Showing papers by "University of Oregon published in 1990"

The Attention System of the Human Brain

Abstract: : The concept of attention as central to human performance extends back to the start of experimental psychology, yet even a few years ago, it would not have been possible to outline in even a preliminary form a functional anatomy of the human attentional system. New developments in neuroscience have opened the study of higher cognition to physiological analysis, and have revealed a system of anatomical areas that appear to be basic to the selection of information for focal (conscious) processing. The importance of attention is its unique role in connecting the mental level of description of processes used in cognitive science with the anatomical level common in neuroscience. Sperry describes the central role that mental concepts play in understanding brain function. As is the case for sensory and motor systems of the brain, our knowledge of the anatomy of attention is incomplete. Nevertheless, we can now begin to identify some principles of organization that allow attention to function as a unified system for the control of mental processing. Although many of our points are still speculative and controversial, we believe they constitute a basis for more detailed studies of attention from a cognitive-neuroscience viewpoint. Perhaps even more important for furthering future studies, multiple methods of mental chronometry, brain lesions, electrophysiology, and several types of neuro-imaging have converged on common findings.

An alternative "description of personality": the big-five factor structure.

Abstract: In the 45 years since Cattell used English trait terms to begin the formulation of his "description of personality," a number of investigators have proposed an alternative structure based on 5 orthogonal factors. The generality of this 5-factor model is here demonstrated across unusually comprehensive sets of trait terms. In the first of 3 studies, 1,431 trait adjectives grouped into 75 clusters were analyzed; virtually identical structures emerged in 10 replications, each based on a different factor-analytic procedure. A 2nd study of 479 common terms grouped into 133 synonym clusters revealed the same structure in 2 samples of self-ratings and in 2 samples of peer ratings. None of the factors beyond the 5th generalized across the samples. In the 3rd study, analyses of 100 clusters derived from 339 trait terms suggest their potential utility as Big-Five markers in future studies.

HIERARCHIES, JOBS, BODIES: A Theory of Gendered Organizations

Abstract: In spite of feminist recognition that hierarchical organizations are an important location of male dominance, most feminists writing about organizations assume that organizational structure is gender neutral. This article argues that organizational structure is not gender neutral; on the contrary, assumptions about gender underlie the documents and contracts used to construct organizations and to provide the commonsense ground for theorizing about them. Their gendered nature is partly masked through obscuring the embodied nature of work. Abstract jobs and hierarchies, common concepts in organizational thinking, assume a disembodies and universal worker. This worker is actually a man; men's bodies, sexuality, and relationships to procreation and paid work are subsumed in the image of the worker. Images of men's bodies and masculinity pervade organizational processes, marginalizing women and contributing to the maintenance of gender segregation in organizations. The positing of gender-neutral and disembodie...

Language Comprehension As Structure Building

Abstract: : This research investigated language comprehension, and in particular, the general, cognitive processes and mechanisms that underlie language comprehension. These general, processes and mechanisms were investigated using a simple framework Gernsbacher (1990) refers to as the 'Structure Building Framework'. According to the Structure Building Framework, the goal of comprehension is to build a coherent, mental representation of 'structure'. To do this, comprehenders must first lay a foundation. Next, they develop the structure by mapping on information when that incoming information is coherent or related to previous information. However, if the incoming information is less coherent or related, comprehenders shift to initiate a new substructure. Thus, most representations comprise several branching substructures. These structure building processes are accomplished by two mechanisms: enhancement, which boosts the activation of some representations, and suppression, which dampens the activation of other representations.

Theories of Creativity

Abstract: This article surveys the range of contemporary theories of creativity. These are heuristically divided into ten categories: developmental, psychometric, economic, stage and componential process, cognitive, problem solving and expertise-based, problem finding, evolutionary, typological, and systems. These perspectives span a range of subtopics, levels of analysis, and emphases within the study of creativity. Beyond the general overview, prospects for the future role and development of theories of creativity are discussed, offering a critical but hopefully constructive appraisal of current theories and their promise for a continued deeper understanding of the nature of creativity.

