Showing papers by "University of California, Irvine published in 1986"

Selective impairment of learning and blockade of long-term potentiation by an N -methyl-D-aspartate receptor antagonist, AP5

Abstract: Recent work has shown that the hippocampus contains a class of receptors for the excitatory amino acid glutamate that are activated by N-methyl-D-aspartate (NMDA) and that exhibit a peculiar dependency on membrane voltage in becoming active only on depolarization. Blockade of these sites with the drug aminophosphonovaleric acid (AP5) does not detectably affect synaptic transmission in the hippocampus, but prevents the induction of hippocampal long-term potentiation (LTP) following brief high-frequency stimulation. We now report that chronic intraventricular infusion of D,L-AP5 causes a selective impairment of place learning, which is highly sensitive to hippocampal damage, without affecting visual discrimination learning, which is not. The L-isomer of AP5 did not produce behavioural effects. AP5 treatment also suppressed LTP in vivo. These results suggest that NMDA receptors are involved in spatial learning, and add support to the hypothesis that LTP is involved in some, but not all, forms of learning.

Culture as Consensus: A Theory of Culture and Informant Accuracy

Abstract: This paper presents and tests a formal mathematical model for the analysis of informant responses to systematic interview questions. We assume a situation in which the ethnographer does not know how much each informant knows about the cultural domain under consideration nor the answers to the questions. The model simultaneously provides an estimate of the cultural competence or knowledge of each informant and an estimate of the correct answer to each question asked of the informant. The model currently handles true-false, multiple-choice, andfill-in-the-blank type question formats. In familiar cultural domains the model produces good results from as few as four informants. The paper includes a table showing the number of informants needed to provide stated levels of confidence given the mean level of knowledge among the informants. Implications are discussed.

On the depletion of Antarctic ozone

Abstract: Recent observations by Farman et al1 reveal remarkable depletions in the total atmospheric ozone content in Antarctica The observed total ozone decreased smoothly during the period from about 1975 to the present, but only in the spring season The observed ozone content at Halley Bay was ∼30% lower in the Antarctic spring seasons (October) of 1980–84 than in the springs of 1957–73 No such obvious perturbation is observable in other seasons, or at other than the very highest latitudes in the Southern Hemisphere, and the magnitude of the observed change there far exceeds climatological variability2 We present here balloonsonde ozone data3,4 which show that these ozone changes are largely confined to the region from about 10 to 20 km, during the period August to October We show that homogeneous (gas phase) chemistry as presently understood cannot explain these observed depletions On the other hand, a unique feature of the Antarctic lower stratosphere is its high frequency of polar stratospheric clouds5, providing a reaction site for heterogeneous reactions A heterogeneous reaction between HCl and ClONO2 is explored as a possible mechanism to explain the ozone observations This process produces changes in ozone that are consistent with the observations, and its implications for the behaviour of HNO3 and NO2 in the Antarctic stratosphere are consistent with observations of those species there, providing an important check on the proposed mechanism Similar ozone changes are obtained with another possible heterogeneous reaction, H2O + ClONO2

An experimental evaluation of the assumption of independence in multiversion programming

Abstract: N-version programming has been proposed as a method of incorporating fault tolerance into software. Multiple versions of a program (i.e. `N') are prepared and executed in parallel. Their outputs are collected and examined by a voter, and, if they are not identical, it is assumed that the majority is correct. This method depends for its reliability improvement on the assumption that programs that have been developed independently will fail independently. An experiment is described in which the fundamental axiom is tested. In all, 27 versions of a program were prepared independently from the same specification at two universities and then subjected to one million tests. The results of the tests revealed that the programs were individually extremely reliable but that the number of tests in which more than one program failed was substantially more than expected. The results of these tests are presented along with an analysis of some of the faults that were found in the programs. Background information on the programmers used is also summarized.

Increased Intestinal Permeability in Patients with Crohn's Disease and Their Relatives: A Possible Etiologic Factor

Abstract: The cause of Crohn's disease is unknown, although alterations in intestinal permeability may play a primary role. Because we were interested in permeability changes that occur before the onset of intestinal inflammation, we took advantage of the known genetic predisposition to this disease and studied not only patients with Crohn's disease, but their clinically unaffected relatives as well. Intestinal permeability was assessed using the marker polyethylene glycol-400 ingested with a standard meal. We found that 17 normal volunteers absorbed 215 +/- 29.6 mg (mean +/- SE), whereas 11 patients with Crohn's disease absorbed 514 +/- 94.7 mg and their 32 healthy relatives absorbed 566 +/- 62.4 mg. The twofold increase in permeability of patients and their relatives (p less than 0.005 compared with controls) indicates that the intestinal defect in the ability to exclude larger sized molecules is not secondary to clinically recognized intestinal inflammation, but is a primary defect that may be an etiologic factor in this disease.

