Decision Making

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  1. What is a decision?
    A commitment to proposition or selection of action, resulting in overt act of choosing, based on evidence, prior knowledge, and beliefs.
  2. What is a choice?
    A final commitment, decision following a deliberation process preceding commitment
  3. What is a tractible decision?
    A decision we can control and influence
  4. Label this classic view of decision making
    Image Upload 1
    • 1: Task & motivation
    • 2: Generate hypothesis 
    • 3: Beliefs & prior knowledge 
    • 4: Sensory input 
    • 5: Useful forms of evidence
    • 6: Generate decision variable 
    • 7: Apply decision rule
    • 8: Motor output
  5. What are visual search tasks, and why are they useful?
    • A stimulus must be discriminated from a distractor. The harder the task, the harder it is to do this
    • Through giving these tasks to monkeys we can gain more insight into how decision making works
  6. How have monkey studies challenged our perception of decision making?
    • Monkeys trained to shift gaze to target in VS task, initially visually responsive neurons in the frontal eye field respond indiscriminately to both targets and distractors.
    • Neural activity THEN evolves to signal location of target BEFORE eye movement to target. Neurons in FEF even discriminate target from distractors with NO eye movements, consistent w/ idea of advance decision making
    • SO sensory input --> decision process --> motor output
  7. What is visual response dependent on?
    The number of action potentials that fire (their strength)
  8. What is the LIP?
    • Lateral intraparietal Area
    • Found within the intraparietal sulcus 
    • Controls eye movement, and is possibly associated with working memory
    • Activity builds up slowly, and is continued after cessation of a visual stimulus
    • Activity predicts the time and direction of the subsequent eye movement, even when the sensory information is ambiguous
    • Evidence that LIP neurons are not simply motor neurons reflecting a decision already made. Choice-dependent differences in activity emerge early in response, and the rate of response build-up depends on stimulus strength (ie. strength of evidence)
  9. What do animal studies tell us about uncertain decisions?
    • Monkeys trained to report net direction of motion in a load of moving dots.
    • Proportion of dots moving in same direction (ambiguity) varied by experimenter.
    • As fraction of dots moving in random directions INCREASES, proportion of correct responses DECREASES.
    • Relationship between behavioural choices and activity of individual neurons in MT visual area, even when motion is weak or absent.
    • Suggests perceptual decisions can be based on weakly correlated activity of small population of MT neurons.
    • Decision of where to move eyes = sensory input --> LIP --> motor input.
  10. Why aren't LIP neurones typical neurones?
    • Not simple sensory neurons: Activity builds slowly and continues after stimulus offset. Activity in them predicts time and direction of eye movement even when sensory info is ambiguous.
    • Not simple motor neurons which reflect already made choice:  Choice-dependent differences in activity emerge early, and rate of response build up depends on strength of evidence.
  11. How does the accumulation of evidence help to drive decision making?
    • MT responds to motion, LIP collects evidence from MT and calculates difference in input from neurons in MT.
    • As difference grows, evidence accumulates.
    • This predicts speed-accuracy trade-off: Reduced threshold, requires less info to make decision (risky and quick). This is biased because it is close to threshold already (risky and quick)
    • Still uncertain if decision involves competition between separate reflexes or evolving state of neural networks.
  12. Label this diagram to now show the decision making model when applied to eye movement 
    Image Upload 2
    • 1: Is the object moving left or right?
    • 2: Left or Right hypothesis generated
    • 3: Beliefs & Prior knowledge of movement 
    • 4: Neural activity in middle temporal area
    • 5: MT preference (left or right)
    • 6: Buildup of LIP activity 
    • 7: LIP activity exceeds either L or R criterion
    • 8: Eyes are moved left or right
  13. How can responses in LIP activity shed light on decision confidence?
    • Monkeys fixate on visual stimulus and make decision on which direction targets moved.
    • Get large reward for correct answer.
    • In 1/2 trials, there was spot monkey could look at to get a small reward if they weren't sure. --> less risky decision, lower pay off.
    • Measured CONFIDENCE in choice.
    • Activity of neurons in LIP predicted whether monkey would take risky/safe choice.
    • Rats had to smell odour and decide which of 2 other odours were most similar. Activity recorded from orbitofrontal cortex (goal-directed decision making) matched prediction of confidence, with rats sure on correct trials and unsure on error trials.
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Decision Making
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