Mechanisms of smooth pursuit eye movements in schizotypy

Causal links between personality disorders and schizophrenia: A Mendelian randomization study

Although observational studies have suggested associations between personality disorders and schizophrenia, the causality of these relationships remains unclear. Determining whether personality disorders causally contribute to schizophrenia could inform early identification and preventive efforts. We performed two-sample Mendelian randomization (MR) analysis using large-scale Genome-wide Association Study data from populations of European ancestry. Because no single nucleotide polymorphism for personality disorders reached the conventional genome-wide significance threshold (P < 5 × 10-8), we sequentially relaxed the criteria (P < 5 × 10-7, P < 5 × 10-6, P < 5 × 10-5) until at least 10 instrumental variables were obtained. Ultimately, 11-95 single nucleotide polymorphism met the relaxed threshold (P < 5 × 10-5), all with F-statistics > 10, thus ensuring robust instrumental variables. The inverse variance weighted method served as our primary MR approach, supplemented by MR-Egger, weighted median, and MR Robust Adjusted Profile Score analyses, to minimize confounding, reverse causation, and weak instrument bias. Inverse variance weighted analysis revealed a significant causal association between genetically predicted personality disorders and schizophrenia (odds ratios = 1.190, 95% confidence intervals: 1.122-1.261, P = 5.51 × 10-9). Additionally, when examining a combined group of specific personality disorders, a similar causal effect was observed (odds ratios = 1.180, 95% confidence intervals: 1.033-1.345, P = .015). The sensitivity analyses showed no evidence of horizontal pleiotropy, thus supporting the robustness of these findings. Our study provides the first genetic evidence that personality disorders may have a causal influence on schizophrenia risk. These results highlight the importance of early screening and targeted interventions in individuals with personality disorders. Future research should expand to more diverse populations, employ dimensional diagnostic frameworks, and investigate the underlying biological and developmental pathways to refine the preventative and therapeutic strategies.

Reduced Visual Function in Schizotypal Traits: An Exploratory Study

BACKGROUND AND HYPOTHESIS

Visual impairments have been proposed as risk factors for psychotic symptoms and illnesses. Visual impairments can considerably impact people's daily lives, but little is known about the impact and diagnostic sensitivity of such abnormalities for schizotypal personality traits. This study aims to explore possible relationships between schizotypy and visual acuity (VA), contrast sensitivity, and parameters that describe eye movements and visual processing times.

STUDY DESIGN

Schizotypy was assessed in 37 participants with the Multidimensional Schizotypy Scale-Brief (MSS-B). For the visual function measures, we used the Acuity-Plus test and the new Eye Movement and Integrated Saccade Latency (EMAIL) test. The latter measures oculomotor performance during an eye movement task, including the visual processing time at the end of each saccade.

STUDY RESULTS

The disorganized dimension of the schizotypy scores predicted VA when measured with black optotypes. Additionally, we found that participants who had higher disorganized scores showed an increased response variability, as assessed through the goodness of fit measure from the EMAIL test.

CONCLUSIONS

These results from this exploratory study extend upon earlier findings from both general and patient samples, highlighting the clinical and subclinical importance of understanding how spatial vision can be affected in people with schizotypal disorganized behavior.

Eye Tracking to Assess the Functional Consequences of Vision Impairment: A Systematic Review

BACKGROUND

Eye tracking is a promising method for objectively assessing functional visual capabilities, but its suitability remains unclear when assessing the vision of people with vision impairment. In particular, accurate eye tracking typically relies on a stable and reliable image of the pupil and cornea, which may be compromised by abnormalities associated with vision impairment (e.g., nystagmus, aniridia).

OBJECTIVES

This study aimed to establish the degree to which video-based eye tracking can be used to assess visual function in the presence of vision impairment.

DATA SOURCES

A systematic review was conducted using PubMed, EMBASE, and Web of Science databases, encompassing literature from inception to July 2022.

STUDY ELIGIBILITY CRITERIA, PARTICIPANTS, AND INTERVENTIONS

Studies included in the review used video-based eye tracking, included individuals with vision impairment, and used screen-based tasks unrelated to practiced skills such as reading or driving.

STUDY APPRAISAL AND SYNTHESIS METHODS

The included studies were assessed for quality using the Strengthening the Reporting of Observational Studies in Epidemiology assessment tool. Data extraction and synthesis were performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines.

RESULTS

Our analysis revealed that five common tests of visual function were used: (i) fixation stability, (ii) smooth pursuit, (iii) saccades, (iv) free viewing, and (v) visual search. The studies reported considerable success when testing individuals with vision impairment, yielding usable data from 96.5% of participants.

LIMITATIONS

There was an overrepresentation of conditions affecting the optic nerve or macula and an underrepresentation of conditions affecting the anterior segment or peripheral retina.

CONCLUSIONS AND IMPLICATIONS OF KEY FINDINGS

The results offer promise for the use of eye tracking to assess the visual function of a considerable proportion of those with vision impairment. Based on the findings, we outline a framework for how eye tracking can be used to test visual function in the presence of vision impairment.

