人眼的阈上调制传递函数

视觉系统的阈上调制传递函数与阈值对比敏感度函数具有明显的区别.但由于阈上测试方法复杂,因而迄今为止阈上调制传递函数的测试数据比阈值对比敏感度函数要少得多.我们应用传统的极限调节法和对比度比配法分别测试了人眼的阈值对比敏感度函数和三种对比度级别的阈上调制传递函数.测试结果表明,一个以DOG(Difference of two Gaussians)函数为基础的函数是一种合理的模型,可由现有阈值对比敏感度函数预测不同对比度和象场亮度级别下的人眼阈上调制传递函激.这个模型也可做为一种有效的人眼生理光学经验公式,用于目视光电成象系统的设计和象质评价.     

Increasing the Catalytic Performance of a Whole Cell Biocatalyst Harboring a Cytochrome P450cam System by Stabilization of an Electron Transfer Component

Catalytic activity of a recombinant Escherichia coli whole cell biocatalyst harboring a cytochrome P450cam monooxygenase system from Pseudomonas putida coupled with enzymatic co-factor regeneration was investigated. About 0.7 μmol camphor was hydroxylated per mg dry cells at 4°C in 50 mM Tris/HCl buffer (pH 7.4) when utilizing a stable putidaredoxin (Pdx) mutant, C73S/C85S-Pdx (Cys73Ser, Cys85Ser double mutant), instead of wild-type Pdx, which was about two-fold improvement in the substrate conversion. Ten-micromole camphor was completely hydroxylated at 20°C in 6 h by 15 mg dry cell weight of whole cell biocatalyst including C73S/C85S-Pdx. Thus, modulation of protein-protein interaction in multicomponent enzymatic catalysis in whole cells is important.     

The responses of photosynthetic gas exchange and chlorophyll a fluorescence to changes of irradiance and temperature in two species of Miscanthus

Photosynthetic CO₂ uptake and chlorophyll (Chl) a fluorescence of C₄ perennial grasses, Miscanthus floridulus (Labill) Warb and M. transmorrisonensis Hayata, from altitudes in central Taiwan of 390 and 2700 m, respectively, were studied at 10 and 25 °C to find if the species differ in their photosynthetic responses to a low temperature, and whether their photosystems 2 become more susceptible to the photoinhibition at low temperatures. For both species, the maximum photosynthetic rate (P_max) was reduced when the leaves were exposed to 10 °C. At irradiances higher than 400 μmol m^-2 s^-1, the values of F_v/F_m were reduced in both species at 10 °C but not at 25 °C, which indicated the photoinhibition at 10 °C. Reductions in P_max and the values of F_v/F_m at 10 °C were lesser in M. transmorrisonensis than in M. floridulus. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of brassinosteroid infiltration prior to cold treatment on ion leakage and pigment contents in rape leaves

The effect of 24-epibrassinolide (BR₂₇) on cold resistance of rape seedlings was studied by ion leakage and photosynthetic pigment degradation measurements. Aqueous solutions of BR₂₇ were injected into cotyledons or primary leaves of rape plants and these plants were incubated at 2 °C or 20 °C. Cold treatment (2 °C) without BR₂₇ injection elevated the membrane permeability in both primary leaves and cotyledons significantly. Surprisingly, injection of leaves with water or 0.467 % aqueous ethanol solution led to a massive increase in membrane permeability after cold stress at 2 °C. The synergistic effect of leaf infiltration and cold on permeability was abolished by 0.05 and 1.00 μM of BR₂₇ in primary leaves and by 1.00 μM of BR₂₇ in cotyledons. On the other hand, BR₂₇ solutions strongly elevated the membrane permeability at 20 °C, while water and ethanol solutions brought about only negligible increases. Water or ethanol infiltrations strongly reduced the leaf contents of chlorophyll (Chl) a, Chl b and carotenoids at 2 °C but less markedly at 20 °C. However, in seedlings exposed to 2 °C pigments content was significantly higher in BR₂₇-treated leaves as compared to water/ethanol control. There were no differences between pigment contents of leaves injected with BR₂₇ solutions or only water/ethanol at 20 °C. The above data strongly support the stress protecting effect of BR₂₇.     

