Showing papers by "University of California, Santa Barbara published in 1980"

Contrast masking in human vision

Abstract: Contrast masking was studied psychophysically. A two-alternative forced-choice procedure was used to measure contrast thresholds for 2.0 cpd sine-wave gratings in the presence of masking sine-wave gratings. Thresholds were measured for 11 masker contrasts spanning three log units, and seven masker frequencies ranging +/- one octave from the signal frequency. Corresponding measurements were made for gratings with horizontal widths of 0.75 degrees (narrow fields) and 6.0 degrees (wide fields). For high contrast maskers at all frequencies, signal thresholds were related to masking contrast by power functions with exponents near 0.6. For a range of low masking contrasts, signal thresholds were reduced by the masker. For the wide fields, high contrast masking tuning functions peaked at the signal frequency, were slightly asymmetric, and had approximately invariant half-maximum frequencies that lie 3/4 octave below and 1 octave above the signal frequency. The corresponding low contrast tuning functions exhibited peak threshold reduction at the signal frequency, with half-minimum frequencies at roughly +/- 0.25 octaves. For the narrow fields, the masking tuning functions were much broader at both low and high masking contrasts. A masking model is presented that encompasses contrast detection, discrimination, and masking phenomena. Central constructs of the model include a linear spatial frequency filter, a nonlinear transducer, and a process of spatial pooling that acts at low contrasts only.

Optimal behavior: can foragers balance two conflicting demands?

Abstract: According to much current theory, organisms should be able to balance the conflicting demands of the need to feed efficiently and the need to avoid preadtors while feeding. In an experimental conflict situation, it was possible to evaluate the relative fitnesses associated with the available choices and to compare the observed behaviors with predictions derived from fitness considerations. A backswimmer, Notonecta hoffmanni, was capable of balancing these two conflicting factors adaptively.

Inductive inference of formal languages from positive data

Abstract: We consider inductive inference of formal languages, as defined by Gold (1967) , in the case of positive data, i.e., when the examples of a given formal language are successive elements of some arbitrary enumeration of the elements of the language. We prove a theorem characterizing when an indexed family of nonempty recursive formal languages is inferrable from positive data. From this theorem we obtain other useful conditions for inference from positive data, and give several examples of their application. We give counterexamples to two variants of the characterizing condition, and investigate conditions for inference from positive data that avoids “overgeneralization.”

Isolation of a yeast centromere and construction of functional small circular chromosomes

Abstract: The centromeric DNA (CEN3) from yeast chromosome III has been isolated on a 1.6 kilobase-pair segment of DNA located near the centromere-linked CDC10 locus of Saccharomyces cerevisiae. When present on a plasmid carrying a yeast chromosomal replicator, CEN3 enables that plasmid to function as a chromosome both mitotically and meiotically. Minichromosomes containing CEN3 are stable in mitosis and segregate as ordinary yeast chromosomes in the first and second meiotic divisions.

East Pacific Rise: Hot Springs and Geophysical Experiments

Abstract: Hydrothermal vents jetting out water at 380° ± 30°C have been discovered on the axis of the East Pacific Rise. The hottest waters issue from mineralized chimneys and are blackened by sulfide precipitates. These hydrothermal springs are the sites of actively forming massive sulfide mineral deposits. Cooler springs are clear to milky and support exotic benthic communities of giant tube worms, clams, and crabs similar to those found at the Galapagos spreading center. Four prototype geophysical experiments were successfully conducted in and near the vent area: seismic refraction measurements with both source (thumper) and receivers on the sea floor, on-bottom gravity measurements, in situ magnetic gradiometer measurements from the submersible Alvin over a sea-floor magnetic reversal boundary, and an active electrical sounding experiment. These high-resolution determinations of crustal properties along the spreading center were made to gain knowledge of the source of new oceanic crust and marine magnetic anomalies, the nature of the axial magma chamber, and the depth of hydrothermal circulation.

The social uses of television

Abstract: Building from the social constructivist view, this paper provides evidence that audience members create specific and sometimes elaborate practical actions involving television in order to gratify particular needs in the context of family viewing. The ethnography of mass communication is recommended as a methodological framework suitable for discovering and documenting these behaviors. Based on findings from systematic participant observation research, and from the pertinent uses and gratifications literature, a typology of the social uses of television, with emphasis on their communicative value, is presented. Mass media are found to be valuable social resources, not unlike language or the occasions for talk, which are particularly useful to the imaginative social member for the construction and maintenance of desired relations at home.

