The Extraction of Depth Structure from Shading and Texture in the Macaque Brain

We used contrast-agent enhanced functional magnetic resonance imaging (fMRI) in the alert monkey to map the cortical regions involved in the extraction of 3D shape from the monocular static cues, texture and shading. As in the parallel human imaging study [1], we contrasted the 3D condition to several 2D control conditions. The extraction of 3D shape from texture (3D SfT) involves both ventral and parietal regions, in addition to early visual areas. Strongest activation was observed in CIP, with decreasing strength towards the anterior part of the intraparietal sulcus (IPS). In the ventral stream 3D SfT sensitivity was observed in a ventral portion of TEO. The extraction of 3D shape from shading (3D SfS) involved predominantly ventral regions, such as V4 and a dorsal potion of TEO. These results are similar to those obtained earlier in human subjects and indicate that the extraction of 3D shape from texture is performed in both ventral and dorsal regions for both species, as are the motion and disparity cues, whereas shading is mainly processed in the ventral stream.     

Spatiotemporally Asymmetric Excitation Supports Mammalian Retinal Motion Sensitivity

1. Download : Download high-res image (223KB)
2. Download : Download full-size image

     

Uniform versus Asymmetric Shading Mediates Crown Recession in Conifers

In this study we explore the impact of asymmetrical vs. uniform crown shading on the mortality and growth of upper and lower branches within tree crowns, for two conifer species: shade intolerant lodgepole pine (Pinus contorta) and shade tolerant white spruce (Picea glauca). We also explore xylem hydraulics, foliar nutrition, and carbohydrate status as drivers for growth and expansion of the lower and upper branches in various types of shading. This study was conducted over a two-year period across 10 regenerating forest sites dominated by lodgepole pine and white spruce, in the lower foothills of Alberta, Canada. Trees were assigned to one of four shading treatments: (1), complete uniform shading of the entire tree, (2) light asymmetric shading where the lower 1/4–1/3 of the tree crown was shaded, (3) heavy asymmetric shading as in (2) except with greater light reduction and (4) control in which no artificial shading occurred and most of the entire crown was exposed to full light. Asymmetrical shading of only the lower crown had a larger negative impact on the bud expansion and growth than did uniform shading, and the effect was stronger in pine relative to spruce. In addition, lower branches in pine also had lower carbon reserves, and reduced xylem-area specific conductivity compared to spruce. For both species, but particularly the pine, the needles of lower branches tended to store less C than upper branches in the asymmetric shade, which could suggest a movement of reserves away from the lower branches. The implications of these findings correspond with the inherent shade tolerance and self-pruning behavior of these conifers and supports a carbon based mechanism for branch mortality – mediated by an asymmetry in light exposure of the crown.     

Shading Beats Binocular Disparity in Depth from Luminance Gradients: Evidence against a Maximum Likelihood Principle for Cue Combination

Perceived depth is conveyed by multiple cues, including binocular disparity and luminance shading. Depth perception from luminance shading information depends on the perceptual assumption for the incident light, which has been shown to default to a diffuse illumination assumption. We focus on the case of sinusoidally corrugated surfaces to ask how shading and disparity cues combine defined by the joint luminance gradients and intrinsic disparity modulation that would occur in viewing the physical corrugation of a uniform surface under diffuse illumination. Such surfaces were simulated with a sinusoidal luminance modulation (0.26 or 1.8 cy/deg, contrast 20%-80%) modulated either in-phase or in opposite phase with a sinusoidal disparity of the same corrugation frequency, with disparity amplitudes ranging from 0’-20’. The observers’ task was to adjust the binocular disparity of a comparison random-dot stereogram surface to match the perceived depth of the joint luminance/disparity-modulated corrugation target. Regardless of target spatial frequency, the perceived target depth increased with the luminance contrast and depended on luminance phase but was largely unaffected by the luminance disparity modulation. These results validate the idea that human observers can use the diffuse illumination assumption to perceive depth from luminance gradients alone without making an assumption of light direction. For depth judgments with combined cues, the observers gave much greater weighting to the luminance shading than to the disparity modulation of the targets. The results were not well-fit by a Bayesian cue-combination model weighted in proportion to the variance of the measurements for each cue in isolation. Instead, they suggest that the visual system uses disjunctive mechanisms to process these two types of information rather than combining them according to their likelihood ratios.     

