Color signals in area MT of the macaque monkey

The relationship between the neural processing of color and motion information has been a contentious issue in visual neuroscience. We examined this relationship directly by measuring neural responses to isoluminant S cone signals in extrastriate area MT of the macaque monkey. S cone stimuli produced robust, direction-selective responses at most recording sites, indicating that color signals are present in MT. While these responses were unequivocal, S cone contrast sensitivity was, on average, 1.0-1.3 log units lower than luminance contrast sensitivity. The presence of S cone responses and the relative sensitivity of MT neurons to S cone and luminance signals agree with functional magnetic resonance imaging (fMRI) measurements in human MT+. The results are consistent with the hypothesis that color signals in MT influence behavior in speed judgment tasks.     

Specialized circuits from primary visual cortex to V2 and area MT

Primary visual cortex recombines inputs from magnocellular (M) and parvocellular (P) streams to create functionally specialized outputs. Understanding these input-output relationships is complicated by the fact that layer 4B, which provides outputs to dorsal visual areas, contains multiple cell types. Using a modified rabies virus that expresses green fluorescent protein, we show that layer 4B neurons projecting to MT are a majority spiny stellate, whereas those projecting to V2 are overwhelmingly pyramidal. Regardless of cell type, MT-projecting neurons have larger cell bodies, more dendritic length, and are deeper within layer 4B. Furthermore, MT-projecting pyramidal neurons are located preferentially underneath cytochrome oxidase blobs, indicating that MT-projecting neurons of both types restrict their dendrites to M-recipient zones. We conclude that MT-projecting layer 4B neurons are specialized for the fast transmission of information from the M pathway, while V2-projecting neurons are likely to mediate slower computations involving mixed M and P signals.     

The response properties of cells in the middle temporal area (area MT) of owl monkey visual cortex

Recordings from 178 single cells in the middle temporal area (area MT) of owl monkey showed that most cells there are orientation- and direction-selective. They also revealed that a powerful range of binocular interactions occur in area MT, with 20% of the cells being responsive to binocular stimulation only, 5% to monocular stimulation only and about 50% of all cells showing some degree of interocular interaction.     

Adaptive surround modulation in cortical area MT

Visual motion perception relies on two opposing operations: integration and segmentation. Integration overcomes motion ambiguity in the visual image by spatial pooling of motion signals, whereas segmentation identifies differences between adjacent moving objects. For visual motion area MT, previous investigations have reported that stimuli in the receptive field surround, which do not elicit a response when presented alone, can nevertheless modulate responses to stimuli in the receptive field center. The directional tuning of this "surround modulation" has been found to be mainly antagonistic and hence consistent with segmentation. Here, we report that surround modulation in area MT can be either antagonistic or integrative depending upon the visual stimulus. Both types of modulation were delayed relative to response onset. Our results suggest that the dominance of antagonistic modulation in previous MT studies was due to stimulus choice and that segmentation and integration are achieved, in part, via adaptive surround modulation.     

Tuned inhibition in perceptual decision-making circuits can explain seemingly suboptimal confidence behavior

Current dominant views hold that perceptual confidence reflects the probability that a decision is correct. Although these views have enjoyed some empirical support, recent behavioral results indicate that confidence and the probability of being correct can be dissociated. An alternative hypothesis suggests that confidence instead reflects the magnitude of evidence in favor of a decision while being relatively insensitive to the evidence opposing the decision. We considered how this alternative hypothesis might be biologically instantiated by developing a simple neural network model incorporating a known property of sensory neurons: tuned inhibition. The key idea of the model is that the level of inhibition that each accumulator unit receives from units with the opposite tuning preference, i.e. its inhibition ‘tuning’, dictates its contribution to perceptual decisions versus confidence judgments, such that units with higher tuned inhibition (computing relative evidence for different perceptual interpretations) determine perceptual discrimination decisions, and units with lower tuned inhibition (computing absolute evidence) determine confidence. We demonstrate that this biologically plausible model can account for several counterintuitive findings reported in the literature where confidence and decision accuracy dissociate. By comparing model fits, we further demonstrate that a full complement of behavioral data across several previously published experimental results—including accuracy, reaction time, mean confidence, and metacognitive sensitivity—is best accounted for when confidence is computed from units without, rather than units with, tuned inhibition. Finally, we discuss predictions of our results and model for future neurobiological studies. These findings suggest that the brain has developed and implements this alternative, heuristic theory of perceptual confidence computation by relying on the diversity of neural resources available.     

