Attention to uninformative features expressed by pigeons in a duration matching-to-sample task

Pigeons were trained on a matching-to-sample task in which they had to respond to a different choice stimulus following the same durations (2 or 10 s) of two different signals. The duration signals consisted of a white light presented from the ceiling and a red light presented from the front wall. Subsequent test performance indicated that matching accuracy declined (1) when the set of choice stimuli following a duration signal differed from the set presented during training, and (2) when the color or location of the duration signal was changed from values used during training. These results are discussed in terms of attention to uninformative features of a visual stimulus.     

Quantity discrimination in felines: a preliminary investigation of the domestic cat (<Emphasis Type="Italic">Felis silvestris catus</Emphasis>)

A large body of studies has investigated the capacity of non-human primates, dogs, birds and lower vertebrates to estimate different quantities of objects or events. Little attention, however, has been devoted to felines, and no study has specifically concentrated on cats’ numerical cognition. The present study aims to investigate the capacity of domestic cats to distinguish between two and three dots in order to obtain food; results showed that cats can be trained to discriminate between the two quantities. Furthermore our research suggests that cats do not spontaneously use numerical information, but rather seem to make use of visual cues that co-vary with numerosity in order to solve the task.     

Physical cognition: birds learn the structural efficacy of nest material

It is generally assumed that birds’ choice of structurally suitable materials for nest building is genetically predetermined. Here, we tested that assumption by investigating whether experience affected male zebra finches’ (Taeniopygia guttata) choice of nest material. After a short period of building with relatively flexible string, birds preferred to build with stiffer string while those that had experienced a stiffer string were indifferent to string type. After building a complete nest with either string type, however, all birds increased their preference for stiff string. The stiffer string appeared to be the more effective building material as birds required fewer pieces of stiffer than flexible string to build a roofed nest. For birds that raised chicks successfully, there was no association between the material they used to build their nest and the type they subsequently preferred. Birds’ material preference reflected neither the preference of their father nor of their siblings but juvenile experience of either string type increased their preference for stiffer string. Our results represent two important advances: (i) birds choose nest material based on the structural properties of the material; (ii) nest material preference is not entirely genetically predetermined as both the type and amount of experience influences birds’ choices.     

Discontinuous and incremental processes in the song learning of birds: evidence for a primer effect

Studies on the song learning in birds revealed a puzzling property of the acquisition system: Stimulus memorization becomes effective after remarkably few exposures, but nevertheless shows a relationship to the frequency of exposure to learning stimuli. This raises questions on the amount of learning that will occur during a given exposure to song. To examine this issue, we tutored handraised fledgling nightingales (Luscinia megarhynchos) with song strings, in which the serial succession of species-typical master songs was altered upon subsequent exposures. The sequencing of imitations obtained from the birds' adult singing revealed the following results: (1) A single exposure was sufficient for subjects to acquire serial information on song-type sequencing. (2) The first exposure to a master string played a key role for this accomplishment. (3) Nevertheless, the acquisition of serial information improved with increasing exposure frequency of master strings. (4) The acquisition of song patterns was not impaired by a non-regular presentation of master song-types. With respect to the particular salience of the first exposure for sequence memorization, we termed the phenomenon primer effect. The findings suggest that stimulus acquisition during perceptual song learning is mediated by a discontinuous process. Once acquired, information is then consolidated gradually, i.e. through an incremental process.     

Chimpanzees (Pan troglodytes): Problem seeking versus the bird-in-hand,least-effort strategy

Fifteen adult chimpanzees were tested on a series of tasks that differed from standard two-choice object discrimination learning problems in one detail: a third choice was sometimes offered, and it consisted of clearly visible and readily accessible food. Even under conditions where they would have to score 100% on the discrimination learning tasks to get as much food as they could get by taking the “free” food, many of the chimpanzees worked on the problems. Individual differences were large and reliable. Frequency of response to a given problem also varied according to how accurately the animals were performing and increased markedly if the hidden food was made a few grams larger than the free food. The chimpanzees did not rely strictly on a “bird-in-hand” strategy or necessarily always work to get the maximum amount of food with the minimum amount of energy expenditure. Whether this is bad economics or good economics depends on the time scale on which one views adaptation.     

