Kable and Glimcher - The Neural Correlates of SV during intertemporal choice Flashcards
(15 cards)
What was the main research method used in this study?
The study used functional magnetic resonance imaging (fMRI) to measure neural activity while subjects made choices between immediate and delayed monetary rewards.
What was the primary goal of this paper?
To show that neural activity in several brain regions tracks the revealed subjective value and preferences of delayed monetary rewards
How was the experiment structured?
Subjects made repeated choices between a fixed immediate reward of $20 and a larger delayed reward that varied randomly from $20.25 to $110, with delays ranging from 6 hours to 180 days.
What was the procedure for estimating subjects’ discount functions?
The researchers estimated discount functions for each subject using data from three preliminary behavioral sessions (without fMRI). They then used these discount functions to calculate inferred subjective values, which were used as regressors for brain activity.
Which brain regions showed significant correlation between neural activity and subject-specific subjective value?
Three main brain regions: ventral striatum, medial prefrontal cortex, and posterior cingulate cortex.
What three patterns of neural activity were observed in relation to subjective value?
1) Increased neural activity when the objective amount of reward increased
2) Decreased activity when delay increased
3) Increased activity when the delayed reward was chosen because it was more valuable
What did the authors find when analyzing data with the beta-delta (sum of exponentials) model?
Results suggested that the theoretically defined beta component discounts more steeply than neural activity, and the theoretically defined delta component discounts less steeply than neural activity. This indicates neural activity tracks subjective value determined from behavior rather than theoretically defined components.
What is a psychometric-neurometric comparison?
A psychometric-neurometric comparison relates neural activity to behavior (including behavior that depends on subjective experiences). It tests whether a particular, externally quantifiable variable influences both psychological and neurobiological measurements in a similar manner.
What is the significance of finding a match between neurometric and psychometric discount functions?
It indicates that choosing between immediate and delayed monetary rewards involves, at a physical level, comparing neurally encoded subjective values. This provides unambiguous evidence that subjective value is explicitly represented in the human brain.
How does this study relate to economic theory?
Economic theory proposes that decision-makers behave “as if” different options have different subjective values. This study shows that the brain actually tracks the subjective value of delayed monetary rewards, suggesting that idiosyncratic preference functions are part of the neural mechanism for choice, not just a theoretical construct.
What limitations did the authors identify in their study?
1) No choices between two delayed rewards were offered
2) No variation in one of the reward choices (the immediate $20)
3) Only individuals with stable discount functions were scanned
What potential issues were there with the button-pressing procedure?
Subjects indicated choices by holding or releasing a button, and the meaning of holding/releasing switched halfway through each session. This could have caused confusion and resulted in subjects selecting incorrect options, especially in the first few trials after the switch.
What potential issue arises from conducting sessions over 1-6 months?
The value of money, people’s circumstances, or needs for immediate/delayed money might have changed over that time, affecting their discounting behavior and brain activity.
How does this paper compare to Kobayashi and Schultz’s research?
Both papers look at brain imaging in response to later rewards, but Kobayashi and Schultz studied monkeys while this paper focused on humans. Additionally, fMRI in this paper is less precise than the techniques used for monkey brains.
What future work did the authors suggest?
1) More closely examine the interaction between outcome and action values
2) Investigate the process by which value signals affect choice
3) Investigate the role of other brain regions
