综述: 初级视皮层的亮度信息加工

亮度(luminance)是最基本的视觉信息.与其他视觉特征相比,由于视神经元对亮度刺激的反应较弱,并且许多神经元对均匀亮度无反应,对亮度信息编码的神经机制知之甚少.初级视皮层部分神经元对亮度的反应要慢于对比度反应,被认为是由边界对比度诱导的亮度知觉(brightness)的神经基础.我们的研究表明,初级视皮层许多神经元的亮度反应要快于对比度反应,并且这些神经元偏好低的空间频率、高的时间频率和高的运动速度,提示皮层下具有低空间频率和高运动速度通路的信息输入对产生初级视皮层神经元的亮度反应有贡献.已经知道初级视皮层神经元对空间频率反应的时间过程是从低空间频率到高空间频率,我们发现的早期亮度反应是对极低空间频率的反应,与这一时间过程是一致的,是这一从粗到细的视觉信息加工过程的第一步,揭示了处理最早的粗的视觉信息的神经基础.另外,初级视皮层含有偏好亮度下降和高运动速度的神经元,这群神经元的活动有助于在光照差的环境中检测高速运动的低亮度物体.

Review: Neural Coding for Luminance in The Primary Visual Cortex

Luminance is the most fundamental visual information. In comparison with other visual attributes, we know less about the neural mechanism responsible for coding luminance due to that visual neurons weakly respond to uniform luminance and many of them do not respond. Responses of a portion of neurons to luminance in the primary visual cortex are slower than those to contrast, which is thought to subserve the perceptual brightness induced by contrast at the borders of uniform luminance. However, our recent studies show that luminance responses of many neurons in the primary visual cortex are faster than contrast responses, and these neurons are more sensitive to lower spatial frequencies, higher temporal frequencies, and faster motion speed. The results indicate that the subcortical inputs of low spatial frequency and high motion speed channels contribute the generation of luminance responses of these neurons. It is known that responses to low spatial frequencies precede those to high spatial frequencies, which is thought to underlie the coarse-to-fine process of information processing in the early visual pathway. The early luminance response we reveal is the response to the extremely low spatial frequency, which is consistent with the temporal course of responses to low-to-high spatial frequencies. The rapid luminance response is the initial step of the coarse-to-fine process and the neural basis for processing the earliest coarse visual information. Moreover, the primary visual cortex contains a group of neurons that prefer luminance decrements and high motion speeds. The activities of these neurons may aid subjects to detect dark objects that are moving at high speeds under dim environment and benefit behaviors of subjects in the visual context.