Casper Kerrén

🚨Preprint! “Bayesian surprise tracks the strength of perceptual insight” - Work with @lindedomingo.bsky.social & @gonzalezgarcia.bsky.social

Ever wondered what factors influence the subjective experience of suddenly understanding a previously unclear input?

Click below:
doi.org/10.64898/202...

Episodic memory encoding fluctuates at a theta rhythm of 3–10 Hz Nature Human Behaviour - Biba et al. show that episodic memory encoding fluctuates at a theta rhythm of 3–10 Hz.

I am excited to share my first paper, showing that episodic memory formation is theta rhythmic, is now published in Nature Human Behavior! Check it out here: rdcu.be/e6pzS. Thanks to my PI, Katherine Duncan, and to my collaborators for their support on this journey! Stay tuned for iEEG follow up 🧠

And the paper of course: www.biorxiv.org/content/10.6...

9/9 Take-home: when attention can’t keep items in the focus, VWM leans toward more abstract, LTM-like/semantic formats that stay more readily accessible than fine perceptual detail. Really fun one to work on with my mates.

8/9 DDM again: sem. effects were primarily pre-accumulation (non-decision time) and selectively larger when items had to be maintained under competing demands.

7/9 Experiment 2 (Immediate vs Delay vs Interference): delay alone didn’t reliably amplify sem. prio, but interference did.

6/9 DDM nailed the dissociation:

Valid cueing eliminated the sem. advantage in non-decision time (access demands reduced).

But it boosted sem. advantages in drift rate (how efficiently evidence is used once decision starts).
So cueing shifts where the sem. edge shows up in the decision pipeline.

5/9 Experiment 1 (retro-cues): tested whether sem. prio is just a decision/selection bias.

Valid cue lets you pre-select the to-be-tested item.

Neutral cue forces you to keep multiple items available until probe.

Result: semantic prioritisation shrinks with valid cues but doesn’t vanish.

4/9 Reanalysis of our earlier dataset: sem. judgements showed a robust reduction in NDT across loads + lags → consistent w faster pre-accumulation access to sem. info. Drift-rate advantages for semantics were conditional (mainly under higher demands: higher load / longer lag btw study & test).

3/9 To figure out why, we used hierarchical drift-diffusion modelling (HDDM) to separate:

Non-decision time (t): pre-accumulation processes (probe processing / access / prep)

Drift rate (v): evidence accumulation efficiency (decision formation)

2/9 The striking behavioural pattern: when multiple items are in VWM, people are faster (and often more accurate) for semantic judgements than perceptual ones.
That’s the reverse of perception, where low-level visual features typically win the race.

1/9 New paper with @gonzalezgarcia.bsky.social and @lindedomingo.bsky.social : “Characterising semantic prioritisation in visual working memory.”
Core question: when we hold visual info briefly in mind, what gets accessed first: perceptual details or semantic meaning?

How do we balance external attention to the outside world and internal attention to our thoughts & memories?

We review evidence that external and internal attention can compete, unfold concurrently, or cooperate!

Loved working on this with @samversc.bsky.social & @tobiasegner.bsky.social!

New preprint 🚨

Across multiple tasks, we show that higher-level info is more readily accessible in WM before evidence accumulation begins. Attention then boosts perceptual detail.

www.biorxiv.org/content/10.6...

A lot of fun with my colleagues @ckerren.bsky.social and @gonzalezgarcia.bsky.social

Our new preprint is out on bioRxiv! @doellerlab.bsky.social
We show that eye-movement sequences actively organize information by aligning with underlying structure and flexibly adapting to cognitive demands in working memory.

www.biorxiv.org/content/10.6...

A teaser figure showing the process of metamers rendered differentially (MRD). Target scene parameters are used to render a target scene. A new scene is initialized from some starting point, and renders are created from this scene. The loss between the initial and target scenes is measured. MRD allows the gradients wrt the loss to be propagated to the scene parameters (e.g. lighting, geometry or material) for gradient-based optimization.

Legit super excited about this work coming out. My amazing doctoral student @ben.graphics has been working on an idea to use physically based differentiable rendering (PBDR) to probe visual understanding. Here, we generate physically-grounded metamers for vision models. 1/4

arxiv.org/abs/2512.12307

Illustration of the hypothesized flows of information between perception, memory and cognitive control in a conceptual model of working memory. Stimuli attributes are processed to varying degrees of abstraction and parts of these representations can be loaded into working memory under the guidance of cognitive control. Familiar stimuli such as the letter B activate visually abstract representations while less familiar stimuli are limited to sensory representations. Information can be shifted both up and down levels of the perceptual hierarchy to build either more or less abstract representations of either perceived or imagined stimuli. Working memories can be shifted into or out of the hierarchy as needed.

We recently published a theoretical review about how compositional and generative mechanisms in working memory provide a flexible engine for creative perception and imagery.

Pre-print:
osf.io/preprints/ps...

Paper: www.sciencedirect.com/science/arti...

