Summary: Decisions based on values depend upon how the two hemispheres of the brain interact, researchers report.
Source: Imperial College London.
Researchers have been able to tap into the decision-making processes in the brain to play with our sense of value.
A number of studies have shown that the two halves of the brain deal with magnitudes – such as time, space, and numbers – in different ways, with the left side of the brain dealing with larger magnitudes and the right side processing smaller magnitudes.
Now, new research suggests that choices based on values, such as financial decisions, are dependent upon how these two halves of the brain interact. What’s more, the subsequent decision-making can be altered by interfering with how the brain processes magnitudes, altering the notion of what things are worth.
In two recently published papers, researchers from Imperial’s Division of Brain Sciences have shown they can influence economic decision-making, altering the way people split a cash pot.
Dr Qadeer Arshad, an honorary lecturer at Imperial and clinical scientist at Charing Cross Hospital, who led the research, said it showed that they could “influence decision-making by interfering with how the brain works”.
Previous work by the group revealed a biological basis for number biases in the brain. Typically, one side of the brain is slightly more dominant, but the way these two halves of the brain interact can affect decision making. Our brains are thought to process numbers using a number of different regions in the left and right halves of the brain, collectively called the fronto-parietal network.
Which side of the brain is more dominant can be revealed through a slight bias towards larger or smaller numbers. Those with a more dominant left hemisphere of the brain are likely to have a bias for larger numbers – which means given a choice they are more likely to pick a larger number – while those with a more dominant right hemisphere are biased, or more likely to pick, lower numbers.
During the first study, participants were asked to pick the midpoint between two random numbers in a limited time period, not giving them enough time to actually calculate – for example, ‘choose the midpoint between 44 and 87’ – to spot any bias for larger or smaller magnitudes.
Their performance was then assessed during a standard decision-making test called the ‘dictator game’, which is often used by economists to model social behaviours. In this setup, people are offered a sum of money (£5) and told they have to share it with a stranger.
“In the study, we found that those people who were biased towards lower numbers were less generous – in that they made less favourable economic decisions towards the stranger, during the task,” explained Dr Arhsad. “Those biased towards larger numbers tended to give more money to the stranger.”
In further trials, they were able to skew the direction of decision-making. They found that dripping water into a participant’s ear and simultaneously viewing a visual stimulus caused the hemispheres to compete, leading to one side of the brain being inhibited – depending on which ear it was applied to.
Using this approach, they could subliminally bias individuals towards either smaller or larger numbers, actively driving choices during decision-making.
Pushing individuals toward small numbers led to a more selfish split, with the player giving less of the pot away. Whereas when the same individuals were pushed to larger numbers resulted in a better outcome for the stranger, with players opting to split more of the £5 pot with them.
Tapping into the process
Dr Arshad said: “The surprising thing is that we could override what they were actually told. At all times they had the same £5, but their brains seemed to ignore that completely and went with how they processed that value.
“In the same person, the £5 was made to appear as £6 or £4, and we were able to alter their corresponding decisions, but at all times, they thought they were making the same economic decisions.”
These findings were backed by a second set of trials involving patients with Parkinson’s disease. Early on in the disease, there can be a mismatch between the hemispheres as one half of the brain is affected more than the other. Based on the trials with healthy volunteers, this mismatch would be expected to shift the number bias, depending on whether the left or ride side was more affected by the disease.
Running the same tests, they found that those with more damage to the right-hemisphere (where the left side of the brain became more dominant) were more biased towards larger numbers and made more generous decisions during the decision making task The opposite was seen in those patients with more damage to the left-hemisphere.
According to the researchers, the findings could prove useful in studying how people make decisions. It could also help to better understand conditions in which the communication between the hemispheres is disrupted, affecting how signals from the body or even outside are perceived.
Dr Arshad explained: “This opens up a way to examine a person neuroscientifically, to see how they make their decisions.”
He added: “It could open up avenues towards treating certain conditions, such as chronic dizziness and pain.
“These are essentially perceptual disorders, based on how you perceive stimuli. In theory, if we could alter how the brain constructs perceptions, we might be able to alter people’s interpretation and behaviour.”
Source: Ryan O’Hare – Imperial College London
Image Source: NeuroscienceNews.com image is adapted from the Imperial College London news release.
