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At least 775 records · Page 43Linked to original sources
PubMed1999

Modelling spatial contrast sensitivity functions for chromatic and luminance-modulated gratings.

We extended our detection model of achromatic spatial vision (Rovamo, J., Mustonen, J., & Näsänen, R. (1994a). Modelling contrast sensitivity as a function of retinal illuminance and grating area. Vision Research, 34, 1301-1314) to colour vision by taking into account the fact that due to the spatio-chromatic opponency of retinal ganglion cells and dorsal lateral geniculate nucleus (dLGN) neurons, equiluminous chromatic gratings are not affected by precortical lateral inhibition. We then tested the extended model by using Mullen's experimental data (Mullen, K. J. (1985). The contrast sensitivity of human color vision to red-green and blue-yellow chromatic gratings. Journal of Physiology, 359, 381-400). The band-pass shape of the spatial contrast sensitivity function for luminance-modulated green and yellow gratings transformed to a low-pass shape, resembling the chromatic spatial contrast sensitivity function for red-green and blue-yellow equiluminous gratings, when the effect of precortical lateral inhibition on grating contrast was computationally removed by dividing luminance contrast sensitivities by spatial frequency (i.e. by af, where a = 1 degree). After the removal of this direct effect of lateral inhibition, there still remained a residual shape difference between the spatial contrast sensitivity functions for chromatic and luminance gratings. It was due to indirect reduction of grating visibility by quantal noise high-pass filtered by precortical lateral inhibition. When this indirect effect of quantal noise was also removed, contrast sensitivity for luminance gratings was about twice the sensitivity for chromatic gratings at all spatial frequencies. This was evidently due to the fact that the chromatic contrast of the equiluminous grating at the opponent stage (Cole, G. R., Hine, T. & McIihagga, W. (1993). Detection mechanisms in L-, M-, and S-cone contrast space. Journal of the Optical Society of America A, 10, 38-51) was about half of the luminance contrast of either of its chromatic component. Thus, if the contrast of the equiluminous chromatic grating were not expressed as the Michelson contrast of one chromatic component grating against its own background (Mullen, K. J. (1985). The contrast sensitivity of human color vision to red-green and blue-yellow chromatic gratings. Journal of Physiology, 359, 381-400) but as chromatic contrast at the opponent stage, contrast sensitivity would be the same for chromatic and luminance gratings.

Color Perception↗
PubMed1993

Looking at pictures: affective, facial, visceral, and behavioral reactions.

Colored photographic pictures that varied widely across the affective dimensions of valence (pleasant-unpleasant) and arousal (excited-calm) were each viewed for a 6-s period while facial electromyographic (zygomatic and corrugator muscle activity) and visceral (heart rate and skin conductance) reactions were measured. Judgments relating to pleasure, arousal, interest, and emotional state were measured, as was choice viewing time. Significant covariation was obtained between (a) facial expression and affective valence judgments and (b) skin conductance magnitude and arousal ratings. Interest ratings and viewing time were also associated with arousal. Although differences due to the subject's gender and cognitive style were obtained, affective responses were largely independent of the personality factors investigated. Response specificity, particularly facial expressiveness, supported the view that specific affects have unique patterns of reactivity. The consistency of the dimensional relationships between evaluative judgments (i.e., pleasure and arousal) and physiological response, however, emphasizes that emotion is fundamentally organized by these motivational parameters.

Analysis of Variance↗
PubMed2005

Perceptual and physiological responses to the visual complexity of fractal patterns.

Fractals have experienced considerable success in quantifying the complex structure exhibited by many natural patterns and have captured the imagination of scientists and artists alike. With ever widening appeal, they have been referred to both as "fingerprints of nature" and "the new aesthetics." Our research has shown that the drip patterns of the American abstract painter Jackson Pollock are fractal. In this paper, we consider the implications of this discovery. We first present an overview of our research from the past five years to establish a context for our current investigations of human response to fractals. We discuss results showing that fractal images generated by mathematical, natural and human processes possess a shared aesthetic quality based on visual complexity. In particular, participants in visual perception tests display a preference for fractals with mid-range fractal dimensions. We also present recent preliminary work based on skin conductance measurements that indicate that these mid-range fractals also affect the observer's physiological condition and discuss future directions based on these results.

Arousal↗
PubMed1985

[Localization of initiating codons in RNA prokaryotes messengers by learning technics].

Learning processes are applied to the recognition of protein coding regions in prokaryotes. Non-contradictory, statistical rules are deduced from a set of known examples of coding regions. These rules allow us to build characteristic patterns on the m-RNA upstream the initiating codon. These rules are applied to recognize more than 180 coding sequences.

Cell Physiological Phenomena↗
PubMed1998

Cisplatin resistance in cyclic AMP-dependent protein kinase mutants.

