Cohen, S., Henin, S., & Parra, L. C. 2017. "Engaging narratives evoke similar neural activity and lead to similar time perception." Scientific Reports.

This study tested the hypothesis that the consistency of the electroencephalographic (EEG) responses across different people watching the same video is a proxy for stimulus engagement. The theory is that when neural activity driven by the identical stimulus is relatively more consistent across people, the group is dedicating their limited attentional resources to processing the narrative. The stimulus is therefore relatively more engaging. On the other hand, when the activity across people's brains diverges, this is a sign that each individual is attending to their internal thoughts, which are not expected to be correlated across individuals. I thus utilized this neural measure of engagement: the similarity of the neural activity across subjects to predict behavioral engagement. Similarly to the model in which neural resources are scarce, and will therefore only be driven by the story if it is engaging, I measured behavioral engagement under the premise that subjects will only dedicate their time or money to a resource that is worth their while. I found that moments of the narrative which evoke relatively more similar neural responses, were also worth more time and money.

Cohen, S. & Parra, L. C. 2016. "Memorable audiovisual narratives synchronize sensory and supramodal neural responses." eNeuro.

When something is more engaging, it should be processed at a deeper level, which should thus lead to a memory enhancement. I hypothesized that memory will be related to an individual’s level of engagement. Using the level of neural similarity across subjects as a proxy for engagement, I wanted to see if individuals whose neural activity was more similar to others hearing the same story had better memory. In line with the idea that brain responses are more cohesive when individuals are more engaged, I found that individuals with neural responses that were more similar to their peers had better memory for the stories.

Cohen, S. S.*, Madsen, J.*, Touchan, G., Robles, D., Lima S. F. A., Henin, S., Parra, L. C. 2018. Neural engagement with online educational videos predicts learning performance for individual students. Neurobiology of Learning and Memory. (* equal contribution)

In the educational context, in the case of increasingly common online learning formats, instructors may be unsure of the engagement and subsequent learning retention of their students. I therefore examined the relationship between neural activity evoked by educational videos and memory for the facts presented in them. Since exams are not always at the forefront of a student’s mind, I tested memory among students who knew their memory would be queried and among those who were unaware of the upcoming assessment. In both groups I found a strong relationship between each student’s test performance and the similarity between their video-evoked brain responses and those of the other students. This measure of neural similarity could also discriminate whether students were allowed to freely attend to the videos, or were in a distracted state due to being forced to engage in another task while watching the videos.

Petroni, A.*, Cohen, S. S.*, Ai, L., Langer, N., Henin, S., Vanderwal, T., Milham, M. P., Parra, L. C. 2018. "The variability of neural responses to naturalistic videos Change with Age and Sex." eNeuro. (* equal contribution)

Here, I asked whether the coherence of neural activity changes with age. One theory is that the older that people are, the more time they have spent in a similar environment. It is therefore possible that older subjects will have more consistent neural responses to the typical situations present in their environment. However, an alternative possibility is that diverse life experiences, which also increase with age, will cause neural responses to become more variable with age. I tested these competing possibilities using EEG. I found that between ages 5 and 44 years brain responses to Hollywood movies and typical classroom scenarios become less correlated with age in EEG. These results support the idea that with maturity neural function becomes more variable.

Cohen, S. S., Tottenham, N., & Baldassano, C. 2022. "Developmental changes in story-evoked responses in the neocortex and hippocampus." eLife.

In this study I found that age related differences in story evoked brain activity cover much of the cortex, and are especially divergent in high-level association areas. This is consistent with the idea that the structured world knowledge that aids in story interpretation does not simply increase with age, but rather morphs from one stable version to another. I therefore tested whether the models that children and adolescents use to organize stories changes with age. I modeled brain data using the hypothesis that people of all ages will represent a coherent scene with one stable pattern of activity, and that this pattern will morph at the boundary between scenes into a new stable pattern. I found that the ability of these models to characterize brain activity changes with age, such that adolescents are better able to structure incoming information than younger children. I also found that the timing of the boundaries between perceived events changes with age, as adolescents are able to anticipate upcoming scene changes better than younger children. These results are likely a byproduct of the increased experience that adolescents have with structuring and characterizing the world.