Miller S M, Liu G B, Ngo T T, Hooper G, Riek S, Carson R G, Pettigrew J D
Vision, Touch and Hearing Research Centre, Department of Physiology and Pharmacology, The University of Queensland, Brisbane, 4072, Australia.
Curr Biol. 2000 Apr 6;10(7):383-92. doi: 10.1016/s0960-9822(00)00416-4.
Binocular rivalry refers to the alternating perceptual states that occur when the images seen by the two eyes are too different to be fused into a single percept. Logothetis and colleagues have challenged suggestions that this phenomenon occurs early in the visual pathway. They have shown that, in alert monkeys, neurons in the primary visual cortex continue to respond to their preferred stimulus despite the monkey reporting its absence. Moreover, they found that neural activity higher in the visual pathway is highly correlated with the monkey's reported percept. These and other findings suggest that the neural substrate of binocular rivalry must involve high levels, perhaps the same levels involved in reversible figure alternations.
We present evidence that activation or disruption of a single hemisphere in human subjects affects the perceptual alternations of binocular rivalry. Unilateral caloric vestibular stimulation changed the ratio of time spent in each competing perceptual state. Transcranial magnetic stimulation applied to one hemisphere disrupted normal perceptual alternations when the stimulation was timed to occur at one phase of the perceptual switch, but not at the other. Furthermore, activation of a single hemisphere by caloric stimulation affected the perceptual alternations of a reversible figure, the Necker cube.
Our findings suggest that interhemispheric switching mediates perceptual rivalry. Thus, competition for awareness in both binocular rivalry and reversible figures occurs between, rather than within, each hemisphere. This interhemispheric switch hypothesis has implications for understanding the neural mechanisms of conscious experience and also has clinical relevance as the rate of both types of perceptual rivalry is slow in bipolar disorder (manic depression).
双眼竞争是指当两只眼睛看到的图像差异过大而无法融合成单一感知时出现的交替感知状态。洛戈泰蒂斯及其同事对这种现象发生在视觉通路早期的观点提出了质疑。他们发现，在警觉的猴子中，尽管猴子报告未看到其偏好的刺激，但初级视觉皮层中的神经元仍会对该刺激做出反应。此外，他们还发现视觉通路中较高水平的神经活动与猴子报告的感知高度相关。这些以及其他发现表明，双眼竞争的神经基础必定涉及较高水平，或许与可逆图形交替所涉及的水平相同。
我们提供的证据表明，人类受试者单个半球的激活或破坏会影响双眼竞争的感知交替。单侧热前庭刺激改变了在每种竞争感知状态下所花费时间的比例。当在感知切换的一个阶段定时施加经颅磁刺激到一个半球时，会破坏正常的感知交替，但在另一个阶段则不会。此外，热刺激对单个半球的激活影响了可逆图形——内克尔立方体的感知交替。
我们的研究结果表明，半球间切换介导了感知竞争。因此，在双眼竞争和可逆图形中，意识竞争发生在每个半球之间，而非半球内部。这种半球间切换假说对于理解有意识体验的神经机制具有启示意义，并且由于双相情感障碍（躁郁症）中这两种类型的感知竞争速率都较慢，所以也具有临床相关性。
