Department of Neurology, The Johns Hopkins University School of Medicine, Baltimore, MD, USA.
J Vestib Res. 2012;22(1):41-54. doi: 10.3233/VES-2011-0436.
Here we investigated how well internal estimates of direction of gravity are preserved over time and if the subjective visual vertical (SVV) and horizontal (SVH) can be used inter-changeably. Fourteen human subjects repetitively aligned a luminous line to SVV, SVH or subjective visual oblique (± 45°) over 5 min in otherwise complete darkness and also in dim light. Both accuracy (i.e., the degree of veracity as reflected by the median adjustment error) and precision (i.e., the degree of reproducability as reflected by the trial-to-trial variability) of adjustments along the principle axes were significantly higher than along the oblique axes. Orthogonality was only preserved in a minority of subjects. Adjustments were significantly different between SVV vs. SVH (7/14 subjects) and between ±45° vs. -45° (12/14) in darkness and in 6/14 and 14/14 subjects, respectively, in dim light. In darkness, significant drifts over 5min were observed in a majority of trials (33/56). Both accuracy and precision were higher if more time was taken to make the adjustment. These results introduce important caveats when interpreting studies related to graviception. The test re-test reliability of SVV and SVH can be influenced by drift of the internal estimate of gravity. Based on spectral density analysis we found a noise pattern consistent with 1/fβ noise, indicating that at least part of the trial-to-trial dynamics observed in our experiments is due to the dependence of the serial adjustments over time. Furthermore, using results from the SVV and SVH inter-changeably may be misleading as many subjects do not show orthogonality. The poor fidelity of perceived ± 45° indicates that the brain has limited ability to estimate oblique angles.
在这里，我们研究了重力方向的内部估计在多长时间内保持不变，以及主观垂直视觉 (SVV) 和水平视觉 (SVH) 是否可以互换使用。14 名人类受试者在完全黑暗和昏暗的光线下，重复将光线调整到 SVV、SVH 或主观斜角（±45°），每次调整持续 5 分钟。沿主坐标轴进行调整的准确性（即反映在中位数调整误差中的准确性）和精度（即反映在试验间变异性中的可重复性）都明显高于沿斜轴进行调整的准确性和精度。只有少数受试者能够保持正交性。在黑暗中，SVV 与 SVH（7/14 名受试者）以及±45°与-45°（12/14 名受试者）之间的调整存在显著差异，而在昏暗的光线下，6/14 和 14/14 名受试者之间也存在显著差异。在黑暗中，大多数试验（33/56）在 5 分钟内观察到明显的漂移。如果调整时间更长，准确性和精度都更高。这些结果在解释与重力感知相关的研究时引入了重要的注意事项。SVV 和 SVH 的测试-再测试可靠性可能会受到重力内部估计漂移的影响。基于频谱密度分析，我们发现了一种与 1/fβ 噪声一致的噪声模式，这表明我们实验中观察到的试验间动态至少部分是由于随着时间的推移对序列调整的依赖性。此外，使用 SVV 和 SVH 相互替换可能会产生误导，因为许多受试者没有表现出正交性。感知到的±45°的保真度较差表明大脑估计斜角的能力有限。