Enhanced protein thermostability from site-directed mutations that decrease the entropy of unfolding

Abstract: It is proposed that the stability of a protein can be increased by selected amino acid substitutions that decrease the configurational entropy of unfolding. Two such substitutions, one of the form Xaa----Pro and the other of the form Gly----Xaa, were constructed in bacteriophage T4 lysozyme at sites consistent with the known three-dimensional structure. Both substitutions stabilize the protein toward reversible and irreversible thermal denaturation at physiological pH. The substitutions have no effect on enzymatic activity. High-resolution crystallographic analysis of the proline-containing mutant protein (Ala-82----Pro) shows that its three-dimensional structure is essentially identical with the wild-type enzyme. The overall structure of the other mutant enzyme (Gly-77----Ala) is also very similar to wild-type lysozyme, although there are localized conformational adjustments in the vicinity of the altered amino acid. The combination of a number of such amino acid replacements, each of which is expected to contribute approximately 1 kcal/mol (1 cal = 4.184 J) to the free energy of folding, may provide a general strategy for substantial improvement in the stability of a protein.

Origin and organization of the zebrafish fate map.

Abstract: We have analyzed lineages of cells labeled by intracellular injection of tracer dye during early zebrafish development to learn when cells become allocated to particular fates during development, and how the fate map is organized. The earliest lineage restriction was described previously, and segregates the yolk cell from the blastoderm in the midblastula. After one or two more cell divisions, the lineages of epithelial enveloping layer (EVL) cells become restricted to generate exclusively periderm. Following an additional division in the late blastula, deep layer (DEL) cells generate clones that are restricted to single deep embryonic tissues. The appearance of both the EVL and DEL restrictions could be causally linked to blastoderm morphogenesis during epiboly. A fate map emerges as the DEL cell lineages become restricted in the late blastula. It is similar in organization to that of an amphibian embryo. DEL cells located near the animal pole of the early gastrula give rise to ectodermal fates (including the definitive epidermis). Cells located near the blastoderm margin give rise to mesodermal and endodermal fates. Dorsal cells in the gastrula form dorsal and anterior structures in the embryo, and ventral cells in the gastrula form dorsal, ventral and posterior structures. The exact locations of progenitors of single cell types and of local regions of the embryo cannot be mapped at the stages we examined, because of variable cell rearrangements during gastrulation.

The similarity index and DNA fingerprinting.

Abstract: DNA-fingerprint similarity is being used increasingly to make inferences about levels of genetic variation within and between natural populations. It is shown that the similarity index--the average fraction of shared restriction fragments--provides upwardly biased estimates of population homozygosity but nearly unbiased estimates of the average identity-in-state for random pairs of individuals. A method is suggested for partitioning the DNA-fingerprint dissimilarity into within- and between-population components. Some simple expressions are given for the sampling variances of these estimators.

Premeiotic Instability of Repeated Sequences in Neurospora crassa

Abstract: Maintenance of a steamlined genome is probably important to a free-living fungus. The period between fertilization and karyogamy in the life cycle of Neurospora and related fungi provides an ideal time for "genome-cleaning". Premeiotic intrachromosomal recombination deletes tandem repeats at high frequency in both homothallic and heterothallic filamentous ascomycetes. This eliminates excess copies of tandemly repeated genes and at the same time favors their homogenization. Heterothallic fungi such as Neurospora also take the bolder steps of mutating and modifying both copies of duplicated sequences, linked or unlinked, by RIP. Because these organisms are outbreeders, and because RIP operates immediately prior to meiosis in cells having nuclei from both parents, the process does not cause much lethality or loss of genetic information. RIP should effectively counter selfish and redundant DNA, and at the same time generate raw material for evolution. In addition, RIP should both prevent chromosomal rearrangements by causing divergence of dispersed repeated sequences and rid a population of duplication-generating rearrangements. Thus, this form of genetic instability potentially stabilizes the gross organization of the genome.

Attention and structure in sequence learning.

Abstract: In this study we investigated the role of attention, sequence structure, and effector specificity in learning a structured sequence of actions

Colocalization of ion channels involved in frequency selectivity and synaptic transmission at presynaptic active zones of hair cells