Polar cyanobacteria versus green algae for tertiary waste-water treatment in cool climates

Forty-nine strains of filamentous, mat-forming cyanobacteria isolated from the Arctic, subarctic and Antarctic environments were screened for their potential use in outdoor waste-water treatment systems designed for cold north-temperate climates. The most promising isolate (strain E18, Phormidium sp. from a high Arctic lake) grew well at low temperatures and formed aggregates (flocs) that could be readily harvested by sedimentation. We evaluated the growth and nutrient uptake abilities of E18 relative to a community of green algae (a Chlorococcalean assemblage, denoted Vc) sampled from a tertiary treatment system in Valcartier, Canada. E18 had superior growth rates below 15°C Canada. (μ = 0.20 d-¹ at 10°C under continuous irradiance of 225 μmol photon m-² s-¹) and higher phosphate uptake rates below 10°C (k = 0.050 d-¹ at 5°C) relative to Vc (μ=0.087 d-¹ at 10°C and k = 0.020 d-¹ at 5°C, respectively). The green algal assemblage generally performed better than E18 at high temperatures (at 25°C, μ = 0.39 d-¹ and k = 0.34 d-¹ for Vc; μ = 0.28 d-¹ and k = 0.33 d-¹ for E18). However, E18 removed nitrate more efficiently than Vc at most temperatures including 25°C. Polar cyanobacteria such as strain E18 are appropriate species for waste-water treatment in cold climates during spring and autumn. Under warmer summer conditions, fast-growing green algae such as the Vc assemblage are likely to colonize and dominate, but warm-water Phormidium isolates could be used at that time. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effects of temperature on purification of eutrophic water by floating eco-island system

The effects of temperature on pollutant removal of two plant species (Oenanthe javanica D.C. and Nasturtium officinale) were evaluated using simulated microcosms of the floating eco-island system (FEIS). Both the planted FEIS (P-FEIS) and the non-planted FEIS (NP-FEIS) dramatically decreased NH₄–N concentration in the hypereutrophic water at low (10 °C), medium (22 °C), and high (35 °C) temperatures, and to a greater extent for the P-FEIS and at medium temperature. The NO₂–N concentration was effectively decreased from 0.23 to 0.01 mg/L after 4 d treatment with the P-FEIS at all the three temperatures, but was slightly increased in the NP-FEIS at low temperature. The P-FEIS could decrease NO₃–N concentration in the eutrophic water over 1–3 times depending on temperature, with greater decrease at high temperature. The remove of total P (TP) reached 78%, on average, with the FEIS treatment for 4 d at all temperatures, which was over three times greater than those with the NP-FEIS at low temperature. The removal rates of Chla, COD_Mn, and BOD₅ by the P-FEIS from the hypereutrophic water were, on average, 70%, 85%, 83% at 22 °C and 35 °C, respectively, while over 1–2 times smaller at 10 °C. More effective removals of Chla, COD_Mn, and BOD₅ (over 1–2 times) were noted with the P-FEIS than those with the NP-FEIS. N. officinale showed more efficiency in removing ammonium and TN at low temperature, and BOD₅ at medium and high temperatures, as compared to O. javanica. Whereas O. javanica could more effectively decrease Chla at 22 °C and 35 °C and COD_Mn at 10 °C than N. officinale after 4 d treatment. Higher dissolved oxygen concentration and pH was found in the FEIS with N. officinale than that with O. javanica D.C. The results imply that plant eco-island system had remarkable purification ability to remove pollutants from hypereutrophic water, and mixed planting of O. javanica D.C. with N. officinale on the FEIS may enhance nutrient removal and water quality improvement of eutrophic water bodies, especially at low temperature season.     

