Neural correlates of perceptual motion coherence.

The motions of overlapping contours in a visual scene may arise from the physical motion(s) of either a single or multiple surface(s). A central problem facing the visual motion system is that of assigning the most likely interpretation. The rules underlying this perceptual decision can be explored using a visual stimulus formed by superimposing two moving gratings. The resultant percept is either that of a single coherently moving 'plaid pattern' (coherent motion) or of the two component gratings sliding noncoherently across one another (noncoherent motion). When plaid patterns are configured to mimic one transparent grating overlying another, the percept of noncoherent motion dominates. We now report that neurons in the visual cortex of rhesus monkeys exhibit changes in direction tuning that parallel this perceptual phenomenon: sensitivity to the motions of the component gratings is enhanced under conditions that favour the perception of noncoherent motion. These results challenge models of cortical visual processing that fail to take into account the contribution of figural image segmentation cues to the analysis of visual motion.     

Neural synchrony correlates with surface segregation rules

To analyse an image, the visual system must decompose the scene into its relevant parts. Identifying distinct surfaces is a basic operation in such analysis, and is believed to precede object recognition. Two superimposed gratings moving in different directions (plaid stimuli) may be perceived either as two surfaces, one being transparent and sliding on top of the other (component motion) or as a single pattern whose direction of motion is intermediate to the component vectors (pattern motion). The degree of transparency, and hence the perception, can be manipulated by changing only the luminance of the grating intersections. Here we show that neurons in two visual cortical areas--A18 and PMLS--synchronize their discharges when responding to contours of the same surface but not when responding to contours belonging to different surfaces. The amplitudes of responses correspond to previously described rate predictions for component and pattern motion, but, in contrast to synchrony, failed to reflect the transition from component to pattern motion induced by manipulating the degree of transparency. Thus, dynamic changes in synchronization could encode, in a context-dependent way, relations among simultaneous responses to spatially superimposed contours and thereby bias their association with distinct surfaces.     

Neural mechanisms of unconscious visual motion priming

The neural correlates of the motion priming were examined in normal young subjects using event-related brain potentials (ERPs) and functional magnetic resonance imaging (fMRI). Visual motion perception can be uncon-sciously biased in favor of a particular direction by a pre-ceding motion in that direction. Motion priming first in-volved an enhancement of ERP amplitude about 100 ms fol-lowing the onset of motion. The amplitudes of ERP compo-nents after 350 ms were also increased. The fMRI results suggest that the early-latency effect reflects modulation of neural responses in extrastriate cortex. Higher-level visual processing areas, including cortical regions MT/MST and the intraparietal cortices were also activated. The findings provide direct evidence that unconscious priming of motion perception is the result of interaction of direction-selective neural responses to motion stimuli. The results cannot be accounted for by refractoriness of neural responses, but in-stead support a theory of motion priming based on motion opponency, as proposed in computational models.     

Neural correlates of decision variables in parietal cortex.

Decision theory proposes that humans and animals decide what to do in a given situation by assessing the relative value of each possible response. This assessment can be computed, in part, from the probability that each action will result in a gain and the magnitude of the gain expected. Here we show that the gain (or reward) a monkey can expect to realize from an eye-movement response modulates the activity of neurons in the lateral intraparietal area, an area of primate cortex that is thought to transform visual signals into eye-movement commands. We also show that the activity of these neurons is sensitive to the probability that a particular response will result in a gain. When animals can choose freely between two alternative responses, the choices subjects make and neuronal activation in this area are both correlated with the relative amount of gain that the animal can expect from each response. Our data indicate that a decision-theoretic model may provide a powerful new framework for studying the neural processes that intervene between sensation and action.     

Neural correlates of mental rehearsal in dorsal premotor cortex

Behavioural and imaging studies suggest that when humans mentally rehearse a familiar action they execute some of the same neural operations used during overt motor performance. Similarly, neural activation is present during action observation in many of the same brain regions normally used for performance, including premotor cortex. Here we present behavioural evidence that monkeys also engage in mental rehearsal during the observation of sensory events associated with a well-learned motor task. Furthermore, most task-related neurons in dorsal premotor cortex exhibit the same activity patterns during observation as during performance, even during an instructed-delay period before any actual observed motion. This activity might be a single-neuron correlate of covert mental rehearsal.     

