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Friday, August 04, 2006

The Framing Effect

Here's new research on the framing effect connecting it particular regions of the brain. How active is your orbital and medial prefrontal cortex? I added the graphs from the more detailed version of the article:

The Emotional Brain Weighs Its Options, by Greg Miller, Neuroscience News of the Week, Science Magazine: Faced with a decision between two packages of ground beef, one labeled "80% lean," the other "20% fat," which would you choose? The meat is exactly the same, but most people would pick "80% lean." The language used to describe options often influences what people choose, a phenomenon behavioral economists call the framing effect. Some researchers have suggested that this effect results from unconscious emotional reactions.

Now a team of cognitive neuroscientists reports findings on page 684 that link the framing effect to neural activity in a key emotion center in the human brain, the amygdala. They also identify another region, the orbital and medial prefrontal cortex (OMPFC), that may moderate the influence of emotion on decisions: The more activity subjects had in this area, the less susceptible they were to the framing effect. "The results could hardly be more elegant," says Daniel Kahneman, an economist at Princeton University who pioneered research on the framing effect 25 years ago (Science, 30 January 1981, p. 453).

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Fig. 1. The financial decision-making task. At the beginning of each trial, participants were shown a message indicating the starting amount of money that they would receive (e.g., "You receive £50")... Subjects were instructed that they would not be able to retain the whole of this initial amount, but would next have to choose between a sure option and a gamble option... The sure option was presented in the Gain frame trials (A) as an amount of money retained from the starting amount (e.g., keep £20 of the £50) and in the Loss frame trials (B) as an amount of money lost from the starting amount (e.g., lose £30 of the £50). The gamble option was represented as a pie chart depicting the probability of winning (green) or losing (red) all of the starting money. The expected outcomes of the gamble and sure options were equivalent. Gain frame trials were intermixed pseudo-randomly with Loss frame trials. No feedback concerning trial outcomes was given during the experiment. [View Larger Version of this Image (114K JPEG file)]

In the new study, a team led by Benedetto De Martino and Raymond Dolan of University College London used functional magnetic resonance imaging (fMRI) to monitor the brain activity of 20 people engaged in a financial decision-making task. At the beginning of each round, subjects inside the fMRI machine saw a screen indicating how much money was at stake in that round: £50, for example. The next screen offered two choices. One option was a sure thing, such as "Keep £20" or "Lose £30." The other option was an all-or-nothing gamble. The odds of winning--shown to the subjects as a pie chart--were rigged to provide the same average return as the sure option. In interviews after the experiment, participants said they'd quickly realized that the sure and gamble options were equivalent, and most said that they had split their responses 50-50 between the two choices.

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Fig. 2. Behavioral results. (A) Percentages of trials in which subjects chose the gamble option in the Gain frame and the Loss frame. Subjects showed a significant increase in the percentage of trials in which the gamble option was chosen in the Loss frame with respect to the Gain frame [61.6% > 42.9% (P < 0.001, t19 = 8.06)]. The dashed line represents risk-neutral behavior (choosing the gamble option in 50% of trials). Error bars denote SEM. (B) Each bar represents, for each individual subject, the percentage difference between how often subjects chose the gamble option in the Loss frame as compared to the Gain frame. A hypothetical value of zero represents a complete indifference to the framing manipulation (i.e., fully "rational" behavior). All participants, to varying degrees, showed an effect of the framing manipulation. [View Larger Version of this Image (66K JPEG file)]

But they hadn't. When the sure option was framed as a gain (as in "Keep £20"), subjects played it safe, gambling only 43% of the time on average. If it was framed as a loss, however, they gambled 62% of the time.

When the researchers examined the fMRI scans, the amygdala stood out. This brain region fired up when subjects either chose to keep a sure gain or elected to gamble in the face of a certain loss. It grew quiet when subjects gambled instead of taking a sure gain or took a sure loss instead of gambling. De Martino suggests that the amygdala activity represents an emotional signal that pushes subjects to keep sure money and gamble instead of taking a loss.

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Fig. 3. fMRI results. (A) Interaction contrast [(Gsure + Lgamble) – (Ggamble + Lsure)]: brain activations reflecting subjects' behavioral tendency to choose the sure option in the Gain frame and the gamble option in the Loss frame (i.e., in accordance with the frame effect). ... (C) Reverse interaction contrast [(Ggamble + Lsure) – (Gsure + Lgamble)]: brain activations reflecting the decision to choose counter to subjects' general behavioral tendency. ... Effects in (A) and (C) were significant at P < 0.001; for display purposes they are shown at P < 0.005. (B and D) Plots of percentage signal change for peaks in right amygdala... (B) and ACC... (D). Error bars denote SEM. [View Larger Version of this Image (136K JPEG file)]

De Martino says he expected to find that subjects with the most active amygdalas would be more likely to keep sure gains and gamble when faced with a certain loss. But no such correlation turned up. Instead, activity in OMPFC best predicted individuals' susceptibility to the framing effect. De Martino speculates that OMPFC integrates emotional signals from the amygdala with cognitive information, such as the knowledge that both options are equally good. "People who are more rational don't perceive emotion less, they just regulate it better," he says.

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Fig. 4. Rationality across subjects: fMRI correlational analysis. Regions showing a significant correlation between rationality index [between-subjects measure of susceptibility to the framing manipulation...] and the interaction contrast image [(Gsure + Lgamble) – (Ggamble + Lsure)] are highlighted. (A) Orbital and medial prefrontal cortex (OMPFC) ... Effects were significant at P < 0.001; for display purposes they are shown at P < 0.005. (B) Plot of the correlation of parameter estimates for R-OFC with the rationality index for each subject (r = 0.8, P < 0.001).

"It's a nice, strong correlation between individual differences in behavior and individual differences in the brain," says Russell Polldrack, a neuroscientist at the University of California, Los Angeles. Yet Elizabeth Phelps, a cognitive neuroscientist at New York University, cautions that fMRI studies alone can rarely prove a brain region's causal role. She suggests examining people with damage to the amygdala or OMPFC to clarify how these regions contribute to the framing effect. [View Larger Version of this Image (148K JPEG file)]

    Posted by on Friday, August 4, 2006 at 12:06 AM in Economics, Science | Permalink  TrackBack (2)  Comments (22)

          

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