Effects of temperature on purification of eutrophic water by floating eco-island system

The effects of temperature on pollutant removal of two plant species (Oenanthe javanica D.C. and Nasturtium officinale) were evaluated using simulated microcosms of the floating eco-island system (FEIS). Both the planted FEIS (P-FEIS) and the non-planted FEIS (NP-FEIS) dramatically decreased NH₄–N concentration in the hypereutrophic water at low (10 °C), medium (22 °C), and high (35 °C) temperatures, and to a greater extent for the P-FEIS and at medium temperature. The NO₂–N concentration was effectively decreased from 0.23 to 0.01 mg/L after 4 d treatment with the P-FEIS at all the three temperatures, but was slightly increased in the NP-FEIS at low temperature. The P-FEIS could decrease NO₃–N concentration in the eutrophic water over 1–3 times depending on temperature, with greater decrease at high temperature. The remove of total P (TP) reached 78%, on average, with the FEIS treatment for 4 d at all temperatures, which was over three times greater than those with the NP-FEIS at low temperature. The removal rates of Chla, COD_Mn, and BOD₅ by the P-FEIS from the hypereutrophic water were, on average, 70%, 85%, 83% at 22 °C and 35 °C, respectively, while over 1–2 times smaller at 10 °C. More effective removals of Chla, COD_Mn, and BOD₅ (over 1–2 times) were noted with the P-FEIS than those with the NP-FEIS. N. officinale showed more efficiency in removing ammonium and TN at low temperature, and BOD₅ at medium and high temperatures, as compared to O. javanica. Whereas O. javanica could more effectively decrease Chla at 22 °C and 35 °C and COD_Mn at 10 °C than N. officinale after 4 d treatment. Higher dissolved oxygen concentration and pH was found in the FEIS with N. officinale than that with O. javanica D.C. The results imply that plant eco-island system had remarkable purification ability to remove pollutants from hypereutrophic water, and mixed planting of O. javanica D.C. with N. officinale on the FEIS may enhance nutrient removal and water quality improvement of eutrophic water bodies, especially at low temperature season.     

Effect of temperature and photon fluence rate on gametophytes and young sporophytes of Laminaria ochroleuca Pylaie

We analysed the effects of temperature and photon fluence rate on meiospore germination, growth and fertility of gametophytes, and growth of young sporophytes of Laminaria ochroleuca. Maximum percentages of germination (91–98%) were obtained at 15°C and 18°C, independent of photon fluence rate. Optimal development of female gametophyte and maximum fecundity and reproductive success of gametophytes occurred at 15°C and 18°C and at 20 and 40 μmol m^–2 s^–1. Maximum relative growth rate of young sporophytes after 2 weeks of culture was achieved under the same conditions. L. ochroleuca gametophytes cannot reproduce and growth of its sporophytes is not competitive at temperatures close to 10°C. Received in revised form: 31 August 2001 Electronic Publication     

光栅显示装置的试制和人眼对比敏感度的测定

本文报道了一个在普通示波器荧光屏上产生光栅和测量对比的方法。由于屏上的光点有一定大小和特殊的光晕,对比度和输入电压线性关系的丧失较快;我们只能测准每厘米(屏上)产生12对线的光栅。用主诉方法,测量了两名受试者的对比敏感度函数,并指出了用这方法测定该函数所带来的微小的不准确性.     

Ultrastructural alterations in mesophyll and bundle sheath chloroplasts of two maize cultivars in response to chilling at high irradiance

