Effect of Forebrain Ablation and Inter-trial Intervals upon Conditioned Avoidance Responses in the Goldfish

Abstract

In Exp. I, the goldfish were trained to avoid from an electric shock by swimming over a partition which divided the test tank into two compartments. The conditioned stimulus was a light which was turned on 15 sec. before the onset of shock. Ten trials per day were given for 25 days with the inter-trial intervals of 60 seconds. After reaching the learning criterion (70% correct responses for consecutive three days) Ss were received forebrain ablation or sham operation before a relearning period (150 trials).
Forebrain removal completely abolished a previously learned avoidance response and prevented relearning. The inter-trial responses were increased with the acquisition of CR and they concentrated into the period just before the next trial. These responses were also completely abolished by forebrain ablation.
Amount of activities measured before and after operation did not significantly differ between two groups, indicating that the deficit is specific to avoidance learning.
In Exp. II, the same procedure as Exp. I was used except for the inter-trial intervals. The inter-trial intervals randomly varied from 15 to 105 sec. (mean was 60 sec.) during a day.
For only 30% of Ss could learn a avoidance response during 300 trials, significant difference was found between the number of subjects which reached the learning criterion in Exp. I and Exp. II. Learning deficit resulted from the random intervals might indicate that Ss in Exp. I partly used the time interval as a cue. Forebrain removal also severely impaired a previously learned avoidance response and the inter-trial responses.