Showing papers by "Boston University published in 1988"

Status quo bias in decision making

Abstract: Most real decisions, unlike those of economics texts, have a status quo alternative—that is, doing nothing or maintaining one's current or previous decision. A series of decision-making experiments shows that individuals disproportionately stick with the status quo. Data on the selections of health plans and retirement programs by faculty members reveal that the status quo bias is substantial in important real decisions. Economics, psychology, and decision theory provide possible explanations for this bias. Applications are discussed ranging from marketing techniques, to industrial organization, to the advance of science.

Anxiety and Its Disorders: The Nature and Treatment of Anxiety and Panic

Abstract: 1. The Experience of Anxiety: Shadow of Intelligence or Specter of Death? 2. Fear, Anxiety, and Theories of Emotion 3. The Nature of Anxious Apprehension 4. The Phenomenon of Panic 5. Provoking Panic in the Laboratory 6. Biological Aspects of Anxiety and Panic 7. True Alarms, False Alarms, and Learned (Conditioned) Anxiety: The Origins of Panic and Phobia 8. The Origins of Anxious Apprehension, Anxiety Disorders, and Related Emotional Disorders: Triple Vulnerabilities 9. Classification of Anxiety Disorders Timothy A. Brown, David H. Barlow 10. Panic Disorder Kamila S. White, David H. Barlow 11. Specific Phobias Martin M. Antony, David H. Barlow 12. Posttraumatic Stress Disorder Terence M. Keane, David H. Barlow 13. Social Phobia (Social Anxiety Disorder) Stefan G. Hofmann, David H. Barlow 14. Generalized Anxiety Disorder Lizabeth Roemer, Susan M. Orsillo, David H. Barlow 15. Obsessive-Compulsive Disorder Gail Steketee, David H. Barlow

Influence of season and latitude on the cutaneous synthesis of vitamin D3: exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin.

Abstract: Sunlight has long been recognized as a major provider of vitamin D for humans; radiation in the UVB (290-315 nm) portion of the solar spectrum photolyzes 7-dehydrocholesterol in the skin to previtamin D3, which, in turn, is converted by a thermal process to vitamin D3. Latitude and season affect both the quantity and quality of solar radiation reaching the earth's surface, especially in the UVB region of the spectrum, but little is known about how these influence the ability of sunlight to synthesize vitamin D3 in skin. A model has been developed to evaluate the effect of seasonal and latitudinal changes on the potential of sunlight to initiate cutaneous production of vitamin D3. Human skin or [3 alpha-3H]7-dehydrocholesterol exposed to sunlight on cloudless days in Boston (42.2 degrees N) from November through February produced no previtamin D3. In Edmonton (52 degrees N) this ineffective winter period extended from October through March. Further south (34 degrees N and 18 degrees N), sunlight effectively photoconverted 7-dehydrocholesterol to previtamin D3 in the middle of winter. These results quantify the dramatic influence of changes in solar UVB radiation on cutaneous vitamin D3 synthesis and indicate the latitudinal increase in the length of the "vitamin D winter" during which dietary supplementation of the vitamin may be advisable.

The ART of adaptive pattern recognition by a self-organizing neural network

Abstract: The adaptive resonance theory (ART) suggests a solution to the stability-plasticity dilemma facing designers of learning systems, namely how to design a learning system that will remain plastic, or adaptive, in response to significant events and yet remain stable in response to irrelevant events. ART architectures are discussed that are neural networks that self-organize stable recognition codes in real time in response to arbitrary sequences of input patterns. Within such an ART architecture, the process of adaptive pattern recognition is a special case of the more general cognitive process of hypothesis discovery, testing, search, classification, and learning. This property opens up the possibility of applying ART systems to more general problems of adaptively processing large abstract information sources and databases. The main computational properties of these ART architectures are outlined and contrasted with those of alternative learning and recognition systems. >