Mice recognize the center of an enclosure

In recent years, it has been shown that animals can localize the geometric center of an area by reference to the shape of the environment. We trained a group of mice (experimental group) to search for a pellet hidden under sand in the center of a square-shaped dry maze. Three weeks later, they were tested in a triangular enclosure half the size of the training area and a circular enclosure double the size of the training area to see transfer to these enclosures. We compared their searching behavior with that of subjects that had received no training. The results show that the experimental group searched the geometric center of each enclosure in both transfer tests, while the untrained control group walked along the walls. This indicates that the experimental group localized the center not by reference to the absolute distance from the corners but by equal distances from all walls (geometric center).     

The contribution of C<Subscript>3</Subscript> and C<Subscript>4</Subscript> plants to the carbon cycle of a tallgrass prairie: an isotopic approach

The photosynthetic pathway composition (C₃:C₄ mixture) of an ecosystem is an important controller of carbon exchanges and surface energy flux partitioning, and therefore represents a fundamental ecophysiological distinction. To assess photosynthetic mixtures at a tallgrass prairie pasture in Oklahoma, we collected nighttime above-canopy air samples along concentration and isotopic gradients throughout the 1999 and 2000 growing seasons. We analyzed these samples for their CO₂ concentration and carbon isotopic composition and calculated C₃:C₄ proportions with a two-source mixing model. In 1999, the C₄ percentage increased from 38% in spring (late April) to 86% in early fall (mid-September). The C₄ percentages inferred from ecosystem respiration measurements in 2000 indicate a smaller shift, from 67% in spring (early May) to 77% in mid-summer (late July). We also sampled daytime CO₂ concentration and carbon isotope gradients above the canopy to determine ecosystem discrimination against ¹³CO₂ during net uptake. These discrimination values were always lower than corresponding nighttime ecosystem respiration isotopic signatures would suggest. After accounting for the isotopic disequilibria between respiration and photosynthesis resulting from seasonal variations in the C₃:C₄ mixture, we estimated canopy photosynthetic discrimination. The C₄ percentage calculated from this approach agrees with the percentage determined from nighttime respiration for sampling periods in both growing seasons. Isotopic imbalances between photosynthesis and respiration are likely to be common in mixed C₃:C₄ ecosystems and must be considered when using daytime isotopic measurements to constrain ecosystem physiology. Given the global extent of such ecosystems, isotopic imbalances likely contribute to global variations in the carbon isotopic composition of atmospheric CO₂.     

Synaptic Vesicle Ultrastructural Changes in the Rat Hippocampus Induced by a Combination of α-Linolenate Deficiency and a Learning Task

Abstract: Rats fed either a safflower oil (α-linolenate-deficient) or a perilla oil (α-linolenate-sufficient) diet through two generations (F1) showed significant differences in the brightness-discrimination learning task. In this task, correct responses were lever-pressing responses, which were reinforced with dietary pellets, and incorrect responses were those with no reinforcement. The inferior learning performance in the safflower oil group was caused mainly by the inferior ability to rectify the incorrect responses through the learning sessions. In the safflower oil group after the learning task, the average densities of synaptic vesicles in the terminals of the hippocampus CA1 region were decreased by nearly 30% as compared with those in the perilla oil group, and it is notable that this difference was not detected without the learning task. These results suggest that dietary oil-induced morphological changes in synapses in the hippocampus of rats are related to the differential learning performance and that the turnover rate of synaptic vesicles in the hippocampus may be an important factor affecting learning performance.     

A word in the hand: action, gesture and mental representation in humans and non-human primates

The movements we make with our hands both reflect our mental processes and help to shape them. Our actions and gestures can affect our mental representations of actions and objects. In this paper, we explore the relationship between action, gesture and thought in both humans and non-human primates and discuss its role in the evolution of language. Human gesture (specifically representational gesture) may provide a unique link between action and mental representation. It is kinaesthetically close to action and is, at the same time, symbolic. Non-human primates use gesture frequently to communicate, and do so flexibly. However, their gestures mainly resemble incomplete actions and lack the representational elements that characterize much of human gesture. Differences in the mirror neuron system provide a potential explanation for non-human primates' lack of representational gestures; the monkey mirror system does not respond to representational gestures, while the human system does. In humans, gesture grounds mental representation in action, but there is no evidence for this link in other primates. We argue that gesture played an important role in the transition to symbolic thought and language in human evolution, following a cognitive leap that allowed gesture to incorporate representational elements.     

