Showing papers by "University of Massachusetts Amherst published in 1981"

Perceptual Structures and Distributed Motor Control

Abstract: The sections in this article are: 1 The Place of Brain Theory Within Cybernetics 2 Concepts from Computer Science and Control Theory 2.1 Programs Need Not Be Stereotypes 2.2 State and Feedback in Control Theory 2.3 Serial Order in Behavior Revisited 3 Visuomotor Coordination in Frog and Toad 3.1 Maps as Control Surfaces 3.2 A Model of Frog Snapping 3.3 The Many Visual Systems 3.4 Summary 4 Perceptual and Motor Schemas 4.1 Perceptual Schemas and the Action-Perception Cycle 4.2 Optic Flow and Control of Movement 4.3 Motor Schemas 4.4 Summary 5 Coordinated Control Programs 5.1 Feedforward 5.2 Interwoven Activation of Motor Schemas 5.3 Skill Acquisition 5.4 Summary 6 The Perspective of Artificial Intelligence 6.1 Programs and Planners 6.2 Program Synthesis and Visuomotor Coordination 6.3 Summary 7 Conclusion

Environmental Sex Determination: Interaction of Temperature and Genotype in a Fish

Abstract: Sex determination in an atherinid fish, the Atlantic silverside (Menidia menidia), is under the control of both genotype and temperature during a specific period of larval development. The sex ratios of the progeny of different females are variable and differ in their responsiveness to temperature. This demonstrates that sex ratio in fishes that normally have separate sexes can be influenced by the environment.

CLU: Reference Manual

Abstract: This document serves both as an introduction to CLU and as a language reference manual. Sections 1 through 4 present an overview of the language. These sections highlight the essential features of CLU, and discuss how CLU differs from other, more conventional, languages. Sections 5 though 13 form the reference manual proper. These sections describe each aspect of CLU in detail, and discuss the proper use of various features. Appendices 1 though III provide concise summaries of CLU''s syntax, data types, and I/O facilities. Appendix IV contains example programs.

Functionally Accurate, Cooperative Distributed Systems

Abstract: A new approach for structuring distributed processing systems, called functionally accurate, cooperative (FA/C), is proposed. The approach differs from conventional ones in its emphasis on handling distribution-caused uncertainty and errors as an integral part of the network problem-solving process. In this approach nodes cooperatively problem-solve by exchanging partial tentative results (at various levels of abstraction) within the context of common goals. The approach is especially suited to applications in which the data necessary to achieve a solution cannot be partitioned in such a way that a node can complete a task without seeing the intermediate state of task processing at other nodes. Much of the inspiration for the FA/C approach comes from the mechanisms used in knowledge-based artificial intelligence (Al) systems for resolving uncertainty caused by noisy input data and the use of approximate knowledge. The appropriateness of the FA/C approach is explored in three application domains: distributed interpretation, distributed network traffic-light control, and distributed planning. Additionally, the relationship between the approach and the structure of management organizations is developed. Finally, a number of current research directions necessary to more fully develop the FA/C approach are outlined. These research directions include distributed search, the integration of implicit and explicit forms of control, and distributed planning and organizational self-design.

Genetic diversity and temporal variation in the e. coli population of a human host

Abstract: Electrophoretic techniques were employed to study variation in chromosomal genes encoding enzymes and in the distribution of cryptic plasmids in the E. coli population of a human host over an 11-month period. Thirteen of the 15 enzymes studied were polymorphic, and mean genetic diversity per locus was 0.39. Among 550 clones isolated from fecal samples, protein electrophoresis revealed 53 distinct electrophoretic types (ETs). Most ETs appeared on only one or a few days and were considered transients, but two (ET-12 and ET-13) were observed many times over extended periods and represented residents. Complete turnover in the transient ETs in the population occurred in periods of from two weeks to a month. ETs appearing in one month showed no particular genetic similarity to those of the previous month. — All but 4 of the 53 ETs carried one or more "cryptic" plasmids with molecular weights ranging from 1 to 80 megadaltons. With few exceptions, the plasmid composition of each ET was unique. In the course of the 11-month sampling period, there were changes in the plasmid profiles of the resident strains ET-12 and ET-13, and also in the profile of a recurrent strain, ET-2, which was isolated on four days. Modification of the plasmid profile of ET-12 involved the sequential addition of relatively high molecular weight bands. For ET-2 and ET-13, the changes in the plasmid profiles were radical, suggesting invasions of new cell types rather than merely the addition and deletion of plasmids. — The results of this study provide three lines of evidence that recombination plays a minor role in the generation of genetic diversity in the E. coli population of a single host. (1) Several pairs of loci were in strong linkage disequilibrium; compared to a randomly generated array of genotypes, the sample of ETs contained an excess of pairs differing at one or two loci and too many pairs with highly distinctive combinations of electromorphs. (2) In most cases where pairs of ETs differed at a single locus and, therefore, could reasonably have been generated by phage- or plasmid-mobilized gene transfer, the plasmid profiles of the pair members were radically different and/or the potentially transmitted alleles were not present in other ETs in the population. (3) Although ET-12 was abundant, being represented by 252 of the 550 clones sampled, the electrophoretic type most similar to ET-12 different from it at six loci, and ET-12 carried two unique alleles. We conclude that most of the genetic diversity observed in this human host is a consequence of successive invasions of E. coli genotypes.

