共查询到20条相似文献，搜索用时 453 毫秒
1.
Limulus rhodopsin: rapid return of transient intermediates to the thermally stable state 总被引：3，自引：0，他引：3
Spectral transitions of rhodopsin in single cells of the Limulus ventral eye were observed both with flash photometry and by measuring the early receptor potential. Even with repetitive stimulus flashes the rhodopsin did not bleach; after each flash the spectral intermediates decayed rapidly to the initial thermally stable state. The pigment returns to the stable state in a time comparable with the duration of the late receptor potential. 相似文献
2.
Fourier analysis of discharge patterns in response to sinusoidal acoustic stimulation provides a consistent and repeatable measure of response phase and amplitude. The variation of the fundamental and harmonic components of the patterns as stimulus parameters are changed is strikingly similar to that of cochlear microphonics. The results are significantly different for single fibers with different characteristic frequencies; the variations parallel those of microphonics recorded from different cochlear turns. 相似文献
3.
Human infants begin to acquire their native language in the first months of life. To determine which brain regions support language processing at this young age, we measured with functional magnetic resonance imaging the brain activity evoked by normal and reversed speech in awake and sleeping 3-month-old infants. Left-lateralized brain regions similar to those of adults, including the superior temporal and angular gyri, were already active in infants. Additional activation in right prefrontal cortex was seen only in awake infants processing normal speech. Thus, precursors of adult cortical language areas are already active in infants, well before the onset of speech production. 相似文献
4.
Interhemispheric asymmetries of different magnitudes were observed in human cortical auditory evoked responses to speech and sound-effect stimuli. The wave with peak asymmetry occurred 100 milliseconds after signal onset. The amount of asymmetry of the amplitude of this wave was related to the meaningfulness to the subject of the auditory stimulus rather than to the mere use of verbal versus nonverbal materials. 相似文献
5.
Speech perception in infants 总被引：18，自引：0，他引：18
Discriminiationi of synthetic speech sounds was studied in 1- and 4-month-old infants. The speech sounds varied along an acoustic dimension previously shown to cue phonemic distinctions among the voiced and voiceless stop consonants in adults. Discriminability was measured by an increase in conditioned response rate to a second speech sound after habituation to the first speech sound. Recovery from habituation was greater for a given acoustic difference when the two stimuli were from different adult phonemic categories than when they were from the same category. The discontinuity in discrimination at the region of the adult phonemic boundary was taken as evidence for categorical perception. 相似文献
6.
C W Tyler 《Science (New York, N.Y.)》1973,181(96):276-278
The spatial limitations of stereoscopic vision were studied by using vertical line stimuli containing sinusoidal disparity variations such that different parts of the line appeared at different depths. Stimuli with a finer grain than about 3 cycles per degree did not elicit depth perception, even though the sinusoidal curvature was clearly visible monocularly. At low spatial frequencies of curvature, stereoacuity was limited to the same extent as the monocular sensitivity. The limiting disparity for Panum's fusional region and the upper depth limit are subject to a scaling effect in proportion to stimulus dimensions. The disparity scaling can be characterized by a fixed maximum angular difference between the parts of the stereoscopic half-images. 相似文献
7.
A visual analog to binaural unmasking was explored. The observer's task was to detect, under stereoscopic viewing conditions, an apertured sinusoidal grating added to a square patch of visual noise. In the experimental condition, the square patch of noise was presented within a frame such that the right-eye noise was a shifted version of the left-eye noise. Because of the disparity in the noise images, subjects perceived, under stereoscopic viewing conditions, that the noise patch was located behind the frame. When sinusoidal signals were added to this noise patch, the signals were clearly more detectable when the signal disparity was zero than when the signal disparity equaled that of the noise patch, demonstrating the existence of visual unmasking. Hence, under appropriate circumstances, binocular processing, in addition to providing information about depth, can also enhance the detectability of visual patterns. 相似文献
8.
9.
A simple model for complex dynamical transitions in epidemics 总被引：2，自引：0，他引：2
Dramatic changes in patterns of epidemics have been observed throughout this century. For childhood infectious diseases such as measles, the major transitions are between regular cycles and irregular, possibly chaotic epidemics, and from regionally synchronized oscillations to complex, spatially incoherent epidemics. A simple model can explain both kinds of transitions as the consequences of changes in birth and vaccination rates. Measles is a natural ecological system that exhibits different dynamical transitions at different times and places, yet all of these transitions can be predicted as bifurcations of a single nonlinear model. 相似文献
10.
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
11.
Auditory evoked potentials during speech perception 总被引：3，自引：0，他引：3
Neural responses evoked by the same binaural speech signal were recorded from ten right-handed subjects during two auditory identification tasks. One task required analysis of acoustic parameters important for making a linguistic distinction, while the other task required analysis of an acoustic parameter which provides no linguistic information at the phoneme level. In the time interval between stimulus onset and the subjects' identification responses, evoked potentials from the two tasks were significantly different over the left hemisphere but identical over the right hemisphere. These results indicate that different neural events occur in the left hemisphere during analysis of linguistic versus nonlinguistic parameters of the same acoustic signal. 相似文献
12.
