Data from: Direct evidence for encoding of motion streaks in human visual cortex

Temporal integration in the visual system causes fast-moving objects to generate static, oriented traces (‘motion streaks’), which could be used to help judge direction of motion. While human psychophysics and single-unit studies in non-human primates are consistent with this hypothesis, direct neural evidence from the human cortex is still lacking. First, we provide psychophysical evidence that faster and slower motions are processed by distinct neural mechanisms: faster motion raised human perceptual thresholds for static orientations parallel to the direction of motion, whereas slower motion raised thresholds for orthogonal orientations. We then used functional magnetic resonance imaging to measure brain activity while human observers viewed either fast (‘streaky’) or slow random dot stimuli moving in different directions, or corresponding static-oriented stimuli. We found that local spatial patterns of brain activity in early retinotopic visual cortex reliably distinguished between static orientations. Critically, a multivariate pattern classifier trained on brain activity evoked by these static stimuli could then successfully distinguish the direction of fast (‘streaky’) but not slow motion. Thus, signals encoding static-oriented streak information are present in human early visual cortex when viewing fast motion. These experiments show that motion streaks are present in the human visual system for faster motion.

视觉系统的时间整合效应会使快速运动物体产生静态定向痕迹（motion streaks），这类痕迹可用于辅助判断运动方向。尽管人类心理物理学研究与非人灵长类的单神经元研究均支持这一假说，但目前仍缺乏来自人类大脑皮层的直接神经证据。首先，本研究通过心理物理学实验证实，快慢运动由不同的神经机制处理：快速运动提升了人类对与运动方向平行的静态定向刺激的知觉阈值，而慢速运动则提升了对与运动方向正交的静态定向刺激的知觉阈值。随后，我们采用功能磁共振成像（functional magnetic resonance imaging）测量人类观察者的脑活动：观察者分别观看沿不同方向运动的快速（"拖影状"）、慢速随机点刺激，或与之对应的静态定向刺激。研究发现，早期视网膜拓扑视觉皮层的脑活动局部空间模式可有效区分不同的静态定向刺激。关键在于，基于上述静态刺激诱发的脑活动训练得到的多变量模式分类器，能够成功区分快速（"拖影状"）运动的方向，却无法区分慢速运动的方向。由此可见，当人类观察快速运动时，早期视觉皮层中存在编码静态定向拖影信息的神经信号。本系列实验证实，人类视觉系统在处理快速运动时确实会产生运动拖影。