How does the brain build a cognitive code

Abstract: This article provides a self-contained introduction to my work from a recent perspective. A thought experiment is offered which analyses how a system as a whole can correct errors of hypothesis testing in a fluctuating environment when none of the system’s components, taken in isolation, even knows that an error has occurred. This theme is of general philosophical interest: How can intelligence or knowledge be ascribed to a system as a whole but not to its parts? How can an organism’s adaptive mechanisms be stable enough to resist environmental fluctuations which do not alter its behavioral success, but plastic enough to rapidly change in response to environmental demands that do alter its behavioral success? To answer such questions, we must identify the functional level on which a system’s behavioral success is defined.

Factors associated with osteoarthritis of the knee in the first national health and nutrition examination survey (hanes i) evidence for an association with overweight, race, and physical demands of work

Abstract: The authors used data from the United States first national Health and Nutrition Examination Survey of 1971-1975 (HANES I) to explore the cross-sectional associations between radiographic osteoarthritis of the knee and a variety of putative risk factors. A total of 5,193 black and white study participants aged 35-74 years, 315 of whom had x-ray-diagnosed osteoarthritis of the knee, were available for analysis. After controlling for confounders, the authors found significant associations of knee osteoarthritis with overweight, race, and occupation, all of which have been suggested by smaller cross-sectional studies. They then focused specifically on those factors. For overweight, they found a strong association between current obesity and osteoarthritis of the knee, with a dose-response effect not previously assessed. This association was also seen for self-reported minimum adult weight, a proxy for long-term obesity, and was present in persons with asymptomatic osteoarthritis of the knee. These findings strongly suggest that obesity is causative. HANES I was the first study in which racial differences in osteoarthritis of the knee could be assessed within the same country. The black women who were studied had an increased risk of disease (odds ratio (OR) = 2.12, 95% confidence interval (CI) = 1.39-3.23) after controlling for age and weight, although the black men did not. Finally, the authors used the US Department of Labor Dictionary of Occupational Titles to obtain characterizations of the physical demands and knee-bending stress associated with occupations and to study the relation between physical demands of jobs and osteoarthritis of the knee. They found for persons aged 55-64 years an association between knee-bending demands and osteoarthritis of the knee (men, OR = 2.45, 95% CI = 1.21-4.97; women, OR = 3.49, 95% CI = 1.22-10.52). Since such occupational physical demands are common, the authors conclude that they may be associated with a substantial proportion of osteoarthritis of the knee.

Art 2: Self-Organization Of Stable Category Recognition Codes For Analog Input Patterns

Abstract: Adaptive resonance architectures are neural networks that self-organize stable pattern recognition codes in real-time in response to arbitrary sequences of input patterns. This article introduces ART 2, a class of adaptive resonance architectures which rapidly self-organize pattern recognition categories in response to arbitrary sequences of either analog of binary input patterns. In order to cope with arbitrary sequences of analog input patterns, ART 2 architectures embody solutions to a number of design principles, such as the stability-plasticity tradeoff, the search-direct access tradeoff, and the match-reset tradeoff. In these architectures, top-down learned expectation and matching mechanisms are critical in self-stabilizing the code learning process. A parallel search scheme updates itself adaptively as the learning process unfolds, and realizes a form of real-time hypothesis discovery, testing, learning, and recognition. After learning self-stabilizes, the search process is automatically disengaged. Thereafter input patterns directly access their recognition codes without any search. Thus recognition time for familiar inputs does not increase with the complexity of the learned code. A novel input pattern can directly access a category if it shares invariant properties with the set of familiar exemplars of that category. A parameter called the attentional vigilance parameter determines how fine the categories will be. If vigilance increases (decreases) due to environmental feedback, then the system automatically searches for and learns finer (coarser) recognition categories. Gain control parameters enable the architecture to suppress noise up to a prescribed level. The architecture's global design enables it to learn effectively despite the high degree of nonlinearity of such mechanisms.

