对象大小的稳定表示,尽管由于观看距离的变化而导致视网膜输入的连续变化,对于在真实的3D世界中感知和行动至关重要。事实上,我们的感知和视觉运动系统表现出尺寸和抓地力的一致性,以补偿视网膜图像随着距离增加的自然收缩。这种尺寸-距离缩放的神经基础在很大程度上仍然未知,尽管多条证据表明规模恒定的操作可能会提前进行,已经处于初级视觉皮层的水平。在这项研究中,我们首次通过使用事件相关电位(ERP)和运动学的组合测量来检查感知和行动过程中大小恒定性的时间动态。要求参与者在固定点上稳定地保持凝视,并对放置在不同距离的不同大小的磁盘执行手动估计或抓取任务。重要的是,目标的物理大小随距离缩放,以产生恒定的视网膜角度.同时,我们使用运动捕捉系统记录了64个头皮电极和手部动作的EEG数据。我们专注于第一个正向视觉诱发成分,在刺激发作后约90ms达到峰值。我们发现更早的潜伏期和更大的振幅响应于匹配视网膜大小的更小的圆盘,不管任务。根据ERP的结果,对于更大的目标,手动估计和峰值抓地力孔径更大。我们还发现了与任务相关的差异在后期的处理阶段从一组中心电极,因此,手动估计的P2分量的平均幅度大于抓握。一起来看,这些发现提供了新的证据,证明真实物体在真实距离的尺寸恒定性发生在最早的皮质阶段,并且早期视觉处理不会随着任务需求而改变.
A stable representation of object size, in spite of continuous variations in retinal input due to changes in viewing distance, is critical for perceiving and acting in a real 3D world. In fact, our perceptual and visuo-motor systems exhibit size and grip constancies in order to compensate for the natural shrinkage of the retinal image with increased distance. The neural basis of this size-distance scaling remains largely unknown, although multiple lines of evidence suggest that size-constancy operations might take place remarkably early, already at the level of the primary visual cortex. In this study, we examined for the first time the temporal dynamics of size constancy during perception and action by using a combined measurement of event-related potentials (ERPs) and kinematics. Participants were asked to maintain their gaze steadily on a fixation point and perform either a manual estimation or a grasping task towards disks of different sizes placed at different distances. Importantly, the physical size of the target was scaled with distance to yield a constant retinal angle. Meanwhile, we recorded EEG data from 64 scalp electrodes and hand movements with a motion capture system. We focused on the first positive-going visual evoked component peaking at approximately 90 ms after stimulus onset. We found earlier latencies and greater amplitudes in response to bigger than smaller disks of matched retinal size, regardless of the task. In line with the ERP results, manual estimates and peak grip apertures were larger for the bigger targets. We also found task-related differences at later stages of processing from a cluster of central electrodes, whereby the mean amplitude of the P2 component was greater for manual estimation than grasping. Taken together, these findings provide novel evidence that size constancy for real objects at real distances occurs at the earliest cortical stages and that early visual processing does not change as a function of task demands.