Abstract: Calcium ions serve as intracellular messengers in 2 activities of hair cells: in conjunction with Ca2(+)-activated K+ channels, they produce the electrical resonance that tunes each cell to a specific frequency of stimulation, and they trigger the release of a chemical synaptic transmitter. Our experiments indicate that both of these functions are conducted within a region that extends a few hundred nanometers around each presynaptic active zone. In focal electrical recordings from the plasma membranes of isolated anuran hair cells, we found nearly all of a cell's Ca2+ channels and Ca2(+)-activated K+ channels clumped at a fixed ratio in an average of 20 clusters on the basolateral membrane surface. Because serial-section electron microscopy indicated that each hair cell has approximately 19 afferent synaptic contacts with a similar distribution upon its basolateral surface, we conclude that the channel clusters coincide with synaptic active zones. Ensemble-variance analysis of current fluctuations indicated that each cell has a total of approximately 1800 Ca2+ channels and approximately 700 Ca2(+)- activated K+ channels; if these are uniformly divided, we estimate that each channel cluster contains approximately 90 Ca2+ and approximately 40 Ca2(+)-activated K+ channels. Freeze-fracture electron microscopy demonstrated an average of 133 large intramembrane particles in the presynaptic membrane at each active zone, an observation that suggests that the particles are the clustered channels. We used the K+ channel's sensitivity to intracellular Ca2+ to assay the concentration of free Ca2+ in the presynaptic cytoplasm, which we found to vary between 10 microM and 1 mM over the physiological range of membrane potentials. The inferred concentrations agreed with the values predicted for free diffusion of Ca2+ away from Ca2+ channels scattered randomly within a 300-nm-diameter synaptic active zone. The close association among Ca2+ channels, Ca2(+)-activated K+ channels, and synaptic active zones is necessary both for the rapid activation of K+ currents required in electrical resonance and for the transmission at afferent synapses of information about the phases of high-frequency stimuli.

Investigating differences in general comprehension skill.

Abstract: For adults, skill at comprehending written language correlates highly with skill at comprehending spoken language. Does this general comprehension skill extend beyond language-based modalities? And if it does, what cognitive processes and mechanisms differentiate individuals who are more versus less proficient in general comprehension skill? In our first experiment, we found that skill in comprehending written and auditory stories correlates highly with skill in comprehending nonverbal, picture stories. This finding supports the hypothesis that general comprehension skill extends beyond language. We also found support for the hypotheses that poorer access to recently comprehended information marks less proficient general comprehension skill (Experiment 2) because less skilled comprehenders develop too many mental substructures during comprehension (Experiment 3), perhaps because they inefficiently suppress irrelevant information (Experiment 4). Thus, the cognitive processes and mechanisms involved in capturing and representing the structure of comprehensible information provide one source of individual differences in general comprehension skill.

Cell movements during epiboly and gastrulation in zebrafish.

Abstract: Beginning during the late blastula stage in zebrafish, cells located beneath a surface epithelial layer of the blastoderm undergo rearrangements that accompany major changes in shape of the embryo. We describe three distinctive kinds of cell rearrangements. (1) Radial cell intercalations during epiboly mix cells located deeply in the blastoderm among more superficial ones. These rearrangements thoroughly stir the positions of deep cells, as the blastoderm thins and spreads across the yolk cell. (2) Involution at or near the blastoderm margin occurs during gastrulation. This movement folds the blastoderm into two cellular layers, the epiblast and hypoblast, within a ring (the germ ring) around its entire circumference. Involuting cells move anteriorwards in the hypoblast relative to cells that remain in the epiblast; the movement shears the positions of cells that were neighbors before gastrulation. Involuting cells eventually form endoderm and mesoderm, in an anterior-posterior sequence according to the time of involution. The epiblast is equivalent to embryonic ectoderm. (3) Mediolateral cell intercalations in both the epiblast and hypoblast mediate convergence and extension movements towards the dorsal side of the gastrula. By this rearrangement, cells that were initially neighboring one another become dispersed along the anterior-posterior axis of the embryo. Epiboly, involution and convergent extension in zebrafish involve the same kinds of cellular rearrangements as in amphibians, and they occur during comparable stages of embryogenesis.

The analysis of population survey data on DNA sequence variation.

Abstract: A technique is presented for the partitioning of nucleotide diversity into within- and between-population components for the case in which multiple populations have been surveyed for restriction-site variation. This allows the estimation of an analogue of FST at the DNA level. Approximate expressions are given for the variance of these estimates resulting from nucleotide, individual, and population sampling. Application of the technique to existing studies on mitochondrial DNA in several animal species and on several nuclear genes in Drosophila indicates that the standard errors of genetic diversity estimates are usually quite large. Thus, comparative studies of nucleotide diversity need to be substantially larger than the current standards. Normally, only a very small fraction of the sampling variance is caused by sampling of individuals. Even when 20 or so restriction enzymes are employed, nucleotide sampling is a major source of error, and population sampling is often quite important. Generally, the degree of population subdivision at the nucleotide level is comparable with that at the haplotype level, but significant differences do arise as a result of inequalities in the genetic distances between haplotypes.