Managing Two Fits of Strategic Human Resource Management

Abstract: A model for developing and implementing human resource management strategies incorporating both an external fit (human resource management fits the developmental stage of the organization) and an internal fit (the components of human resource management complement and support each other) is proposed. Human resource management is seen as having five developmental stages and six strategic components. These are combined to form the Human Resource Strategic Matrix. The implications of these ideas for research and practice are discussed.

Neural dynamics of planned arm movements: emergent invariants and speed-accuracy properties during trajectory formation

Abstract: A real-time neural network model, called the vector-integration-to-endpoint (VITE) model is developed and used to simulate quantitatively behavioral and neural data about planned and passive arm movements. Invariants o farm movements emerge through network interactions rather than through an explicitly precomputed trajectory. Motor planning occurs in the form of a target position command (TPC), which specifies where the arm intends to move, and an independently controlled GO command, which specifies the movement's overall speed. Automatic processes convert this information into an arm trajectory with invariant properties. These automatic processes include computation of a present position command (PPC) and a difference vector (DV). The DV is the difference between the PPC and the TPC at any time. The PPC is gradually updated by integrating the DV through time. The GO signal multiplies the DV before it is integrated by the PPC. The PPC generates an outflow movement command to its target muscle groups. Opponent interactions regulate the PPCs to agonist and antagonist muscle groups. This system generates synchronous movements across synergetic muscles by automatically compensating for the different total contractions that each muscle group must undergo. Quantitative simulations are provided of Woodworth's law, of the speed-accuracy trade-offknown as Fitts's law, of isotonic arm-movement properties before and after deafferentation, of synchronous and compensatory "central-error-correction" properties of isometric contractions, of velocity amplification during target switching, of velocity profile invariance and asymmetry, of the changes in velocity profile asymmetry at higher movement speeds, of the automarie compensation for staggered onset times of synergetic muscles, of vector cell properties in precentral motor cortex, of the inverse relation between movement duration and peak velocity, and of peak acceleration as a function of movement amplitude and duration. It is shown that TPC, PPC, and DV computations are needed to actively modulate, or gate, the learning of associative maps between TPCs of different modalities, such as between the eye-head system and the hand-arm system. By using such an associative map, looking at an object can activate a TPC of the hand-arm system, as Piaget noted. Then a VITE circuit can translate this TPC into an invariant movement trajectory. An auxiliary circuit, called the Passive Update of Position (PUP) model is described for using inflow signals to update the PPC during passive arm movements owing to external forces. Other uses of outflow and inflow signals are also noted, such as for adaptive linearization of a nonlinear muscle plant, and sequential readout of TPCs during a serial plan, as in reaching and grasping. Comparisons are made with other models of motor control, such as the mass-spring and minimumjerk models.

Neural Networks and Natural Intelligence

Abstract: From the Publisher: Stephen Grossberg and his colleagues at Boston University's Center for Adaptive Systems are producing some of the most exciting research in the neural network approach to making computers "think." Packed with real-time computer simulations and rigorous demonstrations of these phenomena, this book includes results on vision, speech, cognitive information processing; adaptive pattern recognition, adaptive robotics, conditioning and attention, cognitive-emotional interactions, and decision making under risk.

Insulin-regulatable tissues express a unique insulin-sensitive glucose transport protein.

Abstract: At least three different glucose transport systems exist in mammalian cells. These are: (1) the constitutively active, facilitative carrier characteristic of human erythrocytes, Hep G2 (ref. 2) cells and rat brain; (2) the Na-dependent active transporter of kidney and small intestine; and (3) the facilitative carrier of rat liver (B. Thorens and H. F. Lodish, personal communication). A fourth possible glucose transport system is the insulin-dependent carrier that may be specific to muscle and adipose tissue. This transporter resides primarily in an intracellular compartment in resting cells from where it translocates to the cell surface upon cellular insulin exposure. This raises the question of whether hormonal regulation of glucose transport is conferred by virtue of a tissue-specific signalling mechanism or a tissue-specific glucose transporter. Here we present data supporting the latter concept based upon a monoclonal antibody against the fat cell glucose transporter that identifies a unique, insulin-regulatable glucose transport protein in muscle and adipose tissue.

