The rattling sound of rattlesnakes (Crotalus viridis) as a communicative resource for ground squirrels (Spermophilus beecheyi) and burrowing owls (Athene cunicularia)

Animal communication involves very dynamic processes that can generate new uses and functions for established communicative activities. In this article, the authors describe how an aposematic signal, the rattling sound of rattlesnakes (Crotalus viridis), has been exploited by 2 ecological associates of rattlesnakes: (a) California ground squirrels (Spermophilus beecheyi) use incidental acoustic cues in rattling sounds to assess the danger posed by the rattling snake, and (b) burrowing owls (Athene cunicularia) defend themselves against mammalian predators by mimicking the sound of rattling. The remarkable similarity between the burrowing owl's defensive hiss and the rattlesnake's rattling reflects both exaptation and adaptation. Such exploitation of the rattling sound has favored alternations in both the structure and the deployment of rattling by rattlesnakes.     

Immediate-early Fos protein levels in brainstem neurons of male and female gonadectomized mice subjected to cold exposure

The expression of the immediate early gene c-fos has been used extensively as a marker for neural activation in response to acute and chronic stressful stimuli in brain and spinal cord. The present study examined the expression of Fos protein in the brainstem nuclei of male and female gonadectomized mice in response to cold stress. Free-floating sections were processed immunohistochemically for Fos protein using standard avidin-biotin complex methods. The number of Fos-positive neurons in each nucleus was determined. Although the experiment was designed to look for gender differences, results were equivalent between females and males. After mice were exposed to a cold ambient temperature (4 degrees C) for 2 h, elevated numbers of Fos-positive neurons were counted in the medullary gigantocellular reticular nucleus, medullary raphe nucleus, nucleus of the solitary tract and in locus coeruleus. However, no elevated expression was found in nucleus ambiguus, nor in neurons of the A1 group, nor the C2 or C3 group. Similar to rats, these results with mice reveal a widespread arousal system in the lower brainstem activated by cold stress in both genders. These findings in gonadectomized mice have set the stage for investigations following hormonal and genetic manipulations.     

Entailment with Near Surety of Scaled Assertions of High Conditional Probability

An assertion of high conditional probability or, more briefly, an HCP assertion is a statement of the type: The conditional probability of B given A is close to one. The goal of this paper is to construct logics of HCP assertions whose conclusions are highly likely to be correct rather than certain to be correct. Such logics would allow useful conclusions to be drawn when the premises are not strong enough to allow conclusions to be reached with certainty. This goal is achieved by taking Adams" (1966) logic, changing its intended application from conditionals to HCP assertions, and then weakening its criterion for entailment. According to the weakened entailment criterion, called the Criterion of Near Surety and which may be loosely interpreted as a Bayesian criterion, a conclusion is entailed if and only if nearly every model of the premises is a model of the conclusion. The resulting logic, called NSL, is nonmonotonic. Entailment in this logic, although not as strict as entailment in Adams" logic, is more strict than entailment in the propositional logic of material conditionals. Next, NSL was modified by requiring that each HCP assertion be scaled; this means that to each HCP assertion was associated a bound on the deviation from 1 of the conditional probability that is the subject of the assertion. Scaling of HCP assertions is useful for breaking entailment deadlocks. For example, it it is known that the conditional probabilities of C given A and of ¬ C given B are both close to one but the bound on the former"s deviation from 1 is much smaller than the latter"s, then it may be concluded that in all likelihood the conditional probability of C given A B is close to one. The resulting logic, called NSL-S, is also nonmonotonic. Despite great differences in their definitions of entailment, entailment in NSL is equivalent to Lehmann and Magidor"s rational closure and, disregarding minor differences concerning which premise sets are considered consistent, entailment in NSL-S is equivalent to entailment in Goldszmidt and Pearl"s System-Z ⁺. Bacchus, Grove, Halpern, and Koller proposed two methods of developing a predicate calculus based on the Criterion of Near Surety. In their random-structures method, which assumed a prior distribution similar to that of NSL, it appears possible to define an entailment relation equivalent to that of NSL. In their random-worlds method, which assumed a prior distribution dramatically different from that of NSL, it is known that the entailment relation is different from that of NSL.     

On the locus of the semantic satiation effect: Evidence from event-related brain potentials

The present study sought to determine whether semantic satiation is merely a by-product of adaptation or satiation of upstream, nonsemantic perceptual processes or whether the effect can have a locus in semantic memory. This was done by measuring event-related brain potentials (ERPs) in a semantic word-detection task involving multiple presentations of primes and critical related and unrelated words in three experiments involving visual (Experiment 1) and auditory (Experiments 2A and 2B) stimuli. Primes varied in their type case (Experiment 1) or pitch (Experiment 2B) in order to discourage sensory adaptation. Prime satiation and relatedness of the primes to the critical word had interacting effects on ERP amplitude to critical words, particularly within the time-window of the N400 component. Because numerous studies have indicated a role for the N400 in semantic processing, modulation of the N400 relatedness effect by prime satiation (with little or no contribution from perceptual adaptation) suggests that semantic memory can be directly satiated, rather than the cost to semantic processing necessarily resulting from impoverishment of perceptual inputs.     

Covert face recognition in neurologically intact participants

Prosopagnosic patients may maintain some ability to recognize familiar faces, although they remain unaware of this ability. This phenomenon – called covert face recognition – was investigated in neurologically intact participants, using priming techniques. Participants were quicker to indicate that a target-name was familiar when the preceding prime-face belonged to the same person compared with an unrelated familiar person. This was observed both when prime-faces could be recognized overtly and when they were presented too briefly to be recognized overtly (Exps. 1 and 2). Thus, covert face recognition was observed in neurologically intact participants. In Exp. 3, participants were quicker to recognize a familiar face when that person's face had been seen previously, but only when it had been recognized overtly on the first encounter. These results are interpreted within the framework of an interactive activation model of face recognition. Received: 21 September 1998 / Accepted: 2 March 1999