The ultrasonic motion detector: A conditioned stimulus for rats in the CER paradigm

Abstract

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-tile-baseline conditioning sessions. During the CER test session, the forward-pairings groul-' showed reliably more suppression to the high-frequency CS. It was concluded that the ultrasonic motion detector can mediate associative response tendencies.The ultrasonic motion detector measures gross motor activity by sensing the changes that such activity produces in an ultrasonic field. It has been suggested that this device possesses several advantages over mechanical motion-detecting devices , namely , readily adjustable sensitivity, conveniently recorded digital output, and apparent unobtrusiveness (Peacock, Hodge, & Thomas, 1966 ;Peacock & Williams , 1962). [n support of this last contention, Peacock and Williams (1962) reported a failure to condition the rat's shuttlebox avoidance response to the 41-kHz signal generated by their device. Moreover, after 100 paired presentations of the signal with a "painful" shock , they observed no conditioned pinna-reflex or changes in respiration and concluded that either their rats were not sensitive to the signal or that its intensity (which was not specitled) was below the rat's threshold.These data stand in marked contrast to the findings of several other studies involving either the motion detector itself or a tone similar in frequency to that produced by the detector. In an early study, Gould and Morgan (1941) reported that rats were able to learn a shock-avoidance response to a 40-kHz CS and suggested that the rat's sensitivity at 40 kHz was as good, if not better, than its sensitivity below 14 kHz. In an investigation of the upper portion (10-50 kHz) of the rat's audiogram using a special discriminative-operant procedure, Gourevitch and Hack (1966) concluded that the rat was most sensitive in a one-octave band in the vicinity of 40 kHz (threshold at 3.5-11 dB, re 0.0002 dyne/cm 2 ). Crowley, Hepp-Reymond, Tabowitz, and Palin (1965) sensitivity at 40 kHz in a cochlear-microphonic study of the rat audiogram.The foregoing studies certainly suggest that perhaps Peacock and Williams (1962) were incorrect in their original assertion as to the unobtrusiveness of the ultrasonic device. Several recent studies have provided additional da ta in this regard. In these studies, a commercially available version of the Peacock and Williams detector was used (manufactured by Alton Electronics). In the first experiment, while attempting to assess the effects of intense, unsignaled, inescapable shock (preshock) on subsequent shock-elicited fighting in rats, Anderson, Murcurio, and Mahoney (l970b) discovered that the presence of the ultrasonic tone during test sessions eliminated the attenuating eff...