Epidemiology of hip and knee osteoarthritis.

Abstract: This review has focused on the prevalence and risk factors associated with knee and hip osteoarthritis. Risk factors for knee osteoarthritis are obesity and major injury, and knee osteoarthritis probably fits into the generalized osteoarthritis diathesis. Repetitive use, such as in jobs requiring heavy labor and knee bending, probably increases the risk of knee osteoarthritis. Hip osteoarthritis is probably frequently secondary to developmental defects. As Rothman (182) has pointed out in discussing causation, this does not necessarily mean that the same factors do not also contribute to causing hip osteoarthritis. Yet, it appears that, in many cases, developmental defects are severe enough to be sufficient causes of hip osteoarthritis. To delineate other causes, it may be necessary to examine risk factors separately in those with and in those without developmental disease. Although large epidemiologic studies are best able to identify the relative contributions of specific risk factors while controlling for other risk factors, new studies need to focus on important unresolved questions. First, longitudinal studies with comprehensive follow-up using repeated radiographic assessments are needed to identify factors that cause development of disease or the onset of symptoms. Second, cohorts with early and possibly asymptomatic disease need to be followed to determine the causes of progression or regression of disease and the natural history of disease. Such cohorts may include those at high risk of injury such as sports enthusiasts or manual laborers.

Glottal airflow and transglottal air pressure measurements for male and female speakers in soft, normal, and loud voice

Abstract: Measurements on the inverse filtered airflow waveform (the "glottal waveform") and of estimated average transglottal pressure and glottal airflow were made from noninvasive recordings of productions of syllable sequences in soft, normal, and loud voice for 25 male and 20 female speakers. Statistical analyses showed that with change from normal to loud voice, both males and females produced loud voice with increased pressure, accompanied by increased ac flow and increased maximum airflow declination rate. With change from normal voice, soft voice was produced with decreased pressure, ac flow and maximum airflow declination rate, and increased dc and average flow. Within the loudness conditions, there was no significant male-female difference in air pressure. Several glottal waveform parameters separated males and females in normal and loud voice. The data indicate higher ac flow and higher maximum airflow declination rate for males. In soft voice, the male and female glottal waveforms were more alike, and there was no significant difference in maximum airflow declination rate. The dc flow did not differ significantly between males and females. Possible relevance to biomechanical differences and differences in voice source characteristics between males and females and across loudness conditions is discussed.

Business Cycles and the Exchange Rate System: Some International Evidence

Abstract: This paper investigates empirically the differences in time?series behavior of key economic aggregates under alternative exchange rate systems. We use a postwar sample of 49 countries to compare the behavior of output. consumption, trade flows, government consumption spending, and real exchange rates under alternative exchange rate systems (pegged, floating, and systems such as the EMS). We then examine evidence from two particular episodes, involving Canada and Ireland, of changes in the exchange rate system. Aside from greater variability of real exchange rates under flexible than under pegged nominal exchange rate systems, we find little evidence of systematic differences in the behavior of other macroeconomic aggregates or international trade flows under alternative exchange rate systems. These results are of interest because a large class of theoretical models implies that the nominal exchange rate system has important effects on a number of macroeconomic quantities.

Multifractal phenomena in physics and chemistry

Abstract: The neologism 'multifractal phenomena' describes the concept that different regions of an object have different fractal properties. Multifractal scaling provides a quantitative description of a broad range of heterogeneous phenomena.

Cell-cell and cell-matrix interactions differentially regulate the expression of hepatic and cytoskeletal genes in primary cultures of rat hepatocytes.