Disc morphogenesis in vertebrate photoreceptors

Abstract: Electron microscopic examination of the bases of adult rod and cone outer segments (rhesus monkey, ground squirrel, and grey squirrel) has led to a new model of disc morphogenesis. In this model the disc surfaces and disc rims develop by separate mechanisms and from separate regions of the membrane of the inner face of the cilium. This membrane is alternately specified into regions that will form either the disc surfaces or the disc rims. The disc surfaces develop by an evagination or outpouching of the ciliary membrane. The two surfaces of an evagination, scleral and vitreal, each form one of the surfaces of adjacent discs. The disc rim is initially specified as a region of ciliary membrane between adjacent disc-surface evaginations. This region grows bilaterally around the circumferences of adjacent discs, zippering together the apposed surfaces to form the rim and completed disc. At the same time it seals the plasma-membrane edges of the evaginations, which have become detached from the surfaces. Incisures form in rod discs by infolding of the rim and surfaces together, and they begin to form before the rim is completed around the disc perimeter. When a number of new discs are developing simultaneously the ciliary membrane at the base of an outer segment consists of a stack of rim forming and surface forming growth points. This model provides, in addition, for the continuous renewal of outer-segment plasma membrane. It also establishes a developmental basis for the structural uniqueness of the disc rim. Finally, it indicates an evolutionary relationship between the discs of vertebrate visual cells and the membrane specializations of invertebrate visual cells.

Soliton dynamics in polyacetylene

Abstract: The equations of motion of the coupled electron-phonon system are integrated in real time for the model of polyacetylene recently proposed. To illustrate the physical behavior of this nonlinear system we consider the time evolution starting from three physically relevant configurations: (i) end generated soliton, (ii) electron-hole pair generation of a charged soliton-antisoliton pair, and (iii) the dressing of an injected electron. The calculations show that the system relaxes within a time of order 10-13 sec, converting excited electron-hole pairs into soliton-antisoliton pairs.

Geometric model for Neogene crustal rotations in southern California

Abstract: Paleomagnetic data from mainly Miocene igneous rocks in southern California suggest that large crustal regions have undergone clockwise rotation during that time. We propose a model whereby many crustal blocks presently bounded on the north and south by east-west—trending sinistral faults have undergone rotations of about 70° to 80° within the Pacific-American right-lateral shear couple. The data suggest that these crustal blocks include the western Transverse Ranges and parts of the offshore Borderland. Our model predicts that the eastern Transverse Ranges, the central Mojave Desert, and the Tehachapi Mountains region have also rotated. The rotated blocks are nested between blocks bounded by northwest-southeast—trending dextral faults. The rotations probably ceased in late Miocene time when the San Andreas fault system broke through southern California and may have begun when the Pacific plate contacted the North American plate in late Oligocene time. This geometric model for rotated blocks predicts that left-slip, right-slip, and rotation occur simultaneously; that the displacements can be calculated from the rotation (and vice versa); and that during the rotation, deep triangular basins open at the join between the rotated and unrotated blocks. It also suggests that dextral slip can occur on northwest-southeast faults without cutting the Transverse Ranges.

Topological excitations and Monte Carlo simulation of Abelian gauge theory

Abstract: We study the phase structure of lattice electrodynamics in three and four dimensions using Monte Carlo simulation, with special emphasis on the topological excitations of the theory. We formulate an operational definition of a monopole and measure the density of monopoles as a function of coupling constant. In three dimensions and for strong coupling in four dimensions monopoles screen external magnetic fields. Below a critical coupling in four dimensions the external field penetrates into the bulk of the medium; this long-range correlation essentially shows that the lattice theory in weak coupling is characterized by a massless photon.

