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Samuel Hewitt, PhD

@samuelhewitt.bsky.social

920 followers 580 following 88 posts

Machine Learning Engineer at Limbic Building AI therapy Previously, Max Planck Centre for Computational Psychiatry @ UCL

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Samuel Hewitt, PhD @samuelhewitt.bsky.social · Mar 18

A little bby from my PhD is published!

we did a complex study to answer a simple Q:
do day-to-day feelings impact choices?

A: Yes. When feeling motivated (independent of other stable or unstable feelings) choices changed because rewards seemed greater.

open access link:
doi.org/10.1073/pnas...

Day-to-day fluctuations in motivation drive effort-based decision-making | PNAS

Internal states like motivation fluctuate substantially over time. However, studies of the neurocomputational mechanims of motivated behavior have ...

doi.org

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Samuel Hewitt, PhD @samuelhewitt.bsky.social · May 15

Here here !! Well done CPSY

Xiaosi Gu @xiaosigu.bsky.social · May 15

🔥💥📣 Excited to announce a new policy at the Computational Psychiatry (CPSY) journal @cpsyjournal.bsky.social. Starting from April 2025, CPSY will compensate reviewers for their time and effort invested in reviewing manuscripts. w/ @drrickadams.bsky.social
cpsyjournal.org/articles/10....

One Small Step Towards Fixing a Broken System | Computational Psychiatry

cpsyjournal.org

Reposted by Samuel Hewitt, PhD

Tobias Hauser @tobiasuhauser.bsky.social · May 14

#OCD is a understudied disorder, meaning that we know way too little about the underlying (brain) processes.
We have thus built the Brain Explorer app www.brainexplorer.net where everyone can easily contribute to understanding OCD.
#MentalHealthAwareness @tueneurocampus.bsky.social @ucl.ac.uk

Brain Explorer - Test your brain power

The brain explorer app for Apple and Android tests your brain functions and helps researchers to understand the brain. Explore your brain power and how brain functions are important for mental health.

www.brainexplorer.net

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Samuel Hewitt, PhD @samuelhewitt.bsky.social · Apr 10

I think that's already the case !! We can stop measuring the function of bored brains now

Samuel Hewitt, PhD @samuelhewitt.bsky.social · Apr 10

2 prompts attached !

prompt for a reinforcement learning game

Samuel Hewitt, PhD @samuelhewitt.bsky.social · Apr 10

it wrote all the front-end code ! just need to connect your database and adjust the trials. I just gave it this image for the style

Samuel Hewitt, PhD @samuelhewitt.bsky.social · Apr 9

@kellydonegan.bsky.social @tobywise.bsky.social

Samuel Hewitt, PhD @samuelhewitt.bsky.social · Apr 9

Hey cognitive scientists

I asked lovable.dev to make me a 2-arm bandit RL task

2 prompts and 3 minutes later
🤯🤯🤯🤯

Play it:
preview--cosmic-bandit-quest.lovable.app

Think of the hours and grad student tears saved 😅

Yes lovable I accept your sponsorship terms

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Samuel Hewitt, PhD @samuelhewitt.bsky.social · Apr 9

Make a choice and get feedback

Samuel Hewitt, PhD @samuelhewitt.bsky.social · Apr 9

Trial 1

Samuel Hewitt, PhD @samuelhewitt.bsky.social · Apr 9

Hello world

An info sheet and consent form for an RL game

Reposted by Samuel Hewitt, PhD

David V. Smith @dvsmith.bsky.social · Mar 25

“Motivation drives changes in the subjective value of reward both in the moment and in the future.”

www.pnas.org/doi/10.1073/...

Day-to-day fluctuations in motivation drive effort-based decision-making | PNAS

Internal states like motivation fluctuate substantially over time. However, studies of the neurocomputational mechanims of motivated behavior have ...

www.pnas.org

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Reposted by Samuel Hewitt, PhD

Jade Duffy @jduffy9.bsky.social · Mar 24

In life, 3 things are certain: death, taxes, and decision-making variability🧠. Our review tinyurl.com/4dcwafc4 explores how computational models 💻 explain variability, their limits, and recent advances. A thread🧵👇

@redmondoconnell.bsky.social @neuromurphy.bsky.social Mark Bellgrove (not on Bluesky)

Disentangling sources of variability in decision-making - Nature Reviews Neuroscience

Identifying the psychological and neurobiological processes underpinning intra-individual variations in choice behaviour presents a formidable challenge. In this Review, Duffy et al. discuss how algor...

www.nature.com

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Samuel Hewitt, PhD @samuelhewitt.bsky.social · Mar 20

When I began my PhD, there was a major disconnect between my own lived experience and the way researchers probed mental health-behaviour links.

