共查询到20条相似文献，搜索用时 15 毫秒
1.
R D Walk 《Science (New York, N.Y.)》1968,162(852):473-475
Human infants were made temporarily monocular with an eye patch. They performed like bginocular infants on the visual cliff at visual depths of 25 centimeters or more. At a visual depth of 12.7 centimeters infants younger than 9 months of age revealed a monocular weakness by turning toward the uncovered eye. 相似文献
2.
Distortions of apparent velocity: a new optical illusion 总被引：1，自引：0，他引：1
J T Enright 《Science (New York, N.Y.)》1970,168(930):464-467
To an observer whose one eye is covered with a relatively strong filter (approximately 90 percent extinction) and who views a landscape from the side window of a moving automobile, the velocity of the vehicle appears to be markedly reduced when the uncovered eye is in the forward or leading position (in the sense of motion of the vehicle); the velocity seems to be increased when the covered eye is in the leading position. The illusion of reduced velocity is accompanied by an apparent dwarfing of objects near the roadside and an apparent foreshortening of the distance between object and observer; the illusion of increased velocity is accompanied by an apparent increase in size of objects and an increase in their apparent distance. These illusions can be understood as corollaries of the well-known Pulfrich phenomenon. 相似文献
3.
Infants prefer to look at an array of objects that corresponds in number to a sequence of sounds. In doing so, infants disregard the modality (visual or auditory) and type (object or event) of items presented. This finding indicates that infants possess a mechanism that enables them to obtain information about number. 相似文献
4.
An essential function of the brain is to detect threats, such as those posed by objects or predators on a collision course. A wide-field, movement-sensitive visual neuron in the brain of the locust was studied by presenting simulated approaching, receding, and translating objects. The neuron's responses could be described simply by multiplying the velocity of the image edge (dtheta/dtau) with an exponential function of the size of the object's image on the retina (e-alpha theta). Because this product peaks before the image reaches its maximum size during approach, this neuron can anticipate collision. The neuron's activity peaks approximately when the approaching object reaches a certain angular size. Because this neuron receives distinct inputs about image size and velocity, the dendritic tree of a single neuron may function as a biophysical device that can carry out a multiplication of two independent input signals. 相似文献
5.
We report a perception-action dissociation in the behavior of normally developing young children. In adults and older children, the perception of an object and the organization of actions on it are seamlessly integrated. However, as documented here, 18- to 30-month-old children sometimes fail to use information about object size and make serious attempts to perform impossible actions on miniature objects. They try, for example, to sit in a dollhouse chair or to get into a small toy car. We interpret scale errors as reflecting problems with inhibitory control and with the integration of visual information for perception and action. 相似文献
6.
Adult cats were trained to discriminate blue from green and gray. Although the cats could discriminate the intensity of stimuli whose areas ranged from 33 to 0.36 square centimeters they could not discriminate color when the stimulus was 0.36 square centimeter (less than 20 degrees visual angle). This influence of stimulus size may account for both positive and negative results of previous studies. 相似文献
7.
Radar cross-section measurements indicate that Ganymede scatters to Earth 12 percent of the power expected from a conducting sphere of the same size and distance. This compares with 8 percent for Mars, 12 percent for Venus, 6 percent for Mercury, and about 8 percent for the asteroid Toro. Furthermore, Ganymede is considerably rougher (to the scale of the wavelength used, 12.6 centimeters) than Mars, Venus, or Mercury. Roughness is made evident in this experiment by the presence of echoes away from the center of the disk. A perfectly smooth target would reflect only a glint from the center, whereas a very rough target would reflect power from over the entire disk. 相似文献
8.
Plano MA Landstrass MI Pan LS Han S Kania DR McWilliams S Ager JW 《Science (New York, N.Y.)》1993,260(5112):1310-1312
Advances in the deposition process have led to dramatic improvements in the electronic properties of polycrystalline diamond films produced by chemical vapor deposition (CVD). It is now possible to produce CVD diamond with properties approaching those of IIa natural diamonds. The combined electron-hole mobility, as measured by transient photoconductivity at low carrier density, is 4000 square centimeters per volt per second at an electric field of 200 volts per centimeter and is comparable to that of the best single-crystal IIa natural diamonds. Carrier lifetimes measured under the same conditions are 150 picoseconds for the CVD diamond and 300 picoseconds for single-crystal diamond. The collection distance at a field of 10 kilovolts per centimeter is 15 micrometers for the CVD diamond as compared to 30 micrometers for natural diamonds. The electrical qualities appear to correlate with the width of the diamond Raman peak. Also, although the collection distance at the highest fields in the films nearly equals the average grain size, there is no evidence of deleterious grain boundary effects. 相似文献
9.
