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At least 1,459 records · Page 81Linked to original sources
PubMed1983

Spatial extent of attention to letters and words.

The spatial extent of attention to visually presented letters and words was investigated using a probe technique. The primary task required subjects to categorize (a) five-letter words, or to categorize the middle letter of (b) five-letter words or (c) five-letter nonwords. The probe task required the subjects to respond when the digit 7 appeared in one of the five letter positions. Probe trials were inserted at the onset of letter and word processing in Experiment 1 and 500 msec after letter and word processing in Experiment 2. In both experiments, probe trials produced a V-shaped function of reaction times across probe positions for the letter-categorization task for word and nonword stimulus conditions. In contrast, a relatively flat reaction time function was found for the word-categorization tasks. An analysis of the data based on a quantitative model of attentional spotlight distributions suggests that the spotlight width in the letter tasks is one letter space, and the spotlight width in the word task is typically five spaces.

Attention↗
PubMed1983

Evaluation and integration of visual and auditory information in speech perception.

Three experiments were carried out to investigate the evaluation and integration of visual and auditory information in speech perception. In the first two experiments, subjects identified /ba/ or /da/ speech events consisting of high-quality synthetic syllables ranging from /ba/ to /da/ combined with a videotaped /ba/ or /da/ or neutral articulation. Although subjects were specifically instructed to report what they heard, visual articulation made a large contribution to identification. The tests of quantitative models provide evidence for the integration of continuous and independent, as opposed to discrete or nonindependent, sources of information. The reaction times for identification were primarily correlated with the perceived ambiguity of the speech event. In a third experiment, the speech events were identified with an unconstrained set of response alternatives. In addition to /ba/ and /da/ responses, the /bda/ and /tha/ responses were well described by a combination of continuous and independent features. This body of results provides strong evidence for a fuzzy logical model of perceptual recognition.

Hearing↗
PubMed1982

The moon illusion: II. A reference theory.

The present theory provides explanations for the moon illusion and related issues involving size and distance perception in natural, outdoor settings. Although some assumptions of previous theories are rejected, other pivotal aspects are retained in this formulation. In particular, the present theory states that both the sky and ground are important referents in judging the spatial extent of the moon. Neither factor alone can account for all the available data, but quantitative models incorporating both factors do quite well when applied to the parametric findings of Holway and Boring, as well as to the results obtained by Kaufman and Rock. The reference theory and its associated class of specific models suggest new theoretical directions and experimental tests to narrow yet further the selection of appropriate explanations for one of visual perception's oldest unsolved puzzles.

Astronomical Phenomena↗
PubMed1986

Separate channels mediate prestimulus facilitation and suppression of rabbit nictitating membrane reflex.

Neurophysiological mechanisms underlying prestimulus-induced facilitation and suppression of reflex amplitude were investigated by using the rabbit nictitating membrane reflex (NMR). Experiment 1 was conducted to investigate the retractor bulbi motoneuron pool in the region of the abducens nucleus. Direct electrical stimulation of the pool caused NM extension, and recordings from the motoneurons showed greatly increased activity under conditions of NMR amplitude facilitation. Decreased motoneuron activity was conspicuously absent under conditions of NMR amplitude suppression. In Experiment 2, the retractor palpebrae tertiae motoneuron pool of the nucleus centralis caudalis was investigated. Direct electrical stimulation of the pool caused NM retraction, and recordings from the motoneurons showed increased activity under conditions of NMR amplitude suppression, but not under conditions of NMR amplitude facilitation. A quantitative model constructed from these neurophysiological results was shown to generate predictions in close accord with directly measured NMR amplitudes under both suppressive and facilitative conditions. From these results it appears that the behaviorally independent processes of NMR amplitude facilitation and suppression are mediated by anatomically independent motoneuron pools and output pathways showing no evidence of central inhibition but opposing each other peripherally through simultaneous excitation of antagonistic muscles.

Abducens Nerve↗
PubMed1995

Learning of physiological responses: II. Classical conditioning of the baroreflex.

The baroreflex can be classically conditioned. In neuromuscular blocked (NMB) rats, electrical stimulation of the aortic depressor nerve (ADN) and dopamine-produced blood pressure rise were effective unconditioned stimuli (UCS) for auditory discriminative classical conditioning. The conditioned response (CR) pattern (bradycardia, vasodilatation, and hypotension > 10 torr) closely resembled that of the unconditioned baroreflex. Conditioned stimulus (CS) specificity was demonstrated by discrimination of baroreflex-associated and nonassociated auditory stimuli, and also by elaborating depressor and pressor CRs to auditory CSs, which respectively had been associated with either baro-afferent (depressor) or tail-shock (pressor) UCSs. The conditioned-baroreflex-magnitude increased with trials. These findings support quantitative models in which CRs interact with and calibrate the gain and dynamic properties of natural reflexes.

