Rhythmic visual flicker is known to induce illusions and altered states of consciousness. Previous research has suggested that the form of “simple” illusions (e.g., geometric patterns) is constrained by the functional architecture of early visual cortical areas. As of yet, the nature of more “complex” illusions (e.g., naturalistic living and non-living things) is under-represented within the current literature. Very recent findings showed that visual imagery vividness correlates positively with the likelihood to experience anomalous percepts. Here, we tested whether imagery ability is associated with individual differences in both susceptibility to, and complexity of, flicker-induced illusions (FII). We recruited a sample of people with aphantasia (the complete lack of visual imagery) and a sample of people with imagery. We found that people with visual imagery were more susceptible to FII than people with aphantasia. Moreover, moderately-vivid imagers were more likely to see complex FII than weakly-vivid imagers, whereas people with aphantasia only experienced simple FII. People with and without imagery experienced a similar range of emotions during Ganzflicker stimulation, but people with imagery experienced more altered states of consciousness. These findings fit with recent research on the connection between visual imagery strength (specifically, the influence of imagery on perception) and visual cortical excitability. Visual imagery ability and anomalous perceptual experience may depend on the same cortical mechanism that gates effects of visual stimulation on natural cortical excitability levels. Future studies will investigate whether more fine-grained changes in cortical excitability induced by different visual flicker frequencies can modulate FII-susceptibility and FII-complexity.
Increased visual cortical excitability in ecstasy users: a transcranial magnetic stimulation study