Abstract: Freshly isolated adult rat hepatocytes exhibit a flat, extended morphology when cultured on dried rat tail collagen in the presence of growth factors; they actively synthesize DNA and express high levels of cytoskeletal mRNAs and proteins (actin, tubulin, cytokeratins, vinculin, alpha-actinin, and desmoplakin), while exhibiting low levels of liver-specific mRNAs (albumin, alpha 1-inhibitor III, and alpha 1-antitrypsin) and limited synthesis and secretion of albumin. Hepatocytes cultured on hydrated gel matrix from the Engelbreth-Holm-Swarm (EHS) mouse tumor form small spherical aggregates and exhibit low DNA, cytoskeletal mRNA, and protein synthesis, while at the same time exhibiting elevated liver-specific mRNAs and albumin production; these cells, therefore, more nearly conform to the program of gene expression seen within the normal animal. Hepatocytes on hydrated rat tail collagen resemble those on dry collagen when cultured at low density, but at high density they form compact trabecular aggregates, synthesize negligible amounts of DNA, and maintain a pattern of gene expression resembling that of hepatocytes seeded on the EHS matrix. If cell morphology is compact, as on EHS or on hydrated rat tail collagen when densely populated, DNA synthesis and expression of cytoskeletal genes are low, while liver-specific mRNAs are abundant. When cells are extended the opposite is the case. Without the growth supplement DNA synthesis is low throughout but gene expression is little affected. These studies point to the importance of cell-cell and cell-matrix interactions in determining the differentiated phenotype of hepatocytes, and they reveal an inverse relationship between cytoskeletal and liver-specific protein expression.

The new corporate strategy

Abstract: STRATEGY FORMULATION: Structure of Business Decision A Model for Strategic Decision Objectives A Practical System of Objectives Synergy and Capability Profiles Concept of Strategy Diversification and Internationalization Competitive Analysis Choice of Portfolio Uses of Strategy GENERAL MANAGEMENT CAPABILITY: The Need for Entrepreneurial Capability Diagnosing General Management Capability Planning Strategic Positive Transformation Assuring Coexistence of Competitive and Entrepreneurial Activities Resistance to Change Four Approaches to Managing Discontinuous Change The Accordian Method of Managing Change Overview of Strategic Behavior.

Association fiber pathways to the frontal cortex from the superior temporal region in the rhesus monkey.

Abstract: The projections to the frontal cortex that originate from the various areas of the superior temporal region of the rhesus monkey were investigated with the autoradiographic technique. The results demonstrated that the rostral part of the superior temporal gyrus (areas Pro, Ts1, and Ts2) projects to the proisocortical areas of the orbital and medial frontal cortex, as well as to the nearby orbital areas 13, 12, and 11, and to medial areas 9, 10, and 14. These fibers travel to the frontal lobe as part of the uncinate fascicle. The middle part of the superior temporal gyrus (areas Ts3 and paAlt) projects predominantly to the lateral frontal cortex (areas 12, upper 46, and 9) and to the dorsal aspect of the medial frontal lobe (areas 9 and 10). Only a small number of these fibers terminated within the orbitofrontal cortex. The temporofrontal fibers originating from the middle part of the superior temporal gyrus occupy the lower portion of the extreme capsule and lie just dorsal to the fibers of the uncinate fascicle. The posterior part of the superior temporal gyrus projects to the lateral frontal cortex (area 46, dorsal area 8, and the rostralmost part of dorsal area 6). Some of the fibers from the posterior superior temporal gyrus run initially through the extreme capsule and then cross the claustrum as they ascend to enter the external capsule before continuing their course to the frontal lobe. A larger group of fibers curves round the caudalmost Sylvian fissure and travels to the frontal cortex occupying a position just above and medial to the upper branch of the circular sulcus. This latter pathway constitutes a part of the classically described arcuate fasciculus.

Anatomic organization of basoventral and mediodorsal visual recipient prefrontal regions in the rhesus monkey.

