the state of being ready to see, understand, and act in a particular situation

One study found that the strongest factor influencing driver alertness was the time of day. 一项研究发现，影响驾驶员警觉性的最强因素是一天中的时间段。

I think a short nap works better than coffee to restore mental alertness. 我认为小睡片刻比喝咖啡更能恢复精神警觉。