In the first of two experiments, three cotton rats (Sigmodon hispidus) and three albino rats were exposed to instrumental escape, unsignaled avoidance, and signaled avoidance, in that order. All subjects learned the escape procedure quickly, with the albino rats having generally shorter latencies, higher response rates, and requiring fewer sessions to reach the criterion. When the avoidance contingency was introduced, the cotton rats continued to respond almost entirely in the presence of the shock, whereas the albino rats responded in its absence, thus displaying effective avoidance behavior. Introduction of a pre-aversive stimulus did not improve the performance of the cotton rats. In the second experiment, five cotton rats and four albino rats were exposed to a free-operant (Sidman) avoidance procedure with a shock-shock interval of 3 sec and a response-shock interval of 20 sec. The cotton rats initiated responding at lower shock intensities than the albino rats, but their asymptotic avoidance responding was far less effective. A Gerbrands rat test chamber and GrasosStadler electromechanical crcuits sved as the apparatus. Electric shock was provided by a 110-v ac shock source which included 200,000 ohms in series with the output. The shock was scrambled to the grid floor of the test chamber. Data were recorded by electromechanical counters and a Gerbrands cumulative recorder.The animals were successively exposed to three experimental contingencies: escape, unsignaled avoidance, and signaled avoidance. No shaping procedure of any type was used. The animals were merely placed in the experimental chamber, and after a 15-min period to allow for adaptation, the shock was turned on.Under the escape contingency, each bar press turned the shock off for 18 sec. Responses during the shock-off period had no effect. The avoidance contingency differed in that responses during the shock-off period served to reset a timer, and thus postpone shock for 18 sec. During the unsignaled component, no cue as to shock imminence was given. During the signaled component, a bank of four 28-v dc bulbs came on 3.5 sec before the shock, and remained on until the animal responded. The lights were mounted behind a translucent panel approximately 2 in. above the bar.Each animal was initially exposed to a shock level of 0.5 ma. This level was increased as necessary to establish and maintain effective 473 1968, 11,[473][474][475][476][477][478] NUMBER 4 (JULY)

Studies of color pecking preferences in newly hatched chicks (Gallus dom.esticus) have shown unimodal preference in the orange region of the spectrum or bimodal preferences at blue and orange. In the present study, darkhatched White Leghorn chicks were tested in darkness with targets illuminated at 1 of 3 radiant intensity levels. Results showed the least amount of pecking at green (541 nm.) and peak preferences in blue-violet and orangered regions. Findings were similar when other dark-hatched chicks were tested in the light (Experiment 2). Overall, findings suggest unlearned pecking preferences for short and long wavelengths, with minimums at green. Possible evolutionary and photochemical bases for such a bimodal wavelength preference function were discussed. Since bimodality was unaffected by target intensity and background, these variables probably do not account for the unimodal function reported by others.

Three groups of albino rats were trained under a free-operant avoidance (Sidman) procedure with equal shock-shock and response-shock intervals. After stable performance was achieved, the animals were concurrently exposed to a brief electric shock after each response. The procedures were as follows: Punishment Schedule I: punishment shock was introduced at an intensity approximately one quarter that of avoidance shock; increments of nearly this same size were made as stable performance was achieved at succeeding punishment shock intensities. Punishment Schedule II: punishment shock was introduced at approximately one-half the intensity of avoidance shock; after stable performance, punishment shock was increased to the same intensity as avoidance shock. Punishment Schedule III: punishment shock was introduced and maintained at the same intensity as avoidance shock. Punishment was continued for all groups until one of two suppression criteria was attained. All animals made fewer responses and received more avoidance shocks as a function of increasing punishment shock. Half of the animals under Punishment Schedule I required punishment shock higher than avoidance shock to meet their assigned suppression criterion. A comparison of all procedures showed that suppression was greater when punishment shock was initially at high intensity.

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Six rats were trained on a Sidman free operant avoidance task. Three ues, shock, intensities were used, two Ss for each intensity. After training, each S was presented with three different ues intensities and differences in responding rate between one ues intensity and another were calculated. It was observed that increasing use intensity :increased avoidance, while decreasing it decreased avoidance. Furthermore, the extent of this change in response rate was found to be a function of the prior ues training intensity .

Evidence has accumulated rapidly to support the hypothesis that neurological anomalies underlie specific forms of learning disability (LD). This article reviews recent studies directed at the electrophysiological assessment of LD children, with emphasis on the brain stem evoked response(BSER) methodology. Child studies appear to indicate that there are significant differences in BSERs between LD and age-matched normal controls. The methodological and statistical differences among these studies, which have clouded the findings and made replication difficult, are reviewed. Improvements in sampling and empirical procedures are suggested, including the use of discriminant analysis to explore BSER asymmetries in LD children. Future inquiry into the measurement and analysis of BSER activity in LD populations is warranted on the basis of these preliminary findings. New information may bring professionals closer to an understanding of the neurological causes of specific subtypes of LD and permit earlier identification of these "at risk" populations.

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