Davey presents expectancy bias as an alternative explanation for preparedness effects in conditioning; this commentary mentions some of the problems in interpreting UCS expectancy designs vis-à-vis conditioning. A further complication is that other CS characteristics also influence conditioning: A recent experiment provided support for Rescorla and Wagner's (1972) hypothesis that the amount of conditioning is smaller when the CS and UCS elicit similarly valenced initial affective responses (as with a fear-relevant CS and shock UCS). Finally, different physiological systems measure different aspects of the conditioning process, a further consideration in interpreting the results of selective association studies.