T. T. Ngo

No Relationship Between Binocular Rivalry Rate and Eye-Movement Profiles in Healthy Individuals: A Bayes Factor Analysis

Binocular rivalry (BR) is an intriguing phenomenon in which conflicting images are presented, one to each eye, resulting in perceptual alternations between each image. The rate of BR has been proposed as a potential endophenotype for bipolar disorder because (a) it is well established that this highly heritable psychiatric condition is associated with slower BR rate than in controls, and (b) an individual’s BR rate is approximately 50% genetically determined. However, eye movements (EMs) could potentially account for the slow BR trait given EM anomalies are observed in psychiatric populations, and there has been report of an association between saccadic rate and BR rate in healthy individuals. Here, we sought to assess the relationship between BR rate and EMs in healthy individuals (N = 40, mean age = 34.4) using separate BR and EM tasks, with the latter measuring saccades during anticipatory, antisaccade, prosaccade, self-paced, free-viewing, and smooth-pursuit tasks. No correlation was found between BR rate and any EM measure for any BR task (p > .01) with substantial evidence favoring this lack of association (BF01 > 3). This finding is in contrast to previous data and has important implications for using BR rate as an endophenotype. If replicated in clinical psychiatric populations, EM interpretations of the slow BR trait can be excluded.

The effect of stimulus strength on binocular rivalry rate in healthy individuals: Implications for genetic, clinical and individual differences studies

Binocular rivalry (BR) occurs when conflicting images concurrently presented to corresponding retinal locations of each eye stochastically alternate in perception. Anomalies of BR rate have been examined in a range of clinical psychiatric conditions. In particular, slow BR rate has been proposed as an endophenotype for bipolar disorder (BD) to improve power in large-scale genome-wide association studies. Examining the validity of BR rate as a BD endophenotype however requires large-scale datasets (n=1000s to 10,000s), a standardized testing protocol, and optimization of stimulus parameters to maximize separation between BD and healthy groups. Such requirements are indeed relevant to all clinical psychiatric BR studies. Here we address the issue of stimulus optimization by examining the effect of stimulus parameter variation on BR rate and mixed-percept duration (MPD) in healthy individuals. We aimed to identify the stimulus parameters that induced the fastest BR rates with the least MPD. Employing a repeated-measures within-subjects design, 40 healthy adults completed four BR tasks using orthogonally drifting grating stimuli that varied in drift speed and aperture size. Pairwise comparisons were performed to determine modulation of BR rate and MPD by these stimulus parameters, and individual variation of such modulation was also assessed. From amongst the stimulus parameters examined, we found that 8cycles/s drift speed in a 1.5° aperture induced the fastest BR rate without increasing MPD, but that BR rate with this stimulus configuration was not substantially different to BR rate with stimulus parameters we have used in previous studies (i.e., 4cycles/s drift speed in a 1.5° aperture). In addition to contributing to stimulus optimization issues, the findings have implications for Levelts Proposition IV of binocular rivalry dynamics and individual differences in such dynamics.

Evidence that eye-movement profiles do not explain slow binocular rivalry rate in bipolar disorder: support for a perceptual endophenotype

Presenting conflicting images simultaneously, one to each eye, produces perceptual alternations known as binocular rivalry (BR). Slow BR rate has been proposed as an endophenotype for bipolar disorder (BD) for use in large‐scale genome‐wide association studies. However, the trait could conceivably reflect eye movement (EM) dysfunction in BD rather than anomalous perceptual processing per se. To address this question, we examined the relationship between EM profiles and BR rate for various stimulus types in BD and healthy subjects. We also examined differences in EM profiles between these groups.

Caloric vestibular stimulation: From diagnosis to therapy?

The World Psychiatric Association (WPA) took up itself in the late 1990s the initiative to plan, design, and implemented an institutional program on the subject of a ‘‘Core Postgraduate Training Curriculum in Psychiatry’’. The conceptualization of this program grew from the realization that educational institutions dedicated to the training of graduate residents in psychiatry were not meeting the unique and current needs that existed, from a training and psychiatric care point of view, in many areas or regions of the world. It was also obvious that educational institutions in some parts of the world lacked the technical skills and professional manpower to entertain curriculum changes along these lines. Over five years has passed since this WPA postgraduate training curriculum was introduced to the field during the XII World Congress of Psychiatry held in Yokohama, Japan, in August 2002. In this symposium, we will address the current problems and needs that exist today with respect to the training of psychiatric residents in Asia, as well as the psychiatric care implementations derived from still existing problems in this very relevant educational area in the field of psychiatry. Potential solutions will also be presented and discussed. Hopefully, fully, this symposium will help to improve the psychiatric education and the quality of psychiatric care currently offered in Asia.