From dots to faces: Individual differences in visual imagery capacity predict the content of Ganzflicker-induced hallucinations

TL;DR

This study shows that individual differences in visual imagery capacity influence the complexity and content of hallucinations induced by Ganzflicker, with stronger imagers experiencing more vivid and naturalistic images.

Contribution

It demonstrates that visual imagery strength predicts the content and perceptual richness of Ganzflicker-induced hallucinations using NLP analysis of participant descriptions.

Findings

Strong imagers describe more complex, naturalistic hallucinations.

Weak imagers report simple geometric patterns.

Richer perceptual associations are linked to stronger imagery.

Abstract

A rapidly alternating red and black display known as Ganzflicker induces visual hallucinations that reflect the generative capacity of the visual system. Individuals vary in their degree of visual imagery, ranging from absent to vivid imagery. Recent proposals suggest that differences in the visual system along this imagery spectrum should also influence the complexity of other internally generated visual experiences. Here, we used tools from natural language processing to analyze free-text descriptions of hallucinations from over 4,000 participants, asking whether people with different imagery phenotypes see different things in their mind's eye during Ganzflicker-induced hallucinations. Topic modeling of descriptions revealed that strong imagers described complex, naturalistic content, while weak imagers reported simple geometric patterns. Using crowd-sourced sensorimotor norms, we also found that participants with stronger imagery used language with richer perceptual associations. These findings may reflect individual variation in coordination between early visual areas and higher-order regions relevant for the imagery spectrum.