Neural correlates, computation and behavioural impact of decision confidence

Humans and other animals must often make decisions on the basis of imperfect evidence. Statisticians use measures such as P values to assign degrees of confidence to propositions, but little is known about how the brain computes confidence estimates about decisions. We explored this issue using behavioural analysis and neural recordings in rats in combination with computational modelling. Subjects were trained to perform an odour categorization task that allowed decision confidence to be manipulated by varying the distance of the test stimulus to the category boundary. To understand how confidence could be computed along with the choice itself, using standard models of decision-making, we defined a simple measure that quantified the quality of the evidence contributing to a particular decision. Here we show that the firing rates of many single neurons in the orbitofrontal cortex match closely to the predictions of confidence models and cannot be readily explained by alternative mechanisms, such as learning stimulus-outcome associations. Moreover, when tested using a delayed reward version of the task, we found that rats' willingness to wait for rewards increased with confidence, as predicted by the theoretical model. These results indicate that confidence estimates, previously suggested to require 'metacognition' and conscious awareness are available even in the rodent brain, can be computed with relatively simple operations, and can drive adaptive behaviour. We suggest that confidence estimation may be a fundamental and ubiquitous component of decision-making.     

Neural correlates of familiarity and conceptual fluency are dissociable at encoding

Familiarity and conceptual fluency belong to explicit and implicit memory respectively. Since familiar- ity and conceptual fluency co-occur at certain circum- stances and share some similarities, it is difficult to distinguish them. By using ERPs, in present study, we sought to differentiate the Dm effects, the differential neural activities due to later memory performances, of familiarity and conceptual fluency at encoding. We used ancient pictographic characters as stimuli, which were categorized as high or low meaningfulness based on the subjective ratings. In Experiment 1, conceptual fluency was observed to be induced exclusively by the repetition of relative meaningful items. In Experiment 2, Dm effects of familiarity and conceptual fluency were observed, respec- tively. In addition, the distribution of conceptual fluency Dm effects was found to be more posterior than that of familiarity Dm effects. These findings provide the disso- ciation of familiarity and conceptual fluency at encoding and further support the distinction between explicit and implicit memory.     

Neural correlates of short-term perceptual learning in orientation discrimination indexed by event-related potentials

The current work investigated the neural correlates of visual perceptual learning in grating orientation discrimination by recording event-related potentials (ERPs) from human adults. Subjects were trained with a discrimination task of grating orientation in three consecutive training sessions within 2 h. While reaction times (RTs) were shortened gradually across training sessions, the N1 was decreased and the P2 was increased over the parietal and occipital areas. A broadly distributed P3 was increased along with more practices. In addition, the time course of learning reflected in the P2 and P3 amplitudes was in line with the changes of reaction times and exhibited a stable level during later training. The impli- cations of these results to the neural mechanisms subserving perceptual learning were discussed.     

隐性否定的表达方式及其语用功能

结合教学中观察到的实例,从语义和语用学的角度分析了英语隐性否定的主要表达方式和功能。英语隐性否定的表达主要通过词汇和语法手段来实现。除了表示否定意义外,隐性否定在特定的语境中还蕴含着某种言下之意或弦外之音。     

浅论中国传统含蓄美概念及陶艺创作中含蓄美的表现

本文对中国传统含蓄美的概念和内容进行了论述，主张中国的陶艺创作应遵循含蓄美的审美特征，在意境的创造上来完成陶艺含蓄美的表现。     

高数解题中的常用方法--挖掘隐含条件

本文通过举例，说明挖掘隐含条件在高数解题中的重要作用。     

SVI隐含波动率模型的时间指数扩展

针对半参数SVI模型提出了避免跨期套利约束模型,根据平稳时间平方根规则,用对数执行价格和剩余期限的特定组合替代了原模型中的对数执行价格.为了使对数执行价格和剩余期限之间的关系更加灵活,引入了新的参数来调整二者之间的组合,并在此基础上提出参数模型构建隐含波动率曲面.最后基于AAPL股票期权进行了实证分析,结果表明,改进半参数模型更具灵活性与精确性,能够较好地构建隐含波动率曲面.     