Abstract: The sources of ipsilateral cortical afferent projections to basoventral and mediodorsal prefrontal cortices that receive some visual input were studied with retrograde tracers (horseradish peroxidase or fluorescent dyes) in eight rhesus monkeys. The basoventral regions injected with tracers included basal (orbital) areas 11 and 12, lateral area 12, and ventral area 46. The mediodorsal regions included portions of medial area 32 and the caudal part of dorsal area 8. These sites represent areas within basoventral and mediodorsal prefrontal cortices that show a gradual increase in architectonic differentiation in a direction from the least differentiated orbital and medial limbic cortices toward the most differentiated cortices in the arcuate concavity. The results showed that the visual input to basoventral and mediodorsal prefrontal cortices originated largely in topographically distinct visual areas. Thus, basoventral sites received most of their visual cortical projections from the inferior temporal cortex. The rostral inferior temporal region was the predominant source of visual projections to orbital prefrontal sites, whereas lateral area 12 and ventral area 46 also received projections which were found more caudally. In contrast, mediodorsal prefrontal sites received most of their visual projections from dorsolateral and dorsomedial visual areas. The cells of origin were located in rostromedial visual cortices after injection of retrograde tracers in area 32 and in more caudal medial and dorsolateral visual areas after injection in caudal area 8. The latter also received substantial projections from visuomotor regions in the caudal portion of the lateral bank of the intraparietal sulcus. These results suggest that the basoventral prefrontal cortices are connected with ventral visual areas implicated in pattern recognition and discrimination, whereas the mediodorsal cortices are connected with medial and dorsolateral occipital and parietal areas associated with visuospatial functions. In addition, the prefrontal areas studied received projections from auditory and/or somatosensory cortices, from areas associated with more than one modality, and from limbic regions. Orbital area 12 seemed to be a major target of projections from somatosensory cortices and the rostral portion of medial area 32 received substantial projections from auditory cortices. The least architectonically differentiated areas (orbital area 11 and medial area 32) had more widespread corticocortical connections, including strong links with limbic cortices. In contrast, areas which showed the highest degree of architectonic differentiation within the basoventral (area 46) and the mediodorsal (area 8) prefrontal cortices had restricted corticocortical connections.

Vibrational spectroscopy of bacteriorhodopsin mutants: light-driven proton transport involves protonation changes of aspartic acid residues 85, 96, and 212

Abstract: Fourier transform infrared (FTIR) difference spectra have been obtained for the bR----K, bR----L, and bR----M photoreactions in bacteriorhodopsin mutants in which Asp residues 85, 96, 115, and 212 have been replaced by Asn and by Glu. Difference peaks that had previously been attributed to Asp COOH groups on the basis of isotopic labeling were absent or shifted in these mutants. In general, each COOH peak was affected strongly by mutation at only one of the four residues. Thus, it was possible to assign each peak tentatively to a particular Asp. From these assignments, a model for the proton-pumping mechanism of bR is derived, which features proton transfers among Asp-85, -96, and -212, the chromophore Schiff base, and other ionizable groups within the protein. The model can explain the observed COOH peaks in the FTIR difference spectra of bR photointermediates and could also account for other recent results on site-directed mutants of bR.

The irritable bowel syndrome and food hypersensitivity.

Abstract: We have studied 262 patients suffering from hay fever and oral allergy syndrome after fruit and vegetable ingestion. The history and the results of RAST and skin test for pollen showed a contemporary presence of systemic and local symptoms in most of the patients; a close connection between age of onset of hay fever and oral allergy syndrome; a frequent association between allergy to some pollens and some vegetables, such as between apple, carrot, pear, cherry with birch pollen and tomato, melon, watermelon with grass pollen.