Effect of boundary layer transport on the fixation of carbon by the giant kelp Macrocystis pyrifera

Abstract: The uptake of inorganic carbon into the thallus of Macrocystis pyrifera (L.) C. Ag. requires first that the inorganic carbon pass through the water medium to the plant surface. This transfer of inorganic carbon to the thallus must take place through a boundary layer. Experiments in water tunnels indicate that the boundary layer adjacent to the M. pyrifera blade may be turbulent in water speeds as low as 1 cm sec-1. Photosynthetic output of the blade can be increased by a factor of 300% by increasing water speeds over the blade surface from 0 to 4 cm sec-1. This is consistent with a decrease in the thickness of the boundary layer. Above 4 cm sec-1, the assimilation of carbon was limiting. The assimilation of carbon is generally known to follow Michaelis-Menten-like kinetics. Combining the two uptake steps into an overall model of carbon uptake agrees well with photosynthetic data obtained from M. pyrifera under varying conditions of water speed and bicarbonate concentrations in the laboratory. The ecological and morphological consequences of these findings are discussed.

Directed percolation and Reggeon field theory

Abstract: Directed bond percolation is shown to be in the same universality class as Reggeon field theory. The critical behaviour and critical exponents near the percolation threshold are thereby inferred.

Motivating autistic children through stimulus variation.

Abstract: This study evaluated the differential effectiveness of two methods of presenting discrimination tasks when teaching autistic children. In a constant task condition, the common method of presenting a single task throughout a session was used. In a varied task condition, the same task was interspersed with a variety of other tasks from the children's clinic curricula. Results showed declining trends in correct responding during the constant task condition, with substantially improved and stable responding during the varied task conditions. In addition, naive observers judged the children to be more enthusiastic, interested, happier, and better behaved during the varied task sessions. These results suggest that "boredom" may be a particularly important variable to control in the treatment of autistic children, and that particular care may be necessary when defining criteria for task acquisition. The results are discussed in relation to the literature on increased responsivity to stimulus novelty and variation.

The responses of a community to disturbance: The importance of successional age and species' life histories.

Abstract: The responses of different successional stages of a temperate intertidal algal community to disturbance were investigated with a field experiment. The experiment was conducted in a low intertidal boulder field in southern California. In this habitat, the top surfaces of boulders are covered with algae. The composition of the assemblage on any particular boulder depends on the length of time since it was last overturned by wave action. When a boulder is overturned, the algae on what was formerly the top surface, are killed in whole or part by a combination of sea urchin grazing, anoxia, light levels below compensation intensity, and mechanical damage caused by crushing or abrasion. The length of time that a boulder remains overturned and the local abundance of sea urchins determines the intensity of the disturbance. When the boulder is righted, recolonization begins either by vegetative regrowth of survivors and/or by spores from outside.

A clear-sky spectral solar radiation model for snow-covered mountainous terrain

Abstract: A clear-sky spectral solar radiation model for direct and diffuse fluxes, combined with topographic calculations from digital terrain data, computes either incident, net, or reflected solar radiation at any point on a snow surface in mountainous terrain. The radiation may be integrated over any wavelength range from 250 to 5000 nm, or over any time step. Atmospheric attenuation parameters are ozone, water vapor, the Angstrom turbidity coefficient and exponent, and the absorptance to reflectance ratio of the atmospheric aerosols. The model derives these, from measurements which may contain both systematic and random errors, by finding the least squares solution to an overdetermined set of nonlinear equations. For calculations over a specified area, it employs table look-up procedures, so that computation speed for the spectral model approaches that for a lumped model. Thus it may be useful as part of a snow surface energy budget calculation over a drainage basin.

Population Density and the Economics of Territorial Defense in a Coral Reef Fish

Abstract: We propose that in some species, local population density can strongly affect the economic defendability of a mating territory. This is so because the numbers of females and potentially interfering males determine allocations of time and energy to reproduction and defense. At low densities, allocations to defense should be small and territorial mating success should initially rise with local density, reflecting the supply of females. If defense takes priority over mating, higher population densities can create a situation in which the time or energy devoted to defense against other males detracts from allocations to reproduction. Thus a point is reached where territorial mating success declines with increasing density, as a function of the number of nonterritorial males. We investigated these hypotheses by recording changes in the daily mating success of territorial males of the bluehead wrasse (Thalassoma bifasciatum) following experimental manipulations of local population size and composition. On large reefs, where mating population densities are already high, territorial mating success varied inversely with changes in overall population density and with changes in nonterritorial male numbers only; changes in female numbers had little effect. Thus at higher densities the demands of defense appear to be more important in determining mating success than the supply of available mates. Territorial mating success varied directly with population density changes only on the smallest experimental reef, where there were few nonterritorial males. The reduction of mating success at higher densities was correlated with a decrease in both the time spent in courtship and the efficiency of courtship itself. The effect of population density should be partic- ularly important in species with short breeding periods and where the male contributes relatively little time or energy to each mating.

