海拔和纬度的变化趋势不明显。
平均注视时间随时间变化趋势不明显，与疲劳无直接相关。
The average time fixation duration trends not obvious change over time, and not directly related to fatigue.
整个分析期内线性变化趋势不明显，但1991-2009年呈明显提前的趋势。
The liner trend of the date was not significant in the whole 51 years, while it advanced significantly from 1991 to 2009.
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