Circadian mismatch and cardiovascular response to a performance challenge: Larks in morning and evening work sessions.

We presented morning chronotype ("Lark") university undergraduate volunteers a more or less difficult Sternberg-type recognition memory task either in the morning (8-11 am) or in the evening (5-8 pm) with instructions that they could win a prize if they were 85% successful. We established morning chronotype using the Composite Scale for Morningness (Smith et al., 1989), employing a tertile split on a pool of scale scores that ranged from 13 (extreme eveningness) to 55 (extreme morningness).