Divided 30 undergraduates into 3 groups according to instructions designed to produce an overestimate, an underestimate, or a correct estimate of the intensity of an unavoidable, noxious sound stimulus delivered on the 10th count of a 20-point count-up presented 6 times. Results show that: (a) physiological arousal during the anticipatory period was directly related to anticipated intensity of noxious stimulation; (b) since the high-threat group showed the greatest reaction to impact but later rated the stimulus as least intense, it is concluded that immediate impact varies directly with expectancy, while reappraisal is influenced by the contrast between the real and the expected stimulus; (c) over trials, there was a reduction in reactivity and the groups became more alike; (d) for heart rate, an increase in deceleration immediately before impact served to reduce heart rate immediately following impact. (PsycINFO Database Record (c) 2006 APA, all rights reserved)