Intramolecular dynamics of chain molecules monitored by fluctuations in efficiency of excitation energy transfer. A theoretical study.

The fluorescence quantum yield of a polymer molecule to which an energy donor chromophore and an energy acceptor chromophore are attached depends on the distance between the donor and acceptor chromophores. If this distance fluctuates with time, the fluorescence intensity is expected to fluctuate as well, and the time course of the intensity fluctuations will be correlated with the time course of the changes in the interchromophore distance. The intensity fluctuations are experimentally measurable if the number of illuminated molecules is small. A theoretical treatment of such fluorescence intensity fluctuations is presented in terms of a parameter that describes the polymer chain dynamics. Computer simulations were performed to illustrate the dependence of the autocorrelation function of the intensity fluctuations on the polymer chain conformation, the interchromophore energy transfer properties, and the macromolecular dynamics. These simulations demonstrate that the intensity fluctuations due to nonradiative energy transfer between chromophores attached to polymer chains can be large enough to be experimentally useful in the study of intramolecular dynamics of macromolecules.     

An improved method for measuring perceived intensity/time relationships in human taste and smell

A method has been improved for recording and processing perceivedintensity/time curves constructed from panel results. A slide-wirepotentiometer, coupled to a microcomputer, is used to storethe data recorded, which are subsequently treated to eliminateend-effects caused by use of the potentiometer. The data arethen averaged according to their statistical distributions intime and intensity directions. This averaging procedure givesa panel curve in which the three main parameters – themaximum perceived intensity, the time of maximum perceived intensity(t_max) and the time after which the flavour is no longer perceived– are averages of all the corresponding individual scores.Results show that a stronger stimulus is perceived longer andmore intensely, but with the same t_maxvalue.     

The Influence of Perceived Stress on Cortical Reactivity: A Proof-Of-Principle Study

The aim of this study was to investigate how perceived stress may affect electroencephalographical (EEG) activity in a stress paradigm in a sample of 76 healthy participants. EEG activity was analyzed using multilevel modeling, allowing estimation of nested effects (EEG time segments within subjects). The stress paradigm consisted of a 3-minute pre-stimulus stress period and a 2-minute post-stimulus phase. At t=3 minutes, a single electrical stimulus was delivered. Participants were unaware of the precise moment of stimulus delivery and its intensity level. In the EEG time course of alpha activity, a stronger increase was observed during the post-stimulus period as compared to the pre-stimulus period. An opposite time course effect was apparent for gamma activity. Both effects were in line with a priori expectations and support the validity of this experimental EEG-stress paradigm. Secondly, we investigated whether interaction effects of stress and coping, as measured with the Perceived Stress Scale-10 questionnaire (PSS-10), could be demonstrated. A higher perceived stress score was accompanied by a greater increase in delta- and theta-activity during the post-stimulus phase, compared to low scores. In contrast, low coping capacity was associated with a stronger decrease in slow beta, fast beta and gamma activity during the post-stimulus phase. The results of the present article may be interpreted as proof-of-principle that EEG stress-related activity depends on the level of subjectively reported perceived stress. The inclusion of psychosocial variables measuring coping styles as well as stress-related personality aspects permits further examination of the interconnection between mind and body and may inform on the process of transformation from acute to chronic stress.     

Acoustic intensity causes perceived changes in arousal levels in music: an experimental investigation

Listener perceptions of changes in the arousal expressed by classical music have been found to correlate with changes in sound intensity/loudness over time. This study manipulated the intensity profiles of different pieces of music in order to test the causal nature of this relationship. Listeners (N = 38) continuously rated their perceptions of the arousal expressed by each piece. An extract from Dvorak''s Slavonic Dance Opus 46 No 1 was used to create a variant in which the direction of change in intensity was inverted, while other features were retained. Even though it was only intensity that was inverted, perceived arousal was also inverted. The original intensity profile was also superimposed on three new pieces of music. The time variation in the perceived arousal of all pieces was similar to their intensity profile. Time series analyses revealed that intensity variation was a major influence on the arousal perception in all pieces, in spite of their stylistic diversity.     

