Computational research on neural mechanism and learning principle for human language acquisition

为了定量研究大脑的高级功能，如语言处理，受试者对任务的反应时(RT)特征可以作为衡量难度的一个很好的指标。在这项研究中，我们测量了亮度辨别反应时任务中依赖刺激持续时间的反应时和错误率。在每个试验中，参与者被展示了两个不同亮度的光斑，时间为短(150ms)或长(1s)。当刺激持续时间较短时，参与者的反应更快，辨别表现比刺激持续时间较长时更差。结果表明，在亮度辨别反应时任务中，视皮层不同的感觉反应决定了反应速度和准确度对刺激时长的依赖性。结果表明，从初级视皮层接收瞬时和持续刺激信息的简单赢家通吃类型神经网络模型成功地再现了正确反应和错误率的反应时分布。对于双选择亮度辨别RT任务中小刺激起始异步性(SOA)的影响，通过引入全局抑制因子以防止感觉信息的不必要整合，并将具有前馈相互抑制的神经元链作为两次闪光的异步性检测器，测量并成功地再现了小刺激起始异步性(SOA)的影响。修订后的模型不仅再现了在有和没有SOA的情况下这些双选择亮度辨别任务的反应，而且还复制了对大范围刺激亮度的超阈值单一刺激检测任务的反应。

To quantitatively investigate the higher-order functions of the brain such as language processing, characteristics of reaction time (RT) of the subjects for tasks can be used as a good measure of difficulty. In this research, RT and error rate that depend on stimulus duration were measured in a luminance-discrimination reaction time task. Two patches of light with different luminance were presented to participants for short (150ms) or long (1s) period on each trial. When the stimulus duration was 'short', the participants responded more rapidly with poorer discrimination performance than they did in the longer duration. The results suggested that different sensory responses in the visual cortices were responsible for the dependence of response speed and accuracy on the stimulus duration during the luminance-discrimination reaction time task. It was shown that the simple winner-take-all-type neural network model receiving transient and sustained stimulus information from the primary visual cortex successfully reproduced RT distributions for correct responses and error rates. Moreover, temporal spike sequences obtained from the model network closely resembled to the neural activity in the monkey prefrontal or parietal area during other visual decision tasks such as motion discrimination and oddball detection tasks.As for the influences from small stimulus onset asynchrony (SOA) in a two-choice luminance-discrimination RT tasks, the dependence on SOAs was measured and successfully reproduced by introducing global inhibitors to prevent unnecessary integration of sensory information, and neuron chains with feedforward mutual inhibition as an asynchronism detector of two flashes, into the model that we proposed. The revised model not only reproduced responses of these two-choice luminance- discrimination tasks both with and without a SOA but also responses in a suprathreshold single-stimulus detection task for a wide range of stimulus luminance.