Maize (Zea mays L.) seedlings of two cultivars (cv. Bastion adapted to W. Europe, and cv. Batan 8686 adapted to the highlands of Mexico), raised in a glasshouse (19–25 °C), were transferred to 4.5 or 9 °C at photon flux density (PPFD) of 950 μmol m⁻² s⁻¹ with 10-h photoperiod for 58 h and then allowed to recover at 22 °C for 16 h (14 h dark and 2 h at PPFD of 180 μmol m⁻² s⁻¹). The ultrastructural responses after 4 h or 26 h at 4.5 °C were the disappearance of starch grains in the bundle sheath chloroplasts and the contraction of intrathylakoid spaces in stromal thylakoids of the mesophyll chloroplasts. At this time, bundle sheath chloroplasts of cv. Batan 8686 formed peripheral reticulum. Prolonged stress at 4.5 °C (50 h) caused plastid swelling and the dilation of intrathylakoid spaces, mainly in mesophyll chloroplasts. Bundle sheath chloroplasts of cv. Batan 8686 seedlings appeared well preserved in shape and structure. Batan 8686 had also higher net photosynthetic rates during chilling and recovery than Bastion. Extended leaf photobleaching developed during the recovery period after chilling at 4.5 °C. This was associated with collapsed chloroplast envelopes, disintegrated chloroplasts and very poor staining.     

Contrast sensitivity in a harbor seal (<Emphasis Type="Italic">Phoca vitulina</Emphasis>)

In this study, the contrast sensitivity function (CSF) of one harbor seal was determined behaviorally in a go-/no-go-experiment at an ambient light of 0.9 lx in air. Contrast sensitivity was assessed as the reciprocal value of the threshold contrast for spatial frequencies varying between 0.03 and 1.5 cycles/deg, which were displayed with contrast ranging from 0.02 to 1 on a TFT monitor with a mean luminance of 3.8 cd/m2. The CSF of the harbor seal shows the general characteristics described for other species with a peak at an intermediate frequency, a low frequency roll-off and a high frequency cut-off towards the harbor seal’s resolution limit determined in a previous study. The position of the CSF’s peak lies at approximately 0.5 cycles/deg and adopts an absolute height of 40. These results compare well with the cat’s CSF assessed at a comparable adaptation light which might reflect similarities in lifestyle and optics.     

Contrast sensitivity functions to stimuli defined in Cartesian, polar and hyperbolic coordinates

Recent electrophysiological studies indicate that cells in the LGN, V1, V2, and V4 areas in monkeys are specifically sensitive to Cartesian, polar and hyperbolic stimuli. We have characterized the contrast sensitivity functions (CSF) to stimuli defined in these coordinates with the two-alternatives forced-choice paradigm. CSFs to Cartesian, concentric, and hyperbolic stimuli have had similar shapes, with peak sensitivity at approximately 3 c/deg. However, the Cartesian CSF peak sensitivity has been at least 0.1 log units higher than that to stimuli in any other coordinate system. The concentric-Bessel CSF has a low-pass shape, peaking at 1.5 c/deg or below. The radial CSF has a bell shape with maximum sensitivity at 8 c/360 degrees. Only the concentric-Bessel CSF could be explained in terms of the components of maximum amplitude of the Fourier transform. Neural models, which in previous studies predicted the responses to Cartesian and polar Glass patterns, failed to account for the full CSFs data.     

Human psychophysics: Functional interpretation for contrast sensitivity versus spatial frequency curve

The hypothesis that neural processing in the human visual pathways compensates for both optical degradation as well as noise contamination at the photoreceptor level is introduced and shown to be consistent with the high frequency portion of the contrast sensitivity function for threshold detection of sinusoidal gratings in addition to the suprathreshold phenomenon of matching sinusoidal gratings of different spatial frequencies. This offers a unifying interpretation for why, at threshold conditions, the high spatial frequency portion of the image is blurred as severely by the nervous system as it is by the optics (e.g. Campbell and Green, 1965) while in extreme suprathreshold conditions the nervous system effectively deblurs the image (e.g. Georgeson and sullivan, 1975; Kulikowski, 1976). These conclusions do not necessitate a highly specific form of visual processing such as Fourier channeling.This research was conducted at Yale University, Department of Ophthalmology and Visual Science, New Haven, Connecticut, USA, throughout which period A.W.S. was a John Simon Guggenheim fellow     

Regression analysis of non-stationary discharges in neurons; Adaptation in the electrosensory afferent of dogfish