Lubricated Squeezing Flow: A New Biaxial Extensional Rheometer

Abstract: Squeezing flow between two disks with lubricated surfaces was found to generate a homogeneous compression or equal biaxial extension in a high viscosity polydimethylsiloxane sample The apparatus is extremely simple: two steel disks with a central rod to provide alignment and prevent sample slip, an LVDT to measure displacement, and a silicone oil bath The mass and area of the upper disk provide for a constant force boundary condition The biaxial viscosity was found to be approximately six times the shear viscosity over biaxial extension rates er from 0003 to 10 s−1 Lubrication could be achieved up to Hencky strains of about 25 Some data were also taken on the same polyisobutylene sample used by Stephenson and Meissner in their biaxial stretching study Agreement was very good

Periodic selection, infectious gene exchange and the genetic structure of e. coli populations

Abstract: As a consequence of sequential replacements by clones of higher fitness (periodic selection), bacterial populations would be continually purged of genetic variability, and the fate of selectively neutral alleles in very large populations of bacteria would be similar to that in demes of sexually reproducing organisms with small genetically effective population sizes. The significance of periodic selection in reducing genetic variability in these clonally reproducing species is dependent on the amount of genetic exchange between clones (recombination). In an effort to determine the relationship between the rates of periodic selection, recombination and the genetically effective sizes of bacterial populations, a model for periodic selection and infectious gene exchange has been developed and its properties analyzed. It shows that, for a given periodic selection regime, genetically effective population size increases exponentially with the rate of recombination.--With the parameters of this model in the range anticipated for natural populations of E. coli, the purging effects of periodic selection on genetic variability are significant; individual populations or lineages of this bacterial species would have very small genetically effective population sizes.--Based on this result, some other a priori considerations and a review of the results of epidemiological and genetic variability studies, it is postulated that E. coli is composed of a relatively limited number of geographically widespread and genetically nearly isolated and monomorphic lineages. The implications of these considerations of the genetic structure of E. coli populations on the interpretation of protein variation and the neutral gene hypothesis are discussed.

Perceptual equivalence of acoustic cues in speech and nonspeech perception

Abstract: Trading relations show that diverse acoustic consequences of minimal contrasts in speech are equivalent in perception of phonetic categories. This perceptual equivalence received stronger support from a recent finding that discrimination was differentially affected by the phonetic cooperation or conflict between two cues for the /slIt/-/splIt/contrast. Experiment 1 extended the trading relations and perceptual equivalence findings to the /sei/-/stei/contrast. With a more sensitive discrimination test, Experiment 2 found that cue equivalence is a characteristic of perceptual sensitivity to phonetic information. Using “sine-wave analogues” of the /sei/-/stei/stimuli, Experiment 3 showed that perceptual integration of the cues was phonetic, not psychoacoustic, in origin. Only subjects who perceived the sine-wave stimuli as “say” and “stay” showed a trading relation and perceptual equivalence; subjects who perceived them as nonspeech failed to integrate the two dimensions perceptually. Moreover, the pattern of differences between obtained and predicted discrimination was quite similar across the first two experiments and the “say”-“stay” group of Experiment 3, and suggested that phonetic perception was responsible even for better-than-predicted performance by these groups. Trading relations between speech cues, and the perceptual equivalence that underlies them, thus appear to derive specifically from perception of phonetic information.