Acoustic Stimulation↗
PubMed2002

Assessing clinically relevant perceptual organization with multidimensional scaling techniques.

Multidimensional scaling (MDS) techniques provide a promising measurement strategy for characterizing individual differences in cognitive processing, which many clinical theories associate with the development, maintenance, and treatment of psychopathology. The authors describe the use of deterministic and probabilistic MDS techniques for investigating numerous aspects of perceptual organization, such as dimensional attention, perceptual correlation, within-attribute organization, and perceptual variability. Additionally, they discuss how formal quantitative models can be used, in conjunction with MDS-derived representations of individual differences in perceptual organization, to test theories about the role of cognitive processing in clinically relevant phenomena. They include applied examples from their work in the areas of eating disorders and sexual coercion.

Coercion↗
PubMed1991

Autonomic determinism: the modes of autonomic control, the doctrine of autonomic space, and the laws of autonomic constraint.

Contemporary findings reveal that the multiple modes of autonomic control do not lie along a single continuum extending from parasympathetic to sympathetic dominance but rather distribute within a 2-dimensional space. The physiological origins and empirical documentation for the multiple modes of autonomic control are considered. Then a formal 2-dimensional conception of autonomic space is proposed, and a quantitative model for its translation into a functional output surface is derived. It is shown that this model (a) accounts for much of the error variance that has traditionally plagued psychophysiological studies, (b) subsumes psychophysiological principles such as the law of initial values, (c) gives rise to formal laws of autonomic constraint, and (d) has fundamental implications for the direction and interpretation of a wide array of psychophysiological studies.

Animals↗
PubMed2001

Retrieval processes in recognition and cued recall.

The present studies used response time (RT) and accuracy to explore the processes and relation of recognition and cued recall. The studies used free-response and signal-to-respond techniques and varied list length and presentation rate. In Experiment 1, the free-RT distributions for recognition had much lower mean and variance than those for cued recall. Similarly, signal-to-respond curves showed fast rates of accumulation of information in recognition and slow rates in recall. (Quantitative models of the results are presented in the companion article by D. E. Diller, P. A. Nobel, and R. M. Shiffrin, 2001). To rule out the possibility that the slower responses in cued recall were due to a fast retrieval process followed by a slow process of cleaning up the retrieved trace for output, additional signal-to-respond tasks provided the relevant alternatives at test. Yet, these conditions showed slow growth rates, similar to those seen in recall. The results support the hypothesis that retrieval processes differ for single-item recognition and cued recall, with retrieval in cued recall (and associative recognition) due to a sequential search.

Adult↗
PubMed1999

Auditory distance perception in rooms.

The perceived distance of a sound source in a room has been shown to depend on the ratio of the energies of direct and reflected sound. Although this relationship was verified in later studies, the research has never led to a quantitative model. The advent of techniques for the generation of virtual sound sources has made it possible to study distance perception using controlled, deterministic stimuli. Here we present two experiments that make use of such stimuli and we show that a simple model, based on a modified direct-to-reverberant energy ratio, can accurately predict the results and also provide an explanation for the 'auditory horizon' in distance perception. The modification of the ratio consists of the use of an integration time of 6 milliseconds in the calculation of the energy of the direct sound. This time constant seems to be important in spatial hearing-the precedence effect is also based on a similar integration window.

Auditory Perception↗
PubMed1997

Robustness in simple biochemical networks.

Cells use complex networks of interacting molecular components to transfer and process information. These "computational devices of living cells" are responsible for many important cellular processes, including cell-cycle regulation and signal transduction. Here we address the issue of the sensitivity of the networks to variations in their biochemical parameters. We propose a mechanism for robust adaptation in simple signal transduction networks. We show that this mechanism applies in particular to bacterial chemotaxis. This is demonstrated within a quantitative model which explains, in a unified way, many aspects of chemotaxis, including proper responses to chemical gradients. The adaptation property is a consequence of the network's connectivity and does not require the 'fine-tuning' of parameters. We argue that the key properties of biochemical networks should be robust in order to ensure their proper functioning.

Adaptation, Physiological↗
PubMed2000

A cellular calculus for signal integration by T cells.

During an immune response numerous receptor-mediated signals delivered to T cells direct their proliferation, survival and differentiation. Here, we describe a quantitative model and in vitro methods for assessing the "calculus" used by T cells to process these multiple signals. The model reveals how T cells convert independently received signals into linear additive effects on division times which, in turn, amplify T cell number exponentially. These results explain why so many ligands can each appear obligatory for T cell activation and argue for a re-examination of the two-signal theory as the basis for decisions between tolerance and activation.

Animals↗
PubMed2006

Imaging single molecules in living cells for systems biology.

