Department of Psychology, University of California at Berkeley, Berkeley, California 94720-1650
Center for Information and Neural Networks, National Institute of Information and Communications Technology, Suita, 565-0871, Japan.
J Neurosci. 2020 Sep 30;40(40):7749-7758. doi: 10.1523/JNEUROSCI.0078-20.2020. Epub 2020 Sep 14.
The perception of duration in the subsecond range has been hypothesized to be mediated by the population response of duration-sensitive units, each tuned to a preferred duration. One line of support for this hypothesis comes from neuroimaging studies showing that cortical regions, such as in parietal cortex exhibit duration tuning. It remains unclear whether this representation is based on the physical duration of the sensory input or the subjective duration, a question that is important given that our perception of the passage of time is often not veridical, but rather, biased by various contextual factors. Here we used fMRI to examine the neural correlates of subjective time perception in human participants. To manipulate perceived duration while holding physical duration constant, we used an adaptation method, in which, before judging the duration of a test stimulus, the participants were exposed to a train of adapting stimuli of a fixed duration. Behaviorally, this procedure produced a pronounced negative aftereffect: A short adaptor biased participants to judge stimuli as longer and a long adaptor-biased participants to judge stimuli as shorter. Duration tuning modulation, manifest as an attenuated BOLD response to stimuli similar in duration to the adaptor, was only observed in the right supramarginal gyrus (SMG) of the parietal lobe and middle occipital gyrus, bilaterally. Across individuals, the magnitude of the behavioral aftereffect was positively correlated with the magnitude of duration tuning modulation in SMG. These results indicate that duration-tuned neural populations in right SMG reflect the subjective experience of time. The subjective sense of time is a fundamental dimension of sensory experience. To investigate the neural basis of subjective time, we conducted an fMRI study, using an adaptation procedure that allowed us to manipulate perceived duration while holding physical duration constant. Regions within the occipital cortex and right parietal lobe showed duration tuning that was modulated when the test stimuli were similar in duration to the adaptor. Moreover, the magnitude of the distortion in perceived duration was correlated with the degree of duration tuning modulation in the parietal region. These results provide strong physiological evidence that the population coding of time in the right parietal cortex reflects our subjective experience of time.
亚秒级范围内的时间感知被假设是由对时长敏感的单位的群体反应介导的，每个单位都调谐到一个偏好的时长。这一假设的一个支持来自于神经影像学研究，这些研究表明，皮质区域，如顶叶皮层，表现出时长调谐。目前尚不清楚这种表示是基于感觉输入的物理时长还是主观时长，这是一个重要的问题，因为我们对时间流逝的感知往往不是真实的，而是受到各种上下文因素的影响。在这里，我们使用 fMRI 研究了人类参与者的主观时间感知的神经相关性。为了在保持物理时长不变的情况下操纵感知时长，我们使用了一种适应方法，在这种方法中，在判断测试刺激的时长之前，参与者会暴露于固定时长的适应刺激序列中。在行为上，这种方法产生了明显的负后效：一个短的适应刺激会使参与者判断刺激更长，而一个长的适应刺激则会使参与者判断刺激更短。时长调谐调制，表现为对与适应刺激时长相似的刺激的 BOLD 反应减弱，仅在右顶下小叶（SMG）和双侧中枕叶中观察到。在个体之间，行为后效的幅度与 SMG 中的时长调谐调制幅度呈正相关。这些结果表明，右 SMG 中的时长调谐神经元群体反映了时间的主观体验。主观时间感是感觉体验的基本维度。为了研究主观时间的神经基础，我们进行了一项 fMRI 研究，使用适应程序，在保持物理时长不变的情况下操纵感知时长。在枕叶皮层和右顶叶皮层内的区域表现出时长调谐，当测试刺激与适应刺激时长相似时，时长调谐会发生调制。此外，感知时长的扭曲幅度与顶叶区域的时长调谐调制幅度相关。这些结果提供了强有力的生理证据，表明右顶叶皮层中的时间群体编码反映了我们对时间的主观体验。
