In psychological terms email is a 'variable-interval reinforcement': we don't know exactly when the good stuff is coming so we have to keep checking.
在心理学上，邮件是变动间隔强化：我们不知道什么时候有价值的邮件会来，所以要不停的查看。
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The new study in Psychological Science was designed to replicate visual tests on motion perception from seminal experiments in the 1970s, with the addition of variable external noise.