Laser scanners are increasingly used in automation and robotic applications as a sensing device for navigation and safety. They have agricultural applications in measuring plant growth rate, tree volume, tree count, 3D imaging, and pattern recognition. Laser scanners are commercially available, but there is very little published information on characteristics and performance of these laser scanners. This study compared two laser scanners, the Sick LMS200 and the Hokuyo URG-04LX, for measurement drift over time, the effect of material and color on measurement accuracy, and the ability to map different surface patterns.Measurement drift over time was studied by determining the distance between the laser scanner sensor and a stationary object at different fixed distances and angles. Distance measurements over time fluctuated with a peak-to-peak value of 10–20 mm. The settling time, which is the time required for the averaged distance data to reach a stable level, increased when measurement distance increased but for a given distance, the settling time remained constant for different angles. At the measurement angle of 90°, the settling times for the LMS200 and the URG-04LX for 50% of the maximum scanner measurement distances were 53 min and 70 min, respectively. Therefore, to obtain accurate distance measurements, the laser scanners should be warmed up for the duration of the settling time before recording measurement data.The measured distance for soft material objects, such as a styrofoam plate and a sheet of dry sponge, was longer than the actual distance. For shiny objects, such as orange tree leaves, transparency film, and a stainless steel plate, the measurement distance was shorter than actual distance. At the measurement angle of 90°, the difference between the longest and shortest measured distance (90% of the maximum scanner measurement distance) was 21.3 mm for the LMS200 and 29.7 mm for the URG-04LX. At the measurement angle of 45°, this difference increased to 73.2 mm for the LMS200; the URG-04LX was not able to detect any objects at 45°.The surface shapes of a cylindrical pipe, a folded cardboard plate with a square-shaped valley, and a folded cardboard plate with a V-shaped valley were well-depicted by the laser scanner. For the object with a V-shaped valley with a true depth of 6.1 cm, the averaged depths measured by the LMS200 and URG-04LX were 6.8 cm and 3.6 cm, respectively. The larger discrepancy in the URG-04LX depth measurement may be caused by the relatively lower angular resolution of the URG scanner, compared to that of the LMS scanner. 相似文献
10.
Apparent motion was used to explore humans' ability to perceive the direction of motion in the visual field. A marked qualitative difference in this ability was found between short- and long-range motion. For short-range motion, the detection of the direction of motion is characterized by parallel operation over a wide visual field (that is, detection performance is independent of the number of objects in an array). When the positional displacement is large relative to an object's size, the direction of motion is detected in a serial manner. The process of detection is limited in this case by the ability to detect other events, such as appearance and disappearance of an object, and the ability to compute their spatio-temporal relations. The results are consistent with a previously suggested division of the motion detection system into short- and long-range processes. The direction of short-range motion can be perceived in parallel (preattentively), whereas long-range motion is attentive and requires more complicated computations. It seems that the detection of long-range motion is a conjunction task, combining the detection of disappearance and appearance. 相似文献
11.
Object recognition is challenging because each object produces myriad retinal images. Responses of neurons from the inferior temporal cortex (IT) are selective to different objects, yet tolerant ("invariant") to changes in object position, scale, and pose. How does the brain construct this neuronal tolerance? We report a form of neuronal learning that suggests the underlying solution. Targeted alteration of the natural temporal contiguity of visual experience caused specific changes in IT position tolerance. This unsupervised temporal slowness learning (UTL) was substantial, increased with experience, and was significant in single IT neurons after just 1 hour. Together with previous theoretical work and human object perception experiments, we speculate that UTL may reflect the mechanism by which the visual stream builds and maintains tolerant object representations. 相似文献
12.
Infant responses to impending collision: optical and real 总被引：2，自引：0，他引：2
Twenty-four infants ranging in age from 2 to 11 weeks responded to symmetrically expanding shadows, which optically specify an approaching object, with an integrated avoidance response and upset. This response did not occur for asymmetrically expanding shadows nor for contracting shadows that specify an object on a miss path and a receding object. The response was observed in all the infants regardless of age, and the addition of kinetic depth information to the displays did not increase the intensity or likelihood of the response. In a second experiment, seven infants defensively reacted to the approach of a real object except when it was on a miss path. 相似文献
13.