Induction of synaptic potentiation in hippocampus by patterned stimulation involves two events.

Abstract: Electrical stimulation of axons in the hippocampus with short high-frequency bursts that resemble in vivo activity patterns produces stable potentiation of postsynaptic responses when the bursts occur at intervals of 200 milliseconds but not 2 seconds. When a burst was applied to one input and a second burst applied to a different input to the same target neuron 200 milliseconds later, only the synapses activated by the second burst showed stable potentiation. This effect was observed even when the two inputs innervated completely different regions of the postsynaptic cells; but did not occur when the inputs were stimulated simultaneously or when the second burst was delayed by 2 seconds. Intracellular recordings indicated that the first burst extended the decay phase of excitatory postsynaptic potentials evoked 200 milliseconds later. These results suggest that a single burst of axonal stimulation produces a transient, spatially diffuse "priming" effect that prolongs responses to subsequent bursts, and that these altered responses trigger spatially restricted synaptic modifications. The similarity of the temporal parameters of the priming effect and the theta rhythm that dominates the hippocampal electroencephalogram (EEG) during learning episodes suggests that this priming may be involved in behaviorally induced synaptic plasticity.

Schematic Assessments of Presidential Candidates

Abstract: This article applies theories of social cognition in an investigation of the dimensions of the assessments of candidates employed by voters in the United States. An empirical description of the public's cognitive representations of presidential candidates, derived from responses to open-ended questions in the American National Election Studies from 1952 to 1984, reveals that perceptions of candidates are generally focused on “personality” characteristics rather than on issue concerns or partisan group connections. Contrary to the implications of past research, higher education is found to be correlated with a greater likelihood of using personality categories rather than with making issue statements. While previous models have interpreted voting on the basis of candidate personality as indicative of superficial and idiosyncratic assessments, the data examined here indicate that they predominately reflect performance-relevant criteria such as competence, integrity, and reliability. In addition, both panel and aggregate time series data suggest that the categories that voters have used in the past influence how they will perceive future candidates, implying the application of schematic judgments. The reinterpretation presented here argues that these judgments reflect a rich cognitive representation of the candidates from which instrumental inferences are made.

Distribution of dynorphin and enkephalin peptides in the rat brain.

Abstract: The neuroanatomical distribution of dynorphin B-like immunoreactivity (DYN-B) was studied in the adult male and female albino rat. The distribution of DYN B in colchicine- and noncolchicine-treated animals was also compared to that of another opioid peptide derived from the prodynorphin precursor dynorphin A (1-8) (DYN 1-8), and an opioid peptide derived from the proenkephalin precursor met-enkephalin-arg-gly-leu (MERGL). DYN B cell bodies were present in nonpyramidal cells of neo- and allocortices, medium-sized cells of the caudate-putamen, nucleus accumbens, lateral part of the central nucleus of the amygdala, bed nucleus of the stria terminalis, preoptic area, and in sectors of nearly every hypothalamic nucleus and area, medial pretectal area, and nucleus of the optic tract, periaqueductal gray, raphe nuclei, cuneiform nucleus, sagulum, retrorubral nucleus, peripeduncular nucleus, lateral terminal nucleus, pedunculopontine nucleus, mesencephalic trigeminal nucleus, parabigeminal nucleus, dorsal nucleus of the lateral lemniscus, lateral superior olivary nucleus, superior paraolivary nucleus, medial superior olivary nucleus, ventral nucleus of the trapezoid body, lateral dorsal tegmental nucleus, accessory trigeminal nucleus, solitary nucleus, nucleus ambiguus, paratrigeminal nucleus, area postrema, lateral reticular nucleus, and ventrolateral region of the reticular formation. Fiber systems are present that conform to many of the known output systems of these nuclei, including major descending pathways (e.g., striatonigral, striatopallidal, reticulospinal, hypothalamospinal pathways), short projection systems (e.g., mossy fibers in hippocampus, hypothalamo-hypophyseal pathways), and local circuit pathways (e.g., in cortex, hypothalamus). The distribution of MERGL was, with a few notable exceptions, in the same nuclei as DYN B. From these neuroanatomical data, it appears that the dynorphin and enkephalin peptides are strategically located in brain regions that regulate extrapyramidal motor function, cardiovascular and water balance systems, eating, sensory processing, and pain perception.

