Tong Jonathan, Ngo Vy, Goldreich Daniel
Department of Psychology, Neuroscience and Behaviour, McMaster University, Hamilton, Ontario, Canada;
Department of Psychology, Neuroscience and Behaviour, McMaster University, Hamilton, Ontario, Canada; McMaster Integrative Neuroscience Discovery and Study, Hamilton, Ontario, Canada; and McMaster University Origins Institute, Hamilton, Ontario, Canada
J Neurophysiol. 2016 Aug 1;116(2):369-79. doi: 10.1152/jn.00029.2016. Epub 2016 Apr 27.
To perceive, the brain must interpret stimulus-evoked neural activity. This is challenging: The stochastic nature of the neural response renders its interpretation inherently uncertain. Perception would be optimized if the brain used Bayesian inference to interpret inputs in light of expectations derived from experience. Bayesian inference would improve perception on average but cause illusions when stimuli violate expectation. Intriguingly, tactile, auditory, and visual perception are all prone to length contraction illusions, characterized by the dramatic underestimation of the distance between punctate stimuli delivered in rapid succession; the origin of these illusions has been mysterious. We previously proposed that length contraction illusions occur because the brain interprets punctate stimulus sequences using Bayesian inference with a low-velocity expectation. A novel prediction of our Bayesian observer model is that length contraction should intensify if stimuli are made more difficult to localize. Here we report a tactile psychophysical study that tested this prediction. Twenty humans compared two distances on the forearm: a fixed reference distance defined by two taps with 1-s temporal separation and an adjustable comparison distance defined by two taps with temporal separation t ≤ 1 s. We observed significant length contraction: As t was decreased, participants perceived the two distances as equal only when the comparison distance was made progressively greater than the reference distance. Furthermore, the use of weaker taps significantly enhanced participants' length contraction. These findings confirm the model's predictions, supporting the view that the spatiotemporal percept is a best estimate resulting from a Bayesian inference process.
为了实现感知,大脑必须对刺激诱发的神经活动进行解读。这颇具挑战性:神经反应的随机性使得对其解读本质上具有不确定性。如果大脑利用贝叶斯推理,根据从经验中得出的预期来解读输入信息,那么感知将会得到优化。贝叶斯推理平均而言会改善感知,但当刺激违背预期时会导致错觉。有趣的是,触觉、听觉和视觉感知都容易出现长度收缩错觉,其特征是对快速连续呈现的点状刺激之间的距离严重低估;这些错觉的根源一直成谜。我们之前提出,长度收缩错觉的出现是因为大脑使用具有低速预期的贝叶斯推理来解读点状刺激序列。我们的贝叶斯观察者模型的一个新预测是,如果刺激更难定位,长度收缩应该会加剧。在此,我们报告一项触觉心理物理学研究,对这一预测进行了测试。20名受试者比较了前臂上的两个距离:一个由两次间隔1秒的轻敲定义的固定参考距离,以及一个由两次间隔t≤1秒的轻敲定义的可调节比较距离。我们观察到了显著的长度收缩:随着t减小,只有当比较距离逐渐大于参考距离时,受试者才会将这两个距离感知为相等。此外,使用较弱的轻敲显著增强了受试者的长度收缩。这些发现证实了模型的预测,支持了时空感知是贝叶斯推理过程产生的最佳估计这一观点。