There is a growing recognition in psychosis research of the importance of hallucinations in modalities other than the auditory. This has focused attention on cognitive and neural processes that might be shared by, and which might contribute distinctly to, hallucinations in different modalities. In this article, I address some issues around the modality-generality of cognitive and neural processes in hallucinations, including the role of perceptual and reality-monitoring systems, top-down and bottom-up processes in relation to the psychological and neural substrates of hallucinations, and the phenomenon of simultaneous multimodal hallucinations of the same entity. I suggest that a functional systems approach, inspired by some neglected aspects of the writings of A. R. Luria, can help us to understand patterns of hallucinatory experience across modalities and across clinical and non-clinical groups. Understanding the interplay between modality-general and modality-specific processes may bear fruit for improved diagnosis and therapeutic approaches to dealing with distressing hallucinations.