Effects of order of presentation of exercise intensities and of sauna baths on perceived exertion during treadmill running

Thirteen male subjects performed a running test on the treadmill consisting of four standard exercise intensities [65%, 75%, 85%, 95% maximal O2 uptake (VO2 max)] presented in ascending, descending or random order. At the end of each exercise intensity, O2 consumption, heart rate (fc), venous blood lactate concentration [( Ia]b) and perceived exertion were assessed. This last variable was determined according to the Borg nonlinear CR-20 scale. The same variables were also determined during exercise at a standard intensity (65% or 95% VO2 max) performed before and after a Finnish sauna bath. Ratings of perceived exertion showed a good test-retest reliability (r = 0.77); they were the same when the exercise intensity was expressed in relative (%VO2 max) or absolute (speed) terms, and were independent of the order of presentation of the exercise. The latter had no effect on fc either but it did, however, influence [Ia]b, which was significantly higher in the descending, as compared to the ascending or random modes of presentation. The sauna bath increased fc at a given exercise intensity, but left perceived exertion and [Ia]b unchanged. It was concluded that at least under the present experimental conditions, fc and venous [Ia]b do not play a major role as determinants of perceived exertion.     

TIME-INTENSITY MEASUREMENT OF MATRIX EFFECTS ON RETRONASAL AROMA PERCEPTION

A computerized time intensity procedure was used to evaluate the retronasal aroma intensity of vanillin and limonene in oil/water emulsion. The maximum perceived retronasal intensity of limonene was decreased as oil content in the emulsion increased, but temporal perception (time to maximum intensity and total duration of perception) was not affected. Total duration of vanillin retronasal aroma increased as oil content increased, and salivary flow rate had a significant effect on perception of vanillin aroma. These results suggest that time intensity measurements may be a valuable tool for evaluating the effects of matrix interactions on retronasal aroma intensity.     

The dynamics of velocity adaptation in human vision

Since Barlow and Hill's classic study of the adaptation of the rabbit ganglion cell to movement [1], there have been several reports that motion adaptation is accompanied by an exponential reduction in spike rate, and similar estimates of the time course of velocity adaptation have been found across species [2-4]. Psychophysical studies in humans have shown that perceived velocity may reduce exponentially with adaptation [5,6]. It has been suggested that the reduction in firing of single cells may constitute the neural substrate of the reduction in perceived speed in humans [1,5-7]. Although a model of velocity coding in which the firing rate directly encodes speed may have the advantage of simplicity, it is not supported by psychophysical research. Furthermore, psychophysical estimates of the time course of perceived speed adaptation are not entirely consistent with physiological estimates. This discrepancy between psychophysical and physiological estimates may be due to the unrealistic assumption that speed is coded in the gross spike rate of neurons in the primary visual cortex. The psychophysical data on motion processing are, however, generally consistent with a model in which perceived velocity is derived from the ratio of two temporal channels [8-14]. We have examined the time course of speed adaptation and recovery to determine whether the observed rates can be better related to the established physiology if a ratio model of velocity processing is assumed. Our results indicate that such a model describes the data well and can accommodate the observed difference in the time courses of physiological and psychophysical processes.     

Oral chemical irritation: does it reduce perceived taste intensity?

In an experiment in which capsaicin was presented in physicalmixture with taste stimuli, no reduction in perceived tasteintensity, relative to the control condition, was observed.This result is inconsistent with previous reports of taste intensityreductions when oral chemical irritants were only periodicallyinterspersed among taste stimuli (Lawless et al., 1985; Lawlessand Stevens, 1984). A second experiment directly compared thetwo presentation formats and their respective control conditionsin a repeated-measures design. The results of that test confirmthat greater apparent reductions in taste intensity are observedwhen the oral irritant is presented as a periodic rinse eventhough perceived irritation under rinse conditions regularlyfalls to levels significantly below those maintained with mixturepresentations. This observation indicates that much of the apparentmasking of taste intensity in the presence of oral irritationis not directly related to irritation level but is sensitiveto procedural variation.     

A ratio model of perceived speed in the human visual system

The perceived speed of moving images changes over time. Prolonged viewing of a pattern (adaptation) leads to an exponential decrease in its perceived speed. Similarly, responses of neurones tuned to motion reduce exponentially over time. It is tempting to link these phenomena. However, under certain conditions, perceived speed increases after adaptation and the time course of these perceptual effects varies widely. We propose a model that comprises two temporally tuned mechanisms whose sensitivities reduce exponentially over time. Perceived speed is taken as the ratio of these filters' outputs. The model captures increases and decreases in perceived speed following adaptation and describes our data well with just four free parameters. Whilst the model captures perceptual time courses that vary widely, parameter estimates for the time constants of the underlying filters are in good agreement with estimates of the time course of adaptation of direction selective neurones in the mammalian visual system.     

