Researchers in clinical psychology and psychiatry have long sought to answer this question. New research by Distinguished Professor Mark F. Lenzenweger at Binghamton University and Weill Cornell Medical College could point the way.

In "Schizotypy 17 years on: Psychotic symptoms in midlife," recently published in theJournal of Abnormal Psychology,Lenzenweger explored the development of psychotic symptoms in 191 individuals with no prior history of psychosis; first assessed in their young adulthood (age 17-18), study participants were assessed a second time in their mid-30s.

Lenzenweger found that subtle differences in perception during their late-teen years predicted the development of hallucinations, delusions, and, in some instances, psychosis later in life. These early perceptual distortions included a heightened awareness of sound or color, uncertainty about the boundaries of one's body, feeling that the world around them is tilting, and similar experiences.

"We discovered that people, who were free of psychotic illness at age 18, would show hallucination and delusion symptoms in mid-life if they showed many very subtle disturbances in their perception early on," he said.

Anxiety and depression played no role in the development of psychotic symptoms in mid-life, he added.

The precise causes of illnesses such as schizophrenia are largely unknown, although genetics and brain-based factors are known to play an essential role. Approximately 3.5 million people have the illness in the United States, with an estimated annual healthcare cost of more than $155 billion.

"These new findings point to a specific focus for future research to drill more deeply into the biological factors driving psychotic illness and real-world experiences in the form of perceptual disturbances," Lenzenweger said. "Understanding the nature of such perceptual aberrations might provide more clues as to what is going on in the development of schizophrenia and other similar conditions."