终止子的概念与结构之辨析

指出一些生物化学,分子生物学及遗传学方面高等院校教材和著作中,较为普遍存在的关于转录终止子概念与结构的描述和解释方面的错误。     

Discrimination of Low-Frequency Tones Employs Temporal Fine Structure

An auditory neuron can preserve the temporal fine structure of a low-frequency tone by phase-locking its response to the stimulus. Apart from sound localization, however, much about the role of this temporal information for signal processing in the brain remains unknown. Through psychoacoustic studies we provide direct evidence that humans employ temporal fine structure to discriminate between frequencies. To this end we construct tones that are based on a single frequency but in which, through the concatenation of wavelets, the phase changes randomly every few cycles. We then test the frequency discrimination of these phase-changing tones, of control tones without phase changes, and of short tones that consist of a single wavelet. For carrier frequencies below a few kilohertz we find that phase changes systematically worsen frequency discrimination. No such effect appears for higher carrier frequencies at which temporal information is not available in the central auditory system.     

Long-Range Surface Plasmon Supported by Asymmetric Bimetallic Structure

With this study, we prove that an asymmetric bimetallic structure can support long-range surface plasmon (LRSP) and propose a procedure for its optimization. By applying different criteria we prove that the plasmon which is supported by the structure is indeed LRSP. Unlike all known asymmetric structures supporting LRSP, our structure provides prism excitation and can be used as a biochip for biosensing. Moreover, we show that the structure supports a plasmon with the same propagation constant as LRSP and which is excited at the interface of metal and buffer. This plasmon can be used as a reference channel providing information for the temperature of the structure.     

Asymmetric Engagement of Amygdala and Its Gamma Connectivity in Early Emotional Face Processing

The amygdala has been regarded as a key substrate for emotion processing. However, the engagement of the left and right amygdala during the early perceptual processing of different emotional faces remains unclear. We investigated the temporal profiles of oscillatory gamma activity in the amygdala and effective connectivity of the amygdala with the thalamus and cortical areas during implicit emotion-perceptual tasks using event-related magnetoencephalography (MEG). We found that within 100 ms after stimulus onset the right amygdala habituated to emotional faces rapidly (with duration around 20–30 ms), whereas activity in the left amygdala (with duration around 50–60 ms) sustained longer than that in the right. Our data suggest that the right amygdala could be linked to autonomic arousal generated by facial emotions and the left amygdala might be involved in decoding or evaluating expressive faces in the early perceptual emotion processing. The results of effective connectivity provide evidence that only negative emotional processing engages both cortical and subcortical pathways connected to the right amygdala, representing its evolutional significance (survival). These findings demonstrate the asymmetric engagement of bilateral amygdala in emotional face processing as well as the capability of MEG for assessing thalamo-cortico-limbic circuitry.     

遮阴对猫爪草光合特性及叶片解剖结构的影响

【目的】探究不同遮阴度对野生植物猫爪草（Ranunculus ternatus Thunb）光合特性和叶片解剖结构的影响,为深入了解其耐阴性以及开展规模化栽植提供理论基础。【方法】采用控制变量法,以盆栽猫爪草为试验材料,设置全光照（CK）、30%遮阴（T1）、50%遮阴（T2）、70%遮阴（T3）和90%遮阴（T4）5个处理,对不同遮阴处理下的光合特性及叶片解剖结构进行分析。【结果】（1）随着遮阴程度增加,叶面积在T3环境下达到最大值,株高和茎粗逐渐降低。（2）随遮阴程度的增加,叶片表观量子效率（AQE）先升后降,在T4处理下显著低于其他处理,而光饱和点（LSP）、光补偿点（LCP）、暗呼吸速率（Rd）和最大净光合速率（Pnmax）逐渐降低;最大荧光（Fm）、可变荧光（Fv）、最大化学效率（Fv/Fm）和PSⅡ潜在活性（Fv/F0）先升后降,初始荧光（F0）热耗散的电子比率（φDo）则先降后升。（3）随着遮阴程度的增加,叶片气孔密度先减后增,并在T3处理达到最小值,上下表皮厚度和海绵组织厚度逐渐降低,组织结构紧密度（CTR）先降后升,组织结构疏松度（SR）先升后降。（4）叶片栅栏组织、海绵组织、叶片厚度及上、下表皮厚度与Rd呈极显著或显著正相关关系;海绵组织厚度、CTR和SR与Pnmax ,以及栅海比（P/S）、SR与AQE均呈显著正相关关系;海绵组织厚度和SR与F0呈显著负相关关系。【结论】猫爪草可以通过降低光合速率和改变叶片结构来提高耐阴性,在全光照下生长良好,也能较好地适应30%-70%遮阴环境。     