英语含蓄否定结构的表达方式及翻译

英语否定结构有其独特的奇妙之处和丰富多样的表达方式，其表达方式主要分为两大类：一是从字面上可以直接看出否定；二种是从字面上看不出否定或句中不出现否定的词，只是在词里含蓄而间接地表示出否定意义．即有否定之义而无否定之形，故称之为含蓄否定(implied negation)。     

基于GMD的隐含最小距离风险中性概率测度提取

提出了一种从期权价格恢复标的资产隐含风险中性概率测度的新方法.在不完全市场条件下,运用高斯混合分布(GMD)构建了恢复最小距离隐含风险中性概率测度的数学优化模型,并进一步讨论模型的求解方法与技巧.采用欧式期权数据,通过数值实验对模型的有效性进行验证.实验结果表明,实际风险中性概率测度可由2个组成部分的高斯混合分布近似,...     

充分挖掘稿件中的审稿信息

把好审稿关是提高期刊学术质量的首要条件,而选择一个专业对口的审稿专家则是审稿过程中的重中之重.由于编辑知识水平的有限性,在把握论文的审稿信息中会发生一些偏差,使送审稿件与审稿专家的可审稿范围不符,造成送审稿件的退回、改审甚至丢失的现象.因此,必须充分把握原稿中所有的审稿信息,以确保稿件送审的准确性.在分析论文基本结构的基础上,逐一挖掘稿件各组成部分的审稿信息.     

Distinct sequence of negative or positive selection implied by thymocyte T-cell receptor densities

Recent evidence suggests that positive and negative selection of thymocytes bearing alpha beta T-cell receptors occurs during the predominant double-positive (CD4+CD8+) stage. But the sequence or stage at which positive or negative selection occurs during thymocyte maturation has not been well defined. Here we use transgenic mice to show that the CD4+CD8+ stage might be further subdivided into CD3lo (low) and CD3in (intermediate) stages. The CD3in stage could represent T cells that have been positively selected, as this stage is dependent on the presence of the appropriate major histocompatibility complex restriction element. In addition, we use two different tolerizing antigens to show that negative selection may occur either before or after this CD3in stage.     

“孔氏之门如用诗”义辩

在《诗品》中,钟嵘的一个＂孔氏之门如用诗＂之喻,令20世纪二三十年代至今的学者为之却步,有少数研究者尝试作出解释,却终不得要领。笔者以此为切入点进行探索,首先针对个别学者对＂孔氏之门如用诗＂之喻的合理性提出的质疑,进行了多重辩驳。在对三种不合钟氏原意的理解作了逐一剖析之后,笔者以一种不同于前人的视角,对＂孔氏之门＂和＂用诗＂作了探究,最终提出了可行的解读方式。     

一类二维非线性发展方程的分块隐式格式与并行计算

为获得可使二维非线性发展方程适合于在并行机上运行的高效率计算方法,给出了二维非线性发展方程的分块隐式格式以及并行数值计算方法,得到了该方法关于A12—稳定性以及并行兼顾的结果,通过数值例子表明了该方法具有良好的使用性和有效性.     

Spatial representation of words in the brain implied by studies of a unilateral neglect patient

Reading and writing require access to stored knowledge about the spelling of words. Presumably, we recognize chair but not chare or chiar as a word of English, and similarly would write 'chair' but not 'chare' or 'chiar', because we access orthographic representations that specify the identity and the order of the graphemes (abstract letter representations) that comprise the spelling of words. Thus, a fundamental problem concerns the content and structure of the hypothesized orthographic representations, and how information about grapheme order is represented and processed. We present evidence from a brain-damaged patient (N.G.) with unilateral neglect that this information is coded spatially. Unilateral neglect is a disorder clinically characterized by the inability to perceive or respond to stimuli presented to the side contralateral to the site of lesion, despite the absence of significant sensory or motor deficits. The patient made reading and spelling errors only on the right half of words, regardless of length. Furthermore, she produced the same pattern of errors in reading and spelling, irrespective of the topographic arrangement of stimuli in reading (horizontal, vertical or mirror-reversed words) and of the type of response in spelling (written, oral or backward oral spelling). This pattern of performance suggests that order information in orthographic representations is coded spatially in a word-centred coordinate system; that is, in a spatially defined coordinate frame whose centre corresponds to the midpoint of a canonical, orientation-invariant representation of the word and not the midpoint of the word stimulus.