment investigated how late an experimenter could stop a participant’s hand and the participant could still successfully stop their response. It sought to determine the “point of no return” for executing a program or when a person can inhibit an action
What is the relationship between reaction time and movemnt complexity?
The more complex a movement, the longer the preparation time, resulting in longer reaction times. For example, it will take longer to react and complete a more complex movement sequence involving more limbs.
What are the effects of blocking a limb?
the first 100 ms of a movement is preprogrammed and cannot be influenced.
What are examples of motor programs?
- Postural (anticipatory) adjustments
- Flexible reflexes