杉木人工林林分叶面积动态变化规律

叶面积与树木生长密切相关,是量化树木潜在生产能力的重要因子,其动态变化直接驱动林木生长的变化,但目前学者们对于林分叶面积动态变化规律却持有不同的观点。以亚热带不同气候区杉木人工林为研究对象,基于54个样地,共144株解析木的数据,采用6种生长方程通过非线性混合效应模型分别构建杉木单木叶面积模型和林分密度模型,将二者相乘得到林分叶面积动态变化模型,进而探究其动态变化规律。结果表明,以样地作为随机效应因子,考虑Logistic方程a参数上的随机效应,同时不考虑异方差结构的混合模型(样地水平)作为单木叶面积的最优模型;以地区作为随机效应因子,考虑Logistic方程a参数上的随机效应,同时不考虑异方差结构的混合模型(总体平均水平)作为林分密度的最优模型;林分叶面积动态变化呈单峰形式,幼龄阶段增长较快,达到峰值后迅速下降,之后下降幅度减少。本研究在考虑林分自然稀疏的前提下从生长模型的角度证明了杉木林分叶面积动态变化呈单峰型,而非达到顶峰后保持不变,同时也表明林分叶面积达到顶峰后下降是由于林分密度的降低引起的。研究结果对于合理经营不同气候梯度的杉木人工林具有重要意义。     

Context-dependent changes in functional circuitry in visual area MT

Animals can flexibly change their behavior in response to a particular sensory stimulus; the mapping between sensory and motor representations in the brain must therefore be flexible as well. Changes in the correlated firing of pairs of neurons may provide a metric of changes in functional circuitry during behavior. We studied dynamic changes in functional circuitry by analyzing the noise correlations of simultaneously recorded MT neurons in two behavioral contexts: one that promotes cooperative interactions between the two neurons and another that promotes competitive interactions. We found that identical visual stimuli give rise to differences in noise correlation in the two contexts, suggesting that MT neurons receive inputs of central origin whose strength changes with the task structure. The data are consistent with a mixed feature-based attentional strategy model in which the animal sometimes alternates attention between opposite directions of motion and sometimes attends to the two directions simultaneously.     

滇金丝猴分布区森林面积变化的时空特征及其影响因素

森林生态系统是滇金丝猴(Rhinopithecus bieti)的主要生境,森林面积变化会直接影响滇金丝猴的生存。本研究基于全球森林变化(Global Forest Change)数据,采用Theil-Sen趋势分析和Mann-Kendall检验、热点分析与地理探测器模型等方法,探讨了滇金丝猴分布区2001—2019年森林面积变化的时空特征及其影响因素。结果表明:(1)近20年间,滇金丝猴分布区森林面积变化总量为3.81×10~4 hm~2,约占研究区森林面积的2.44%,逐年森林面积变化呈现较大的年际波动,其中5个保护地森林面积变化总量达5456 hm~2,约占研究区森林面积变化总量的14.3%,老君山风景区和云岭保护区森林面积变化的比例较高;(2)滇金丝猴分布区森林面积变化趋于缓和,其中森林面积减少呈现显著增加的区域面积为1.03×10~5 hm~2,占整个研究区面积的2.9%;森林面积减少呈现显著减少的区域面积为3.05×10~5 hm~2,占整个研究区面积的7.9%;同时森林面积变化的热点区域面积呈不断下降的趋势;(3)滇金丝猴分布区森林面积变化呈现向低海拔、高坡度转移的趋势;...     

