• binocular rivalry;
  • bipolar disorder;
  • bipolar I disorder;
  • bipolar II disorder;
  • endophenotype

Objective:  When dissimilar figures are presented to each eye individually, perception alternates spontaneously between each monocular view. This phenomenon, known as binocular rivalry, has been used as a powerful tool to investigate conscious visual awareness. Of clinical relevance, Pettigrew and Miller (Proc Biol Sci 1998; 265: 2141-2148) found slow perceptual alternation rates in patients with bipolar I disorder (BD-I). For a better understanding of differences between BD-I and bipolar II disorder (BD-II), we examined whether perceptual alternation rates of binocular rivalry differ between the two subtypes of bipolar disorder.

Methods:  The subjects comprised 25 healthy controls, 11 patients with BD-I, and 17 patients with BD-II. They underwent binocular rivalry examination. One-way analysis of variance was conducted to determine differences in the phase duration of binocular rivalry between the control, BD-I, and BD-II groups.

Results:  Significant differences were observed in the mean phase duration of binocular rivalry between the groups. Although the medication administered did not differ significantly between the BD-I and BD-II patients, the phase duration was significantly longer among the BD-I patients than the BD-II patients and controls, whereas no significant difference was observed in the phase duration between the BD-II patients and controls.

Conclusion:  The present results reveal a significant difference in the mean phase duration of binocular rivalry between subjects with BD-I and those with BD-II, suggesting the presence of some neurobiological difference between these two subtypes of bipolar disorder.