Visual hallucinations can be simple (flashes, patterns) or complex (objects, scenes). Two experimental methods—Ganzflicker (high-frequency flickering light) and Ganzfeld (uniform visual field deprivation)—induced hallucinations in healthy participants. Simple hallucinations were more common than complex ones under both conditions. Ganzflicker produced more simple hallucinations than Ganzfeld, while complex hallucinations occurred at similar rates. Consequently, the proportion of complex hallucinations was higher during Ganzfeld. Correlations in hallucination frequency and duration across conditions suggest shared mechanisms, likely involving visual cortex excitability. Simple hallucinations may stem from heightened bottom-up input, especially in Ganzflicker, while complex hallucinations may rely on top-down processes less influenced by visual stimulation.
Conscious perception of a word's meaning can occur even when its visual features are inaccessible. In an experiment, participants viewed briefly flashed, visually masked words. When a semantically related spoken word followed, they could better detect and identify the previous word but could not report its letter casing or screen position. This suggests that a semantic representation can reach awareness via retro-cueing after sensory details are masked, supporting theories that conscious access relies on a secondary broadcasting process largely independent of early sensory buildup.
Hallucinatory experiences, defined as perception without external stimuli, occur in both pathological and non-pathological states and are divided into simple and complex types. Non-pathological visual hallucinations can be induced experimentally using different methods. This study compared two techniques: flicker and perceptual deprivation (Ganzfeld) in 20 participants, measuring hallucination frequency and complexity through button press, retrospective drawing, interviews, and questionnaires. Simple hallucinations were more common than complex hallucinations with both techniques. Flicker elicited more hallucinations on average, but Ganzfeld hallucinations lasted longer.