In this work, I present the application of single-molecule imaging to systems biology and discuss the relevant technical issues within this context. Imaging single molecules has made it possible to visualize individual molecules at work in living cells. This continuously improving technique allows the measurement of non-invasively quantitative parameters of intracellular reactions, such as the number of molecules, reaction rate constants and diffusion coefficients with spatial distributions and temporal fluctuations. This detailed information about unitary intracellular reactions is essential for constructing quantitative models of reaction networks that provide a systems-level understanding of the mechanisms by which various cellular behaviors are emerging.

Cell Physiological Phenomena↗
PubMed2002

Overview of the Alliance for Cellular Signaling.

The Alliance for Cellular Signaling is a large-scale collaboration designed to answer global questions about signalling networks. Pathways will be studied intensively in two cells--B lymphocytes (the cells of the immune system) and cardiac myocytes--to facilitate quantitative modelling. One goal is to catalyse complementary research in individual laboratories; to facilitate this, all alliance data are freely available for use by the entire research community.

B-Lymphocytes↗
PubMed2004

Computational roles for dopamine in behavioural control.

Neuromodulators such as dopamine have a central role in cognitive disorders. In the past decade, biological findings on dopamine function have been infused with concepts taken from computational theories of reinforcement learning. These more abstract approaches have now been applied to describe the biological algorithms at play in our brains when we form value judgements and make choices. The application of such quantitative models has opened up new fields, ripe for attack by young synthesizers and theoreticians.

Animals↗
PubMed2006

Negligible glacial-interglacial variation in continental chemical weathering rates.

Chemical weathering of the continents is central to the regulation of atmospheric carbon dioxide concentrations, and hence global climate. On million-year timescales silicate weathering leads to the draw-down of carbon dioxide, and on millennial timescales chemical weathering affects the calcium carbonate saturation state of the oceans and hence their uptake of carbon dioxide. However, variations in chemical weathering rates over glacial-interglacial cycles remain uncertain. During glacial periods, cold and dry conditions reduce the rate of chemical weathering, but intense physical weathering and the exposure of carbonates on continental shelves due to low sea levels may increase this rate. Here we present high-resolution records of the lead isotope composition of ferromanganese crusts from the North Atlantic Ocean that cover the past 550,000 years. Combining these records with a simple quantitative model of changes in the lead isotope composition of the deep North Atlantic Ocean in response to chemical weathering, we find that chemical weathering rates were two to three times lower in the glaciated interior of the North Atlantic Region during glacial periods than during the intervening interglacial periods. This decrease roughly balances the increase in chemical weathering caused by the exposure of continental shelves, indicating that chemical weathering rates remained relatively constant on glacial-interglacial timescales. On timescales of more than a million years, however, we suggest that enhanced weathering of silicate glacial sediments during interglacial periods results in a net draw-down of atmospheric carbon dioxide, creating a positive feedback on global climate that, once initiated, promotes cooling and further glaciation.

Journal Article↗
PubMed2003

The nature of molecular recognition by T cells.

Considerable progress has been made in characterizing four key sets of interactions controlling antigen responsiveness in T cells, involving the following: the T cell antigen receptor, its coreceptors CD4 and CD8, the costimulatory receptors CD28 and CTLA-4, and the accessory molecule CD2. Complementary work has defined the general biophysical properties of interactions between cell surface molecules. Among the major conclusions are that these interactions are structurally heterogeneous, often reflecting clear-cut functional constraints, and that, although they all interact relatively weakly, hierarchical differences in the stabilities of the signaling complexes formed by these molecules may influence the sequence of steps leading to T cell activation. Here we review these developments and highlight the major challenges remaining as the field moves toward formulating quantitative models of T cell recognition.

Abatacept↗
PubMed2005

Determination of absolute protein numbers in single synapses by a GFP-based calibration technique.

To build a quantitative model of molecular organization of neurons, it is essential to have information about the number of protein molecules at individual synapses. Here we developed a method to estimate absolute numbers of individual proteins at actual excitatory synapses by calibrating the fluorescence intensity of microspheres with single EGFP molecules. In cultured hippocampal neurons, we observed a monotonous increase of postsynaptic protein numbers per single synapse during neuronal differentiation and subsequent stabilization. At maturity we calculated that a single excitatory postsynaptic site contains 100-450 of individual postsynaptic proteins, such as PSD-95, GKAP, Shank and Homer. This narrow range of postsynaptic protein content suggests relatively simple stoichiometry of postsynaptic molecular organization. The EGFP-based calibration technique provides an unprecedented general method for estimating the amounts of proteins in macromolecular complexes.

Animals↗
PubMed2005

Reconstruction of cellular signalling networks and analysis of their properties.

The study of cellular signalling over the past 20 years and the advent of high-throughput technologies are enabling the reconstruction of large-scale signalling networks. After careful reconstruction of signalling networks, their properties must be described within an integrative framework that accounts for the complexity of the cellular signalling network and that is amenable to quantitative modelling.

Animals↗