Perceived Loudness of Self-Generated Sounds Is Differentially Modified by Expected Sound Intensity

Performing actions with sensory consequences modifies physiological and behavioral responses relative to otherwise identical sensory input perceived in a passive manner. It is assumed that such modifications occur through an efference copy sent from motor cortex to sensory regions during performance of voluntary actions. In the auditory domain most behavioral studies report attenuated perceived loudness of self-generated auditory action-consequences. However, several recent behavioral and physiological studies report enhanced responses to such consequences. Here we manipulated the intensity of self-generated and externally-generated sounds and examined the type of perceptual modification (enhancement vs. attenuation) reported by healthy human subjects. We found that when the intensity of self-generated sounds was low, perceived loudness is enhanced. Conversely, when the intensity of self-generated sounds was high, perceived loudness is attenuated. These results might reconcile some of the apparent discrepancies in the reported literature and suggest that efference copies can adapt perception according to the differential sensory context of voluntary actions.     

Modeling and measurements of fungal growth and morphology in submerged fermentations

Generalizing results from fungal fermentations is difficult due to their high sensitivity toward slight variation in starting conditions, poor reproducibility, and difference in strains. In this study a mathematical model is presented in which oxygen transfer, agitation intensity, dissolved oxygen tension, pellet size, formation of mycelia, the fraction of mycelia in the total biomass, carbohydrate source consumption, and biomass growth are taken into account. Two parameters were estimated from simulation, whereas all others are based on measurements or were taken from literature. Experimental data are obtained from the fermentations in both 2 L and 100 L fermentors at various conditions. Comparison of the simulation with experiments shows that the model can fairly well describe the time course of fungal growth (such as biomass and carbohydrate source concentrations) and fungal morphology (such as pellet size and the fraction of pellets in the total biomass). The model predicts that a stronger agitation intensity leads to a smaller pellet size and a lower fraction of pellets in the total biomass. At the same agitation intensity, pellet size is hardly affected by the dissolved oxygen tension, whereas the fraction of mycelia decreases slightly with an increase of the dissolved oxygen tension in the bulk. All of these are in line with observations at the corresponding conditions.     

Satiation in cutaneous saltation.

The extent of cutaneous saltation (the illusory displacement of a tap presented to one skin locus by another tap occurring close in time at another locus) was modified by a "preconditioning" stimulus presented prior to and at a site distant from the saltatory test pattern. The 10-sec vibratory preconditioning (PC) stimulus appears to be analogous to inspection figures that "satiate" the perceptual field in experiments on figural aftereffects, producing changes in the perceived size, position, or shape of subsequent stimuli. The direction of displacement of the saltatory phantom was always away from the locus of the prior PC stimulus, consistent with results observed in studies of visual and kinesthetic aftereffects. Th- amount of repulsion and the rate at which the saltatory phantom returned to its initial position depend on the intensity, locus, and number of PC stimuli. As with figural aftereffects, these results resist explanation by peripheral mechanisms such as adaptation.     

Oral chemical irritation: psychophysical properties

Concentration series of four oral chemical irritants derivedfrom spices (capsicum oleoresin, vanillyl nonamide, piperineand ginger oleoresin) were evaluated for perceived intensityand perceived areas of sensation over time. Growth of sensationwith concentration was described by power function relationshipsand decrements in sensation over time were described by exponentialdecay. Peak sensation intensity was correlated with stimulatedsalivary flow rate. The number of oral areas reported as irritatedincreased with concentration and decreased over time. Whilesome differences were observed among compounds in the areasof stimulation, the dorsal tongue surface and tongue edges werehighly responsive to all compounds. A sequential desensitizationwas observed, in which stimuli were perceived as less strongwhen following a stronger irritant than when following a weakerone.     

