Psychophysical discrimination with more than two stimuli

A generalization is suggested of H. D. Landahl's theory of psychophysical discrimination by considering instead of two cross-inhibiting parallel chains of neural pathways,n such chains. The probabilities of then possible different reactions are in such a case expressed by (n−1) ple integrals. Forn=3 the method is illustrated by evaluating the probability of a reaction to the weakest of the three stimuli.     

Evaluation of spatial discrimination performances of newborn infants with the visual pursuit of structured stimuli]

Pursuit eye movements have been recorded with the photo-oculographic technique from newborn infants during the presentation of stimulations specific for spatial discrimination functions. 72.5 per cent of 51 subjects whose eye movements have been recorded have successfully followed stimuli of spatial frequency up to 0.4 cycles per degree. Estimations of grating visual acuity are similar to those provided by the preferential looking technique.     

Note on psychophysical discrimination with more than two stimuli

H. D. Landahl's well-known theory of psychophysical discrimination between two stimuli (Psychometrica,3, 107–125, 1938) is generalized to the case ofn mutually inhibiting stimuli, such that all the corresponding reactions are mutually incompatible so that only one response at most can occur at a time. It is shown that while in the two-stimulus case a “no-response” situation does not necessarily need to occur, in the case ofn stimuli andn responses a “no-response” situation always occurs with finite probability. Therefore, there is a probabilityP _i of the occurrence of each responsei as well as a probabilityP _e of no response, with . The probabilitiesP _i andP _e are expressed in terms of the intensities of then stimuliS _i and in terms of then distribution functions of the fluctuations at then corresponding connections. The expressions are in the form of sums ofn-tuple integrals of the products of the distribution functions, the limits of integration being determined by the intensities of then stimuli.     

Influence of interfering stimuli on contingent negative variation]

The aim of this study was to examine the influence of interfering stimuli on subjects' C.N.V. With a labyrinthic stimulation before association S1-S2 and arithmetic calculation task between S1 and S2, the C.N.V. showed a statistically significant variation (P less than 0.025): it became prolonged after the response to S2. Provocation of a prolonged C.N.V. could be used as criterion to determine an individual threshold of stress.     

Bilateral taste stimulation: spatial summation with weak NaCl stimuli

Recently, we reported that doubling the stimulated area on oneside of the tongue increased the detection probabilities oflow intensity NaCl stimuli according to a simple probabilitysummation model. In the present study spatial summation wasinvestigated with both ipsilateral and bilateral stimulation.For thirteen subjects the sensitivity to and the detection probabilitiesof five low intensity NaCl stimuli were determined. Stimulationwas performed with filter papers of two different sizes underthree main conditions: a circular area on either of the twotongue sides, half that circle on either of the two tongue sidesand two half circles on both sides of the tongue simultaneously.The half circles were presented in two orientations, a medialand a lateral one. The results showed that (a) doubling thestimulated area yielded the same increase in sensitivity forthe ipsilateral conditions as for the bilateral conditions;(b) the detection probabilities for both the ipsilateral andthe bilateral double-sized stimuli could be predicted accordingto the probability summation hypothesis and (c) the medial andlateral parts of the tongue were equally sensitive to NaCl inthe ipsilateral case, but showed significant differences withbilateral stimulation.     

Within-host spatial dynamics of viruses and defective interfering particles

Defective-interfering (DI) viruses arise spontaneously by deletion mutations. The shortened genomes of the DI particles cannot replicate unless they coinfect a cell with a wild-type virus. Upon coinfection, the DI genome replicates more quickly and outcompetes the wild type. The coinfected cell produces mostly DI viruses. At the population level, the abundances of DI and wild-type viruses fluctuate dramatically under some conditions. In other cases, the DI viruses appear to mediate persistent infections with relatively low levels of host cell death. This moderation of viral damage has led some to suggest DI particles as therapeutic agents. Previous mathematical models have shown that either fluctuation or persistence can occur for plausible parameter values. I develop new mathematical models for the population dynamics of DI and wild-type viruses. My work extends the theory by developing specific predictions that can be tested in the laboratory. These predictions, if borne out by experiment, will explain the key processes that control the diversity of observed outcomes. The most interesting prediction concerns the rate at which killed host cells are replaced. A low rate of replacement causes powerful epidemics followed by a crash in viral abundance. As the rate of replacement increases, the frequency of oscillations increases in DI and wild-type viral abundances, but the severity (amplitude) of the fluctuations declines. At higher replacement rates for host cells, nearly all cells become infected by DI particles and a low level of fluctuating, wild-type viremia persists.     

