[Effects of shock experience on aversiveness caused by the scream of other rats: overshadowing tests of the association assumption].

Distress responses of rats like screams are aversive for other rats. This study was conducted to determine some of the conditions affecting these aversive properties. Eighteen rats were trained to press a lever to obtain food on a FR4 schedule, then assigned to Shock-experienced group (SE). Overshadow group (OS), and Control group (CNT). SE received three 1-second shocks (1 mA) a day for two days in a grid-floor box. The procedure for OS was the same as that for SE except that a 40-W lamp was lit 30 seconds before the onset of the shock. CNT received neither lights nor shocks. During the next eight days, rats received FR4 schedule with the same procedure as for training except that lights (40 W) or screams (65 dB) were presented for 1 minute. When lights were presented, OS showed marked response suppression but SE and CNT showed little one. When screams were presented, SE revealed strong suppression although CNT and OS showed weak one. These results indicate that aversion to screams was determined by Pavlovian conditioning.