Incremental Learning from Noisy Data

Abstract: Induction of a concept description given noisy instances is difficult and is further exacerbated when the concepts may change over time. This paper presents a solution which has been guided by psychological and mathematical results. The method is based on a distributed concept description which is composed of a set of weighted, symbolic characterizations. Two learning processes incrementally modify this description. One adjusts the characterization weights and another creates new characterizations. The latter process is described in terms of a search through the space of possibilities and is shown to require linear space with respect to the number of attribute-value pairs in the description language. The method utilizes previously acquired concept definitions in subsequent learning by adding an attribute for each learned concept to instance descriptions. A program called STAGGER fully embodies this method, and this paper reports on a number of empirical analyses of its performance. Since understanding the relationships between a new learning method and existing ones can be difficult, this paper first reviews a framework for discussing machine learning systems and then describes STAGGER in that framework.

Molecular orbital theory of the properties of inorganic and organometallic compounds 4. Extended basis sets for third‐and fourth‐row, main‐group elements

Abstract: Two new series of efficient basis sets for third- and fourth-row, main-group elements have been developed. Split-valence 3-21G basis sets have been formulated from the minimal expansions by Huzinaga, in which each atomic orbital has been represented by a sum of three Gaussians. The original expansions for s− and p−type orbitals (except those for 1s) have been replaced by new combinations in which the two sets of orbitals (of the same n quantum number) share Gaussian exponents. The Huzinaga expansions for 1s, 3d and 4d (fourth-row elements only) have been employed without further alteration. The valence atomic functions 4s, 4p for third-row elements; 5s, 5p for fourth-row elements have been split into two and one Gaussian parts. Supplemented 3-21G(*) representations have been formed from the 3-21G basis sets by the addition of a set of single d−type Gaussian functions. The performance of 3-21G and 3-21G(*) basis sets is examined with regard to the calculation of equilibrium geometries, normal mode vibrational frequencies, reaction energies, and electric dipole moments involving a variety of normal and hypervalent compounds containing third- and fourth-row, main-group elements. The supplementary functions incorporated into the 3-21G(*) basis sets are generally found to be important, especially for the proper description of equilibrium bond lengths and electric dipole moments. 3-21G(*) representations are recommended for general use in lieu of the unsupplemented 3-21G basis sets.

Software safety: why, what, and how

Abstract: Software safety issues become important when computers are used to control real-time, safety-critical processes. This survey attempts to explain why there is a problem, what the problem is, and what is known about how to solve it. Since this is a relatively new software research area, emphasis is placed on delineating the outstanding issues and research topics.

A Language Theory of Discrimination

Abstract: Any advanced industrial society is composed of a number of speech communities with different verbal and nonverbal languages. In particular, in the United States blacks and whites and men and women have sharply differing methods of speaking and listening. This paper develops a model in which people can only work together if they "speak" the same language and in which it is costly to learn a second language. The competitive market will tend to minimize communication through segregation, but if interaction is required, the cost will be borne by the minority. A number of nontrivial predictions are derived from the model.

Reduction in number of immunostained GABAergic neurones in deprived-eye dominance columns of monkey area 17.

Abstract: The primary visual cortex (area 17) of the Old World monkey is divided into alternating right- and left-eye dominance columns that are highly modifiable by visual experience during a critical period in development but display little morphological or physiological plasticity during adult life. However, changes in immunocytochemical staining for a calcium/calmodulin-dependent protein kinase occur in visual cortical neurones of adult monkeys after brief monocular deprivation and concentrations of putative neurotransmitters or their related enzymes can be altered with changes in neuronal activity in other systems. We therefore examined the effects of monocular deprivation on the immunocytochemical staining for gamma-aminobutyric acid (GABA) and its synthetic enzyme, glutamic acid decarboxylase (GAD), in adult monkey area 17. The staining for GABA and GAD in neuronal somata and terminals was markedly reduced within ocular dominance columns associated with a removed or a visually deprived eye, suggesting that the GABA concentration in cortical neurones may depend on their levels of activity. Thus area 17 of adult monkeys may retain a greater degree of plasticity than previously recognized and sensory experience can profoundly affect transmitter levels, in the cortex, apparently by regulating levels of a synthetic enzyme.