Adaptive episodic memory: how multiple memory representations drive behavior in humans and nonhumans | Physiological Reviews | American Physiological Society Episodic memory is a declarative long-term memory of a specific past experience. As such, it is multifaceted, encompassing both the objective and subjective components of that experience. These components can be flexibly represented at different levels of granularity, from precise, context-specific details to generalized, gistlike representations. In this review, we suggest that 1) multiple representations of an episodic memory at different levels of granularity are simultaneously encoded into a memory trace and 2) the relative weighting of these representations determines the extent to which a memory is reconstructed or reproduced at retrieval. We propose that this representational flexibility drives adaptive behavior by prioritizing reconstruction or reproduction depending on the age of the memory, its relationship to prior knowledge, current attentional goals or task demands, and individual differences. Drawing on research in humans and nonhuman animals, we show a close correspondence between psychological and neural representations of a memory across encoding, consolidation, and retrieval. Specifically, we discuss how hippocampal activity in humans and engram formation and activation in rodents support the reproduction of detailed memory representations, whereas schema formation across species, mediated by the medial prefrontal cortex, facilitates reconstruction and generalization to guide behavior. Finally, we consider how species- and individual-level differences shape episodic memory representations. By integrating findings across species, we illustrate how the correspondence between neural and psychological representations enables multiple memory representations to balance stability and flexibility, ultimately driving adaptive behavior.

How do memories guide behaviour?

Multiple memory representations, from detailed to gist-like, let us flexibly reconstruct or reproduce past experiences to behave adaptively across species.

Now out in Physiological Reviews with Morris Moscovitch, Melanie Sekeres & @brianlevine.bsky.social!

Building compositional tasks with shared neural subspaces Nature - The brain can flexibly perform multiple tasks by compositionally combining task-relevant neural representations.

Thrilled that my paper is out in the @nature.com. We explored how the brain builds complex tasks by compositionally combining simpler sub-task representations. The brain flexibly performs multiple tasks by dynamically reusing neural subspaces for sensory inputs and motor actions

rdcu.be/eRVUk

New discovery! Value-based decisions reorganize neural state space. Options are first encoded in orthogonal subspaces Then the selected option rotates into a "readout subspace".
Neural subspace reorganization reflects value-based decision making.
www.biorxiv.org/content/10.6...
#neuroscience

1/7 Can infants recognise the world around them? 👶🧠 As part of the FOUNDCOG project, we scanned 134 awake infants using fMRI. Published today in Nature Neuroscience, our research reveals 2-month-old infants already possess complex visual representations in VVC that align with DNNs.

High-dimensional structure underlying individual differences in naturalistic visual experience Han and Bonner reveal that individual visual experience arises from high-dimensional neural geometry distributed across multiple representational scales. By characterizing the full dimensional spectru...

Human visual cortex representations may be much higher-dimensional than earlier work suggested, but are these higher dimensions of cortical activity actually relevant to behavior? Our new paper tackles this by studying how different people experience the same movies. 🧵 www.cell.com/current-biol...

I’m excited to share our preprint ‘Phase similarity between similar objects indicates representational merging across retrieval training but not sleep.’ We use EEG to compare representational changes to memories across retrieval-mediated and sleep-based consolidation www.biorxiv.org/content/10.6...

How are memories consolidated during sleep?
Excited to share another preprint: hippocampal SWRs route memory content to the cortex via interregional co-reactivation of concept cells, optimized by slow-oscillation–spindle coupling. With the great @tschreiner.bsky.social @humansingleneuron.bsky.social

A unifying account of replay as context-driven memory reactivation A context-driven memory model simulates a wide range of characteristics of waking and sleeping hippocampal replay, providing a new account of how and why replay occurs.

Really thrilled that this paper led by @neurozz.bsky.social is now published in its final version in @elife.bsky.social!!

This is a memory-focused (as opposed to RL-focused) account of the detailed characteristics of forward and backward awake and sleep replay!

elifesciences.org/articles/99931

Inference over hidden contexts shapes the geometry of conceptual knowledge for flexible behaviour Flexible decision-making in uncertain environments requires inferring the relevant context and focusing on behaviourally relevant information. We tested the hypothesis that the brain supports this pro...

We don’t learn the world as it is. We rapidly infer what matters, with belief and attention reciprocally shaping each other as neural geometry adapts.

Thanks to @stephanie-theves.bsky.social, @mikael-johansson.bsky.social, Peter Gärdenfors, @doellerlab.bsky.social.

www.biorxiv.org/content/10.1...

Critically, inference stretches neural distances along relevant dimensions and compresses irrelevant ones right before a decision, predicts faster RTs, and this re-shaping precedes feedback-related frontal theta tracking model-derived PE.

The brain’s representational space flexes with inferred complexity.

Neural effective dimensionality scales up in 2D vs 1D, and is higher on correct vs incorrect trials. In 2D, the two attended features show up as near-orthogonal axes in a shared planar manifold plane.
6/8

Eyes tell the same story
Gaze selectively shifts toward task-relevant features, irrelevant features drop out. Gaze entropy decreases as beliefs stabilise, and negative prediction errors from the HSI model trigger broader sampling (exploration), while positive PEs tighten focus (exploitation).
5/8

A Hidden State Inference (HSI) model best explained choices and inferred contexts, beating Q-learning variants (standard, forgetting, counterfactual).

HSI captures something structurally different from incremental RL.
4/8