Manual tracking of visual targets by trained monkeys

Area of Science:

• Neuroscience
• Systems Neuroscience
• Motor Control

Background:

• Visuomotor systems are crucial for interacting with the environment.
• Understanding the control strategies in visuomotor tracking is essential for explaining complex behaviors.

Purpose of the Study:

• To investigate the control mechanisms monkeys use for visuomotor tracking of moving targets.
• To model the frequency response and identify the factors contributing to tracking performance.

Main Methods:

• Monkeys were trained to track visual targets using a joystick.
• Sinusoidal and pseudorandom waveforms were used to determine the frequency response.
• Linear feedforward and non-linear sampled feedback models were employed for analysis.

Main Results:

• The visuomotor system's frequency response was characterized by a low-pass filter and time delay.
• A non-linear sampled feedback model with a loop delay of 250-280 ms provided a more realistic representation.
• Intermittent movements were key to maintaining tracking stability despite inherent delays.
• Feedforward control and internal models of target waveforms improved performance, especially for predictable targets.

Conclusions:

• Intermittent control strategies enable stable and effective visuomotor tracking in the presence of significant loop delays.
• Monkeys utilize predictive mechanisms, including internal models and feedforward control, to optimize tracking of predictable visual stimuli.
• Feedforward control becomes dominant at higher target frequencies, indicating limitations in modeling long-cycle targets.