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PubMed2000

The control of saccadic adaptation: implications for the scanning of natural visual scenes.

Accurate scanning of natural scenes depends on: (1) attentional selection of the target; (2) spatial pooling over the attended target to compute the precise landing position; and (3) adaptive modification of saccades to ensure saccadic accuracy. The present experiments studied adaptation. Adaptive modifications were induced by displacing the target during saccades. Adaptation was found to be: (1) similar for a small target point and a large target circle, despite the differences in the spatial pattern of landing position errors for each; (2) unaffected by instructions to look part way to the target, even though such instructions altered landing position error relative to the target; and (3) insensitive to symbolic cues disclosing the direction of the intra-saccadic displacement. Briefly delaying the presentation of the post-saccadic target greatly reduced adaptation. Neither corrective saccades, nor the position errors that trigger corrections, were involved in adaptation because corrective saccades rarely occurred with a large target circle even though the circle produced as much adaptation as the single point. Taken together, the results do not support the traditional notion that post-saccadic retinal position error controls adaptation. We propose that adaptation relies on a comparison of the actual post-saccadic retinal image with the post-saccadic image that would be predicted based on a representation of the planned saccade. Such a comparison: (1) is consistent with our results; (2) may be more effective than retinal position error in controlling adaptation in natural visual scenes containing large targets and backgrounds; and (3) is similar to the motion-based adaptive mechanisms associated with the VOR. Similarity between the adaptive control of saccades and adaptive control of the VOR raises the possibility that the most important role of saccadic adaptation may be the coordination of eye and head movements during shifts of gaze.

Adaptation, Physiological↗
PubMed2001

Evidence for the application of rules in Pavlovian electrodermal conditioning with humans.

Two Pavlovian SCR conditioning experiments investigated interference effects in sequential training of positive and negative patterning discriminations in humans. In Experiment 1, positive patterning (A-, B-, AB+) was trained in Phase 1, immediately followed by a negative patterning schedule (C+, D+, CD-). We predicted that human participants would learn a specific numerosity rule in positive patterning, which interferes with the subsequent negative patterning schedule. In Experiment 2, negative patterning (C+, D+, CD-) was trained in Phase 1, followed by a positive patterning schedule (A-, B-, AB+) in Phase 2. Because human participants would learn an abstract 'separate-versus-together'- or 'opposite'-rule to solve the negative patterning discrimination in Phase 1, there should be less interference in positive patterning in Phase 2 where the separate/together-rule could be applied, too. In both experiments, the initial patterning discriminations were acquired successfully. In Experiment 1, human participants totally failed to solve the Phase 2 discrimination, while in Experiment 2 appropriate response differentiation developed in Phase 2. Thus, without pre-experience human participants seem to utilize a specific numerosity-rule in positive patterning and a separate/together-rule in negative patterning.

Adult↗
PubMed1976

Why a Y is not a V: a new look at the distinctive features of letters.

Although a feature detection theory of pattern recognition is consistent with many recent physiological and psychological findings, the specific rules governing the perception of the distinctive features of letters have not yet been determined. This article presente two new experimental procedures for determining these rules. Both procedures are demonstrated by the investigation of the specific rule involved in the perception of the letter attribute leg which distinguishes Y from V, F from C, and H from U. Whereas previous methods investigating the distinctive features of letters have focused primarily on archetypal letter forms, the present methods are based upon an investigation of ambiguous characters, those characters which can be assigned either of two letter labels with equal probability. One of these procedures allows for the investigation of these rules without the influence of external context, whereas the other allows for an investigation of the particular effects that external context can have on these rules.

Discrimination, Psychological↗
PubMed1975

Pattern learning and the control of behaviour by all-inhibitory neural network hierarchies.

An all-inhibitory network which learns by selective disconnection of synapses is described. This is similar to an 'associative net'; however, it is simpler in that its neurons do not need to perform arithmetical operations, and the net does not require additional threshold modulating neurons in order to cope with input patterns which are incomplete, or of differing sizes. This fundamental simplicity permits a greater variety and density of connections. These can multiply the capacity of the nets to learn complex sequences of patterns without being saturated. An "all-connected" net is described which has the holograph-like capacity to reconstruct the whole of an input pattern from part patterns without involving delays or threshold devices. All of these inhibitory nets can construct themselves by means of simple random growth processes, without incurring any loss of learning capacity of holographic properties. Similarly, synapses can be allowed to potentiate with use, so that reaction times are progressively reduced by practice, without any reduction in the quality of the performance. Inhibitory connections between arrays can give patterns in one array control over the allocation of channels in which lower arrays store learned information. A description is given of a model, decentralised, inhibitory hierarchy consisting of inter-connected arrays which can learn to execute goal-directed TOTE-type programs of behaviour by means of a simple 'putting-through' procedure.

Axons↗
PubMed2003

PPARgamma and PPARdelta negatively regulate specific subsets of lipopolysaccharide and IFN-gamma target genes in macrophages.