Eye movement control during reading: Evidence for direct control

Abstract: In three experiments, subjects read text as their eye movements were monitored and display changes in the text were made contingent upon the eye movements. In one experiment, a window of text moved in synchrony with the eyes. In one condition, the size of the window was constant from fixation to fixation, while in the other condition the size of the window varied from fixation to fixation. In the other experiments, a visual mask was presented at the end of each saccade which delayed the onset of the text, and the length of the delay was varied. The pattern of eye movements was influenced by both the size of the window and the delay of the onset of the text, even when the window size or text delay was varying from fixation to fixation. However, there was also evidence that saccade length was affected by the size of the window on the prior fixation and that certain decisions to move the eye are programmed either before the fixation begins or are programmed during the fixation but without regard to the text ...

Xenon NMR: Chemical shifts of a general anesthetic in common solvents, proteins, and membranes

Abstract: The rare gas xenon contains two NMR-sensitive isotopes in high natural abundance. The nuclide 129Xe has a spin of 1/2: 131Xe is quadrupolar with a spin of 3/2. The complementary NMR characteristics of these nuclei provide a unique opportunity for probing their environment. The method is widely applicable because xenon interacts with a useful range of condensed phases including pure liquids, protein solutions, and suspensions of lipid and biological membranes. Although xenon is chemically inert, it does interact with living systems; it is an effective general anesthetic. We have found that the range of chemical shifts of 129Xe dissolved in common solvents is ca. 200 ppm, which is 30 times larger than that found for 13C in methane dissolved in various solvents. Resonances were also observed for 131Xe in some systems; they were broader and exhibited much greater relaxation rates than did 129Xe. The use of 129Xe NMR as a probe of biological systems was investigated. Spectra were obtained from solutions of myoglobin, from suspensions of various lipid bilayers, and from suspensions of the membranes of erythrocytes and of the acetylcholine receptor-rich membranes of Torpedo californica. These systems exhibited a smaller range of chemical shifts. In most cases there was evidence of a fast exchange of xenon between the aqueous and organic environments, but the exchange was slow in suspensions of dimyristoyl lecithin vesicles.

Associative search network: A reinforcement learning associative memory

Abstract: An associative memory system is presented which does not require a "teacher" to provide the desired associations. For each input key it conducts a search for the output pattern which optimizes an external payoff or reinforcement signal. The associative search network (ASN) combines pattern recognition and function optimization capabilities in a simple and effective way. We define the associative search problem, discuss conditions under which the associative search network is capable of solving it, and present results from computer simulations. The synthesis of sensory-motor control surfaces is discussed as an example of the associative search problem.

Concept or Computation: Students' Understanding of the Mean.

Abstract: In statistics, and in everyday life as well, the arithmetic mean is a frequently used average. The present study reports data from interviews in which students attempted to solve problems involving the appropriate weighting and combining of means into an overall mean. While mathematically unsophisticated college students can easily compute the mean of a group of numbers, our results indicate that a surprisingly large proportion of them do not understand the concept of the weighted mean. When asked to calculate the overall mean, most subjects answered with the simple, or unweighted, mean of the two means given in the problem, even though these two means were from different-sized groups of scores. For many subjects, computing the simple mean was not merely the easiest or most obvious way to initially attack the problem; it was the only method they had available. Most did not seem to consider why the simple mean might or might not be the correct response, nor did they have any feeling for what their results represented. For many students, dealing with the mean is a computational rather than a conceptual act. Knowledge of the mean seems to begin and end with an impoverished computational formula. The pedagogical message is clear: Learning a computational formula is a poor substitute for gaining an understanding of the basic underlying concept.

Human factors comparison of a procedural and a nonprocedural query language

Abstract: Two experiments testing the ability of subjects to write queries in two different query languages were run. The two languages, SQL and TABLET, differ primarily in their procedurality; both languages use the relational data model, and their Halstead levels are similar. Constructs in the languages which do not affect their procedurality are identical. The two languages were learned by the experimental subjects almost exclusively from manuals presenting the same examples and problems ordered identically for both languages. The results of the experiments show that subjects using the more procedural language wrote difficult queries better than subjects using the less procedural language. The results of the experiments are also used to compare corresponding constructs in the two languages and to recommend improvements for these constructs.

Liquid crystal polymers. IV. Thermotropic polyesters with flexible spacers in the main chain

Abstract: Two closely related series of polyesters that contain mesogenic units interconnected by flexible spacers along the main chain were prepared and characterized for their liquid crystal properties. All of these polymers showed theotropic behavior, which was examined by DSC, hot-stage microscopy on a polarizing microscope, small-angle light and wide-angle x-ray scattering methods, and visual observation of stir-opalescence of the polymer melts. The effect of the length of the flexible spacer and the nature of the substituent, which is on the central aromatic ring of the mesogenic unit, on the stability and molecular order of the mesophase for each of the polymers was investigated and the results are discussed on the basis of the thermodynamic data obtained.

