Abstract
Predicting the sensory consequences of saccadic eye movements likely plays a crucial role in planning sequences of saccades and in maintaining visual stability despite saccade-caused retinal displacements. Deficits in predictive activity, such as that afforded by a corollary discharge signal, have been reported in patients with schizophrenia, and may lead to the emergence of positive symptoms, in particular delusions of control and auditory hallucinations. We examined whether a measure of delusional thinking in the general, non-clinical population correlated with measures of predictive activity in two oculomotor tasks. The double-step task measured predictive activity in motor control, and the in-flight displacement task measured predictive activity in trans-saccadic visual perception. Forty-one healthy adults performed both tasks and completed a questionnaire to assess delusional thinking. The quantitative measure of predictive activity we obtained correlated with the tendency towards delusional ideation, but only for the motor task, and not the perceptual task: Individuals with higher levels of delusional thinking showed less self-movement information use in the motor task. Variation of the degree of self-generated movement knowledge as a function of the prevalence of delusional ideation in the normal population strongly supports the idea that corollary discharge deficits measured in schizophrenic patients in previous researches are not due to neuroleptic medication. We also propose that this difference in results between the perceptual and the motor tasks may point to a dissociation between corollary discharge for perception and corollary discharge for action.
Highlights
Identifying the sources of our sensations is fundamental to normal cognition
corollary discharge-like signal (CD) Failure and Delusional Ideation in Healthy Individuals movement displaces the retinal location of visual objects, yet we do not experience the visual world as constantly shifting
Failure to identify oneself as the source of one’s own sensations occurs in schizophrenic patients presenting positive symptoms such as auditory hallucinations, thought insertions or delusions of influence [4], in which patients experience their own speech, thought or actions as being caused by an external agent rather than by their own will.It has been proposed that these symptoms could be underscored by low-level deficits in sensory-predictive mechanisms [5,6]
Summary
Identifying the sources of our sensations is fundamental to normal cognition. Every body movement–arms or eyes–leads to sensory changes that are due to the displacement of the effector, and not to the outside world. Failure to identify oneself as the source of one’s own sensations (i.e. misattribution of agency) occurs in schizophrenic patients presenting positive symptoms such as auditory hallucinations, thought insertions or delusions of influence [4], in which patients experience their own speech, thought or actions as being caused by an external agent rather than by their own will.It has been proposed that these symptoms could be underscored by low-level deficits in sensory-predictive mechanisms [5,6]. A complementary approach to exploring the link between agency disorders in schizophrenia and sensory-predictive mechanisms is to quantify delusion-like thinking in healthy individuals, and test whether this correlates with sensory-predictive measures Using this approach, Teufel et al [17] found that the degree of tactile sensory attenuation arising from predictive processes correlates negatively with the tendency towards delusional ideation. Measuring behaviour from the same subjects in both a motor and a perceptual task allowed us to test the hypothesis of a dissociation between self-movement information for action and for perception, and the respective relationship to delusional ideation
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