Joiner Wilsaan M, Lee Jung-Eun, Lasker Adrian, Shelhamer Mark
Department of Biomedical Engineering, The Johns Hopkins University, School of Medicine, Baltimore, MD 21287, USA.
Vision Res. 2007 Jun;47(12):1645-54. doi: 10.1016/j.visres.2007.02.013. Epub 2007 Apr 18.
Previously we have shown that repetitive predictive saccades to alternating visual targets are mediated by an internal clock. That is, when subjects track a periodic visual stimulus alternating at a high rate (a small inter-stimulus interval, ISI, of 500 or 833 ms), they use an internal estimate of stimulus timing to pre-program the eye movement timing. Auditory pacing tones at the same rate also generate predictive saccades. It is natural to ask if an identical internal clock is used to generate the predictive saccades in each case. We hypothesized that if subjects can use auditory information to establish an internal estimate of stimulus timing--as we demonstrated can be done with visual targets--then the distributions of predictive inter-saccade intervals should demonstrate the well-known "Scalar Property" for either Auditory Cued or Visual Cued stimuli: inter-saccade interval histograms should be almost identical when each is divided by its mean. However, when making reactive saccades to a pacing stimulus (at a low rate), there should be a difference in the timing statistics between Auditory and Visual pacing, due to differences in sensory processing. We report here that the variances of inter-saccade intervals at three predictive pacing rates (ISIs of 500, 833, and 1000 ms) are equivalent, whereas the variance for Auditory Cued Pacing was greater than that for Visual Cued Pacing during reactive saccades at two reactive pacing rates (ISIs of 1667 and 2500 ms). When the inter-saccade interval histograms at the predictive pacing rates were normalized, the distributions were nearly identical for both Visual and Auditory Cued Pacing, which means that the Scalar Property holds for predictive saccades from either pacing stimulus. These results suggest that (1) an internal timing reference (clock) can be established by either auditory or visual information and (2) during predictive tracking the variability in saccade timing is due to the variability in the internal timing representation, while during reactive tracking the variability in saccade timing depends on the sensory modality used to trigger the saccades.
此前我们已经表明，对交替视觉目标的重复性预测性扫视是由一个内部时钟介导的。也就是说，当受试者追踪以高速率交替出现的周期性视觉刺激（刺激间隔短，即ISI为500或833毫秒）时，他们会使用刺激时间的内部估计来预先设定眼球运动的时间。相同速率的听觉起搏音也会产生预测性扫视。很自然会问，在每种情况下产生预测性扫视是否使用了相同的内部时钟。我们假设，如果受试者能够利用听觉信息来建立刺激时间的内部估计——正如我们所证明的对视觉目标可以做到的那样——那么预测性扫视间隔的分布对于听觉提示或视觉提示刺激都应表现出众所周知的“标量特性”：当每个扫视间隔直方图除以其平均值时，它们应该几乎相同。然而，当对起搏刺激做出反应性扫视时（速率较低），由于感觉处理的差异，听觉起搏和视觉起搏之间在时间统计上应该存在差异。我们在此报告，在三种预测性起搏速率（ISI为500、833和1000毫秒）下扫视间隔的方差是相等的，而在两种反应性起搏速率（ISI为1667和2500毫秒）下的反应性扫视过程中，听觉提示起搏的方差大于视觉提示起搏的方差。当预测性起搏速率下的扫视间隔直方图被归一化时，视觉和听觉提示起搏的分布几乎相同，这意味着标量特性适用于来自任何一种起搏刺激的预测性扫视。这些结果表明：（1）内部时间参考（时钟）可以通过听觉或视觉信息建立；（2）在预测性追踪过程中，扫视时间的变异性是由于内部时间表征的变异性，而在反应性追踪过程中，扫视时间的变异性取决于用于触发扫视的感觉模态。