Cognitive-perceptual traits associated with autism and schizotypy influence use of physics during predictive visual tracking

Schizophrenia and autism spectrum disorder (ASD) can disrupt cognition and consequently behaviour. Traits of ASD and the subclinical manifestation of schizophrenia called schizotypy have been studied in healthy populations with overlap found in trait profiles linking ASD social deficits to negative schizotypy and ASD attention to detail to positive schizotypy. Here, we probed the relationship between subtrait profiles, cognition and behaviour, using a predictive tracking task to measure individuals' eye movements under three gravity conditions. A total of 48 healthy participants tracked an on-screen projected ball under familiar gravity, inverted upward acceleration (against gravity) and horizontal gravity control conditions while eye movements were recorded and dynamic performance quantified. Participants completed ASD and schizotypy inventories generating highly correlated scores, r = 0.73. All tracked best under the gravity condition, producing anticipatory downward responses from stimulus onset which were delayed under upward inverted gravity. Tracking performance was not associated with overall ASD or schizotypy trait levels. Combining measures using principal components analysis (PCA), we decomposed the inventories into subtraits unveiling interesting patterns. Positive schizotypy was associated with ASD dimensions of rigidity, odd behaviour and face processing, which all linked to anticipatory tracking responses under inverted gravity. In contrast, negative schizotypy was associated with ASD dimensions of social interactions and rigidity and to early stimulus-driven tracking under gravity. There was also substantial nonspecific overlap between ASD and schizotypy dissociated from tracking. Our work links positive-odd traits with anticipatory tracking when physics rules are violated and negative-social traits with exploitation of physics laws of motion.

Facial emotion recognition processes according to schizotypal personality traits: An eye-tracking study

Facial emotion recognition has been shown to be impaired among patients with schizophrenia and, to a lesser extent, among individuals with high levels of schizotypal personality traits. However, aspects of gaze behavior during facial emotion recognition among the latter are still unclear. This study therefore investigated the relations between eye movements and facial emotion recognition among nonclinical individuals with schizotypal personality traits. A total of 83 nonclinical participants completed the Schizotypal Personality Questionnaire (SPQ) and performed a facial emotion recognition task. Their gaze behavior was recorded by an eye-tracker. Self-report questionnaires measuring anxiety, depressive symptoms, and alexithymia were administered. At the behavioral level, correlation analyses showed that higher SPQ scores were associated with lower surprise recognition accuracy scores. Eye-tracking data revealed that higher SPQ scores were associated with shorter dwell time on relevant facial features during sadness recognition. Regression analyses revealed that the total SPQ score was the only significant predictor of eye movements during sadness recognition, and depressive symptoms were the only significant predictor of surprise recognition accuracy. Furthermore, dwell time predicted response times for sadness recognition in that shorter dwell time on relevant facial features was associated with longer response times. Schizotypal traits may be associated with decreased attentional engagement in relevant facial features during sadness recognition and impede participants' response times. Slower processing and altered gaze patterns during the processing of sad faces could lead to difficulties in everyday social situations in which information must be rapidly processed to enable the successful interpretation of other people's behavior.

Positive and Negative Symptoms Are Associated with Distinct Effects on Predictive Saccades

The predictive saccade task is a motor learning paradigm requiring saccades to track a visual target moving in a predictable pattern. Previous research has explored extensively anti-saccade deficits observed across psychosis, but less is known about predictive saccade-related mechanisms. The dataset analysed came from the studies of Crawford et al, published in 1995, where neuroleptically medicated schizophrenia and bipolar affective disorder patients were compared with non-medicated patients and control participants using a predictive saccade paradigm. The participant groups consisted of medicated schizophrenia patients (n = 40), non-medicated schizophrenia patients (n = 18), medicated bipolar disorder patients (n = 14), non-medicated bipolar disorder patients (n = 18), and controls (n = 31). The current analyses explore relationships between predictive saccades and symptomatology, and the potential interaction of medication. Analyses revealed that the schizophrenia and bipolar disorder diagnostic categories are indistinguishable in patterns of predictive control across several saccadic parameters, supporting a dimensional hypothesis. Once collapsed into predominantly high-/low- negative/positive symptoms, regardless of diagnosis, differences were revealed, with significant hypometria and lower gain in those with more negative symptoms. This illustrates how the presentation of the deficits is homogeneous across diagnosis, but heterogeneous when surveyed by symptomatology; attesting that a diagnostic label is less informative than symptomatology when exploring predictive saccades.

Evidence of inverted gravity-driven variation in predictive sensorimotor function

We move our eyes to place the fovea into the part of a viewed scene currently of interest. Recent evidence suggests that each human has signature patterns of eye movements like handwriting which depend on their sensitivity, allocation of attention and experience. Use of implicit knowledge of how earth's gravity influences object motion has been shown to aid dynamic perception. We used a projected ball-tracking task with a plain background offering no context cues to probe the effect of acquired experience about physical laws of gravitation on performance differences of 44 participants under a simulated gravity and an atypical (upward) antigravity condition. Performance measured by the unsigned difference between instantaneous eye and stimulus positions (RMSE) was consistently worse in the antigravity condition. In the vertical RMSE, participants took about 200 ms longer to improve to the best performance for antigravity compared to gravity trials. The antigravity condition produced a divergence of individual performance which was correlated with levels of questionnaire-based quantified traits of schizotypy but not control traits. Grouping participants by high or low traits revealed a negative relationship between schizotypy trait level and both initiation and maintenance of tracking, a result consistent with trait-related impoverished sensory prediction. The findings confirm for the first time that where cues enabling exact estimation of acceleration are unavailable, knowledge of gravity contributes to dynamic prediction improving motion processing. With acceleration expectations violated, we demonstrate that antigravity tracking could act as a multivariate diagnostic window into predictive brain function.