Cook et al (1986) examined the acquisition of fears in people by pairing pictures with a brief but unpleasant electric shock. The four pictures they used were: a spider; a flower; a mushroom; a snake. During a test, they were shown the same pictures and their level of stress was monitored via electrocardiogram (for heart rate). There were no differences between these images if they hadn't been followed by shock. However, if these images had been paired with a shock, fear was more potently expressed to the pictures of spiders and snakes than flowers and mushrooms. How might the results of this experiment be interpreted?
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