Saccade size in reading depends upon character spaces and not visual angle

Abstract: Recently there has been a considerable amount of research involving the use of eye movements to study the reading process (Rayner, 1978). This trend is similar to another large-scale research effort undertaken a number of years ago that also dealt with eye movements and reading (Huey, 1908; Tinker, 1958, 1963; Woodworth, 1938). One difference between the earlier research and the more current work is that more sophisticated equipment is now used and display changes contingent upon the position of the eye can be made (McConkie & Rayner, 1975; O'Regan, 1980; Rayner, 1975). Much of the research using dynamic display changes has focused on perceptual aspects of the reading process. Despite this widespread activity, it is still the case that a rather elementary aspect concerning visual factors has not been adequately resolved. That is, it remains unclear as to whether saccades are executed to traverse a certain amount of visual angle or a certain number of letters. For example, eye movements in reading might average around 2 deg of visual angle (Rayner, 1978) because they serve the purpose of bringing text into foveal vision for detailed analysis. If saccades are determined by a critical visual angle, then when viewing distance is decreased (or if the letters are larger) and fewer characters fall within the fovea, the number of characters per saccade will decrease. On the other hand, larger letters or closer viewing distances might allow the letters to be perceived farther out in extrafoveal vision. Is so, readers might execute saccades of a greater visual angle in order to cover a desired number of characters. If either of these alternatives is correct, measures of saccade length in one metric (either visual angle or character spaces) will remain constant as letter size or viewing distance is altered (both change the size of the retinal image, hence the number of letters falling within the fovea), while measures in the other metric will change drastically as retinal image size changes. Huey (1908) and O'Regan (1980) have addressed

Landmark learning: An illustration of associative search

Abstract: In a previous paper we defined the associative search problem and presented a system capable of solving it under certain conditions. In this paper we interpret a spatial learning problem as an associative search task and describe the behavior of an adaptive network capable of solving it. This example shows how naturally the associative search problem can arise and permits the search, association, and generalization properties of the adaptive network to bee clearly illustrated.

Length-Dry Weight Relationships of Some Freshwater Zooplanktona

Abstract: Biomass of zooplankton can be estimated from the relation between length and weight by measuring the appropriate dimension of length on individual zooplankton Length-dry weight relationships for 15 species of freshwater crustacean zooplankton collected from the Connecticut River were determined Length-weight equations can be used to rapidly determine the biomass of zooplankton species when it is impractical to directly measure their weights

Patterns of Conflict Resolution and Marital Satisfaction

Abstract: an intensive survey of fertility decision-making, both Spouses in 244Northern California marriages responded to questions a bout the kinds of they encounter, their style of conflict resolution, the expected oftheir conflict, and their marital satisfaction. Four main \"tYPes\"0f resolution were found based on the 488 individual partnen' reports: (1) a nonintimaie-aggressivc pattern, (11) a nonintimatc-nonaggressivc one, ('11) an intimate-aggressive pattern, and (1V) an intimate-nonaggressive One. who perceived their marriage in Type 1 were generally least aatisficd. tlnd those in Type I V most satisfied, with Types I1 and 111 intermediate. The meaning of this typology and its correlates, as well as its wider implications. are discussed.

Three Studies of Deficits in Pantomimic Expression and Pantomimic Recognition in Aphasia

Abstract: Studies were conducted to investigate aphasic deficits in pantomimic behaviors. Three groups of subjects were used: 47 aphasics; 27 right-hemisphere-damaged; and 11 controls. Study I replicates a p...

Fish muscle lipolysis—a review

Abstract: Lipolysis occurs extensively in fish muscle post-mortem and is associated with quality deterioration in the frozen tissue. Fish muscle lipolysis is presented in the context of basic fish muscle physiology and lipid composition. Phospholipase A and lipases from fish muscle have been described and characterized. The reaction is usually followed by measurement of free fatty acid production, and several colorimetric assays are available. Processing and storage treatments have been shown to influence the extent and rate of lipolysis in fish muscle; most of the research in this area has been directed at the effects of frozen storage. The interaction of lipolysis and lipid oxidation is a particularly intriguing area of study as triglyceride hydrolysis leads to increased oxidation while phospholipid hydrolysis produces the opposite effect.