Sebastian Hellmann

If you’re in #Munich 🥨 and curious about decision-making, perception, and cognition through a translational lens, join us for a seminar I’m hosting on Oct 30 with three fantastic speakers: @jkesby.bsky.social (visiting from 🇦🇺), @miguelbengala.bsky.social, and @jacob-lab.bsky.social 🧠💡

Hosting a WebSite on a Disposable Vape Someone's trash is another person's web server.

you heard of running Doom on random gadgets but have you ever heard of…
“Hosting a WebSite on a Disposable Vape”
bogdanthegeek.github.io/blog/project...
this explains how!
((the internet is healing 😌))
#IndieDev

Just back from this - I was the misfit invited speaker who knows nothing about psychology. It was really educational for me, expanded my view of theory construction problems in the human sciences.

Introducing hMFC: A Bayesian hierarchical model of trial-to-trial fluctuations in decision criterion! Now out in @plos.org Comp Bio.
led by Robin Vloeberghs with @anne-urai.bsky.social Scott Linderman

Paper: desenderlab.com/wp-content/u... Thread ↓↓↓

#PsychSciSky #Neuroscience #Neuroskyence

"Learning to be confident: How agents learn confidence based on prediction errors"! Now out in @cognitionjournal.bsky.social led by @pierreledenmat.bsky.social

Paper: desenderlab.com/wp-content/u... Thread ↓↓↓

#AcademicSky #PsychSciSky #Neuroscience #Neuroskyence

An array of 9 purple discs on a blue background. Figure from Hinnerk Schulz-Hildebrandt.

A nice shift in perceived colour between central and peripheral vision. The fixated disc looks purple while the others look blue.

The effect presumably comes from the absence of S-cones in the fovea.

From Hinnerk Schulz-Hildebrandt:
arxiv.org/pdf/2509.115...

Unfortunately, for the variance on the probability scale, the speed up vanishes.

Thanks for the kind words.
Glad to see that people already account for this in some packages. Not sure whether it helps a lot, but using the direct computations instead of using numerical integration may still speed up things a bit (about 20 times on my machine)

Excited to share joint work with Ulf Hahnel and @sgluth.bsky.social on investigating how attribute translations - a widely implemented behavior intervention - lead to more ecological consumer choices. Main results are below, but check out our preprint 👇
www.researchsquare.com/article/rs-7...

The good news: We provide a simple, correct computation that accounts for this variability, ensuring accurate group-level inferences. This fix is crucial for reliable conclusions in all cognitive models with constrained parameters.

Check out the details to improve your hierarchical analyses!

A Figure with two panels, demonstrating the transformation of a normally distributed random variable resulting from transforming the values using the standard normal CDF to the interval 0 to 1. The figure shows the discrepancy between the mean of the transformed values and the result from simply transforming the mean of the normal distribution using the standard normal CDF. The left side shows a normal distribution with low variance, such that the transformed values also show small variance and a symmetrical shape. The mean of the transformed values and the value resulting from transforming the mean directly coincide. The right side shows a distribution with high variance. Due to the non-linearity of the normal CDF, the distribution of transformed values is non-symmetrical and highly skewed. The mean of the distribution is therefore pulled to the center of the range 0 to 1, compared to the result from directly transforming the mean of the normal distribution.

(e.g. the standard normal CDF) and normal distributions to fit the group-level distribution.
But we cannot simply apply the same transformation to the mean of the real-valued normal distribution to derive the group-level mean on the parameter scale! This ignores individual variability.

Line graphs comparing correct and biased computations for exponential and probit (Φ) transformations in statistical modeling. Colored lines show how the bias changes with different group means and standard deviations.

If you’re estimating group-level means of constraint parameters, which are fitted with nonlinear transformations, beware that a common approach can produce biased estimates—especially with high individual variability.

For constraint parameters, we often use nonlinear transformations...

For all who use Bayesian hierarchical models, have a look at our new preprint, out now together with @linushof.bsky.social @nunobusch.bsky.social and @thorstenpachur.bsky.social

osf.io/preprints/ps...

