Mathematical models of memory-based decisions
A shelf of tasty food snacks in the behavioral lab. Snacks are used as stimulus material to motivate participants to make decisions in line with their personal preferences.
Project Objectives
Memory exerts an important influence on decision-making, as we use our recollections of past experiences and events to inform the choices we make. We spoke to Dr Sebastian Gluth about his group’s work on both investigating the cognitive and neural processes involved in decision-making, and developing mathematical models of how those decisions are reached. A clear distinction is drawn in decision sciences between value-based and perceptual decisions. With perceptual decisions, there is an objective criteria of what is right or wrong, so a traffic light could be red, amber or green for example, and a driver decides on whether to move accordingly. “If you think it’s red but it’s actually green, then you will make an error,” says Dr Sebastian Gluth, Head of the Center for Decision Neuroscience at the University of Basel. With a value-based decision, however, there is no single, objectively correct thing to do. “Some people like Coke, others like Pepsi for example,” continues Dr Gluth. “We can only infer what a person wants by observing that person’s behaviour. And based on that we might then be able to infer what is good for a person or not.” Value-based decisions As the Principal Investigator of a project backed by the Swiss National Science Foundation, Dr Gluth is investigating the basis on which people make value-based decisions, bringing together several strands of research. One aim in the project is to identify the cognitive and neural processes involved in making these decisions. “How do they take place? How can we set up mathematical models to explain why a person chooses a particular option, or predict the probability that they will choose that?” outlines Dr Gluth. Most of the earlier decision-making models focused on what the person was going to choose, but Dr Gluth and his team are now adding another dimension. “We are developing models that also make predictions about how fast we make decisions, and how confident we are about our decisions,” he explains. Evidence accumulation models are an important tool in this respect, enabling researchers to make predictions on how quickly an individual will make value-based decisions, such as what snack they might want to choose from a vending machine or what shirt to wear on a night out. The idea behind this is that individuals retrieve memories about the available options and thereby accumulate evidence for choosing one of them over time. “It develops over time, until you reach a certain
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Picture of the Decision Neuroscience team during the annual meeting of the Society for Neuroeconomics in Philadelphia in 2018.
point of confidence in what you want. That’s when you make your decision,” says Dr Gluth. Analysis of electroencephalography (EEG) signals from the human brain and singleunit activity in the monkey brain for example suggests that once a certain threshold of accumulated neural activity is reached then a decision is made. “The choice is always made at the point when this EEG signal, or singleunit recording signal, reaches a specific level,” explains Dr Gluth. There are however certain so-called biases in our memory which are also an important consideration in the project. It might be
that an individual has a particularly strong recollection of one option for example, while their memory of a second option is less vivid, which Dr Gluth says will affect their decisionmaking. “Even if the value of the different options is pretty similar, then they will still have a clear preference towards the option that they remember more vividly. So the strength of memory drives your preferences,” he outlines. Researchers are probing how individuals make these decisions, using familiar stimuli. “We ask people how much they like different options and to rate them on a scale from 1-10, maybe they rate option A as 5 and B as 5. Then they are asked to choose between them,” says Dr Gluth. The study participants have to make the decision based on their memories of the different options, rather than visual evidence. While it might be expected that there would be a fairly equal spread, as they had previously given the same rating to the two options, Dr Gluth says that a fairly clear pattern emerges. “We see that they pick A more often. The reason is that they can remember A better than B,” he explains. This effect might be even more pronounced in elderly people, another area of interest to Dr Gluth and his colleagues in the project. “We know that elderly people experience a decline in their episodic memory, so this memory bias might be even stronger in elderly people compared to younger people,” he says.
The influence of episodic memory on value-based decision making Most of our everyday decisions require us to retrieve important information from our memories. The goal of the SNF project “The influence of episodic memory on value-based decision making” is therefore to uncover the psychological, computational and neural principles of how our memories shape our preferences and decisions. This research question is addressed by combining mathematical modeling of choice behavior with modern neuroimaging tools.
Mathematical models This research is part of the wider goal of developing a deeper understanding of the interplay between memory and decisionmaking. Alongside conducting experiments, Dr Gluth and his colleagues are also developing a mathematical model of how memory influences decision-making processes, building on previous research. “A lot has been written about these evidence accumulation models, which are mathematical models of decision making. There’s also a lot of literature on how memory should work, and mathematical models of
in nature at this stage, Dr Gluth believes that it could bring wider benefits in future, for example in helping people who have experienced a decline in their memory to make good decisions. “If you understand the cognitive system better, then you can devise better technologies,” he explains. “For instance, insights into the visual system can help you to arrange the road system in a more optimal way. A famous example of this is that a lot of cars previously crashed at a road bend in Chicago because they were going too fast and failed to brake. Lines have since been painted on the street, and the distance between
How do value-based decisions take place? How can we set up mathematical models to explain why a person chooses a particular option, or predict the probability that they will choose that? memory. We try to combine these two aspects,” he says. One major question concerns whether information is retrieved from the memory strictly before a decision is initiated. “Do you first try to retrieve information from your memory, and after you have done this in your brain you start making your decision? Or does this happen in parallel?” continues Dr Gluth. The working hypothesis in the project is that information is retrieved more or less in parallel with decision-making, which will inform the ongoing development of the mathematical model. While research is largely fundamental
them gets smaller to make drivers think they are accelerating, and therefore they hit the brake.” This can be thought of as an example of nudge theory in action, essentially the use of behavioural insights to influence individual behaviour. While the project’s work holds wider relevance in these terms, Dr Gluth says the primary focus is more on fundamental research at this stage. “We are in the process of finishing some projects, and we hope to finalise some more publications over the next few months. There are also other projects, like our work with EEG signals, where we’re still analysing the data,” he outlines.
Experimental set up for a combined EEG and eye-tracking study. The eye-tracker is situated just below the computer screen.
Project Funding
Funded by the Swiss National Science Foundation - SNF Project #100014_172761 / 1
Project Partners
• Jörg Rieskamp, Department of Psychology, University of Basel, Switzerland • Ian Krajbich, Department of Psychology and Department of Economics, The Ohio State University, USA
Contact Details
Project Coordinator, Sebastian Gluth, PhD Assistant Professor University of Basel Faculty of Psychology Decision Neuroscience Missionsstrasse 62a 4055 Basel Switzerland T: +41 61 207 06 06 E: sebastian.gluth@unibas.ch W: http://p3.snf.ch/Project-172761
Gluth, S., Sommer, T., Rieskamp, J., and Büchel, C. (2015). Effective connectivity between hippocampus and ventromedial prefrontal cortex controls preferential choices from memory. Neuron 86, 1078–1090. Weilbächer, R., and Gluth, S. (2017). The interplay of hippocampus and ventromedial prefrontal cortex in memory-based decision making. Brain Sciences 7, 4.
Sebastian Gluth, PhD
Sebastian Gluth, PhD is currently assistant professor and head of the Decision Neuroscience lab at the Department of Psychology of the University of Basel. He studied psychology at the Humboldt University Berlin and received his PhD from the University of Hamburg. Prof. Gluth’s work addresses the cognitive and neural foundation of decision making and learning processes.
The left panel shows a heat map of eye movements when participants made decisions between two options shown within the green and red squares. Warm colors indicate more fixations. The goal of using eye tracking is to investigate how people distribute their attention while making decisions from memory. The right panel shows time-frequency plots of EEG data when participants made decisions from memory. Warm colors indicate increased spectral power. The decrease in spectral power at lower frequencies (~20 Hz) before the response reflects the preparation of movement. The goal of using EEG is to understand how memory and decision-making processes emerge and interact over time.
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