Fondazione Santa Lucia IRCCS, Rome, Italy.
Neuropsychologia. 2010 May;48(6):1842-52. doi: 10.1016/j.neuropsychologia.2010.03.009. Epub 2010 Mar 19.
The ability of effectively representing time ensures the efficiency and accuracy of sensory and motor processing. It is well documented that in still observers, subjective time varies in response to variations of external sensory inputs. However, it is still poorly understood how inertial inputs, which enable coding of body displacements in space, affect timekeeping processes in a dynamic agent. Here, we investigated the effects of rotatory body accelerations on the reproduction of an acoustic isochronous pacing rhythm. In a first experiment, healthy participants performed a finger tapping task in which responses were either synchronized to the rhythm (Synchronization), or performed in absence of the rhythm following its withdrawal (Continuation). Both tasks were performed in presence and absence of sinusoidal acceleratory rotations along the vertical head-body axis. We found that the representation of the target frequency varied continuously as a function of periodic variations of vestibular-proprioceptive information. However, the effects on Synchronization and Continuation were opposite in directionality: increases in velocity were associated to increases in Continuation tapping rate (indicating a subjective shortening of the target interval), and decreases in Synchronization tapping rate. This was due to different temporal delays with which body motion affected tapping rate generation in these two conditions. A second control experiment, which lacked a representational component of time, confirmed that body displacements in Experiment 1 had indeed affected an internal timekeeper, and not motor responses triggered by its operation. A third control experiment, procedurally identical to Experiment 1 with the exception of an increased displacement frequency, allowed us to establish that Continuation tapping rate varied anticipatorily with respect to body motion, while Synchronization tapping rate varied with a delay in response to body movements. The observed consistent directionality in timing error, can be considered an adaptive response of internal timing mechanisms to body movements in space, where greater rates of displacement prompt accelerated timed responses.
有效地表示时间的能力确保了感觉和运动处理的效率和准确性。有充分的文献记载，在静止的观察者中，主观时间会随着外部感觉输入的变化而变化。然而，对于惯性输入如何影响动态主体中的计时过程，人们仍知之甚少。惯性输入使身体在空间中的位移得以编码。在这里，我们研究了旋转身体加速度对声音等时起搏节律再现的影响。在第一个实验中，健康参与者执行了一个手指敲击任务，在该任务中，响应要么与节奏同步（同步），要么在节奏撤回后没有节奏地执行（延续）。这两个任务都是在存在和不存在沿着垂直头身轴的正弦加速旋转的情况下进行的。我们发现，目标频率的表示连续地作为前庭本体感觉信息周期性变化的函数而变化。然而，对同步和延续的影响在方向上是相反的：速度的增加与延续敲击率的增加有关（表示目标间隔的主观缩短），而同步敲击率的降低。这是由于在这两种情况下，身体运动对敲击率产生的影响具有不同的时间延迟。第二个控制实验，缺乏时间的表示成分，证实了实验 1 中的身体位移确实影响了内部计时器，而不是由其操作触发的运动反应。第三个控制实验，与实验 1 程序相同，除了增加了位移频率，使我们能够确定延续敲击率随着身体运动而提前变化，而同步敲击率随着对身体运动的反应延迟而变化。观察到的定时误差的一致方向性，可以被认为是内部定时机制对空间中身体运动的适应性反应，其中更大的位移速度促使更快的定时反应。
