Healthy individuals possess an intact ability to distinguish between events that occur as a result of their own actions and events that occur as the result of someone else's.
This ability to attribute "self-agency" appears to be disrupted in individuals experiencing many kinds of delusions, including those associated with schizophrenia: Auditory hallucinations, thought insertions, and other so-called delusions of influence are all hallmarks of the psychopathology associated with the disease. In the presence of these delusions, self-produced sensory information is misperceived as being caused by an outside influence.
In a new study that investigates how healthy individuals and schizophrenia patients interpret their visual worlds, scientists have shed light on the question of whether a broad disruption in the ability to ascribe self-agency might be related to symptoms of schizophrenia.
The work is reported in the June 21 issue of Current Biology by a group of researchers including Axel Lindner of the Hertie Institute for Clinical Brain Research and the California Institute of Technology.
In their study, the researchers compared the abilities of healthy individuals and schizophrenia patients to distinguish motion in the external world from motion caused by their own eye movements. In both cases, images pass over the surface of the retina, but the brain normally interprets such images very differently depending on whether the eyes and head are stationary. This interpretation is a specific example of agency attribution. The healthy brain can tell if the movement on the retina is caused by shifting the eyes (in which case image motion is "removed" from perception, and the visual world is experienced as stationary) or if movement on the retina cannot be attributed to shifts in gaze (in which case it is perceived as the actual movement of external objects).
Lindner and colleagues observed a clear correlation between the strength of certain delusions experienced by schizophrenia patients and the amount of "world motion" that these patients perceive while moving their eyes. This correlation supports the view that delusions of influence in schizophrenia may be due to a deficit in a general mechanism that allows healthy individuals to properly attribute agency to sensory experiences.