Time course of color induction in the honeybee

Color induction in the honeybee is investigated in color discrimination experiments. An individual bee walks in a dark arena and is trained to a self-luminant stimulus presented from below. In the dual-choice tests the dark background is replaced by a colored induction stimulus. Choice behavior is recorded by TV camera and analyzed by computer. Successive color induction is separated from simultaneous induction by analysis of the walking paths. Only successive color induction occurs. Simultaneous effects are not observed. That is a stimulus acts as a color inducing stimulus only when the bee crosses this stimulus. Thus, the color perceived by a given eye region is found to be dependent on the viewing history, but not on the stimuli presented simultaneously on neighboring parts of the retina. Color induction in the honeybee described in terms of selective sensitivity decrease (adaptation) does not explain all behavioral effects induced by the stimulus. The time course of successive color induction is calculated from the exposure times to the induction stimulus and from the choice behavior. The data suggest that color induction is complete after a few seconds. Photoreceptor adaptation is sufficient to explain the observed time course.     

Perception of everyday odors--correlation between intensity, familiarity and strength of hedonic judgement.

In this study, 40 Japanese, 44 German and 39 Mexican women were presented with 18 everyday odorants. They were asked to rate them for intensity on a six-point scale from not detectable to very strong, for pleasantness on an 11-point scale from -5, to neutral at 0, to +5, and for familiarity on a six-point scale from completely unknown to extremely familiar. Consistent positive correlations were found between paired rating scores for the three measures, and although they were not particularly strong (r(s) range, 0.19-0.60), for most odorants all three correlations were significant. Similar results were obtained whether the data were analyzed on an individual or a national basis. Most notable were the consistent positive correlations between perceived intensity and ratings of familiarity and hedonic strength. It is suggested that the perceived intensity of the odorants depended not only on stimulus concentration but probably also on experience-dependent factors.     

Qualitative and aqualitative intensity components of odour mixtures

The perception of the intensity of components of odorous mixturesis related to the overall mixture intensity in a complex mannerwhich has not so far been adequately modelled. Hypoadditivity,where the total perceived intensity of a mixture is less thanthe sum of the component intensities which arise when the substancesare presented in pure form at equivalent chemical concentrations,has been known for many years. An experiment on series of 56mixtures of amyl butyrate and bergamot at supra-threshold concentrationsfound that the total qualitatively unspecified intensity ofsuch mixtures can be greater than the sum of the identifiedcomponent intensities as judged in the context of the mixture.To reconcile an apparent contradiction, and to bring into onepsychophysical framework results from diverse procedures, amodel of mixed qualitative and aqualitative odour intensityis advanced, incorporating some evidence on the difference betweendetection and recognition processes. Each component in a mixturemay, in this theory, both partially mask the qualitative intensityof the other, and simultaneously convert some part of the other'sintensity into an aqualitative form.     

Toward a consensus on radiobiology teaching to radiation oncology residents

There are approximately 82 radiation oncology residency programs in the United States, which provide training opportunities for about 400 residents. All accredited radiation oncology residency programs must have at least one basic scientist on the faculty, and it is these individuals who often assume, wholly or in part, the responsibility of teaching radiation and cancer biology to radiation oncology residents in preparation for the American College of Radiology (ACR) In-Training Examination in Radiation Oncology and the American Board of Radiology (ABR) written examinations. In response to a perceived lack of uniformity in radiation and cancer biology curricula currently being taught to residents and a perceived lack of guidance for instructors in formulating course content for this population, a special session was presented at the Forty-eighth Annual Radiation Research Society meeting on April 23, 2001. The session, entitled "Toward a Consensus on Radiobiology Teaching to Radiation Oncology Residents", was focused on issues related to teaching radiobiology to radiation oncology residents and targeted for individuals who actively teach radiation and cancer biology as well as coordinators of residency training programs. The speakers addressed current challenges and future problems facing instructors and programs. Among these were lack of feedback on resident performance on ABR and ACR written examinations and on course content, uncertainty about what topics residents must know to pass the ABR examination, and, in the near future, a reduction (due to retirement) of instructors qualified to teach radiobiology. This article provides a synopsis of the information that was presented during that session, offers a glimpse into how the ABR and ACR examinations are prepared and details of the content of past and future examinations, and summarizes the activities of the Joint Working Group on Radiobiology Teaching which was formed to educate instructors, to establish a consensus for course curricula, and to improve the overall quality of resident teaching.