Depth inferences from vertically imbedded cephalopods

Raup, D. M.: Depth inferences from vertically imbedded cephalopods.
Vertically imbedded cephalopods are not uncommon in the fossil record. Experiments with modern Nautilus show that after death the shell cannot maintain a vertical orientation on the sea floor unless the depth is less than about 10 m. At greater depths, hydrostatic pressure causes flooding of the phragmocone sufficient to make the shell fall over. The depth limit applies whether the shell floats after death or not. Calculations made on data from six ammonite species indicate that the same depth limit can be applied to fossil coiled cephalopods. Vertical preservation can occur in deeper water only if the shell is vertically oriented upon impact and if the sediment is such as to trap the shell in that position.     

Estimating Cell Depth from Somatic Mutations

The depth of a cell of a multicellular organism is the number of cell divisions it underwent since the zygote, and knowing this basic cell property would help address fundamental problems in several areas of biology. At present, the depths of the vast majority of human and mouse cell types are unknown. Here, we show a method for estimating the depth of a cell by analyzing somatic mutations in its microsatellites, and provide to our knowledge for the first time reliable depth estimates for several cells types in mice. According to our estimates, the average depth of oocytes is 29, consistent with previous estimates. The average depth of B cells ranges from 34 to 79, linearly related to the mouse age, suggesting a rate of one cell division per day. In contrast, various types of adult stem cells underwent on average fewer cell divisions, supporting the notion that adult stem cells are relatively quiescent. Our method for depth estimation opens a window for revealing tissue turnover rates in animals, including humans, which has important implications for our knowledge of the body under physiological and pathological conditions.     

Discrimination: from behaviour to brain

Discrimination is a skill needed by many organisms for survival: decisions about food, shelter, and mate selection all require the ability to distinguish among stimuli. This article reviews the how and why of discrimination and how researchers may exploit this natural skill in the laboratory to learn more about what features of stimuli animals use to discriminate. The paper then discusses the possible neurophysiological basis of discrimination and proposes a model, based on one of stimulus-association put forth by Beninger and Gerdjikov (2004) [Beninger, R.J., Gerdjikov, T.V., 2004. The role of signaling molecules in reward-related incentive learning. Neurotox. Res., 6, 91-104], to account for the role of dopamine in how an animal learns to discriminate rewarded from non-rewarded stimuli.     

Effects of Shading on Shoot Morphology, Wood Production and Structure of Nothofagus procera Seedlings

Four-year-old seedlings of Nothofagus procera were grown outof doors in pots while subjected to two levels of shading (mediumand dense shades) and to full light. Shoot morphological andwood anatomical studies showed that growing N. procera in mediumlight, rather than in full light, can result in fewer leaves,but higher shoot growth, a greater amount of fibres, a widerwood growth increment and thicker fibre walls. Significant positivecorrelations were found between the rate of shoot extensionand the rate of wood production. Conversely, significant negativecorrelations were obtained between fibre lumen diameter andfibre wall thickness. The significance of these findings isdiscussed. Southern beech, Nothofagus procera, shading, shoot morphology, wood production, wood anatomy     

