Federighi Pamela, Wong Aaron L, Shelhamer Mark
Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins University School of MedicineBaltimore, MD, USA; University of FirenzeFirenze, Italy.
Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins University School of MedicineBaltimore, MD, USA; Department of Neurology, Johns Hopkins University School of MedicineBaltimore, MD, USA.
Front Hum Neurosci. 2017 Mar 7;11:100. doi: 10.3389/fnhum.2017.00100. eCollection 2017.
Saccades exhibit variation in performance from one trial to the next, even when paced at a constant rate by targets at two fixed locations. We previously showed that amplitude fluctuations in consecutive predictive saccades have fractal structure: the spectrum of the sequence of consecutive amplitudes has a power-law () form, indicative of inter-trial correlations that reflect the storage of prior performance information to guide the planning of subsequent movements. More gradual decay of these inter-trial correlations coincides with a larger magnitude of spectral slope α, and indicates stronger information storage over longer times. We have previously demonstrated that larger decay exponents (α) are associated with faster adaptation in a saccadic double-step task. Here, we extend this line of investigation to predictive saccade endpoints (i.e., movement errors). Subjects made predictive, paced saccades between two fixed targets along a horizontal or vertical axis. Endpoint fluctuations both along (on-axis) and orthogonal to (off-axis) the direction of target motion were examined for correlations and fractal structure. Endpoints in the direction of target motion had little or no correlation or power-law scaling, suggesting that successive movements were uncorrelated (white noise). In the orthogonal direction, however, the sequence of endpoints did exhibit inter-trial correlations and scaling. In contrast, in our previous work the scaling of saccade amplitudes is strong along the target direction. This may reflect the fact that while saccade amplitudes are neurally programmed, endpoints are not directly controlled but instead serve as a source of error feedback. Hence, the lack of correlations in on-axis endpoint errors suggests that maximum information has been extracted from previous movement errors to plan subsequent movement amplitudes. In contrast, correlations in the off-axis component indicate that useful information still remains in this error (residual) sequence, suggesting that saccades are less tightly controlled along the orthogonal direction.
扫视运动在每次试验中的表现都存在差异，即使由两个固定位置的目标以恒定速率引导。我们之前表明，连续预测性扫视运动的幅度波动具有分形结构：连续幅度序列的频谱具有幂律（）形式，这表明试验间的相关性反映了先前表现信息的存储，以指导后续运动的规划。这些试验间相关性的更缓慢衰减与更大的频谱斜率α相关，表明在更长时间内有更强的信息存储。我们之前已经证明，在扫视双步任务中，更大的衰减指数（α）与更快的适应相关。在这里，我们将这一研究方向扩展到预测性扫视运动的终点（即运动误差）。受试者在水平或垂直轴上的两个固定目标之间进行预测性、有节奏的扫视运动。研究了沿目标运动方向（轴上）和与目标运动方向正交（轴外）的终点波动的相关性和分形结构。目标运动方向上的终点几乎没有相关性或幂律缩放，这表明连续运动是不相关的（白噪声）。然而，在正交方向上，终点序列确实表现出试验间的相关性和缩放。相比之下，在我们之前的工作中，扫视幅度在目标方向上的缩放很强。这可能反映了这样一个事实，即虽然扫视幅度是由神经编程的，但终点不是直接控制的，而是作为误差反馈的来源。因此，轴上终点误差缺乏相关性表明，已经从先前的运动误差中提取了最大信息，以规划后续运动幅度。相比之下，轴外分量的相关性表明，有用信息仍然存在于这个误差（残余）序列中，这表明扫视在正交方向上的控制不太严格。