A case study of incremental concept induction

Abstract: Application of machine induction techniques in complex domains promises to push the computational limits of non-incremental, search intensive induction methods. Learning effectiveness in complex domains requires the development of incremental, cost effective methods. However, discussion of dimensions for comparing the utility of differing incremental methods has been lacking. In this paper we introduce 3 dimensions for characterizing incremental concept induction systems which relate to the cost and quality of learning. The dimensions are used to compare the respective merits of 4 incremental variants of Quinlan's learning from examples program, ID3. This comparison indicates that cost effective induction can be obtained, without significantly detracting from the quality of induced knowledge.

Analysis of the normalized LMS algorithm with Gaussian inputs

Abstract: The LMS adaptive filter algorithm requires a priori knowledge of the input power level to select the algorithm gain parameter μ for stability and convergence. Since the input power level is usually one of the statistical unknowns, it is normally estimated from the data prior to beginning the adaptation process. It is then assumed that the estimate is perfect in any subsequent analysis of the LMS algorithm behavior. In this paper, the effects of the power level estimate are incorporated in a data dependent μ that appears explicitly within the algorithm. The transient mean and second-moment behavior of the modified LMS (NLMS) algorithm are evaluated, taking into account the explicit statistical dependence of μ upon the input data. The mean behavior of the algorithm is shown to converge to the Wiener weight. A constant coefficient matrix difference equation is derived for the weight fluctuations about the Wiener weight. The equation is solved for a white data covariance matrix and for the adaptive line enhancer with a single-frequency input in steady state for small μ. Expressions for the misadjustment error are also presented. It is shown for the white data covariance matrix case that the averaging of about ten data samples causes negligible degradation as compared to the LMS algorithm. In the ALE application, the steady-state weight fluctuations are shown to be mode dependent, being largest at the frequency of the input.

Digestive physiology is a determinant of foraging bout frequency in hummingbirds.

Abstract: Hummingbirds are among the smallest endothermic vertebrates. Because they forage by energetically costly hovering, and because weight-specific basal metabolic rates increase with decreasing body size, their basal and active metabolic rates are among the highest recorded. Hummingbirds fuel these metabolic requirements mainly with highly concentrated sugar in nectar, which they extract rapidly and efficiently1,2 by an unknown mechanism. It is especially puzzling that, despite their high energy requirements, hummingbirds spend only ∼20% of their waking hours feeding, but 75% perched and apparently doing nothing3,4. Here we report the first measurement of nutrient absorption by hummingbird intestine and present a new method for measuring crop-emptying times. We find that hummingbird intestine has the highest active glucose transport rate and lowest passive glucose permeability reported for any vertebrate. Crop-emptying time may limit feeding-bout frequency and could largely account for the time spent perched.

Human Capital Versus Sorting: The Effects of Compulsory Attendance Laws

Abstract: Under the educational sorting hypothesis a state compulsory school attendance law will increase the educational attainment of high-ability workers who are not directly affected hy the law. Under the human capital hypothesis such laws affect only those individuals whose hehavior is directly constrained. We find that compulsory attendance laws do increase enrollment rates in age groups they do not affect directly. Thus, our results contradict the human capital hypothesis and are consistent with the sorting hypothesis. I. INTRODUCTION The last decade has seen considerable debate between supporters of the human capital and sorting models of education. The former assert that the effect of education on wages reflects increased productivity. The latter maintain that it reflects, at least in part, correlation between education and unobserved ability. Workers use education to signal their ability, while employers use education to screen workers. Despite the importance of the debate, no fully convincing tests of the hypotheses have been developed. In fact, many members of the profession maintain (at least privately) that these hypotheses cannot be tested against each other and that the debate must therefore be relegated to the realm of ideology. In this paper we show that the models can be tested against each other by examining the effects of state compulsory school attendance laws. We show that under the human capital hypotheis, such laws will affect the educational attainment only of those who in the absence of the law would have left school prior to the minimum school leaving age. On the other hand, under the sorting hypothesis the effects of the law will percolate through the system, increasing educational attainment even among workers not directly constrained by the law. Our results are consistent with the predictions of the sorting model.