Natural and synthetic agonists of the peroxisome proliferator-activated receptor gamma (PPARgamma) regulate adipocyte differentiation, glucose homeostasis, and inflammatory responses. Although effects on adipogenesis and glucose metabolism are genetically linked to PPARgamma, the PPARgamma dependence of antiinflammatory responses of these substances is less clear. Here, we have used a combination of mRNA expression profiling and conditional disruption of the PPARgamma gene in mice to characterize programs of transcriptional activation and repression by PPARgamma agonists in elicited peritoneal macrophages. Natural and synthetic PPARgamma agonists, including the thiazolidinedione rosiglitazone (Ro), modestly induced the expression of a surprisingly small number of genes, several of which were also induced by a specific PPARdelta agonist. The majority of these genes encode proteins involved in lipid homeostasis. In contrast, Ro inhibited induction of broad subsets of lipopolysaccharide and IFN-gamma target genes in a gene-specific and PPARgamma-dependent manner. At high concentrations, Ro inhibited induction of lipopolysaccharide target genes in PPARgamma-deficient macrophages, at least in part by activating PPARdelta. These studies establish overlapping transactivation and transrepression functions of PPARgamma and PPARdelta in macrophages and suggest that a major transcriptional role of PPARgamma is negative regulation of specific subsets of genes that are activated by T helper 1 cytokines and pathogenic molecules that signal through pattern recognition receptors. These findings support a physiological role of PPARgamma in regulating both native and acquired immune responses.

Base Sequence↗
PubMedDate not supplied

Early online detection of upper airway obstructions in obstructive sleep apnoea syndrome (OSAS) patients.

The obstructive sleep apnoea syndrome (OSAS) is a diagnosis related to snoring and caused by a collapse in the upper airway. OSAS patients suffer from desaturated oxygen levels during sleep as well as daytime sleepiness. In this paper, we propose a system able to identify and detect respiratory disorders online based on monitoring the airflow amplitude from a sleeping OSAS patient. By the use of chi(2)-analysis and a Haar wavelet transform on signals performed offline, reference templates indicating the specific apnoea pattern for four different patients are constructed and used for similarity matching against online signals. Detection is performed in the early stages of an upcoming airway dysfunction, thus providing an opportunity to alert the patient at sleep. The system-testing results indicate robust performance and flexibility for the patient. Our proposed solution can in turn operate as an alternative to today's OSAS treatment of choice, the continuous positive airway pressure (CPAP).

Airway Obstruction↗
PubMedDate not supplied

Vascular dilatation in the pelvis: identification with CT and MR imaging.

Focal or diffuse dilatation of pelvic vessels is observed occasionally on computed tomographic or magnetic resonance images. Two major mechanisms may account for dilatation. The first mechanism is development of collateral channels as a result of venous obstruction or stenosis. Symptoms associated with vessel dilatation vary according to the level of obstruction. Portal hypertension also may result in the formation of numerous collateral vessels. In addition, left renal venous compression between the aorta and the superior mesenteric artery, which results in blood flow from the left renal vein toward the left gonadal vein, causes a variety of symptoms. The second major mechanism for dilatation is increased blood flow through collateral vessels associated with a neoplasm or vascular lesion. Hypervascular pelvic tumors such as uterine leiomyomas, gestational trophoblastic neoplasms, ovarian solid tumors, and mesenteric tumors may be associated with a marked increase in the number of draining vessels. The assessment of such vessels can assist in identification of tumor origins. Visual recognition of abnormal pelvic vasculature and abnormal hemodynamics is clinically important because it helps to improve diagnosis of a wide variety of pelvic and systemic diseases. Moreover, recognition of abnormal hemodynamics facilitates understanding of the physiology of such conditions. Recognition of the pattern of collateral channels also assists in identification of the level of narrowing even when the level is not readily apparent and is dependent on postural position.

Adult↗
PubMed2006

Converging evidence for triple word form theory in children with dyslexia.

This article has 3 parts. The 1st part provides an overview of the family genetics, brain imaging, and treatment research in the University of Washington Multidisciplinary Learning Disabilities Center (UWLDC) over the past decade that points to a probable genetic basis for the unusual difficulty that individuals with dyslexia encounter in learning to read and spell. Phenotyping studies have found evidence that phonological, orthographic, and morphological word forms and their parts may contribute uniquely to this difficulty. At the same time, reviews of treatment studies in the UWLDC (which focused on children in Grades 4 to 6) and other research centers provide evidence for the plasticity of the brain in individuals with dyslexia. The 2nd part reports 4 sets of results that extend previously published findings based on group analyses to those based on analyses of individual brains and that support triple word form awareness and mapping theory: (a) distinct brain signatures for the phonological, morphological, and orthographic word forms; (b) crossover effects between phonological and morphological treatments and functional magentic resonance imaging (fMRI) tasks in response to instruction, suggestive of cross-word form computational and mapping processes; (c) crossover effects between behavioral measures of phonology or morphology and changes in fMRI activation following treatment; and (d) change in the relationship between structural MRI and functional magnetic resonance spectroscopy (fMRS) lactate activation in right and left inferior frontal gyri following treatment emphasizing the phonological, morphological, and orthographic word forms. In the 3rd part we discuss the next steps in this programmatic research to move beyond word form alone.