遮光对连香树幼苗光合特性及其叶片解剖结构的影响

以2年生连香树实生苗为材料,在田间通过黑色遮阳网设置全光照(L₀)及透光率55%(L₁)、25%(L₂)和10%(L₃)4种光环境,研究遮光对连香树幼苗光合作用及叶片解剖结构的影响。结果表明：(1)连香树幼苗叶片P_n在全光和L₁处理下呈非典型的“乁”形变化,未出现“午休”现象,中午14:00出现极值,而在L₂和L₃处理下变化相对缓和,极值出现在中午12:00;叶片G_s呈现与P_n类似的变化趋势,而C_i则呈基本一致的凹形变化。(2)各处理P_n、G_s和T_r的日均值均表现为L₀＞L₁＞L₂＞L₃,而C_i的日均值则呈相反的顺序;P_n与G_s、T_r、气温和光合有效辐射均呈极显著正相关关系(P＜0.01)。(3)全光照连香树幼苗的光补偿点(LCP)、光饱和点(LSP)、暗呼吸速率(R_d)均显著高于遮光处理,并维持较高的P_n而未出现明显的光抑制;遮光导致幼苗的LCP、LSP、R_d显著降低,有利于充分利用弱光,以满足低光环境下植株的正常生长。(4)与全光照相比,遮光下连香树叶片气孔密度显著变小,但气孔器长度、气孔器宽度、单个气孔器面积显著增加,气孔器面积百分比减少,影响幼苗细胞内外的水分和气体传递。(5)遮光条件下,连香树叶片明显变薄,表皮细胞厚度减小,栅栏组织(PT)厚度降低,排列变得疏松,海绵组织(ST)厚度增加,PT/ST相应减小。(6)与全光照相比,强度遮光下(L₂和L₃)连香树幼苗生长受阻,苗高(H)和基径(D)明显减小,生物量模型D²H下降;而轻度遮光(L₁)下幼苗H和D、H/D和D₂H均未出现显著变化。研究发现,连香树具有一定的光忍耐性和喜光性,对光照条件的生态幅较宽,轻度遮光影响较小,但强度遮光对连香树幼苗气体交换参数和光合响应特征产生了显著影响,同时影响了叶片的解剖结构和气孔分布特征,从而影响连香树幼苗的生长形态。在育苗生产中,适度遮光有利于降低气温、减小蒸腾,但遮光后田间有效辐射强度应保持在自然光强的55%以上。     

遮荫对黑茶藨子叶片形态结构和光合特性的影响

以黑茶藨子为试验材料,通过人工遮荫的方式,研究了不同遮荫强度（全光照、20%和60%遮荫）和遮荫时间（初期、中期和后期）对黑茶藨子叶片形态解剖结构和光合特性的影响。结果表明：（1）20%、60%遮荫处理的叶片厚度均显著低于全光照处理,上下表皮厚度则高于全光照处理;随着遮荫强度的加大,栅栏组织与海绵组织厚度比值大小均呈减少趋势,随着遮荫时间的延长,呈增加趋势。（2）遮荫初期和中期,20%遮荫处理的叶片净光合速率（P_n）比全光照和60%遮荫处理的值略高,但差异并不显著（P>0.05）,其蒸腾速率（T_r）、水分利用效率（WUE）也略有增加;但是,60%遮荫处理的叶片净光合速率（P_n）显著低于全光照处理（P<0.05）。遮荫后期,60%遮荫处理的叶片净光合速率（P_n）显著高于全光照处理,且水分利用效率（WUE）、气孔导度（G_s）、蒸腾速率（T_r）均显著高于全光照和20%遮荫处理。综上所述,遮荫处理导致叶片厚度减少,海绵组织比例增加,有利于减少透射光中的光量子丧失,提高光能利用效率;生长早期和中期作20%轻度遮荫处理,后期作60%中度遮荫处理能提高植株对光和水分的利用效率、维持较高的光合速率、延缓衰老。     

Role of Secondary Structure in Discrimination between Constitutive and Inducible Activators

We have examined structural differences between the proto-oncogene c-Myb and the cyclic AMP-responsive factor CREB that underlie their constitutive or signal-dependent activation properties. Both proteins stimulate gene expression via activating regions that articulate with a shallow hydrophobic groove in the KIX domain of the coactivator CREB-binding protein (CBP). Three hydrophobic residues in c-Myb that are conserved in CREB function importantly in cellular gene activation and in complex formation with KIX. These hydrophobic residues are assembled on one face of an amphipathic helix in both proteins, and mutations that disrupt c-Myb or CREB helicity in this region block interaction of either factor with KIX. Binding of the helical c-Myb domain to KIX is accompanied by a substantial increase in entropy that compensates for the comparatively low enthalpy of complex formation. By contrast, binding of CREB to KIX entails a large entropy cost due to a random coil-to-helix transition in CREB that accompanies complex formation. These results indicate that the constitutive and inducible activation properties of c-Myb and CREB reflect secondary structural characteristics of their corresponding activating regions that influence the thermodynamics of formation of a complex with CBP.     