Trying to predict and explain the presence of African trypanosomes in tsetse flies.

Trypanosome infections identified by polymerase chain reaction on field-caught tsetse flies from various locations were analyzed with respect to factors intrinsic and extrinsic to the trypanosome-tsetse association. These factors were then simultaneously analyzed using artificial neural networks (ANNs) and the important factors were identified to predict and explain the presence of trypanosomes in tsetse. Among 4 trypanosome subgroups (Trypanosoma brucei s.l., T. congolense of the 'savannah' and of the 'riverine-forest' types, and T. simiae), the presence of the 2 types of T. congolense was predictable in more than 80% of cases, suggesting that the model incorporated some of the key variables. These 2 types of T. congolense were significantly associated in tsetse. Among all the examined factors, it was the presence of T. congolense savannah type that best explained the presence of T. congolense riverine forest type. One possible biological mechanism would be 'hitchhiking,' as previously suspected for other parasites. The model could be improved by adding other important variables to the trypanosome tsetse associations.     

Bias in normalization: Causes,consequences, detection and remedies

Introduction Normalization is an optional step in LCIA that is used to better understand the relative importance and magnitude of the impact category indicator results. It is used for error checking, as a first step in weighting, and for standalone presentation of results. A normalized score for a certain impact category is obtained by determining the ratio of the category indicator result of the product and that of a reference system, such as the world in a certain year or the population of a specific area in a certain year. Biased Normalization In determining these two quantities, the numerator, the denominator, or both can suffer from incompleteness due to a lack of emission data and/or characterisation factors. This leads to what we call a biased normalization. As a consequence. the normalized category indicator result can be too low or too high. Some examples from hypothetical and real case studies demonstrate this. Consequences of Biased Normalization Especially when for some impact categories the normalized category indicator result is right, for others too low, and for others too high, severe problems in using normalized scores can show up. It is shown how this may affect the three types of usage of normalized results: error checking, weighting and standalone presentation. Detection and Remedies of Biased Normalization Some easy checks are proposed that at least alert the LCA practitioner of the possibility of a biased result. These checks are illustrated for an example system on hydrogen production. A number of remedies of this problem is possible. These are discussed. In particular, casedependent normalization is shown to solve some problems, but on the expense of creating other problems. Discussion It appears that there is only one good solution: databases and tables of characterisation factors must be made more completely, so that the risk of detrimental bias is reduced. On the other hand, the use of the previously introduced checks should become a standard element in LCA practice, and should be facilitated with LCA software. ESS-Submission Editor: Duane A. Tolle (tolled@battelle.org)     

土地覆盖变化检测方法比较——以内蒙古草原区为例

随着对地观测技术的不断发展,遥感影像分辨率逐渐提高,促进了基于遥感影像的变化检测从传统像元级的检测向面向对象的检测转变。为了探究面向对象的变化检测方法在土地覆盖变化检测中的有效性和适用性,对面向对象的变化检测方法与常规的变化检测方法进行对比评价。以内蒙古鄂尔多斯和包头地区为试验区,选取2002年及2011年的Landsat TM/ETM+影像为数据源,比较了图像代数运算、图像变换、图像空间结构特征和面向对象的多种变化检测方法,对研究区两期土地覆盖进行了变化检测研究。结果表明:面向对象的变化检测方法在总体精度、kappa系数上都有明显的优越性,总体精度均在87.42%以上,尤其以面向对象的变化矢量分析方法精度最高,达91.56%。此外,主成分差异法也有较好的检测效果,总体精度为87.83%。对总体精度较高的3种方法在不同土地覆盖变化类型中检测效果的研究表明:对于研究区几种主要土地覆盖变化类型,面向对象的变化矢量分析法均有较理想的检测效果,平均精度为85%左右,且始终优于面向对象的光谱向量相似法,以居民地及旱地相关的变化类型最为明显;主成分差异法对不同土地覆盖变化类型检测效果差异很大,对其中4种变化类型的精度甚至达到了93%以上,但对于检测草地与裸地间转化精度很低,甚至只有8.69%;在与工矿用地有关的土地覆盖变化类型中,面向对象的变化矢量分析法的精度明显高于主成分差异法,而在与居民地有关的变化类型中,主成分差异法表现出一定优势。     

