In an attempt to resolve conflicting data concerning the conditioned-stimulus properties of the 40-kHz signal generated by the ultrasonic motion detector, the high-frequency signal (96-112 dB) was used as the CS in a CER experiment. Rats receiving forward pairings of the tone with shock showed progressive decreases in activity in the presence of the tone as compared to controls during off-the-baseline conditioning sessions. During the CER test session, the forward-pairings group showed reliably more suppression to the high-frequency CS. It was concluded that the ultrasonic motion detector can mediate associative response tendencies.
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