Our interest was to evaluate changes in fixation duration as a function of time-on-task (TOT) during a random saccade task. We employed a large, publicly available dataset. The frequency histogram of fixation durations was multimodal and modelled as a Gaussian mixture. We found five fixation types. The ``ideal'' response would be a single accurate saccade after each target movement, with a typical saccade latency of 200-250 msec, followed by a long fixation (> 800 msec) until the next target jump. We found fixations like this, but they comprised only 10% of all fixations and were the first fixation after target movement only 23.4% of the time. More frequently (57.4% of the time), the first fixation after target movement was short (117.7 msec mean) and was commonly followed by a corrective saccade. Across the entire 100 sec of the task, median total fixation duration decreased. This decrease was approximated with a power law fit with R^2=0.94. A detailed examination of the frequency of each of our five fixation types over time on task (TOT) revealed that the three shortest duration fixation types became more and more frequent with TOT whereas the two longest fixations became less and less frequent. In all cases, the changes over TOT followed power law relationships, with R^2 values between 0.73 and 0.93. We concluded that, over the 100 second duration of our task, long fixations are common in the first 15 to 22 seconds but become less common after that. Short fixations are relatively uncommon in the first 15 to 22 seconds but become more and more common as the task progressed. Apparently. the ability to produce an ideal response, although somewhat likely in the first 22 seconds, rapidly declines. This might be related to a noted decline in saccade accuracy over time.

翻译：本研究旨在评估随机眼跳任务中注视持续时间随任务时间（TOT）的变化规律。我们采用了一个大型公开数据集进行分析。注视持续时间的频率直方图呈现多峰分布，我们使用高斯混合模型对其进行建模，最终识别出五种注视类型。理论上“理想”的反应模式应是：每次目标移动后仅执行一次准确眼跳（典型眼跳潜伏期为200-250毫秒），随后维持长时注视（>800毫秒）直至下一次目标跳变。我们确实发现了此类注视，但其仅占全部注视事件的10%，且仅有23.4%的概率在目标移动后首次出现。更常见的情况是（57.4%的概率），目标移动后的首次注视持续时间较短（平均117.7毫秒），且通常伴随校正性眼跳。在整个100秒的任务过程中，注视总持续时间的中位数呈下降趋势，该变化可通过幂律函数拟合（R²=0.94）。对五种注视类型频率随TOT变化的详细分析表明：三种短时注视类型随TOT增加而愈发频繁，两种长时注视类型则逐渐减少。所有类型随时间的变化均符合幂律关系（R²值介于0.73-0.93之间）。我们得出结论：在100秒的任务时长内，长时注视在前15-22秒较为常见，之后逐渐减少；短时注视在前15-22秒相对少见，但随任务推进愈发频繁。显然，产生理想反应的能力虽在前22秒有一定概率出现，但会快速衰退。这种现象可能与已知的眼跳准确性随时间下降的趋势存在关联。