Interspike interval histograms, as usually regarded for the estimation of statistical variabilities in neuronal spike trains, were applied to non-stationary dynamic responses of a PD receptor. Sliding mean values were introduced describing the average receptor response on defined, recurrent stimuli; mean spike frequencies and interspike intervals were computed a) for fixed sequential analysis periods (of e.g. 500 ms), b) for analysis periods shifted by every consecutive interspike interval (thus the number of spikes being constant), and c) by fitting the dynamic responses for suitable analytic functions (e.g. exponential functions). With these methods variabilities in the non-stationary neuronal impulse patterns were investigated for electrosensory PD afferents in Lorenzinian ampulla of dogfish (Scyliorhinus canicula) with electric stimuli up to 50 nA and defined temperatures between 7° C and 25° C. In this temperature range all investigated ampullae were spontaneously active, the irregularities in neuronal discharges and averaged spike frequencies depended strongly on temperature, the latter showing maxima between 13° C and 19° C. In preparations with small disturbances we generally found static interspike interval histograms following approximatively a Gaussian distribution. The same was true for the momentary spike frequency and its deviation during the dynamic response to given electrical stimuli. A suprathreshold rectangular current (e.g.-0.5 nA) led to a marked but transient synchronisation in spike generation; the higher the stimulus strength, the smaller the standard deviation (s.d.) from mean spike frequency in the beginning of the dynamic response; during adaptation the s.d. increased up to that of the static response frequency. Relating, however, s.d. for different currents, times, and temperatures to the corresponding mean spike frequency led to fairly constant coefficients of variation; s.d. was approximatively a linear function of the sliding mean value even in the dynamic response of the electroreceptor (scaling).Supported by the Deutsche Forschungsgemeinschaft (Br 310/11)     

Evoked potentials of the cat inferior colliculus to acoustic stimuli simulating sound source movement with different velocities in opposite directions

Amplitude changes of inferior colliculus evoked potentials (EPs) in anaesthetized adult cats were studied under presentation of acoustic stimuli simulating both azimuth-moving and stationary sound source. The movement was simulated with gradual changes of interaural time delay between binaurally presented click trains. It was shown that the amplitude of EPs elicited by "moving" signals depended on the velocity of movement. Amplitude differences between EPs to "moving" and stationary stimuli were observed under motion velocities up to 320 deg./s. The greatest response amplitudes in different experiments took place under velocities within the range of 67-320 deg./s with most of them recorded under velocities of 170 and 125 deg./s. Amplitude of the responses to lateral-medial movement with any velocity were always greater than those to opposite direction of movement with the same velocity.     

Real-time monitoring of nasal mucosal pH during carbon dioxide stimulation: implications for stimulus dynamics

Carbon dioxide is a commonly employed irritant test compound in nasal chemesthetic studies because it is essentially free of olfactory stimulus properties. CO(2) is thought to act via hydration to H(2)CO(3) and dissociation to H(+) in nasal mucus, with resulting activation of acid sensors. However, transient changes in nasal mucosal pH have not been documented during CO(2) stimulation in humans. We placed a small pH probe on the floor of the right anterior nasal cavity during CO(2) stimulation in eight human subjects with historically high (>30%) and low (< or =20%) CO(2) detection thresholds. Three second pulses of CO(2) (15-45% v/v) paired with air in random order (12-15 s inter-stimulus interval; 60 s inter-trial interval) were administered by nasal cannula at 5 l/min. in an ascending series. For each subject, both a CO(2) detection threshold and suprathreshold psychophysical ratings [psi; labeled magnitude scale] were generated. All subjects showed phasic drops in pH associated with CO(2) stimulation (DeltapH). For all subjects combined, a positive correlation was apparent between applied [CO(2)] and both DeltapH and psi, as well as between DeltapH and psi themselves (P < 0.0001 for each comparison). Subjects with historically low CO(2) thresholds showed steeper dose-response curves for psi as a function of both applied [CO(2)] and DeltapH, but not for DeltapH as a function of applied [CO(2)]. For the six of eight subjects with measurable pH changes at threshold, DeltapH was positively related to log [CO(2) threshold] (P < 0.01). These data imply that variability in CO(2) detection thresholds and suprathreshold rating may derive from intrinsic differences in neural sensitivity, rather than differences in stimulus activation to hydrogen ion.     