The emergence of cisplatin resistance poses a major problem to the successful treatment of a variety of human malignancies. Therefore, understanding the molecular mechanisms that underlie cisplatin resistance could significantly improve the clinical efficacy of this cytotoxic agent. Various studies have described that cellular sensitivity to cisplatin can be influenced by several signal transduction pathways. In this review, we examine the role of the cyclic AMP-dependent protein kinase (PKA) in the modulation of drug resistance in cancer. By a somatic mutant genetic approach, the role of PKA in the development of resistance to chemotherapeutic agents has been investigated. A series of mutants with decreased PKA activity was examined for their sensitivity to cisplatin. PKA mutants with defective regulatory (RIalpha) subunits, but not altered catalytic (C) subunits, exhibit increased resistance to cisplatin, as well as other DNA-damaging agents. Furthermore, since RIalpha subunit mutants show enhanced DNA repair we, therefore, hypothesize that functional inactivation of PKA may result in increased recognition and repair of cisplatin lesions. Alternatively, it seems likely that mutation of the RIalpha subunit may affect cellular sensitivity to various anticancer drugs, suggesting that the RIalpha subunit may have other physiological functions in addition to inhibiting the kinase activity of the C subunit. Therefore, exploitation of cyclic AMP levels or functional alteration of the R subunit may potentiate the cytotoxicity of chemotherapeutic agents and circumvent drug resistance in cancer. More importantly, the altered pattern and mechanism of drug resistance may offer the opportunity to investigate novel regulatory functions of the RIalpha subunit of PKA.

Antineoplastic Agents↗
PubMed2006

C-type lectin-like receptors on myeloid cells.

Host defence against pathogens requires the recognition of conserved microbial molecules, or 'pathogen-associated molecular patterns' (PAMPs), by their receptors termed 'pattern recognition receptors' (PRRs), represented most notably by toll-like receptors (TLRs) and C-type lectins. The 'non-classical' C-type lectins (these that lack the residues involved in calcium binding, required for carbohydrate binding) are traditionally thought of as being restricted to natural killer (NK) or T cells, playing important roles in immune surveillance. In recent years, however, a growing number of these receptors have been identified on myeloid cells, both of human and mouse origin. In contrast to their NK counterparts that primarily control cellular activation through recognition of major histocompatibility antigen (MHC) class I and related molecules, the myeloid-expressed receptors appear to have a far more diverse range of functions and ligands, including those of exogenous origin. Some of C-type lectin-like molecules possess activating/inhibitory signalling motifs that trigger downstream signalling events, suggesting the role for these receptors as positive/negative regulators of granulocyte and monocyte functions. With the exception of a few myeloid NK-like lectins, the natural ligands for most of these receptors remain unidentified, making it difficult to define their functions in normal physiological, inflammatory or pathological conditions. Importantly, in some cases, these novel C-type lectin-like lectins, encoded by genes from the same gene cluster, can act as receptor/ligand pairs, additionally contributing to the regulation of myeloid cell functions or their interaction with other (like NK) cell types. However, the relevance and importance of such interactions still needs to be assessed. Although few of the myeloid-expressed C-type lectins have been characterized in detail, we review here each of these receptors and highlight their prospective roles in innate and adaptive immunity.

Animals↗
PubMed1990

Electrical potential of transfer RNAs: codon-anticodon recognition.

Calculations of the electrostatic potentials were made around yeast elongator phenylalanine, aspartate tRNAs, and yeast initiator methionine tRNA in aqueous solution at physiological ionic strength. The calculations were carried out with a finite difference algorithm for solving the nonlinear Poisson-Boltzmann equation that incorporates the screening effects of the electrolyte, the exclusion of ions by the molecule, the molecular shape, and the different polarizabilities of the solvent and the tRNA. The initiator tRNA is surrounded by uniformly spaced contours of negative potential. The elongator tRNAs are also surrounded by a similar contour pattern except in the anticodon region where there is a pronounced "hole" in the potential surface. This hole is caused by an invagination of the potential contours, which also results in an increase in the local field strength. The effect of this hole is that the anticodon region in the elongator tRNAs is the least negative, or conversely the most positive, region of the molecule. This hole, which is not found when simple Coulombic potentials are used, is due both to the structure of the elongator tRNA anticodon loops and to the different polarizabilities of the solvent and tRNA. The existence of the potential hole in elongator tRNAs may account in part for their ability to associate with other negatively charged macromolecules, in particular mRNA. Moreover, it suggests that the anticodon loop of elongator tRNAs is the energetically most favorable point of approach of mRNA to tRNA.

Anticodon↗
PubMed1979

Monocular deprivation and the signal transmission by X- and Y-neurons of the cat lateral geniculate nucleus.

