Stereoscopic correspondence for ambiguous targets is affected by elevation and fixation distance

Binocular correspondence must be determined if disparity is to be used to provide information about three-dimensional shape. The current study investigated whether knowledge of the statistical distribution of disparities in the natural environment is employed in this process. A simple model, which produces distributions of distances similar to those found in the natural environment, was used to predict the distribution of disparities in natural images. This model predicts that crossed disparities will be more likely as (i) stimulus elevation decreases below fixation and (ii) fixation distance increases. To determine whether these factors influence binocular correspondence for human observers, ambiguous stereograms were presented to observers, as stimulus elevation and fixation distance were manipulated. Clear biases were observed in the depth perceived in these stereograms, which were more likely to be seen as closer than fixation (i) for stimuli presented below fixation and (ii) as fixation distance increased. These results suggest that binocular correspondence is determined in a manner consistent with the distributions of disparities expected in natural scenes.     

Familiarity with speech affects cortical processing of auditory distance cues and increases acuity

Several acoustic cues contribute to auditory distance estimation. Nonacoustic cues, including familiarity, may also play a role. We tested participants' ability to distinguish the distances of acoustically similar sounds that differed in familiarity. Participants were better able to judge the distances of familiar sounds. Electroencephalographic (EEG) recordings collected while participants performed this auditory distance judgment task revealed that several cortical regions responded in different ways depending on sound familiarity. Surprisingly, these differences were observed in auditory cortical regions as well as other cortical regions distributed throughout both hemispheres. These data suggest that learning about subtle, distance-dependent variations in complex speech sounds involves processing in a broad cortical network that contributes both to speech recognition and to how spatial information is extracted from speech.     

Stereoscopic observation of enzyme distribution in lowicryl K4M-embedded specimens by conventional electron microscopy

The present investigation was undertaken to explore the value of the Lowicryl K4M embedding technique for enzyme histochemical examination of semi-thin sections. The low-temperature embedding procedure with Lowicryl K4M was found to provide favorable conditions for preservation of enzyme activity in tissue samples. We tested the histological effects of various fixatives; the best results were obtained using 4% paraformaldehyde when testing for AcPase, AlPase, TPPase, and Mg-ATPase in the dorsal root ganglion. The three-dimensional cellular fine structure could be clearly seen in stereo pair pictures under stereoscopy.     

Stereoscopic surface perception

Physiological, computational, and psychophysical studies of stereopsis have assumed that the perceived surface structure of binocularly viewed images is primarily specified by the pattern of binocular disparities in the two eyes' views. A novel set of stereoscopic phenomena are reported that demonstrate the insufficiency of this view. It is shown that the visual system computes the contrast relationships along depth discontinuities to infer the depth, lightness, and opacity of stereoscopically viewed surfaces. A novel theoretical framework is introduced to explain these results. It is argued that the visual system contains mechanisms that enforce two principles of scene interpretation: a generic view principle that determines qualitative scene geometry, and anchoring principles that determine how image data are quantitatively partitioned between different surface attributes.     

Stereoscopic depth constancy

Depth constancy is the ability to perceive a fixed depth interval in the world as constant despite changes in viewing distance and the spatial scale of depth variation. It is well known that the spatial frequency of depth variation has a large effect on threshold. In the first experiment, we determined that the visual system compensates for this differential sensitivity when the change in disparity is suprathreshold, thereby attaining constancy similar to contrast constancy in the luminance domain. In a second experiment, we examined the ability to perceive constant depth when the spatial frequency and viewing distance both changed. To attain constancy in this situation, the visual system has to estimate distance. We investigated this ability when vergence, accommodation and vertical disparity are all presented accurately and therefore provided veridical information about viewing distance. We found that constancy is nearly complete across changes in viewing distance. Depth constancy is most complete when the scale of the depth relief is constant in the world rather than when it is constant in angular units at the retina. These results bear on the efficacy of algorithms for creating stereo content.This article is part of the themed issue ‘Vision in our three-dimensional world’.     

Conditions of observation and social distance in groups of squirrel monkeys,Saimiri sciureus

Observation conditions were very influential in determining the social distance among members of groups of squirrel monkeys. With observer visible to the animals and recording by talking into a tape recorder the monkeys did not show a consistent pattern of social distance as reflected by actual space and frequency of bodily contacts, whereas when the observer was concealed, looking through a one-way vision screen and recording silently by marking on paper, the subjects tended to group in unisexual clusters, with that of the females showing higher cohesiveness.     

Comparative aerial and underwater visual acuity of the mink, Mustela vison schreber, as a function of discrimination distance and stimulus luminance

The aerial threshold visual angle of mink rose from 15.4 min at 10 cm stimulus distance to 19.1 min at 90 cm and the underwater angle varied from 32.7 min at 10 cm to 46.6 min at 90 cm, all at 34 mL luminance. At constant 30 cm stimulus distance, the aerial angle rose from 15 min at 34 mL to 51.7 min at 0.012 mL, the underwater angle from 31.4 min at 34 mL to 95 min at 0.012 mL, the aerial and underwater data forming similar curves. If mink hunt in water at somewhat higher light levels than in air they can obtain equal acuities in the two media.     

Stereoscopic and contrast-defined motion in human vision.

There is considerable evidence for the existence of a specialized mechanism in human vision for detecting moving contrast modulations and some evidence for a mechanism for detecting moving stereoscopic depth modulations. It is unclear whether a single second-order motion mechanism detects both types of stimulus or whether they are detected separately. We show that sensitivity to stereo-defined motion resembles that to contrast-defined motion in two important ways. First, when a missing-fundamental disparity waveform is moved in steps of 0.25 cycles, its perceived direction tends to reverse. This is a property of both luminance-defined and contrast-defined motion and is consistent with independent detection of motion at different spatial scales. Second, thresholds for detecting the direction of a smoothly drifting sinusoidal disparity modulation are much higher than those for detecting its orientation. This is a property of contrast-modulated gratings but not luminance-modulated gratings, for which the two thresholds are normally identical. The results suggest that stereo-defined and contrast-defined motion stimuli are detected either by a common mechanism or by separate mechanisms sharing a common principle of operation.     

稻—鱼—蛙立体农业生态效益的研究

我国是一个稻米生产大国 ,古代劳动人民早已认识到稻田中的鱼、蛙与水稻生长的互利关系。三国时代就有稻田养鱼的记载 :“郫县子鱼黄鳞赤尾 ,出稻田可以作酱”;宋朝诗人辛弃疾的词句 :“稻花香里说丰年 ,听取蛙声一片”,生动地描述了那种自然景象。但是到目前为止 ,对稻 -鱼 -蛙共生生态系统的系统研究还较缺乏。本文旨在通过在稻田中放养美国青蛙及草鱼 ,进行立体种养殖来分析探讨稻 -鱼 -蛙立体农业的生态效益 ,为该项技术的深入研究、生产的推广普及提供一些理论依据。放草鱼夏花 2 0 0尾 ,进行经济效益的比较试验。1 .3　秧苗的栽插与鱼…     

稻－萍－蟹立体农业的效益

稻－萍－蟹立体农业的效益朱清海，李毓鹏，徐春河（辽宁省盘锦市土肥工作站，１２４０１０）魏晓敏毛艳，朱浩峥（辽宁省盐碱地利用研究所，盘锦１２４２００）（辽宁省盘锦市土肥工作站，１２４０１０）ＢｅｎｉｆｉｔｏｆＳｔｅｒｅｏｓｃｏｐｉｃＡｇｒｉｃｕｌｔｕｒ...