Brain Mapping↗
PubMed2003

Substrate specificity of glutaminyl cyclases from plants and animals.

Glutaminyl cyclases (QC) catalyze the intramolecular cyclization of N-terminal glutamine residues of peptides and proteins. For a comparison of the substrate specificity of human and papaya QC enzymes, a novel continuous assay was established by adapting an existing discontinuous method. Specificity constants (kcat/Km) of dipeptides and dipeptide surrogates were higher for plant QC, whereas the selectivity for oligopeptides was similar for both enzymes. However, only the specificity constants of mammalian QC were dependent on size and composition of the substrates. Specificity constants of both enzymes were equally pH-dependent in the acidic pH-region, revealing a pKa value identical to the pKa of the substrate, suggesting similarities in the substrate conversion mode. Accordingly, both QCs converted the L-beta homoglutaminyl residue in the peptide H-beta homoGln-Phe-Lys-Arg-Leu-Ala-NH2 and the glutaminyl residues of the branched peptide H-Gln-Lys(Gln)-Arg-Leu-Ala-NH2 as well as the partially cyclized peptide H-Gln-cyclo(N epsilon-Lys-Arg-Pro-Ala-Gly-Phe). In contrast, only QC from C. papaya was able to cyclize a methylated glutamine residue, while this compound did not even inhibit human QC-catalysis, suggesting distinct substrate recognition pattern. The conversion of the potential physiological substrates [Gln1]-gastrin, [Gln1]-neurotensin and [Gln1]-fertilization promoting peptide indicates that human QC may play a key role in posttranslational modification of most if not all pGlu-containing hormones.

Amino Acids↗
PubMed2002

DNA topoisomerase I from mycobacteria--a potential drug target.

DNA topoisomerases are ubiquitous group of enzymes altering the topology of DNA by concerted breakage and rejoining of the phosphodiester backbone of DNA. The enzymes are classified based on the pattern of DNA cleavage. Type IA enzymes found in all bacteria nick the DNA and attach themselves covalently to the 5' side of the nick during the first transesterification reaction. Most of the information on this group of enzymes comes from studies with E. coli topoisomerase I and III. Members of type IA group are single subunit Zn(++) metalloenzymes recognizing single stranded DNA without high degree of sequence specificity during relaxation reaction of negatively super coiled DNA. So far no inhibitors are known for this group of enzymes inspite of their important role in maintaining homeostasis of DNA topology. Molecular characterization of DNA topoisomerase I from mycobacteria has revealed some of the important features of type IA enzymes hitherto unknown and provide scope for identifying novel inhibitors. The present review describes the recent developments in the area summarizing the distinctive features of mycobacterial topoisomerase I. The enzyme has several properties not shared by either type IA or IB enzymes with respect to DNA binding, recognition, sequence specificity and interaction pattern. The physiological basis of the unusual features is discussed. The unique properties described would aid in developing the enzyme as a target molecule in pharmaceutical design. In addition, the findings lead to address some fundamental questions on the intracellular role of topoisomerase I in the biology of mycobacteria which are one of the most formidable group of pathogenic organisms.

Amino Acid Sequence↗
PubMed1997

Perception of a border defined by rapidly reversing luminance contrast.

We report a new visual illusion of a perceptual boundary visible between two contiguous regions of equal luminance when the intensity is modulated with a temporal frequency that is higher than the critical fusion rate. Measurements of the luminance threshold of the perceptual border with various slopes of the luminance gradient yielded a function suggestive of the range of ocular instability. These findings raise the possibility that this new border illusion may be influenced by involuntary ocular motion during fixation.

Adult↗
PubMed1993

Quantitative evaluation of the function of looking at visual target in optokinetic nystagmus.

A new method is presented to qualitatively evaluate the function of OKN which certainly looks at a visual target. Optokinetic stimulation was given to a test subject by projecting stripes with a 5 degrees visual angle width at 30 degrees intervals, which was accelerated by 1 degree/s2 up to 100 degrees/s. The correlation between slow phase and fast phase was computed with our program. Two correlations were mixed in a normal response, one indicated low correlation and the other high correlation. As normal subjects look at wide interval visual targets one by one regardless of the target velocity, low correlation type OKN beats are considered to be those which certainly look at the visual target. In order to quantitatively analyze this type of OKN, approximate regression lines of the low correlation type, [y = ax + b (x: slow phase velocity, y: fast phase amplitude or velocity)], were computed by the minimum square method. In normal subjects, value a indicates low and value b high velocity and their normal limits are determined. The results of cases with central disequilibrium indicate that this analysis provides information of pathological OKN different from that of such conventional parameters as slow phase velocity and number of nystagmus beats.

Dominance, Cerebral↗