1. In adult cats deprived monocularly from the second week of life, single neurons were recorded from the optic tract (OT), the lateral geniculate body (pars dorsalis, LGN) and the optic radiation (OR). The neurons were classified according to their visual response properties (Y/X) or their latencies to OT electrical stimulation (class I/II). 2. A close positive correlation (greater than 95%) was found between the visual classification and the latency classification (Y = I, X = II). 3. The relative frequency of class I/Y-neurons was reduced in the group of pattern-deprived LGN neurons, but normal in the pattern-deprived OR neurons. 4. The ratio of the r1 and r2 wave amplitude of the OR-evoked potentials elicited by electrical stimulation of the normal or the deprived eye optic nerve was not affected by pattern deprivation. 5. The activity pattern of neurons recorded from the LGN or the OR did not differ in normal and pattern-deprived neurons belonging to the same class (on-center/off-center; Y/X). The same was true for the neuronal responses to electrical stimulation of the OT at different stimulus frequencies (1-200 stimuli/s). 6. The average maintained activity of pattern-deprived OT or OR neurons recorded while the eyelids of the deprived eye were still closed was either equal to or even somewhat higher than the average activity of the corresponding normal neurons. This was true when the patterned stimuli were presented stationary or were moved at random within the visual field simulating the effect of eye and head movements. The pattern deprivation effects found morphologically and physiologically in the visual cortex are, therefore, not induced by a diminished average activity of the input neurons from the deprived eye.

Animals↗
PubMed2004

A computational framework for cortical learning.

Recent physiological findings have revealed that long-term adaptation of the synaptic strengths between cortical pyramidal neurons depends on the temporal order of presynaptic and postsynaptic spikes, which is called spike-timing-dependent plasticity (STDP) or temporally asymmetric Hebbian (TAH) learning. Here I prove by analytical means that a physiologically plausible variant of STDP adapts synaptic strengths such that the presynaptic spikes predict the postsynaptic spikes with minimal error. This prediction error model of STDP implies a mechanism for cortical memory: cortical tissue learns temporal spike patterns if these spike patterns are repeatedly elicited in a set of pyramidal neurons. The trained network finishes these patterns if their beginnings are presented, thereby recalling the memory. Implementations of the proposed algorithms may be useful for applications in voice recognition and computer vision.

Action Potentials↗
PubMed2003

Structures of calcineurin and its complexes with immunophilins-immunosuppressants.

Calcineurin (CN) is a Ca(2+)/calmodulin-dependent serine/threonine protein phosphatase and is involved in many physiological processes such as T-cell activation and cardiac hypertrophy. The crystal structures of CN and its complexes with FKBP12-FK506 and cyclophilin-cyclosporin showed that the two structurally unrelated immunophilins-immunosuppressants bind to a common composite surface made up of the residues from both catalytic subunit and regulatory subunit of CN. The recognition of the immunophilins and immunosuppressive drugs is achieved by common but few distinct CN residues. However, the binding pattern of FKBP12-FK506 such as hydrogen bonding is significantly different from that of CyPA-CsA. This common but distinct recognition may indicate capacity of the composition surface for binding of other inhibitory proteins. The recognition site and the active site are adjacent and form an "L" shaped cleft. This implies that the immunophilin recognition site may also serve as a recognition site to define the narrow substrate specificity of calcineurin.

Binding Sites↗
PubMed1987

Vasopressin injections impair working memory in a delayed matching to sample task in rats.

Effects of vasopressin were measured in a nonspatial working memory task: food-reinforced, delayed matching to sample. Subcutaneous injections of 0.2 microgram of lysine vasopressin (LVP) or saline were alternately administered to Sprague-Dawley rats after the presentation of the sample and compared to the effect of the same treatments given to a yoked control group of rats. Different durations of sample presentation (5 and 30 min) and various retention intervals (10 min, 3 h, 24 h) were selected. The results showed that LVP never facilitated retention performance: there was no improvement under conditions of weak memory (short presentation of the sample and long retention interval); moreover LVP abolished the facilitation normally obtained when either the length of the sample presentation was longer or the duration of the retention interval was shorter. The performance after the injection of the peptide was differentially impaired, according to brightness of the sample which had been presented: after the presentation of the white box, LVP injections lead to more errors and after that of the black one the treatment induced an increase in latencies of response. All these data may suggest that the physiological consequences of hormonal modifications triggered by the LVP injection are processed along with the stimuli of the learning episode and interfere with the learned positive value of the sample.

Animals↗
PubMed1999

An array immunosensor for simultaneous detection of clinical analytes.

