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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.
What is a choice?
A final commitment, decision following a deliberation process preceding commitment
What is a tractible decision?
A decision we can control and influence
Label this classic view of decision making
- 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
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
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
What is visual response dependent on?
The number of action potentials that fire (their strength)
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)
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.
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.
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.
Label this diagram to now show the decision making model when applied to eye movement
- 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
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.