Cutaneous sensory afferents recorded from the nervus intramandibularis ofGallus gallus vardomesticus

Summary The responses of single sensory afferent nerve fibres were recorded from small nerve bundles of the intramandibular nerve of the chicken following thermal and mechanical stimulation of the beak. Thermoreceptors, nociceptors and mechanoreceptors were identified and their responses characterized.Of the thermoreceptors identified 11 units were classified as cold receptors, which responded to cooling the receptive field by increasing the discharge rate and had conduction velocities in the range 0.83 to 4.4 m/s. Only one warm unit was identified.Two classes of nociceptors were identified: mechano-thermal (polymodal) nociceptors and high threshold mechanical nociceptors. The discharge characteristics and stimulus-response curves of both types were described. While the mechanothermal nociceptors were exclusively C-fibres (c.v. 0.4 to 1.86 m/s), the high threshold mechanoreceptors contained both C and A delta fibres (c.v. 1 to 5.5 m/s). Thermal response thresholds for the mechano-thermal units ranged from 41 to 50 °C with mechanical thresholds of 2 to over 50 g. Mechanical thresholds for the high threshold units ranged from 5 to over 50 g.The mechanoreceptors were either slowly or rapidly adapting. The pattern of response together with stimulus-response curves were presented for the slowly adapting units. Conduction velocities of the slowly adapting units varied from 0.7 to 20 m/s and mechanical threshold from 0.1 to 2 g. On the basis of their response to a vibrating, and a ramp-and-hold mechanical stimulus, the rapidly adapting units were divided into Herbst and Grandry units with only the Herbst units responding accurately to the vibrating stimulus. Both units had fibres conducting in the 50 m/s range with thresholds in the 0.1 to 10 g range.The results are discussed in relation to the receptors found in other avian species and mammalian peripheral sensory afferents.Abbreviations c.v. conduction velocity - RA rapidly adapting (receptors) - SA slowly adapting (receptors)     

Area summation in human vision at and above detection threshold

The initial image-processing stages of visual cortex are well suited to a local (patchwise) analysis of the viewed scene. But the world's structures extend over space as textures and surfaces, suggesting the need for spatial integration. Most models of contrast vision fall shy of this process because (i) the weak area summation at detection threshold is attributed to probability summation (PS) and (ii) there is little or no advantage of area well above threshold. Both of these views are challenged here. First, it is shown that results at threshold are consistent with linear summation of contrast following retinal inhomogeneity, spatial filtering, nonlinear contrast transduction and multiple sources of additive Gaussian noise. We suggest that the suprathreshold loss of the area advantage in previous studies is due to a concomitant increase in suppression from the pedestal. To overcome this confound, a novel stimulus class is designed where: (i) the observer operates on a constant retinal area, (ii) the target area is controlled within this summation field, and (iii) the pedestal is fixed in size. Using this arrangement, substantial summation is found along the entire masking function, including the region of facilitation. Our analysis shows that PS and uncertainty cannot account for the results, and that suprathreshold summation of contrast extends over at least seven target cycles of grating.     

Changes in perceived contrast of suprathreshold gratings as a function of orientation and spatial frequency

Orientation anisotropy for suprathreshold gratings of different spatial frequencies was measured using a contrast matching procedure. Observers matched the contrast of sine-wave gratings of various orientations to a vertical reference grating set at different reference contrasts. At threshold, the size of the anisotropy increased with spatial frequency, confirming previous results. When the reference grating contrast was set above threshold, the anisotropy declined, and eventually disappeared for gratings of medium spatial frequencies. At higher spatial frequencies, although the relative anisotropy became smaller, it did not disappear within the range of contrasts used in this study. For medium, but not for high spatial frequencies, the data are consistent with Kulikowski's (1976) model of effective contrast constancy.