I am currently in Paris, France working with Etienne Koechlin at the École normale supérieure (ENS) on a project aimed at understanding the consequences of specific forms of brain damage on decision making processes. The goal of this post is to give a little background on some of the work we’ve done so far, and a description of the project I’m working on in Paris.
For the past few years, members from the Brittlab and the DAAG lab (headed by James Danckert) have been studying potential causes of some curious deficits that present themselves following right hemisphere brain damage. These deficits include problems with empathy, theory of mind (i.e., inferring the mental states of others), solving riddles, and even humour appreciation. Although seemingly disparate, we and others have proposed that these patient deficits stem from difficulties appropriately updating their beliefs or expectations when faced with information that does not match their current beliefs. (A full review of our position on the topic will soon be published in the Canadian Journal of Experimental Psychology).
To study updating in patients, we have primarily used two paradigms. The first has participants play computerized versions of the children’s game rock-paper-scissors. Participants try to win as often as possible against a computer that starts with a particular strategy (e.g., choose ‘rock’ 80% of the time) then switches to new strategies at unannounced points during the task (e.g., switch to choosing ‘paper’ 80% of the time). We have used this task to measure how quickly and effectively participants can update their plays in response to a computer’s shift in strategy. The second paradigm we use was developed by Elisabeth Stöttinger, and requires participants to identify pictures that gradually morph from a first object (e.g., a cat) to a second object (e.g., a swan). In this task we used the number of pictures required to identify the second object as a proxy for the amount of evidence required to update from the first to the second object.
Using both of these paradigms we’ve demonstrated that RBD patients do indeed have more trouble updating than healthy adults or left brain damaged (LBD) patients. They take longer to update to strategy shifts in our rock-paper-scissors task, and require more pictures to see the second image in the picture morphing task. Additionally, we found that RBD patients’ updating performance on the rock-paper-scissors task correlated with their performance on the picture morphing task. Taken together our evidence suggests that damage to the right hemisphere causes generic updating problems, and could be at the core of many of the seemingly disparate deficits observed in this patient population.
My current project is to follow-up on this original work and get a more detailed understanding of the updating deficits we’ve found in RBD patients. To do this, our lab is working in collaboration with Etienne Koechlin and his research group in Paris. He and members of his lab created a detailed computational model (dubbed the PROBE model) that they’ve used to explain the computations involved in the way humans learn from experience and adapt to change. They’ve used this model to identify some of the core cognitive components of adaptive decision making, and have used it in conjunction with fMRI to identify the network of brain regions involved in these processes.
In Canada, we had left and right brain damaged patients perform a task that was designed by the Koechlin lab to be used with the PROBE model. I have brought these data to Paris to learn to apply this computational model to our data in hopes of identifying the cognitive mechanisms that are affected in patients that have trouble updating. With enough data, we also hope to use voxel-based lesion symptom mapping to link specific sites of brain damage to deficits identified by the model.
This is an extremely exciting opportunity for me to learn more about some cutting edge computational modeling techniques, and apply it to a topic that I find really fascinating. It’s also a great opportunity to experience what research is like in a different country.
More updates to come!