To find a target object in a crowded scene, a face in a crowd for example, the visual system might turn the neural representation of each object on and off in a serial fashion, testing each representation against a template of the target item. Alternatively, it might allow the processing of all objects in parallel but bias activity in favor of those neurons that represent critical features of the target, until the target emerges from the background. To test these possibilities, we recorded neurons in area V4 of monkeys freely scanning a complex array to find a target defined by color, shape, or both. Throughout the period of searching, neurons gave enhanced responses and synchronized their activity in the gamma range whenever a preferred stimulus in their receptive field matched a feature of the target, as predicted by parallel models. Neurons also gave enhanced responses to candidate targets that were selected for saccades, or foveation, reflecting a serial component of visual search. Thus, serial and parallel mechanisms of response enhancement and neural synchrony work together to identify objects in a scene. To find a target object in a crowded scene, a face in a crowd for example, the visual system might turn the neural representation of each object on and off in a serial fashion, testing each representation against a template of the target item. Alternatively, it might allow the processing of all objects in parallel but bias activity in favor of those neurons that represent critical features of the target, until the target emerges from the background. To test these possibilities, we recorded neurons in area V4 of monkeys freely scanning a complex array to find a target defined by color, shape, or both. Throughout the period of searching, neurons gave enhanced responses and synchronized their activity in the gamma range whenever a preferred stimulus in their receptive field matched a feature of the target, as predicted by parallel models. Neurons also gave enhanced responses to candidate targets that were selected for saccades, or foveation, reflecting a serial component of visual search. Thus, serial and parallel mechanisms of response enhancement and neural synchrony work together to identify objects in a scene. 相似文献
14.
The chemoautotrophic fixation of carbon dioxide by bacteria is responsible for an appreciable component of the organic carbon in a sulfide-rich marine mud. A peak of carbon dioxide fixation (at 40 centimeters subbottom) coincides with peaks in the organic carbon content, the ratio of carbon to nitrogen, and bacterial cell counts. Stimulation of fixation by thiosulfate and inhibition by anaerobic conditions implicate the chemoautotrophic sulfur bacteria as primary producers in this environment. 相似文献
15.
Téglás E Vul E Girotto V Gonzalez M Tenenbaum JB Bonatti LL 《Science (New York, N.Y.)》2011,332(6033):1054-1059
Many organisms can predict future events from the statistics of past experience, but humans also excel at making predictions by pure reasoning: integrating multiple sources of information, guided by abstract knowledge, to form rational expectations about novel situations, never directly experienced. Here, we show that this reasoning is surprisingly rich, powerful, and coherent even in preverbal infants. When 12-month-old infants view complex displays of multiple moving objects, they form time-varying expectations about future events that are a systematic and rational function of several stimulus variables. Infants' looking times are consistent with a Bayesian ideal observer embodying abstract principles of object motion. The model explains infants' statistical expectations and classic qualitative findings about object cognition in younger babies, not originally viewed as probabilistic inferences. 相似文献
16.
A 0.6-centimeter-thick sublayer was found in horizontal flow profiles obtained by traversing a heated thermistor from 19 centimeters above to 2 centimeters below the water-sediment interface in 200-meter-deep water on the Oregon continental shelf. In this sublayer the speed of the current varies linearly with distance above the sediment. Estimates of viscous stress from this sublayer and turbulent stress from the profile agree within 5 percent. Stress calculated from a current-meter spectrum agrees within its 95 percent confidence limits. 相似文献
17.
为了拍摄烤烟烟叶反射和透射图像并实时显示物距大小,研发了烟叶图像拍摄与物距显示试验装置,该装置包括图像采集装置和物距测量显示装置。图像采集装置由支架、载物板、标准光源等组成,构成图像的采集平台,物距测量显示装置由容栅传感器(KX/MS-50)及数码显示系统构成,用于显示拍摄物距的大小。拍摄装置可以同时采集烟叶的反射和透射图像,反射图像和透射图像的物距大小通过测量系统显示。该文给出该装置的主要功能和设计方案,并对装置中的各子系统的设计方法和实现技术进行了介绍。 相似文献
18.
B R Bugelski 《Science (New York, N.Y.)》1967,157(795):1464-1465
Automobiles approaching red traffic signals at night appear to go beyond them when viewed from some distance to the rear. The phenomenon is doubly illusory because the higher of two objects has been presumed to appear more distant. The illusion is probably limited to small visual angles (about 2 degrees). 相似文献
19.
设计了具有主光源尧辅助光源,物镜距离可调的玉米籽粒图像采集实验箱,应用数码相机采集实验箱载物台上玉米籽粒的图像。以玉米籽粒形状特征、颜色特征为对象,分析同一物镜距离下辅助光源的放置方式与强度对图像采集的影响,光源确定的情况下物镜距离对图像采集的影响。结果表明：闪光灯留下的光斑影响特征提取,辅助光源平行和垂直放置尧物镜距离在26~31 cm范围内较佳。 相似文献
20.
腐殖酸对土壤汞向植株迁移的影响 总被引：9，自引：0，他引：9
通过莴笋盆栽试验,研究了腐殖酸对土壤汞向植株迁移的影响,结果表明：腐殖酸的施用可抑制土壤汞向植株迁移,对土壤汞的最大固定率超过90%;但不同种类的腐殖酸对土壤汞迁移的抑制作用不同,胡敏酸的抑制作用强于富里酸。 相似文献