Human brain evoked potentials and discrimination of short acoustic stimuli with various frequency

We found that the mismatch negativity (MMM) was absent in evoked potentials in passive condition for frequency deviant acoustical stimuli when stimulus duration was only 11-30 ms. But it was shown that it is possible for participants to fairly well discriminate these stimuli and the component N2b in RP was generated without preceding MMN. Processing negativity also was absent in potentials by the minimal stimulus duration (11 ms). Auditory discrimination nevertheless was still possible, but reaction time and number of committed errors increased significantly.     

Does pigeon homing depend on stimuli perceived during displacement?

Summary In order to test whether stimuli perceived during passive displacement are important for the subsequent homing, pigeons were transported in an apparatus designed to prevent them from receiving relevant information: The experimental birds were continuously rotated quite rapidly (1.5 cps, radial acceleration about 4 g); in addition, they were exposed to an artificial magnetic field and supplied with bottled air. Control birds were transported in open-air cages on top of the van with free view to all sides.Five pairs of releases from equal distances in opposite directions were conducted. Experienced birds were released at distances of about 15, 90, and 300 km from the loft, inexperienced birds at distances of about 180km. In each pair of releases both groups of pigeons were significantly homeward oriented. Neither in initial orientation nor in homing performance nor in the distribution of recoveries were the experimental birds inferior to the controls or in any perceptable way different from them.It is concluded that homing of passively displaced pigeons is not primarily based on information gathered during the outward journey.Abbreviations EP experimental pigeon(s) - CP control pigeon(s) The possibility to maintain our pigeon loft in a building that belongs to the Zoological Institute (Prof. M. Lindauer) of the University of Würzburg is gratefully acknowledged.     

Coxiella burnetii avoids macrophage phagocytosis by interfering with spatial distribution of complement receptor 3

Phagocytosis is a highly localized event requiring the formation of spatially and temporally restricted signals. Numerous microorganisms have taken advantage of this property to invade host cells. Coxiella burnetii, the agent of Q fever, is an obligate intracellular bacterium that has developed a survival strategy in macrophages based on subversion of receptor-mediated phagocytosis. The uptake of C. burnetii is mediated by alpha(v)beta(3) integrin and is restricted by impaired cross-talk of alpha(v)beta(3) integrin and complement receptor 3 (CR3) (CD11b/CD18). In this study, we showed that CR3 molecules remained outside the pseudopodal extensions induced by C. burnetii in THP-1 monocytes, although alpha(v)beta(3) integrin was present in the pseudopods. Chemoattractants such as RANTES restored CR3 localization to the front of pseudopodal extensions and increased C. burnetii phagocytosis, demonstrating that the localization of CR3 is critical for bacterial uptake. In addition, monocyte activation due to the expression of HIV-1 Nef protein also restored CR3-mediated phagocytosis of C. burnetii by allowing CR3 redistribution toward bacterial-induced pseudopods. The redistribution of CR3 and increased C. burnetii phagocytosis in THP-1 cells stimulated by RANTES or expressing Nef were associated with the inhibition of intracellular replication of C. burnetii. Hence, the localization of CR3 is critical for bacterial phagocytosis and also for the control of bacterial replication. This study describes a nonpreviously reported strategy of phagocytosis subversion by intracellular pathogens based on altered localization of monocyte receptors.     

Qualitative discrimination of sweet stimuli: behavioural study on rats

Rats conditioned to avoid drinking a sucrose solution or a glucosesolution were tested for generalization of the learned aversionto three lower concentrations of these sweeteners. The behaviouralresponses indicated two types of discrimination. The first one,after two seconds, is of a qualitative nature; the second one,after five seconds, is of a quantitative nature showing an aversiveresponse depending on the concentration. Cross-aversion to tengustatory stimuli showed on the basis of the qualitative discriminationthat the rats discriminate between the different sweetenersin a similar way as man does.     