The relation between the activity of a single neocortical neuron and the dynamics of the network in which it is embedded was explored by single-unit recordings and real-time optical imaging. The firing rate of a spontaneously active single neuron strongly depends on the instantaneous spatial pattern of ongoing population activity in a large cortical area. Very similar spatial patterns of population activity were observed both when the neuron fired spontaneously and when it was driven by its optimal stimulus. The evoked patterns could be used to reconstruct the spontaneous activity of single neurons. 相似文献
13.
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
14.
15.
Two pigeons matched to sample on the basis of color or line orientation when a sample consisted of a value for each stimulus dimension or a value for only one dimension. When the duration of the sample stimulus was varied to maintain constant performance, compound stimuli required more time than single elements. 相似文献
16.
Diel fluorescence patterns were discovered in phytoplankton sampled over 7000 kilometers of the South Pacific Ocean that appear indicative of iron-limiting growth conditions. These patterns were rapidly lost after in situ iron enrichment and were not observed during a 15,000-kilometer transect in the Atlantic Ocean where iron concentrations are relatively high. Laboratory studies of marine Synechococcus sp. indicated that the patterns in the South Pacific are a unique manifestation of iron limitation on the fluorescence signature of state transitions. Results suggest that primary productivity is iron limited not only throughout the equatorial Pacific but also over much of the vast South Pacific gyre. 相似文献
17.
K D Roeder 《Science (New York, N.Y.)》1966,154(756):1515-1521
Insect-eating bats find their aerial food by sonar, through emitting ultrasonic chirps and locating sources of echoes. Certain moths have ears sensitive to these chirps and can detect bats well beyond the range of the bats' sonar. On hearing a distant bat, many moths turn and fly directly away from the source of ultrasound. Only one sense cell in each ear of a moth provides the primary nervous information for this response. This article describes my initial attempts to find out how a moth's central nervous system processes the train of chirps reaching its two ears. The ear of a restrained moth is exposed to a sequence of artifically generated ultrasonic pulses that approximates the cries made by a bat. This stimulus can be varied with respect to ultrasonic frequency (pitch), pulse intensity, pulse duration, the interval between pulses, and pulse-train duration. The more sensitive acoustic sense cell responds to all frequencies between about 15,000 and 80,000 cycles per second, but the signal that it transmits to the moth's central nervous system contains no measure of frequency within this range. However, this nerve signal reports variations in the other parameters of the stimulus. The acoustic fiber connects, in the central nervous system, with various nerve cells that transform the signal farther. The signal from a pulse-marker neuron contains no measures of pulse intensity or pulse duration, reporting only changes in interpulse interval and pulse-train duration. A train-marker neuron reports only the duration of the pulse train. The stimulus parameters may be likened to keys, each of which is necessary to gain admittance through a given door but becomes superfluous once this door has been passed. This analogy suggests one of the ways in which a signal is transformed in its passage through the nervous system, and how its specificity is assured in eliciting a given response. In addition to undergoing this kind of transformation, neural signals generated in the two directionally sensitive ears must be combined if a flying moth is to steer a course away from a distant bat. Neurons have been discovered in the central ganglia which summate signals from the right and left ears. Other neurons are inhibited in their activity by stimulation of one ear. The moth may combine signals from these neurons with motor-nerve information on the attitude of its own wings, which act as oscillating baffles modifying its directional acoustic sensitivity 20 to 40 times a second as it flaps an erratic path through the darkness. 相似文献
18.
[目的/意义]识别信息需求的情境因素对于理解信息需求的产生机制具有重要意义.[方法/过程]本研究从百度知道社会问答平台上爬取了2019.12.31～2020.3.30期间网民关于新冠肺炎的提问数据,采用内容分析法、共现网络分析法等方法,识别网民信息需求主题、揭示信息需求主题关联、发现不同信息需求主题在各种情境因素下的特... 相似文献
19.
R I Lanyon 《Science (New York, N.Y.)》1969,164(878):451-452
In spontaneous speech and oral reading of stutterers, likelihood of nonfluency occurring on any word is not related to the amount of information carried by that word. The same is true for spontaneous speech of normal speakers. Previous contrary findings can be accounted for by the relationship between information value and word length. 相似文献
20.
Astrocytes have long been thought to act as a support network for neurons, with little role in information representation or processing. We used two-photon imaging of calcium signals in the ferret visual cortex in vivo to discover that astrocytes, like neurons, respond to visual stimuli, with distinct spatial receptive fields and sharp tuning to visual stimulus features including orientation and spatial frequency. The stimulus-feature preferences of astrocytes were exquisitely mapped across the cortical surface, in close register with neuronal maps. The spatially restricted stimulus-specific component of the intrinsic hemodynamic mapping signal was highly sensitive to astrocyte activation, indicating that astrocytes have a key role in coupling neuronal organization to mapping signals critical for noninvasive brain imaging. Furthermore, blocking astrocyte glutamate transporters influenced the magnitude and duration of adjacent visually driven neuronal responses. 相似文献