Levels of Vision: From Computational Models to Psychedelics | Marco Aqil @ QRI Amsterdam Meetup 2025

In this presentation, Marco Aqil shares research from his recently defended PhD, exploring two complementary approaches to understanding visual perception and brain dynamics. The first part focuses on population receptive field models and how psychedelics alter visual processing, while the second examines graph neural fields for modeling brain dynamics and geometric hallucinations.

Marco Aqil (https://x.com/marcoaqil) is a neuroscientist and mathematician specializing in computational models of visual perception and brain dynamics. He led the first psychedelic fMRI study in Amsterdam using psilocybin to investigate alterations in visual context processing. He's the founder of the Amsterdam Psychedelic Research Association (https://apra.science). His work bridges sophisticated mathematical modeling with experimental neuroscience to understand how the brain constructs visual experience.

Timestamps:
0:05 - Introduction and acknowledgments
1:01 - Population receptive field models explained
1:58 - Overview of fMRI as a research tool
2:04 - Early Gaussian models for visual processing
2:40 - Advanced models: Difference of Gaussian and compression
4:05 - Unifying visual processing models through divisive normalization
5:44 - Model comparison and performance analysis
6:27 - Activation and normalization constants
8:47 - Neurotransmitter receptors as algorithmic modulators
10:24 - Using the Human Connectome Project dataset with PET receptor data
11:58 - Correlations between model parameters and receptor densities
13:13 - First section recap and transition to psilocybin study
13:34 - Introduction to psilocybin research challenges
14:44 - Double-blind study design with placebo, 5mg and 10mg doses
16:16 - Subjective effects measurements
16:40 - Ebbinghaus illusion experiment results
18:16 - Brain response analysis with population receptive field models
19:35 - Effects of psilocybin on visual context processing
20:54 - Part one conclusion: psychedelics alter fundamental aspects of perception
21:37 - Transition to graph neural fields research
22:20 - Introduction to neural field models on graphs
24:00 - Using graph Laplacians and Fourier transforms on arbitrary spaces
26:22 - Wilson-Cowan dynamics on cortical surfaces
27:46 - Analyzing spatiotemporal power spectra (CHAOS)
34:05 - Recent work combining fMRI and MEG data modeling
38:56 - Geometric hallucinations as revealing visual system architecture
41:16 - Creating motion illusions with simple harmonic patterns
42:24 - Conclusions on how simple computations create complex experiences
44:54 - Q&A session

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