Auditory evoked brain responses: Intensity functions from bipolar human scalp recordings

Average evoked brain responses were computed from four simultaneous recordings during binaural tone stimulation at 10 intensity levels. Amplitudes and latencies were measured for the prominent components, and linear regression coefficients were computed. The results indicate that the sensitivity of the evoked response to stimulus intensity is dependent upon the selection of the appropriate measure. Linear amplitude functions were demonstrated. Additional research relating these responses to psychophysical measures is suggested.     

Detection of extraneous signals during sentence recognition

In two separate experiments, 40 Ss were presented with recorded sentences during each of which a click occurred. Ss had to depress a key as soon as they heard the click. RTs were f aster when the click was located at the major syntactic break of the sentence compared with RTs to clicks not at a break. This confirmed the hypothesis that processing load is a function of the surface structure of sentences, although the role of minor breaks was not clear. A second finding was that RTs were slower when the click was in the first rather than in the second half of the sentence. This can also be explained in terms of differential processing loads.     

Polydipsia induced in the rat by a second-order schedule

Drinking was studied in rats pressing a bar on a second-order schedule in which every third completion of a 1-min fixed interval was followed by food presentation. A brief flash of light signaled the completion of each fixed-interval component. The rats drank not only after the food presentations but also after presentations of the light flash alone. A high rate of steady drinking followed intervals terminated by a food presentation. Drinking that followed intervals terminated by a light flash alone was of comparable rate, but characteristically interrupted by bar pressing. When 250-mg food pellets were used instead of 45-mg pellets, both drinking and bar-pressing rates increased substantially.     

The effects of amount of training per reversal on successive reversals of a color discrimination

Three groups of pigeons were trained on a red-green discrimination in which the stimuli were alternately presented in a multiple schedule of reinforcement. The discrimination was reversed 24 times. Groups were given 1, 2, or 4 hr of training on each discrimination. Increasing the length of training had two principal effects on reversal performance: it increased the rate of extinction of responding to one of the stimuli and increased the rate of reacquisition of responding to the other. The latter effect involved both an increase in reacquisition of responding to a positive stimulus within reversals and an increase in recovery of responding to the previous negative stimulus between reversals. Improvements in performance of each group over the series of reversals were qualitatively similar to the two effects of length of training on each discrimination, and were analogous to effects obtained in other studies involving overtraining and successive reversals of simultaneous discriminations.