A fluorescence-based immunosensor has been developed for simultaneous analysis of multiple samples. A patterned array of recognition elements immobilized on the surface of a planar waveguide is used to "capture" analyte present in samples; bound analyte is then quantified by means of fluorescent detector molecules. Upon excitation of the fluorescent label by a small diode laser, a CCD camera detects the pattern of fluorescent antigen:antibody complexes on the sensor surface. Image analysis software correlates the position of fluorescent signals with the identity of the analyte. This immunosensor was used to detect physiologically relevant concentrations of staphylococcal enterotoxin B (SEB), F1 antigen from Yersinia pestis, and D-dimer, a marker of sepsis and thrombotic disorders, in spiked clinical samples.

Antigens, Bacterial↗
PubMed1971

Composition of basal and stimulated hepatic bile in baboons, and the formation of cholesterol gallstones.

The baboon, Papio, has been found to be a model for the study of the pathogenesis of cholesterol cholelithiasis in man. Studies of the physiologic variations in hepatic bile composition indicate a cyclic pattern to the proportions of cholesterol, lecithin, and bile salt in hepatic bile. During reabsorption of the bile salt pool from the intestines (stimulated flow), hepatic bile is characteristically undersaturated with cholesterol. After reabsorption of the bile salt pool (basal flow), hepatic bile is characteristically supersaturated with cholesterol. This typical pattern of basal and stimulated hepatic bile occurs irrespective of the presence of cholesterol stones in the baboon. Recognition of these two types of hepatic bile and their interrelationship during admixture in the gallbladder provides new insight into the pathogenesis of gallstone formation.

Animals↗
PubMed1988

Luminance-contrast evoked responses and color-contrast evoked responses in the human electroretinogram.

Pattern electroretinograms to onset-offset stimuli were studied in response to luminance-contrast (e.g. red-black or green-black) and color-contrast (e.g. red-green) stripe patterns of equal luminance. Onset responses to color-contrast patterns show no spatial selectivity and a constant peak latency at all spatial frequencies, a behavior different from that of luminance-contrast evoked responses (spatial selectivity and increasing peak latency with spatial frequency). These results are tentatively related to the physiology of tonic and phasic primate retinal ganglion cells and to the spatially selective and non-selective human contrast sensitivity to respectively luminance-contrast and color-contrast gratings.

Color Perception↗
PubMed2002

Children's food acceptance patterns: the interface of ontogeny and nutrition needs.

Children's eating behaviors are driven by nutrient needs for growth and health, their developmental stage, and by physical and social aspects of the feeding environment. Engendering healthful eating styles requires recognition of children's needs and abilities and a positive, structured environment in which learning and self-regulation are encouraged.

Child↗
PubMed1979

The internal representation of solid shape with respect to vision.

It is argued that the internal model of any object must take the form of a function, such that for any intended action the resulting reafference is predictable. This function can be derived explicitly for the case of visual perception of rigid bodies by ambulant observers. The function depends on physical causation, not physiology; consequently, one can make a priori statements about possible internal models. A posteriori it seems likely that the orientation sensitive units described by Hubel and Wiesel constitute a physiological substrate subserving the extraction of the invariants of this function. The function is used to define a measure for the visual complexity of solid shape. Relations with Gestalt theories of perception are discussed.

Form Perception↗
PubMed1995

Automatic access to object identity: attention to global information, not to particular physical dimensions, is important.

The authors examined whether, by attending to physical properties of objects, participants can prevent the activation of semantic information. Participants received a reference object followed by a display containing both a matching target and a distractor. In Experiments 1 and 2, participants attended to motion and to surface texture, respectively. Some evidence for the processing of semantic information occurred. This result contrasted with a previous study in which no evidence for semantic information processing was apparent in a color matching task (M. Boucart & G.W. Humphreys, 1994). In Experiment 3, pictures were used with outline contours composed of randomly distributed red and green dots, one color being overrepresented. Participants matched pictures according to the dominant color. Evidence for semantic processing emerged. The authors suggest that these results cannot be explained in terms of attention operating differently on separate physiological channels. Instead it is proposed that what is crucial in activating stored object representations is whether the global configuration of the picture is processed.

Adult↗
PubMed1988

Simultaneous processing of spatial and chromatic components of patterned stimuli by the human visual system.

We report measurements on discrimination of orientation and magnification made for elements differentiated in colour and/or luminance from their background. By performing measurements at a series of background luminances and for fixed luminance of the elements, we show that with colour contrast, discrimination for both spatial parameters is unimpaired when the background is at isoluminance with the elements. Under simple luminance contrast, however, these discriminations become poorer when the background luminance is within some +/- 5% of that of the elements, and are completely absent when the two values are the same. A deuteranomalous subject is unable to make the spatial discrimination around the isoluminance point for colour contrasts which are too small for him to distinguish, but for which subjects with normal colour vision maintain spatial discriminations at isoluminance. This observation establishes that the physiological mechanisms of normal colour vision, rather than stimulus artefacts, mediate the observed spatial discriminations. We conclude that the visual processing of colour and spatial parameters such as orientation and magnification are intrinsically related to each other.

Adult↗