Environmental jolts and industry revolutions: organizational responses to discontinuous change

Abstract: The organizational change literature contains diverse characterizations of change processes with contradictory implications for strategic mianagers. Many inconsistencies are resolved by classifying models of organizational change according to the primary mode of change (continuous or discontinuous) and the primary level at which change occurs (organization or industry) to yield four basic types of change: adaptation, metamorphosis, evolution, and revolution. These types influence organizations' adaptive responses, shape industries' competitive structures, and constrain researchers' methods of inquiry. This paper identifies a gap in the literature: theory and research focusing on discontinuous changes occurring at the industry level of analysis. A perspective on this type of change is developed, and applied in a historical analysis of the hospital induistry. Data from a longitudinal field study are used to illustrate various organizational responses to discontinuities.

pH-Induced Denaturation of Proteins : a single salt bridge contributes 3-5 kcal/mol to the free energy of folding of T4 lysozyme

Abstract: The energetics of a salt bridge formed between the side chains of aspartic acid 70 (Asp70) and histidine 31 (His31) of T4 lysozyme have been examined by nuclear magnetic resonance techniques. The pKa values of the residues in the native state are perturbed from their values in the unfolded protein such that His31 has a pKa value of 9.1 in the native state and 6.8 in the unfolded state at 10 degrees C in moderate salt. Similarly, the aspartate pKa is shifted to a value of about 0.5 in the native state from its value of 3.5-4.0 in the unfolded state. These shifts in pKa show that the salt bridge is stabilized 3-5 kcal/mol. This implies that the salt bridge stabilizes the native state by 3-5 kcal/mol as compared to the unfolded state. This is reflected in the thermodynamic stability of mutants of the protein in which Asp70, His31, or both are replaced by asparagine. These observations and consideration of the thermodynamic coupling of protonation state to folding of proteins suggest a mechanism of acid denaturation in which the unfolded state is progressively stabilized by protonation of its acid residues as pH is lowered below pH 4. The unfolded state is stabilized only if acidic groups in the folded state have lower pKa values than in the unfolded state. When the pH is sufficiently low, the acid groups of both the native and unfolded states are fully protonated, and the apparent unfolding equilibrium constant becomes pH independent. Similar arguments apply to base-induced unfolding.(ABSTRACT TRUNCATED AT 250 WORDS)

Protein splicing converts the yeast TFP1 gene product to the 69-kD subunit of the vacuolar H(+)-adenosine triphosphatase.

Abstract: The TFP1 gene of the yeast Saccharomyces cerevisiae encodes two proteins: the 69-kilodalton (kD) catalytic subunit of the vacuolar proton-translocating adenosine triphosphatase (H(+)-ATPase) and a 50-kD protein. The 69-kD subunit is encoded by the 5' and 3' thirds of the TFP1 coding region, whereas the 50-kD protein is encoded by the central third. Evidence is presented that both the 69-kD and 50-kD proteins are obtained from a single translation product that is cleaved to release the 50-kD protein and spliced to form the 69-kD subunit.

Mutation Load and the Survival of Small Populations

Abstract: Previous attempts to model the joint action of selection and mutation in finite popu- lations have treated population size as being independent of the mutation load. However, the accumulation of deleterious mutations is expected to cause a gradual reduction in population size. Consequently, in small populations random genetic drift will progressively overpower selection making it easier to fix future mutations. This synergistic interaction, which we refer to as a mu- tational melt-down, ultimately leads to population extinction. For many conditions, the coefficient of variation of extinction time is less than 0.1, and for species that reproduce by binary fission, the expected extinction time is quite insensitive to population carrying capacity. These results are consistent with observations that many cultures of ciliated protozoans and vertebrate fibroblasts have characteristic extinction times. The model also predicts that clonal lineages are unlikely to survive more than 104 to 105 generations, which is consistent with existing data on parthenogenetic animals. Contrary to the usual view that Muller's ratchet does more damage when selection is weak, we show that the mean extinction time declines as mutations become more deleterious. Although very small sexual populations, such as self-fertilized lines, are subject to mutational melt- downs, recombination effectively eliminates the process when the effective population size exceeds a dozen or so. The concept of the effective mutation load is developed, and several procedures for estimating it are described. It is shown that this load can be reduced substantially when mutational effects are highly variable.

Vacuum Rabi splitting as a feature of linear-dispersion theory: Analysis and experimental observations.

Abstract: The spectral and temporal response of an optical cavity resonantly coupled to an ensemble of barium atoms has been investigated experimentally. The empty-cavity trnasmission resonances are found to split in the presence of the atoms and, under these conditions, the cavity's temporal response is found to be oscillatory. These effects may be viewed as a manifestation of a vacuum-field Rabi splitting, or as a simple consequence of the linear absorption and dispersion of the intracavity atoms.