Attention to surfaces modulates motion processing in extrastriate area MT

In the visual system, early atomized representations are grouped into higher-level entities through processes of perceptual organization. Here we present neurophysiological evidence that a representation of a simple object, a surface defined by color and motion, can be the unit of attentional selection at an early stage of visual processing. Monkeys were cued by the color of a fixation spot to attend to one of two transparent random-dot surfaces, one red and one green, which occupied the same region of space. Motion of the attended surface drove neurons in the middle temporal (MT) visual area more strongly than physically identical motion of the non-attended surface, even though both occurred within the spotlight of attention. Surface-based effects of attention persisted even without differential surface coloring, but attentional modulation was stronger with color. These results show that attention can select surface representations to modulate visual processing as early as cortical area MT.     

Feature-based anticipation of cues that predict reward in monkey caudate nucleus

A subset of caudate neurons fires before cues that instruct the monkey what he should do. To test the hypothesis that the anticipatory activity of such neurons depends on the context of stimulus-reward mapping, we examined their activity while the monkeys performed a memory-guided saccade task in which either the position or the color of a cue indicated presence or absence of reward. Some neurons showed anticipatory activity only when a particular position was associated with reward, while others fired selectively for color-reward associations. The functional segregation suggests that caudate neurons participate in feature-based anticipation of visual information that predicts reward. This neuronal code influences the general activity level in response to visual features without improving the quality of visual discrimination.     

Traits explain community disassembly and trophic contraction following experimental environmental change

Many ecosystems are currently undergoing dramatic changes in biodiversity due to habitat loss and climate change. Responses to global change at the community level are poorly understood, as are the impacts of community disassembly on ecosystem‐level processes. Uncertainties remain regarding the patterns of extirpation and persistence under single vs. multiple forms of environmental change. Here, we use a trait‐based and food web approach to examine the effects of experimentally changing moisture, temperature and habitat ‘openness’ on a functionally important group of microarthropods associated with a boreal forest floor bryosphere (detrital moss) system. Overall, the outcome of community disassembly was mediated by the correlation between our environmental factors and species traits, particularly body size. Minor increases in summer temperatures maintained greater species richness, whereas drought stress had a significant negative effect on community‐level abundance and richness. These effects were reflected in modifications to the community‐wide body‐size spectra. Habitat openness alleviated biodiversity loss in the larger‐bodied species of the most abundant taxonomic group, but did not fully mitigate the effects of drought. The most striking result of this experiment was an overall contraction of the food web among persistent species under drought stress (i.e. those not extirpated by environmental change). These results suggest that major changes in boreal microarthropod community structure are likely to occur in response to common forms of global change. Moreover, the contraction in trophic structure even amongst tolerant species suggests that ecosystem function within the bryosphere can be altered by environmental change.     

Attentional modulation strength in cortical area MT depends on stimulus contrast

The attentional modulation of sensory information processing in the visual system is the result of top-down influences, which can cause a multiplicative modulation of the firing rate of sensory neurons in extrastriate visual cortex, an effect reminiscent of the bottom-up effect of changes in stimulus contrast. This similarity could simply reflect the multiplicity of both effects. But, here we show that in direction-selective neurons in monkey visual cortical area MT, stimulus and attentional effects share a nonlinearity. These neurons show higher response gain for both contrast and attentional changes for intermediate contrast stimuli and smaller gain for low- and high-contrast stimuli. This finding suggests a close relationship between the neural encoding of stimulus contrast and the modulating effect of the behavioral relevance of stimuli.