Screenshot of the article "How Convincing Is a Crowd? Quantifying the Persuasiveness of a Consensus for Different Individuals and Types of Claims"

We know that a consensus of opinions is persuasive, but how reliable is this effect across people and types of consensus, and are there any kinds of claims where people care less about what other people think? This is what we tested in our new(ish) paper in @psychscience.bsky.social

We ran a randomized controlled trial to see how much AI coding tools speed up experienced open-source developers.

The results surprised us: Developers thought they were 20% faster with AI tools, but they were actually 19% slower when they had access to AI than when they didn't.

📢 @markkho.bsky.social & I are recruiting a joint postdoc interested in computational models of social interaction & mental health

💻 Ideal candidates have experience w/ multi-player web-based experiments & computational modeling

📅 Apps are reviewed on a rolling basis

🔗 apply.interfolio.com/165809

Confidence in absence as confidence in counterfactual visibility: a CogSci proceedings paper with star MSc student Maya Schipper, is now out on PsyArXiv:

osf.io/preprints/ps...

🧵👇

🚨 PhD position (75%, TV-L E13) at LMU Munich!
Join our DFG funded META REP project on heterogeneity & replicability in psychology.
Work on meta analysis, simulations, modeling in R/Python.
📅 Apply by July 15
🔗 shorturl.at/939tP
🔗 shorturl.at/2bRLD
👇🧵

#EduSky A must-read esp. if you use AI tools, are being made to "just try them" at school, or are having your students use them.

Thanks so much, also for your support and your wisdom. It has been a pleasure to be your Padawan ;)

🧠 Job Alert: Postdoc Position Available!
We're hiring a postdoc as part of the exciting DFG Research Unit on Belief Updating 🔬
🔍 What we're looking for:
Strong quantitative skills & passion for belief updating research
📍 Location: University of Hamburg
⏰ Duration: 2 years, full-time
🔗 Link below

Hairy ball theorem - Wikipedia

'How is this economics?'
en.m.wikipedia.org/wiki/Hairy_b...

Please spread the word!

Psych Science is recruiting volunteers to help conduct computational reproducibility checks.
If you have experience writing reproducible analysis scripts in psychology, and want to join the team, please apply!

www.psychologicalscience.org/publications...

🎉 Thrilled to share the press releases of our study 🎉
English from @elife.bsky.social: elifesciences.org/for-the-pres...
German from @uni-hamburg.de: www.uni-hamburg.de/newsroom/pre...

Dynamic modulation of confidence based on the metacognitive skills of collaborators! Now out in @cognitionjournal.bsky.social New work from
@felixhermans.bsky.social Simon Gaia @majafr.bsky.social
and me! Paper here: pubmed.ncbi.nlm.nih.gov/40262423/ Details ↓↓↓

Postdoc Opportunity in Cognitive Computational Neuroscience 🧠
Join us at TU Dresden (Germany) to model decision-making + brain data using probabilistic modelling

📅 Apply by April 30, 2025
🔗 tud.link/9d2n92

Please share! 🔁

#compneuro #CognitiveNeuroscience #postdoc @bernsteinneuro.bsky.social

Model-Based Neuroscience and Cognition Summer School Visit the post for more.

Join us in Amsterdam for the 11th Model-Based Neuroscience & Cognition Summer School. Gain a solid foundation in Bayesian evidence-accumulation modeling and explore its integration with neuroscience or advanced computational frameworks, including reinforcement-learning models. modelbasedneurosci.com

Podcast: Maja Göpel, Transformationsforscherin „Wir können alles lösen, solange wir uns entscheiden, zusammenwirken zu wollen.“ Ihr Thema ist die Veränderung und die Frage, warum es uns genau die so schwerfällt. Maja Göpel ermuntert zu einem positiven Blick auf die Probleme unserer Zeit. Statt nur über Zumutungen zu lamentiere...

Die Blaue Couch ist ein sehr schönes Format mit viel Zeit und einer tollen Moderatorin: herzlichen Dank #DominiqueKnoll

www.ardaudiothek.de/episode/blau...

Congratulations to @linushof.bsky.social from our lab @tum.de for being the runner-up at this year’s #teap2025 poster competition! His research shows that people search adaptively in decisions from experience.

The short paper on the statConfR package together with Sascha Meyen and @sehellmann.bsky.social has now been published. Reviews in JOSS are not only about the paper but also the code, which I think is a great idea, especially for cognitive modelling.