Depth Discrimination in Diffuse Optical Transmission Imaging by Planar Scanning Off-Axis Fibers: INITIAL Applications to Optical Mammography

We present a method for depth discrimination in parallel-plate, transmission mode, diffuse optical imaging. The method is based on scanning a set of detector pairs, where the two detectors in each pair are separated by a distance δD_i along direction δD_i within the x-y scanning plane. A given optical inhomogeneity appears shifted by α_iδD_i (with 0≤ α_i ≤1) in the images collected with the two detection fibers of the i-th pair. Such a spatial shift can be translated into a measurement of the depth z of the inhomogeneity, and the depth measurements based on each detector pair are combined into a specially designed weighted average. This depth assessment is demonstrated on tissue-like phantoms for simple inhomogeneities such as straight rods in single-rod or multiple-rod configurations, and for more complex curved structures which mimic blood vessels in the female breast. In these phantom tests, the method has recovered the depth of single inhomogeneities in the central position of the phantom to within 4 mm of their actual value, and within 7 mm for more superficial inhomogeneities, where the thickness of the phantom was 65 mm. The application of this method to more complex images, such as optical mammograms, requires a robust approach to identify corresponding structures in the images collected with the two detectors of a given pair. To this aim, we propose an approach based on the inner product of the skeleton images collected with the two detectors of each pair, and we present an application of this approach to optical in vivo images of the female breast. This depth discrimination method can enhance the spatial information content of 2D projection images of the breast by assessing the depth of detected structures, and by allowing for 3D localization of breast tumors.     

遮光对红果榆幼苗光合作用及叶片解剖结构的影响

为揭示不同光照条件下红果榆幼苗光合生理及叶片结构的变化,推测其耐荫性,设置L_(0)(辐射光强100%)、L1(辐射光强45%)、L_(2)(辐射光强25%)和L_(3)(辐射光强18%)4种不同的光环境,研究了遮光对红果榆幼苗光合作用参数、叶片形态及解剖结构的影响。结果表明:不同遮光处理下P_(n)呈现出不对称的凸型变化。L_(1)处理下P_(n)变幅较大,最大值出现在午时,午后P_(n)开始急剧下降。而遮光处理下光合有效辐射(PAR)显著不足,各时点P_(n)绝对值显著减小,峰值降低。相应地,G_(s)表现出先升高后降低,而G_(i)呈现先降后升的凹形变化。不同遮光条件下P_(n)的日均大小序列为L_(0)>L_(1)>L_(2)>L_(3)。遮光显著影响红果榆幼苗的光响应参数。弱光条件下红果榆幼苗LCP、LSP显著降低,P_(nmax)、R_(d)均明显变小。遮光影响叶片的形态发育。随着遮光强度的加大,单叶面积(SLA)增加,比叶重(LMA)减小,比叶面积(LAM)增大,并与对照相比呈现显著差异(P<0.05)。遮光条件下红果榆叶片厚度变小,表皮细胞(EP)厚度变薄,栅栏组织(PT)和海绵组织(ST)厚度均明显降低。红果榆苗期表现出一定的喜光性,对弱光具有一定的生理调节能力,但是重度郁闭将导致幼苗营养不良。光照条件不足可能是影响红果榆种实成苗、种群更新的重要外因。生产实践中,建议对密度过大的自然林实施适度疏伐,增进通风透光,适度清理林内凋落物,为野生种群的更新繁衍创造条件。     

遮荫处理对绞股蓝叶形态结构及光合特性的影响

研究了田间栽培和盆栽绞股蓝(Gynostemmapentaphyllum)在不同程度遮荫处理下的叶形态结构及光合特性的变化。结果表明,两种栽培方式下的绞股蓝叶形态结构及光合特性具有相似的变化规律。具体表现为叶形态结构受光照强度影响较大,与全日照相比,遮荫条件下叶面积增大,叶色深绿,叶片厚度以及栅栏组织和海绵组织厚度小,维管束不发达,表现出阴生叶的特点。同时,遮荫条件下叶片的叶绿素含量和净光合速率高于全日照处理。这些特点表明,绞股蓝属于喜阴植物,遮荫处理有利于其生长发育。