Influence of stimuli size on color discrimination in capuchin monkeys

Large-field trichromacy is a general feature of protanope and deuteranope humans, provided that the stimuli size extends to an 8 degrees visual angle. In this study we compared the performance of five male and three female tufted capuchin monkeys (Cebus apella) in discriminating pairs of Munsell color papers. Human subjects were also studied in two-choice discrimination tests, using the same stimuli and apparatus employed for the monkeys. The results show that although the dichromatic humans showed improved discrimination with larger versions of the stimuli, the dichromatic monkeys exhibited the same performance for both stimuli sizes. Thus, Cebus apella apparently do not present large-field trichromacy-at least for the conditions in the present experiments.     

Differential displacement of classical cadherins by VE-cadherin

VE-cadherin is an endothelial cell-specific, type II classical cadherin that plays an important role in permeability, vasculogenesis, and vascular remodeling. Endothelial cells express equal levels of VE- and N-cadherin; VE-cadherin is present injunctions while N-cadherin is diffusely expressed over the surface of the cell. The present study was designed first to determine if the ability of VE-cadherin to displace N-cadherin from junctions was endothelial-cell specific, and second to determine if VE-cadherin could displace other classical cadherins from cell junctions. Our data suggest that VE-cadherin specifically influences the cellular localization of N-cadherin, independent of cell type, and does not effect the localization of other classical cadherins.     

The spatial frequency discrimination function at low contrasts

Spatial frequency difference thresholds for sinewave gratings near contrast threshold were measured using a two-alternative forced-choice technique, and the threshold frequency differences were plotted as a proportion of standard frequency for standards from 2 to 7 cycles/degree. This function shows reliable local maxima and minima, and these features are more pronounced than they are when stimuli of 30% contrast are used. This result is consistent with the notion that at low contrasts, fewer spatial frequency channels are above threshold in the area of the visual field covered by the stimulus than when the stimulus is at high contrast.     

On the phylogeny of asymmetry and spatial discrimination

We define and develop the fundamental experimental conditions required for an organism to demonstrate the capacity for spatial discrimination. It is then shown that concomitant with evolutionary progression in organisms, there is a corresponding increase in the dimensions of functional asymmetry, and in the quantity and dimensionality of spatial discrimination. It is also shown that the mismatch in asymmetry between the human body form and functional mechanism, and a demonstrated weakness in left--right discrimination, implies that the human organism is in transition between archetypal stages of phylogeny. Implications for the phenomena of mirrorimage reversal and left--right confusion are discussed. It is further argued that the development of functional asymmetry is an inherent principle of evolution.     

Differential activation of Escherichia coli chemoreceptors by blue-light stimuli

Enteric bacteria tumble, swim slowly, and are then paralyzed upon exposure to 390- to 530-nm light. Here, we analyze this complex response in Escherichia coli using standard fluorescence microscope optics for excitation at 440 +/- 5 nm. The slow swimming and paralysis occurred only in dye-containing growth media or buffers. Excitation elicited complete paralysis within a second in 1 muM proflavine dye, implying specific motor damage, but prolonged tumbling in buffer alone. The tumbling half-response times were subsecond for onset but more than a minute for recovery. The response required the chemotaxis signal protein CheY and receptor-dependent activation of its kinase CheA. The study of deletion mutants revealed a specific requirement for either the aerotaxis receptor Aer or the chemoreceptor Tar but not the Tar homolog Tsr. The action spectrum of the wild-type response was consistent with a flavin, but the chromophores remain to be identified. The motile response processed via Aer was sustained, with recovery to either step-up or -down taking more than a minute. The response processed via Tar was transient, recovering on second time scales comparable to chemotactic responses. The response duration and amplitude were dependent on relative expression of Aer, Tar, and Tsr. The main response features were reproduced when each receptor was expressed singly from a plasmid in a receptorless host strain. However, time-resolved motion analysis revealed subtle kinetic differences that reflect the role of receptor cluster interactions in kinase activation-deactivation dynamics.