The lowest spatial frequency channel determines brightness perception

This study investigates the role played by individual spatial scales in determining the apparent brightness of greyscale patterns. We measured the perceived difference in brightness across an edge in the presence of notch filtering and high-pass filtering for two stimulus configurations, one that elicits the perception of transparency and one that appears opaque. For both stimulus configurations, the apparent brightness of the surfaces delimited by the border decreased monotonically with progressive (ideal) high-pass filtering, with a critical cut-off at 1 c/deg. Using two octave ideal notch filtering, the maximum detrimental effect on apparent brightness was observed at about 1c/deg. Critical frequencies for apparent brightness did not vary with contrast, viewing distance, or surface size, suggesting that apparent brightness is determined by the channel tuned at 1 c/deg. Modelling the data with the local energy model [Morrone, M. C., & Burr, D. C. (1988). Feature detection in human vision: a phase dependent energy model. Proceedings of the Royal Society (London), B235, 221-245] at 1c/deg confirmed the suggestion that this channel mediates apparent brightness for both opaque and transparent borders, with no need for pooling or integration across spatial channels.     

Statistics of Boundaries in Ultrasonic B-Scan Images

The existence of edges and boundaries in regions of interest (ROIs) in B-scan images alters the statistics of the backscattered echo from the ROI. Boundaries are the result of at least two different types of scattering scenarios in tissue, and the Nakagami model, which is being used extensively in ultrasound, is unlikely to fit the statistics of the backscattered echo under these conditions. Furthermore, there are very few other statistical models exist that describe the statistics of the backscattered echo from regions containing boundaries. In this work, the gamma mixture density and the recently proposed McKay density are explored as two viable models to fill this void. Justifications of these models are presented along with methods for estimating their parameters. Random number simulations and studies on tissue-mimicking phantoms indicate that the McKay and gamma mixture densities are the best for the modeling of the backscattered echo intensity when boundaries are present in the regions of interest.     

基于《素问·咳论》的咳类疾病诊疗网络构建

目的:对《素问·咳论》所载咳类疾病进行本体网络构建,实现咳类疾病的病因病机、临床表现和治疗穴位间关系的可视化表达,辅助厘清咳类疾病的临床诊疗体系。方法:基于《素问·咳论》原文提取节点和边,构建咳类疾病诊疗网络数据库后,导入Gephi 0.9.2软件中进行复杂网络分析。依次进行统计、排序、分割等外观处理,最终以网络图的形式具象化展示咳类疾病的诊疗关系。结果:建立含有76个节点的节点库及含有167条边(244次逻辑关系)的边库,并据此绘制出咳类疾病诊疗网络图。该网络以五脏六腑咳为主体,“肺”“胃”节点的加权度及节点连接的边的权重均高居前列,“寒”在病因节点中加权度较高,“太渊”“足三里”在治疗穴位节点中加权度较高。结论:咳是肺之本症,但五脏六腑皆可犯肺作咳。“聚于胃,关于肺”是对咳类疾病病机的高度概括,临床诊疗中应重视“气之本”肺和“五脏之本”胃。治疗时应当重视太渊和足三里2个穴位。同时,根据治未病理论,应注意既病防变,预防疾病向表里之腑和三焦传变。     

色差分析法测定治偏痛微丸圆整度的计算方法研究

在以色差分析边缘跟踪方法的基础上,针对所采集的小丸图像的特点,将小丸边缘检测和边缘点连接结合为一体,提出一种基于标准圆形状知识指导下的色差分析自适应边缘跟踪方法,实现了小丸图像边缘特征点的全自动定位。实验表明,该方法快速而有效。     

Motion detection and the coincidence of structure at high and low spatial frequencies

We used filtered random dot kinematograms and natural images to examine how motion detection depends the relative locations of structures defined at low and high spatial frequencies. The upper displacement limit of motion (D(max)), the lower displacement limit (D(min)) and motion coherence thresholds were unaffected by the degree of spatial coincidence between high and low spatial frequency structures i.e. whether they were consistent or inconsistent with a single feature. However motion detection was possible between band-pass filtered random dot patterns whose peak frequencies were separated by up to 4 octaves. The first result implicates spatial frequency selective motion detectors that operate independently. The second result implicates a motion system that can integrate the displacements of edges defined by widely separated spatial frequencies. Both are required to account for the two results, and they appear to operate under very similar conditions.     

No aliasing at edges in normal viewing

Although spatial aliasing by the extrafoveal retina can occur under natural viewing conditions, it does not commonly disturb our vision. One possible explanation for this is that real scenes do not have sufficient power in the high frequencies to produce aliasing. We examined whether aliasing distorted the appearance of a high contrast edge, which is a common stimulus in the environment. Observers made a two-interval forced-choice discrimination between low-pass filtered and unfiltered edges at 0, 10, 20, and 40 deg eccentricity. This discrimination could be made only when frequency components were removed below both the cone and ganglion cell Nyquist frequencies at each eccentricity. Since supra-Nyquist frequency components could not be detected in edges, they are incapable of producing aliasing.