Motor Effort Alters Changes of Mind in Sensorimotor Decision Making. Burk, Ingram, Franklin, Shadlen, Wolpert. PLOS One 2014.

  1. Studies when people change decisions after already committing to an action, and can even happen in situations where the stimulus provided is removed once movement starts (that means that the change takes place after the stimulus is already removed)
  2. Looks at the threshold where decisions change, and here proposes that it is linked to the physical effort associated with the movement (and how far the first target is from the second)
  3. Based on drift-diffusion model
  4. Change in time between stimulus removal and movement change are usually on the order of 400ms (because its removed after motion starts, its removal can’t impact the original motion, but is processed once it starts)
  5. “Fits of the model showed that the change of mind bound did not require as much information as for the initial decision and also that not all the information in the processing pipeline was used, that is there was a limited time for which new information was processed.”
  6. Random dot motion test, with a yoke that had to be moved to one of two positions to indicate motion.  Once motion stopped, stimulus was extinguished
  7. Model holds that there is two decision boundaries: one to start the initial motion, and another to cause change in motion to second target (the model has accumulation going after stimulus until a timeout, or a change in motion, whichever occurs first)
  8. Changes of mind were most common when the motion data was weak, and motion initiated in the wrong direction (in most cases, the changes lead to the correct choice being made)
  9. The 400ms measured is consistent with previous studies on humans and monkeys (neural recordings in the monkey have about “200 ms latency to the start of evidence accumulation […] and latency from the signature of decision termination to the initiation of the behavioral response. (~70 ms for saccades […] and ~170 ms for reaches[…])”
  10. 3 of 4 subjects reduced rate of direction change as the angular separation (and therfore end distance) of targets increased
  11. One model holds that there is different populations representing the left and right choice (as opposed to just one) and that there is “… a race between two diffusion mechanisms […].  This implies that processing in the post-initiation period may not begin at the termination bound for the initial choice, but at a more intermediate value achieved by the losing mechanism.”
    1. A model for DDM thats not just 2AFC
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