Ernst Mayr's influence on the history and philosophy of biology: A personal memoir

Mayr has made both conceptual and professional contributions to the establishment of the history and philosophy of biology. His conceptual contributions include, among many others, the notion of population thinking. He has also played an important role in the establishment of history and philosophy of biology as viable professional disciplines.     

Language Learning and the Politics of Belonging: Sudanese Women Refugees Becoming and Being"American"

In this article, I explore the complicated relationship between ideologies of language and language learning, discourses of immigration and belonging, and the actual lived experiences of individual language learners. The analysis demonstrates how questions of educational access, economic stability, and social membership are all influenced by a range of social, political, and historical factors, particularly for recently arrived immigrants and refugees from war-torn African contexts.     

Key Residues Defining the μ-Opioid Receptor Binding Pocket: A Site-Directed Mutagenesis Study

Abstract: Structural elements of the rat μ-opioid receptor important in ligand receptor binding and selectivity were examined using a site-directed mutagenesis approach. Five single amino acid mutations were made, three that altered conserved residues in the μ, δ, and κ receptors (Asn¹⁵⁰ to Ala, His²⁹⁷ to Ala, and Tyr³²⁶ to Phe) and two designed to test for μ/δ selectivity (Ile¹⁹⁸ to Val and Val²⁰² to Ile). Mutation of His²⁹⁷ in transmembrane domain 6 (TM6) resulted in no detectable binding with [³H]DAMGO (³H-labeled d -Ala², N -Me-Phe⁴,Gly-ol⁵-enkephalin), [³H]bremazocine, or [³H]ethylketocyclazocine. Mutation of Asn¹⁵⁰ in TM3 produces a three- to 20-fold increase in affinity for the opioid agonists morphine, DAMGO, fentanyl, β-endorphin_1–31, JOM-13, deltorphin II, dynorphin_1–13, and U50,488, with no change in the binding of antagonists such as naloxone, naltrexone, naltrindole, and nor-binaltorphamine. In contrast, the Tyr³²⁶ mutation in TM7 resulted in a decreased affinity for a wide spectrum of μ, δ, and κ agonists and antagonists. Altering Val²⁰² to Ile in TM4 produced no change on ligand affinity, but Ile¹⁹⁸ to Val resulted in a four- to fivefold decreased affinity for the μ agonists morphine and DAMGO, with no change in the binding affinities of κ and δ ligands.     

Duration discrimination in the mouse (<Emphasis Type="Italic">Mus musculus</Emphasis>)

Detection thresholds for an increment in duration of a 10-kHz pure tone were determined in the NMRI mouse using a Go/NoGo-procedure and the method of constant stimuli. Thresholds for reference durations of 50, 100 and 200 ms were obtained presenting the signals at a fixed level or at a level varying by ±3 dB. Thresholds were determined using signal-detection theory (d=1.0 or d=1.8) and the criterion of 50% correct responses. For a fixed level, the average Weber fraction T/T (criterion of d=1.8) significantly decreased from 1.18 or 1.23 at reference durations of 50 or 100 ms, respectively, to 0.97 at a reference duration of 200 ms. Thresholds were on average reduced by 46.8 or 55.4% for the threshold criteria d=1 or 50% correct responses, respectively. There was no effect of randomizing the level on the discrimination threshold. Duration discrimination in the NMRI mouse does not follow Webers law. The results are consistent with a mechanism summing up neural impulses over the duration of the stimulus. The psychoacoustic data are compared with results obtained by Brand et al. (J Acoust Soc Am 51:1291–1223, 2000) on the representation of acoustic signal duration in the mouse inferior colliculus.