Abstract
Background
Perceptual spatial suppression is a phenomenon in which the perceived strength of a stimulus in space is reduced when the stimulus is surrounded by other stimuli. For motion perception, two studies so far have suggested that spatial suppression and sensitivity to motion perception is also reduced in patients with schizophrenia.
Studies to date have been conducted in patients with chronic schizophrenia, however, whether these abnormalities are present at the onset of the disorder or whether they emerge during the course of the illness has not been examined, and no study has assessed whether these abnormalities are specific to schizophrenia or whether they are present in other psychotic disorders. Furthermore, if reduced spatial suppression and sensitivity for motion in schizophrenia are related to a glutamatergic hypofunction, as suggested by a recent study (Schallmo et al., 2019), these reductions may be more accentuated in patients who fail to respond to first-line antipsychotic treatment.
Methods
Sample: 33 patients with a first psychotic episode (16 females, age=16.4±0.6) and 17 healthy controls (9 females, age=17.2±0.61). Exclusion criteria for both groups were: intellectual disability according to DSM-V criteria. For healthy controls, exclusion criteria also included having a first degree relative with a history of psychotic disorder, current or past diagnosis of psychiatrics disorders. Instruments: The perceptual test was performed on a tablet, and consisted of a briefly presented grating (small or large) drifted sideways (the direction was chosen at random with equal probability), in which the participant was instructed to report the perceived direction. Clinical assessment at illness onset and 12 week follow-up: Positive and Negative Symptom Scales (PANSS), Kiddie Schedule for Affective Disorders and Schizophrenia, Present and Lifetime version and Structured Clinical Interview for DSM-IV. Non-response to treatment was defined as lack of 50% reduction in PANSS positive or negative scores at 12 weeks, any change in antipsychotics or need for combinations due to lack of clinical response. Psychophysical analysis: Motion sensitivity was estimated independently of lapses of attention, which were assessed by including trials in which the motion stimulus was easily discriminated.
Results
Patients and healthy controls were homogeneous in age (t=-.720, p=,537) and sex (X2=0.38, p=0.542). In patients, mean treatment response rates was 56.5%. Patients had similar scores of positive and negative symptomatology (positive symptoms= 21±7,13; negative symptoms= 18,4±8,18; general symptoms= 40,7±13,07). At 12 weeks 43,8% had a diagnosis of affective psychosis (bipolar disorder, depressive disorder with psychotic symptoms).
Patients with a first psychotic episode, regardless of diagnosis or response to treatment, had less motion sensitivity than healthy controls (f=6.397, p=0.0148). No significant differences were found between groups in surround suppression and no significant correlations were observed between spatial suppression and clinical symptoms.
Discussion
To our knowledge, this is the first study to find abnormal motion sensitivity in patients with a first episode of psychosis. Our measure of sensitivity, given that it was not contaminated by lapses, indicates that patients had a genuine motion perception deficit rather than an inability to focus on the task. Our results also suggest that motion sensitivity may not be specific to patients with schizophrenia but may also characterize affective psychoses. Larger studies may be needed to clarify whether there is a relationship between motion sensitivity and severity of symptoms and response to treatment.
Perspective Cues Make Eye-specific Contributions to 3-D Motion Perception