Original Research: Abstract for “Influence of Biases in Numerical Magnitude allocation on Human Pro-Social Decision Making” by Qadeer Arshad, Yuliya Nigmatullina, Shuaib Siddiqui, Mustafa Franka, Saniya Mediratta, Sanjeev Ramachandaran, Rhannon Lobo, Paresh Malhotra, R. Edward Roberts, and Adolfo M. Bronstein in Journal of Neurophysiology. Published online September 14 2017 doi:10.1152/jn.00472.2017
Full open access research for “Biased numerical cognition impairs economic decision-making in Parkinson’s disease” by Qadeer Arshad, Angela Bonsu, Rhannon Lobo, Anne-Sophie Fluri, Rahuman Sheriff, Peter Bain, Nicola Pavese, and Adolfo M. Bronstein in Annals of Clinical and Translational Neurology. Published online September 8 2017 doi:10.1002/acn4.449
Influence of Biases in Numerical Magnitude allocation on Human Pro-Social Decision Making
Over the past decade neuroscientific research has attempted to probe the neurobiological underpinnings of human pro-social decision-making. Such research has almost ubiquitously employed tasks such as the dictator game or similar variations (i.e. ultimatum game). Considering the explicit numerical nature of such tasks, it is surprising that the influence of numerical cognition upon decision-making during task performance remains unknown. Whilst performing these tasks, participants typically tend to anchor upon a 50:50 split that necessitates an explicit numerical judgement (i.e. number-pair bisection). Accordingly, we hypothesise that the decision-making process during the dictator game recruits overlapping cognitive processes to those known to be engaged during number-pair bisection. We observed that biases in numerical magnitude allocation correlated with the formulation of decisions during the dictator game. That is, intrinsic biases towards smaller numerical magnitudes were associated with the formulation of less favourable decisions, whereas biases towards larger magnitudes were associated with more favourable choices. We proceeded to corroborate this relationship by subliminally and systematically inducing biases in numerical magnitude towards either higher or lower numbers using a visuo-vestibular stimulation paradigm. Such subliminal alterations in numerical magnitude allocation led to proportional and corresponding changes to an individual’s decision-making during the dictator game. Critically, no relationship was observed between neither intrinsic nor induced biases in numerical magnitude on decision-making when assessed using a non-numerical based pro-social questionnaire. Our findings demonstrate numerical influences upon decisions formulated during the dictator game and highlight the necessity to control for confounds associated with numerical cognition in human decision-making paradigms.
“Influence of Biases in Numerical Magnitude allocation on Human Pro-Social Decision Making” by Qadeer Arshad, Yuliya Nigmatullina, Shuaib Siddiqui, Mustafa Franka, Saniya Mediratta, Sanjeev Ramachandaran, Rhannon Lobo, Paresh Malhotra, R. Edward Roberts, and Adolfo M. Bronstein in Journal of Neurophysiology. Published online September 14 2017 doi:10.1152/jn.00472.2017
Biased numerical cognition impairs economic decision-making in Parkinson’s disease
Previous findings suggest a context-dependent bihemispheric allocation of numerical magnitude. Accordingly, we predicted that lateralized motor symptoms in Parkinson’s disease (PD), which reflect hemispheric asymmetries, would induce systematic lateralized biases in numerical cognition and have a subsequent influence on decision-making.
In 20 PD patients and matched healthy controls we assessed numerical cognition using a number-pair bisection and random number generation task. Decision-making was assessed using both the dictator game and a validated questionnaire.
PD patients with predominant right-sided motor symptoms exhibited pathological biases toward smaller numerical magnitudes and formulated less favorable prosocial choices during a neuroeconomics task (i.e., dictator game). Conversely, patients with left-sided motor symptoms exhibited pathological biases toward larger numerical magnitudes and formulated more generous prosocial choices. Our account of context-dependent hemispheric allocation of numerical magnitude in PD was corroborated by applying our data to a pre-existing computational model and observing significant concordance. Notably, both numerical biasing and impaired decision-making were correlated with motor asymmetry.
Accordingly, motor asymmetry and functional impairment of cognitive processes in PD can be functionally intertwined. To conclude, our findings demonstrate context-dependent hemispheric allocation and encoding of numerical magnitude in PD and how biases in numerical magnitude allocation in Parkinsonian patients can correspondingly impair economic decision-making.
“Biased numerical cognition impairs economic decision-making in Parkinson’s disease” by Qadeer Arshad, Angela Bonsu, Rhannon Lobo, Anne-Sophie Fluri, Rahuman Sheriff, Peter Bain, Nicola Pavese, and Adolfo M. Bronstein in Annals of Clinical and Translational Neurology. Published online September 8 2017 doi:10.1002/acn4.449