Competitive interactions between california reef fishes of the genus embiotoca

Abstract: Embiotoca lateralis and E. jacksoni are very similar morphologically and exhibit the greatest dietary overlap within a guild of microcarnivorous subtidal reef fishes off Santa Barbara, California. Within this zone of sympatry, they segregate by depth: E. lateralis numerically dominates shallow reef areas covered by various algae, from which it picks its prey; E jacksoni dominates and forages over deeper areas covered by a relatively food-poor "turf" of sessile invertebrates and small algae. E. lateralis rarely fed from turf-covered substrates experimentally translocated from deep water, while E. jacksoni frequently fed from translocated shallow algae. In allopatry, however, each species occupies all reef depths and commonly forages over both food substrates. When E. lateralis was experimentally removed from a reef inhabited by both species, E. jacksoni entered shallow areas and foraged over algae. However, removing E. jacksoni from another reef did not affect the distribution of E. lateralis. E. lateralis aggressively dominated E. jacksoni, and E. jacksoni avoided foraging near E. lateralis. E. lateralis eventually entered and foraged over deep reef areas only when all shallow algae and E. jacksoni were removed. Sympatric population densities of E. lateralis, here at the southern margin of its geographical range, are much lower than those of allopatric populations elsewhere. Hence, shallow food sources may be sufficiently abundant that marginal E. lateralis populations occupy only this richest end of the bathymetric reef food gradient. This situation may provide a competitive refuge for E. jacksoni in less productive deep reef areas, thus maintaining the coexistence of these species within the same habitat.

The belief-bias effect in formal reasoning: the influence of knowledge on logic.

Abstract: The present study examines the applicability of a rational model of categorical inference (e.g., Revlis, 1975b) to account for the apparently irrational decisions students reach on categorical syllogisms. In Experiment 1, students judged the logical validity of emotionally neutral conclusions to controversial premises. Of the reasoners’ decisions, 80% can be accounted for by the application of rational rules to their idiosyncratic encoding of the syllogistic premises. In Experiment 2, students were asked to solve syllogisms whose conclusions varied in truth value. When asked to reason about controversial, if not emotional, material, students do not suspend rational choice, but rather, their decisions are judicious ones, flowing logically from their idiosyncratic understanding of the materials reasoned about. When errors do occur, they result from an interrupt to rational processes and reflect conflict between competing goals rather than a switch to irrational decision processes.

Patterns of growth, energy utilization and reproduction in some meso- and bathypelagic fishes off Southern California

Abstract: We have studied growth, energy use and reproduction in 4 mesopelagic fishes and 5 bathypelagic fishes living off Southern California (USA). All of the mesopelagic species underwent diurnal vertical migrations, while none of the bathypelagic species did so. The life histories of these pelagic fishes were compared among themselves and with epipelagic sardines and anchovies studied by others. The epipelagic species had the highest growth rates (estimated from otoliths, expressed in standard length or kilocalories), the mesopelagic species had the lowest growth rates and the bathypelagic species had intermediate growth rates. The relatively rapid growth rates of the bathypelagic fishes were achieved by high relative growth efficiencies made possible by low metabolic rates. Of the species studied, the lifespans of the epipelagic and bathypelagic species ranged from 4 to 8 yr and the lifespans of mesopelagic species from 5 to 8 yr. Data on egg diameters suggest that the mesopelagic species first reproduce in their 3rd yr, while the bathypelagic species do so in their last year. Epipelagic fishes generally have a large size, rapid growth, long life and early, repeated reproduction. Mesopelagic fishes are characterized by small size, slow growth, long life and early, repeated reproduction. Bathypelagic fishes generally have large size, rapid growth, somewhat shorter lives and late reproduction, which is possible a single event. The latter pattern is evidently feasible only in a rather stable environment where juvenile survivorship would always display relatively low variability. Many unusual characteristics of deep-living animals have possibly been selected by factors peculiar to the environment; however, such characteristics are just as likely to have been selected by factors equally present in many other environments, but not expressed there due to masking selective forces. In particular, we have in mind the darkness, stability and homogeneity of the bathypelagic realm as phenomena which represent the effective absence of many selective forces.