Lorenz has maintained two peculiar characteristics about imprinting. One of them is a irreversibility of the following response. The other is a critical period of the acquisition of the response.
In the course of ontogenical development, animals will be inevitably exposed various stimuli, so that the following response may be affected with them. If the effects were negative, the response will gradually decrease. Conversely, if the effects were positive or neutral, the response will be fascilitated or maintained.
In this experiment, two experimental conditions were examined. One is a rearing condition (isolation and socialization). The other is an exposing condition of the imprinting stimulus (exposure of everyday, every 10 days, and every 20 days). Most of newly hatched chicks (except for ones in two A'groups) were exposed to the imprinting stimulus within first 8 hr. after hatching and then they were exposed to it for consecutive three days. On the fourth day, they were divided into 10 groups represented in Table 1. Each subject recieved the imprinting training according to the experimental design as shown in Table 1. However the subjects of two A' groups were not exposed to the same imprinting stimulus till 6-day-old.
The response measures used in this experiment were the cumulative following response time and the score. The latter was given by algebraic summation of the frequency of the positive and negative response. These variables were measured as the performance of imprinting on Days 4, 14, and 24 posthatch respectively.
The results of this study may be summarized as follows :
1. The following responses tended to decrease first abruptly and then relatively constant in almost every group except for A'group. Then the performances of 14-day-old were almost equal to those of 24-day-old. (Fig. 1 and Table 2)
2. The effect of the rearing condition itself on the following response was not manifest in both before and after critical period. (Fig. 2 and 1)
3. When animals were isolated till about 14-day-old, the performances of every 10 day exposure groups tended to be better than those of every 10 days exposure groups, but when they were not, the differences of both groups were not significant.
On the contrary, when animals had social experience till about 24-day-old, the performances of every 10 days exposure groups showed to be better than those of everyday exposure groups, but when they had no social experience, the differences of both groups were not significant.
But every 20 days exposure groups were significantly worse than both everyday and every 10 days exposure groups. (Fig. 1)
4. The existence of a critical period sensitive to the moving stimulus were obviously recognized in the early phase of ontogeny. (Fig. 3, 4, 5)
It may be that the decrease of the following response with development should be due to the effect of the complex facter including social experience, stimulus experience, and developmental stage on the response.
The author did not recognize the irreversibility of following response, but the existence of critical period.
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