Ionization and phase behavior of fatty acids in water: application of the Gibbs phase rule

Abstract: The phase behavior of several medium-chain (10- and 12-carbon) and long-chain (18-carbon) fatty acids in water was examined as a function of the ionization state of the carboxyl group. Equilibrium titration curves were generated above and below fatty acid and acid-soap chain melting temperatures and critical micelle concentrations, and the phases formed were characterized by X-ray diffraction, 13C NMR spectroscopy, and phase-contrast and polarized light microscopy. The resulting titration curves were divided into five regions: (i) at pH values less than 7, a two-phase region containing oil or fatty acid crystals and an aqueous phase; (ii) at pH approximately 7, a three-phase region containing oil, lamellar, and aqueous (or fatty acid crystals, 1:1 acid-soap crystals, and aqueous) phases; (iii) between pH 7 and 9, a two-phase region containing a lamellar fatty acid/soap (or crystalline 1:1 acid-soap) phase in an aqueous phase; (iv) at pH approximately 9, a three-phase region containing lamellar fatty acid-soap (or crystalline 1:1 acid-soap), micellar, and aqueous phases; and (v) at pH values greater than 9, a two-phase region containing micellar and aqueous phases. Interpretation of the results using the Gibbs phase rule indicated that, for oleic acid/potassium oleate, the composition of the lamellar fatty acid/soap phase varied from approximately 1:1 to 1:3 un-ionized to ionized fatty acid species. In addition, constant pH regions observed in titration curves were a result of thermodynamic invariance (zero degrees of freedom) rather than buffering capacity. The results provide insights into the physical states of fatty acids in biological systems.(ABSTRACT TRUNCATED AT 250 WORDS)

Initiating ESL Students Into the Academic Discourse Community: How Far Should We Go?

Abstract: In the interest of finding ways to help their students succeed in university studies, college-level L2 writing researchers and teachers have endeavored for years to define the nature of academic writing tasks. The effort to determine what academic writing is and what ESL students need to know in order to produce it has led to the development of a number of different approaches to the teaching of writing. Most recently, this effort has led to a problematic trend toward having teachers of English, including teachers of freshman composition, teach students to write in other disciplines. This trend has emerged in response to criticism of previous writing programs, analyses of surveys of academic writing tasks, and movements such as Writing Across the Curriculum and English for specific purposes. This article reviews studies of L1 writing programs in which students learn to write in various disciplines, discusses the implications of the researchers' findings, and argues that (a) the teaching of writing in the disciplines should be left to the teachers of those disciplines and (b) L2 English composition teachers should focus on general principles of inquiry and rhetoric, with emphasis on writing from sources.

Neural dynamics of 1-D and 2-D brightness perception: A unified model of classical and recent phenomena

Abstract: Computer simulations of a neural network model of 1-D and 2-D brightness phenomena are presented. The simulations indicate how configural image properties trigger interactions among spatially organized contrastive, boundary segmentation, and filling-in processes to generate emergent percepts. They provide the first unified mechanistic explanation of this set of phenomena, a number of which have received no previous mechanistic explanation. Network interactions between a Boundary Contour (BC) System and a Feature Contour (FC) System comprise the model. The BC System consists of a hierarchy of contrast-sensitive and orientationally tuned interactions, leading to a boundary segmentation. On and off geniculate cells and simple and complex cortical cells are modeled. Output signals from the BC System segmentation generate compartmental boundaries within the FC System. Contrast-sensitive inputs to the FC System generate a lateral filling-in of activation within FC System compartments. The filling-in process is defined by a nonlinear diffusion mechanism. Simulated phenomena include network responses to stimulus distributions that involve combinations of luminance steps, gradients, cusps, and corners of various sizes. These images include impossible staircases, bull’s-eyes, nested combinations of luminance profiles, and images viewed under nonuniform illumination conditions. Simulated phenomena include variants of brightness constancy, brightness contrast, brightness assimilation, the Craik-O’Brien-Cornsweet effect, the Koffka-Benussi ring, the Kanizsa-Minguzzi anomalous brightness differentiation, the Hermann grid, and a Land Mondrian viewed under constant and gradient illumination that cannot be explained by retinex theory.