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The purpose of the present study was to investigate the effects of the fluctuation of US-duration during conditioning training upon the acquired properties of the backward CS paired with electric shock as US. CS was a 5-sec illumination and US was an electric shock to four paws of white rat, delivered through a grid floor. According to the 2×3 factorial design animals were assigned to six groups. One of the classification of the design was done by the type of conditioning, i. e.. backward, forward, and control treatments, while the other was made by the duration of US, i. e., fixed vs. fluctuated US durations. During conditioning training, animals received USs 15 times in irregular intervals averaging 60 sec. In the backward conditioning group, the onset of CS was always coincided with the termination of US, while in the forward conditioning group the termination of CS coincided with the onset of US. In the control group, CSs were interspersed semi-randomly among USs : i. e., Ss in this group were treated in the same manner as those in the other two groups except that they did not receive any temporally correlated presentation of US and CS. In the “fixed-US” groups the duration of shock was always 10 seconds, whereas in the “fluctuated-US” groups it was varied semi-randomly between two levels, 15 sec and 5 sec. After the conditioning training, a metal bar was inserted in the experimental box, and the presentation of the light was made contingent upon S's bar-press response, and the bar-press frequency was recorded.Principal findings were : 1. Constant and fluctuated US-duration during conditioning training produced no differential effects upon the number of bar-press responses.2. As to the mean level of bar-press frequency, the backward group gave the highest level, the forward group the lowest, and the control group the middle in both of the US conditions, but forward conditioning group did not differ significantly from the control group. This casts some doubt upon the neutrality of the control CS.3. With respect to trends displayed in the curves of responding by the two backward groups, decreasing trends were observed, which were in conflict with the increasing trends observed in the previous study.In conclusion, although the present study presented findings which seemed to be in accordance with the hypothesis of secondary reinforcing properties of the backward CS paired with electric shock, provided the effect of the control CS was taken as the base, no definite statement can be made as yet about the validity of the proposition that “acquired properties of forward and backward CSs are opposite (BARLOW, 1956), ” until more knowledge is obtained.

doubutsu shinrigaku nempou/dōbutsu shinrigaku nenpō

SOME AQUIRED PROPERTIES OF THE BACKWARD CS PAIRED WITH AN ELECTRIC SHOCK AS US : THE EFFECTS OF FLUCTUATED US-DURATION UPON A CERTAIN SECONDARY PROPERTY OF THE BACKWARD CS IN THE RAT