I hope this work inspires others to use new designs to appreciate the complexity of human beings and their experiences.
link.growkudos.com/1f5ss3bn1ts

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Samuel Hewitt, PhD @samuelhewitt.bsky.social · Mar 20

this is super cool and clever. Well done, really like it. Sth like this has been scratching at me for a while too - congrats on putting it together

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Reposted by Samuel Hewitt, PhD

Quentin Huys @docqhuys.bsky.social · Mar 18

This is a great study, if I may say. We have had a lot of data showing correlations between subjective assessments and behaviour between individuals. With this study, we are starting to see how they interact over days within individuals. Congratulations @samuelhewitt.bsky.social!

Samuel Hewitt, PhD @samuelhewitt.bsky.social · Mar 18

Day-to-day fluctuations in motivation drive effort-based decision-making | PNAS

Internal states like motivation fluctuate substantially over time. However, studies of the neurocomputational mechanims of motivated behavior have ...

doi.org

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Samuel Hewitt, PhD @samuelhewitt.bsky.social · Mar 18

Thanks Quentin!

Samuel Hewitt, PhD @samuelhewitt.bsky.social · Mar 18

thanks Micah !!

Samuel Hewitt, PhD @samuelhewitt.bsky.social · Mar 18

game demo: ema-motivation.web.app
repository: github.com/DevComPsy/re...

mobile study

ema-motivation.web.app

Samuel Hewitt, PhD @samuelhewitt.bsky.social · Mar 18

woopsy sorry, will correct!

here is a link to the full repo
github.com/DevComPsy/re...

and you can also play a demo of the game on your phone here:
ema-motivation.web.app

GitHub - DevComPsy/reward-effort-2afc-firebase-EMA-motivation: pre-print fork

pre-print fork. Contribute to DevComPsy/reward-effort-2afc-firebase-EMA-motivation development by creating an account on GitHub.

github.com

Samuel Hewitt, PhD @samuelhewitt.bsky.social · Mar 18

thank you to brilliant collaborators Prof @docqhuys.bsky.social and Dr Agnes Norbury (now Thymia) and my PhD supervisor Prof @tobiasuhauser.bsky.social

Samuel Hewitt, PhD @samuelhewitt.bsky.social · Mar 18

I hope it goes without saying that all data and code, including the smartphone game are available

osf.io/3mhqb/

EMA motivation

Data and code for the project all task and analysis code: https://github.com/DevComPsy/reward-effort-2afc-firebase-EMA-motivation Hosted on the Open Science Framework

osf.io

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Samuel Hewitt, PhD @samuelhewitt.bsky.social · Mar 18

This suggests that specific transient feelings can drive computational decision mechanisms in the future.

We think this study design can allow many new questions in computational psychiatry, bridging long established lab theories with real, human experiences and potentially clinical translation

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Samuel Hewitt, PhD @samuelhewitt.bsky.social · Mar 18

State motivation-choice coupling was driven by fluctuations in reward sensitivity. This is a fancy way of saying that when more motivated, (the same) rewards seemed more rewarding.

What I think is SUPER 😎 is that this was not only rewards NOW, but also rewards at the NEXT timepoint.

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Samuel Hewitt, PhD @samuelhewitt.bsky.social · Mar 18

State motivation was a critical source of variability in choices over time (leading to greater willingness to make effort, duh).

But state motivation also interacted with trait-motivation, meaning that people with LOWER trait (higher apathy) had even stronger state-choice coupling.

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Samuel Hewitt, PhD @samuelhewitt.bsky.social · Mar 18

N.B. our game could also reliably capture effort-based choices and the model-parameters which govern this value-based decision