Cell-autonomous action of zebrafish spt-1 mutation in specific mesodermal precursors

Abstract: In zebrafish, as in Xenopus, the well-orchestrated cell movements of gastrulation can be dissected into several components, including epiboly, involution, convergence and extension. Embryos homozygous for the recessive lethal mutation spt-1(b104) or 'spadetail' have a complex set of defects in the trunk of the embryo that may arise secondarily after loss of one of these movements, convergence, from those precursors that would normally have given rise to trunk somitic mesoderm. We have now tested this hypothesis by transplanting cells between wild-type and mutant embryos, to identify the cells that spt-1 affects directly. Our results show that the mutation autonomously affects only those mesodermal precursors located along the lateral margin of the early gastrula blastoderm. Other mesodermal cells and all ectodermal precursors seem not to require function of the wild-type gene. Our findings reveal an unexpectedly delicate genetic control of vertebrate gastrulation.

Changes in Posture Control Across the Life Span—A Systems Approach

Abstract: In this article, a systems approach to the development of posture control across the life span and its integration with voluntary tasks such as walking is described. Research shows a clear cephalocaudal gradient in the development of postural responses. Postural muscle synergies develop appropriate temporal organization through experience in each new level of postural skill development. Sensory inputs contributing to posture control influence postural responses very early in development, with responses being elicited by vision alone, or by somatosensory and vestibular cues in isolation. Studies of older adults indicate small, but significant, increases in onset latencies and disruptions in the temporal organization of postural muscle responses when subjects are given external threats to balance. In addition, older adults, like young children, use antagonist muscles more often in coactivation with agonist muscles. Older adults also have more difficulty balancing when sensory inputs are reduced experimentally or pathologically. Ankle dorsiflexor muscle weakness is also a factor in balance dysfunction in the older adult.

Toward a Technology of “Nonaversive” Behavioral Support:

Abstract: Nonaversive behavior management is an approach to supporting people with undesirable behaviors that integrates technology and values. Although this approach has attracted numerous proponents, more ...

Hydrophobic stabilization in T4 lysozyme determined directly by multiple substitutions of Ile 3.

Abstract: Replacing the isoleucine at amino-acid position three of bacteriophage T4 lysozyme causes changes in the thermodynamic stability of the protein that are directly related to the hydrophobicity of the substituted residue. Structural analysis confirms that the hydrophobic stabilization is proportional to the reduction of the surface area accessible to solvent on folding.

Apparent Motion of the Human Body

Abstract: Observers viewed pairs of alternating photographs of a human body in different positions. Shortest-path motion solutions were pitted against anatomically possible movements. With short stimulus onset asynchronies (SOAs), observers tended to report the shortest path despite violations of anatomical constraints. However, with longer SOAs observers became increasingly likely to report the anatomically possible, but longer, paths. This finding, in conjunction with those from a second study, challenges the accepted wisdom that apparent motion paths are independent of the object. Instead, our findings suggest that when given enough time and appropriate stimuli, the visual system prefers at least some object-appropriate apparent motion paths.

The rate of morphological evolution in mammals from the standpoint of the neutral expectation

Abstract: A comparison of the evolutionary rates of cranial morphology in mammals with the neutral expectation suggests that stabilizing selection is a predominant evolutionary force keeping the long-term diversification of lineages well below its potential. The rate of morphological divergence of almost all lineages, including the great apes, is substantially below the minimum neutral expectation. The divergence of the modern races of man is slightly above the minimum neutral rate but well below the maximum rate. Therefore, there is no need to invoke extraordinary mutational mechanisms, such as regulatory gene evolution, to explain what has been perceived as rapid morphological evolution in mammals. Nor does it appear that behavioral drive needs to be invoked to explain rapid morphological evolution in hominoids. Outside of man, the long-term rate of phenotypic evolution in the great apes is actually lower than that for other mammals. The data suggest that, immediately after reproductive isolation, most lineages d...

Enhanced protein thermostability from designed mutations that interact with alpha-helix dipoles.

Abstract: Two different genetically engineered amino-acid substitutions designed to interact with α-helix dipoles in T4 lysozyme are shown to increase the thermal stability of the protein. Crystallographic analyses of the mutant lysozyme structures suggest that the stabilization is due to electrostatic interaction and does not require precise hydrogen bonding between the substituted amino acid and the end of the α-helix.