Relative importance of perceptual and mnemonic variance in human temporal bisection.

We investigated the relative contributions of perception and reference memory to behavioural variability in a temporal discrimination with human subjects. We used two temporal bisection tasks. In both tasks each trial consisted of a sequential presentation of three intervals, two standards, and a probe, and subjects were asked to judge the similarity of each probe against the two standards. In a "single bisection", the standards' duration was constant across trials. In a "roving bisection", the two standards were trial unique. We compared our results with the predictions from a model related to Scalar Expectancy Theory, with the added assumption that the decision process minimizes the expected number of errors given the information available. The model shows that if errors in reference memory were dominant the psychometric function should be identical for single and roving tasks, and if perceptual errors were dominant the psychometric function should be steeper for the single than for the roving bisection. As we found that psychometric functions were steeper for the single than for the roving tasks, we concluded that perceptual errors are dominant.

Therapy of visceral leishmaniasis in renal transplant recipients intolerant to pentavalent antimonials.

Visceral leishmaniasis should be suspected in renal transplant recipients in whom a fever develops of unknown origin. A 53-year-old renal transplant recipient developed pyrexia, hepatosplenomegaly, and pancytopenia 4 years after transplantation. Antileishmaniasis serology was negative, and the diagnosis was confirmed through bone marrow examination. Treatment with glucantine (N-methylglucamine antimoniate) led to acute pancreatitis, and treatment with ketoconazole plus allopurinol for 21 days was effective to eradicate Leishmania donovani.

Experimental evidence for offspring learning in parent-offspring communication.

The offspring of birds and mammals solicit food from their parents by a combination of movements and vocalizations that have come to be known collectively as 'begging'. Recently, begging has most often been viewed as an honest signal of offspring need. Yet, if offspring learn to adjust their begging efforts to the level that rewards them most, begging intensities may also reflect offsprings' past experience rather than their precise current needs. Here we show that bird nestlings with equal levels of need can learn to beg at remarkably different levels. These experiments with hand-raised house sparrows (Passer domesticus) indicated that chicks learn to modify begging levels within a few hours. Moreover, we found that the begging postures of hungry chicks in natural nests are correlated with the average postures that had previously yielded them parental feedings. Such learning challenges parental ability to assess offspring needs and may require that, in response, parents somehow filter out learned differences in offspring signals.

Sibling competition stabilizes signalling resolution models of parent-offspring conflict.

Young of altricial birds use conspicuous displays to solicit food from their parents. There is experimental evidence that the intensity of these displays is correlated with the level of food deprivation of young, and that parents respond to increased levels of solicitation by increasing the rate of food delivery to the nest. Game-theoretical models based on the handicap principle show that, when solicitation is costly, there is a signalling equilibrium at which there is a one-to-one correspondence between the condition of the young and the intensity of their display. Parents use this information to adjust their levels of investment on the current offspring. However, the models also have a non-signalling equilibrium, and computer simulations show that only the non-signalling equilibrium is stable. Here I show that when direct sibling competition is introduced into the model, in such a way that parents have control on the amount of food provided to the nest, but not on the way the food is allocated among siblings, the non-signalling equilibrium disappears and the signalling equilibrium becomes stable.

Behavioral adjustment to modifications in the temporal parameters of the environment.

We study the dynamics of behavioral transitions when European starlings (Sturnus vulgaris) experience stepwise changes in the value of a meaningful time interval. Subjects were primed to respond at a certain time T1. After extensive training, the primed time changed to a new value T2. In Experiment 1 subjects were reinforced on 40% of the trials and they experienced a single transition which lasted until asymptotic behavior was reached. Starlings showed a progressive adjustment to T2, with no obvious discontinuities. In Experiment 2, probability of reinforcement was initially 20%, and the schedule switched to extinction after a varied number of trials were reinforced at the post-transition time. The number of post-transition reinforcements was used as independent variable. Behavior was examined in extinction to judge the state of temporal performance after a controlled amount of experience. Under these conditions, adjustment to T2 took place in two stages, and there was an intermediate phase when behavior changed little. These results are consistent with the hypotheses that animals continuously update the subjective probabilities that reinforcement comes at any given time and that responding occurs when the current estimate is above a certain threshold. We show that in spite of the continuous updating of time estimates, responding can show either continuous or discontinuous adjustments depending on the vicinity of the pre- and post-transition times and the probability of reinforcement.

Instability of signaling resolution models of parent-offspring conflict.

Recent signaling resolution models of parent-offspring conflict have provided an important framework for theoretical and empirical studies of communication and parental care. According to these models, signaling of need is stabilized by its cost. However, our computer simulations of the evolutionary dynamics of chick begging and parental investment show that in Godfray's model the signaling equilibrium is evolutionarily unstable: populations that start at the signaling equilibrium quickly depart from it. Furthermore, the signaling and nonsignaling equilibria are linked by a continuum of equilibria where chicks above a certain condition do not signal and we show that, contrary to intuition, fitness increases monotonically as the proportion of young that signal decreases. This result forces us to reconsider much of the current literature on signaling of need and highlights the need to investigate the evolutionary stability of signaling equilibria based on the handicap principle.

The evolution of begging: signaling and sibling competition.

In many species, young solicit food from their parents, which respond by feeding them. Because of the difference in genetic make-up between parents and their offspring and the consequent conflict, this interaction is often studied as a paradigm for the evolution of communication. Existent theoretical models demonstrate that chick signaling and parent responding can be stable if solicitation is a costly signal. The marginal cost of producing stronger signals allows the system to converge to an equilibrium: young beg with intensity that reflects their need, and parents use this information to maximize their own inclusive fitness. However, we show that there is another equilibrium where chicks do not beg and parents' provisioning effort is optimal with respect to the statistically probable distribution of chicks' states. Expected fitness for parents and offspring at the nonsignaling equilibrium is higher than at the signaling equilibrium. Because nonsignaling is stable and it is likely to be the ancestral condition, we would like to know how natural systems evolved from nonsignaling to signaling. We suggest that begging may have evolved through direct sibling fighting before the establishment of a parental response, that is, that nonsignaling squabbling leads to signaling. In multiple-offspring broods, young following a condition-dependent strategy in the contest for resources provide information about their condition. Parents can use this information even though it is not an adaptation for communication, and evolution will lead the system to the signaling equilibrium. This interpretation implies that signaling evolved in multiple-offspring broods, but given that signaling is evolutionarily stable, it would also be favored in species which secondarily evolved single-chick broods.

Bacteraemia by P. aeruginosa associated with nephrotic syndrome after shunt operation for hydrocephalus.

One patient of sepsis by P. aeruginosa after the implanting of a ventriculoatrial valve following extirpation of an expansive intracranial process is studied. During the evolution of the septic process there appeared as associated nephrotic syndrome with histologic lesions corresponding to an acute exudative glomerular nephritis. The germ became resistant to the antibiotics used, carbenicillin plus gentamicin, being later sensitive only to fosfomycin with which finally complete cure was achieved.