Two pigeons were trained to peck a key under several multiple variable-interval variableinterval schedules of reinforcement; different numbers of reinforcements were scheduled in two components of equal duration which were correlated with red and green illumination of the response key respectively. The results showed: (1) that the total number of responses in a scssion was proportional to the one-sixth power of the total number of reinforcements delivered in that session; and (2) that the ratio of responses between the two components was equal to the one-third power of the ratio of reinforcements between them. This latter exponent may be regarded as reflecting the sensitivity of the distribution of responses between the components to the distribution of reinforcements. It was suggested that the effects of a number of complex schedules of reinforcement could be summarized by different values of this exponent.When two variable-interval (VI) schedules of reinforcement are combined, responding maintained by each is partly determined by reinforcements delivered under the other schedule. This interaction occurs both under concurrent schedules, in which two or more schedules operate simultaneously for responses on dlifferent keys, and under multiple schedules, in which two or more schedules operate successively for responses on a single key. This similarity between concurrent and multiple schedules, however, does not extend to the way in which responses are distributed between each of the component schedules which constitute the total schedule. Under concurrent VI VI schedules, pigeons match the distribution of responses between keys to the distribution of reinforcements between keys (Herrnstein, Catania, 1963). Under multiple VI VI schedules these distributions are not matched (Reynolds, 1963).Catania (1963) has written a series of equations which gives a precise quantitative de-'The data presented are from Exp.

The development of auditory temporal acuity was studied in 56 children aged 6-12 years and compared with that of 8 adults. Acuity was measured by determining the minimum detectable duration of a brief cessation in a noise band with the 2-alternative forced-choice method. For detection of gaps in a broadband noise, acuity improved significantly with age and reached adult values by 11 years. The minimum detectable duration was significantly shorter at higher levels of the noise. For narrow-band noises, acuity also improved significantly with age and depended on the center frequency of the band. The improvement in temporal acuity with age was attributed to the development of sensory processes and not to age-related changes in nonsensory factors.

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Although the sex of the offspring in mammals is commonly viewed as a matter of chance (depending on whether an X or a Y chromosome-bearing spermatozoon reaches the ovum first), evolutionary biologists have shown that offspring sex ratios are often significantly related to maternal dominance, a characteristic that has been shown to be linked to testosterone in female mammals, including humans. Hence, we hypothesized that variations in female testosterone might be related to reproductive mechanisms associated with sex determination, with higher levels of follicular testosterone being associated with a greater likelihood of conceiving a male. To investigate this hypothesis we collected follicular fluid and cumulus-oocyte complexes from bovine antral follicles. Individual matched samples of follicular fluid were assayed for testosterone, whereas the oocytes were matured, fertilized, and cultured in vitro. The resultant embryos were sexed by PCR. The level of testosterone in the follicular fluid was then compared with sex of the embryo (n = 171). Results showed that follicular testosterone levels were significantly higher for subsequently male embryos (Mann-Whitney U = 2823; P [one-tailed] = 0.016). When we excluded embryos from follicles in which the estradiol-to-testosterone ratio was more than 1 (leaving a sample size of 135), the same result held (Mann-Whitney U = 1667; P [one-tailed] = 0.009). Thus, bovine ova that developed in follicular fluid with high concentrations of testosterone in vivo were significantly more likely to be fertilized by Y chromosome-bearing spermatozoa.

No abstract

On the basis of evidence suggesting a maternal involvement in the determination of the sex of the offspring, we took ova at the point of ovulation from crossbred heifers, fertilised them, and established the sex of the embryos. At the same time we took individual-matched samples of follicular fluid from each follicle of origin, and measured the levels of testosterone and oestradiol, blind to the sex of the embryo. We found no effect of oestradiol on sex in either primary or subordinate follicles. But bovine ova from subordinate follicles that had follicular fluid with a high concentration of testosterone (in vivo) were later more likely to be fertilised by a Y-chromosome-bearing spermatozoon (in vitro). These, along with similar results from other researchers, suggest that further study of the relationship between mammalian follicular hormones at the time of conception and subsequent sex of offspring, may help resolve some of the problems associated with theories of adaptive control of the sex ratio in mammals.

The biases to which the same‐different task is prone can be accounted for by having subjects rate their confidence that two stimuli are the same or different. The rating method of detection theory was therefore used to study the discriminability of two concentrations of a fruit drink. A model in which the decision variable was the difference in sensory strength of the two samples provided a satisfactory fit to the Receiver Operating Characteristics of four of the five subjects. The bias‐free index of discriminability, d′, was estimated for each subject. A combined operating characteristic, derived from jackknifing the data of the individual subjects, revealed an asymmetry characteristic of the differencing model. The results suggest that the same‐different task, which is readily understood by subjects, can provide an unbiased measure of the discriminability of foods or beverages.

Repeated stimuli elicit progressively smaller responses and elevated sensory and/or pain thresholds (habituation). The present experiments were designed to determine the rate of habituation of perceptual responses to supraliminal painful and non-painful cutaneous stimuli. Changes in the perceived intensity of electrical stimuli applied to the digital nerves of the index finger were determined by a matching procedure in which subjects set the current applied to the index finger of one hand to match the perceived intensity of a stimulus train (5 pulses at 20 Hz) applied to the other index finger. Twenty-five volunteers took part in 7 experiments in which both non-painful (2.5 times the sensory threshold Ts) and painful (1.2 times the pain threshold Tp) stimulus trains were presented. Subjects were required to match the stimuli at 30 s intervals over a period of 7.5 min. The percentage change in matching current (Y) was fitted by the function Y = -20.7*[1-exp(-0.56*t)] for both painful and non-painful stimuli repeated at 2 Hz. Responses recovered completely within 2 min of cessation of the stimulation. The degree of habituation increased or decreased with the rate of stimulus presentation. These results did not depend on changes in afferent fibre recruitment or fatigue because the afferent volley on the median nerve remained constant throughout the period of stimulation. Thus perceptual responses to the perceived intensity of supraliminal painful and non-painful stimuli delivered to the index finger habituate to the same extent, and the extent of the habituation is a function of the frequency of presentation of the stimulus.