Removal of monocular interactions equates rivalry behavior for monocular, binocular, and stimulus rivalries

When the two eyes are presented with conflicting stimuli, perception starts to fluctuate over time (i.e., binocular rivalry). A similar fluctuation occurs when two patterns are presented to a single eye (i.e., monocular rivalry), or when they are swapped rapidly and repeatedly between the eyes (i.e., stimulus rivalry). Although all these cases lead to rivalry, in quantitative terms these modes of rivalry are generally found to differ significantly. We studied these different modes of rivalry with identical intermittently shown stimuli while varying the temporal layout of stimulation. We show that the quantitative differences between the modes of rivalry are caused by the presence of monocular interactions between the rivaling patterns; the introduction of a blank period just before a stimulus swap changed the number of rivalry reports to the extent that monocular and stimulus rivalries were inducible over ranges of spatial frequency content and contrast values that were nearly identical to binocular rivalry. Moreover when monocular interactions did not occur the perceptual dynamics of monocular, binocular, and stimulus rivalries were statistically indistinguishable. This range of identical behavior exhibited a monocular (∼50 ms) and a binocular (∼350 ms) limit. We argue that a common binocular, or pattern-based, mechanism determines the temporal constraints for these modes of rivalry

Temporal aspects of binocular slant perception

We investigate temporal aspects of binocular slant perception in the presence and absence of a visual reference. Subjects judge slant induced by large-field stereograms of which one half-image is either horizontally scaled or sheared relative to the other half-image. Each stimulus is presented for different ob- servation periods ranging from 0.1 to 19.2 sec. We quantitatively corroborate earlier findings that perceived slant develops significantly faster and to higher levels with visual reference than without it. In daily life, when we are active, there will not be much time for slant to develop. We find that if observation periods are brief (a few seconds or less) slant is poorly perceived if there is no visual reference. We conclude that the visual system is relatively insensitive to large-field horizontal scale and shear

Is there an interaction between perceived direction and perceived aspect ratio in stereoscopic vision?

In monocular vision, the horizontal/vertical aspect ratio (shape) of a fronto-parallel rectangle can be based upon the comparison of the perceived directions of the rectangle's edges. In binocular vision of a typical three-dimensional scene (when occlusions are present) this is not the case: fronto-parallel rectangles would be perceived in a distorted fashion if an observer were to base perceived aspect ratio on the perceived directions of the rectangle's edges. We psychophysically investigated stereoscopically perceived aspect ratios of fronto-parallel occluding and occluded rectangles for various distances and fixation depths. We found that observers did not perceive the distortions as predicted on the basis of the above-mentioned comparison of the perceived visual direction of the edges of the rectangle. Our results strongly suggest that the mechanism that determines perceived aspect ratio is dissociated from the mechanism that determines perceived direction. The consequences of the findings for the Kanizsa, Poggendorff, and horizontal/vertical illusions are discussed

Temporal aspects of stereoscopic slant estimation: An evaluation and extension of Howard and Kaneko's theory

We investigated temporal aspects of stereoscopically perceived slant produced by the following transformations: horizontal scale, horizontal shear, vertical scale, vertical shear, divergence and rotation, between the half-images of a stereogram. Six subjects viewed large field stimuli (70 deg diameter) both in the presence and in the absence of a visual reference. The presentation duration was: 0.1, 0.4, 1.6, 6.4 or 25.6 s. Without reference we found the following: Rotation and divergence evoked considerable perceived slant in a number of subjects. This finding violates the recently published results of Howard and Kaneko. Slant evoked by vertical scale and shear was similar to slant evoked by horizontal scale and shear but was generally less. With reference we found the following: Vertical scale and vertical shear did not evoke slant. Slant due to rotation and divergence was similar to slant due to horizontal scale and shear but was generally less. According to the theory of Howard and Kaneko, perceived slant depends on the difference between horizontal and vertical scale and shear disparities. We made their theory more explicit by translating their proposals into linear mathematical expressions that contain weighting factors that allow for both slant evoked by rotation or divergence, subject-dependent underestimation of slant and other related phenomena reported in the literature. Our data for all stimulus durations and for all subjects is explained by this unequal-weighting extension of Howard and Kaneko's theory

Bi-stability in perceived slant when binocular disparity and monocular perspective specify different slants.

We examined how much depth we perceive when viewing a depiction of a slanted plane in which binocular disparity and monocular perspective provide different slant information. We exposed observers to a grid stimulus in which the monocular--and binocular-specified grid orientations were varied independently across stimulus presentations. The grids were slanted about the vertical axis and observers estimated the slant relative to the frontal plane. We were particularly interested in the metrical aspects of perceived slant for a broad spectrum of possible combinations of disparity--and perspective-specified slants. We found that observers perceived only one grid orientation when the two specified orientations were similar. More interestingly, when the monocular--and binocular-specified orientations were rather different, observers experienced perceptual bi-stability (they were able to select either a perspective--or a disparity-dominated percept)

The influence of large scanning eye movements on stereoscopic slant estimation of large surfaces

The results of several experiments demonstrate that the estimated magnitude of perceived slant of large stereoscopic surfaces increases with the duration of the presentation. In these experiments subjects were free to make eye movements. A possible explanation for the increase is that the visual system needs to scan the stimulus with eye movements (which take time) before it can make a reliable estimate of slant. We investigated the influence of large scanning eye movements on stereoscopic slant estimation of large surfaces. Six subjects estimated the magnitude of slant about the vertical or horizontal axis induced by large-field stereograms of which one half-image was transformed by horizontal scale, horizontal shear, vertical scale, vertical shear, divergence or rotation relative to the other half-image. The experiment was blocked in three sessions. Each session was devoted to one of the following fixation strategies: central fixation, peripheral (20 deg) fixation and active scanning of the stimulus. The presentation duration in each of the sessions was 0.5, 2 or 8 sec. Estimations were done with and without a visual reference. The magnitudes of estimated slant and the perceptual biases were not significantly influenced by the three fixation strategies. Thus, our results provide no support for the hypothesis that the time used for the execution of large scanning eye movements explains the build-up of estimated slant with the duration of the stimulus presentation

Stability of binocular depth perception with moving head and eyes

We systematically analyse the binocular disparity field under various eye, head and stimulus positions and orientations. From the literature we know that certain classes of disparity which involve the entire disparity field (such as those caused by horizontal lateral shift, differential rotation, horizontal scale and horizontal shear between the entire half-images of a stereogram) lead to relatively poor depth perception in the case of limited observation periods. These classes of disparity are found to be similar to the classes of disparities which are brought about by eye and head movements. Our analysis supports the suggestion that binocular depth perception is based primarily (for the first few hundred milliseconds) on classes of disparity that do not change as a result of ego-movement

Application of the improved factor method to the environmental impact assessment of buildings

By defining the role of service life within a LCA and indicating what can be achieved by a sound service life prediction, the environmental assessment of buildings can be more accurate. Aspects that will be looked in this paper at are the fixed service life within the current assessments, the different phases within service life and the rate of replacement of components. A description is given of preliminary results of research undertaken to develop a life cycle assessment method specifically for "flexible" buildings. This paper describes different aspects of the way to execute such an environmental calculation. The link between environmental load and the building sector is elaborated and emphasis is placed on the differences between the environmental load in the building sector and other sectors. Certain aspects related to environmental calculations are important when determining the environmental load of a building are reviewed and further illustrated using three examples of LCA for a building. The use of the factor method is described when undertaking environmental calculations and additional information is given for enhanced calculations suggesting that the proposed changes make LCA calculations in the building sector more accurate

Application of the improved factor method to the environmental impact assessment of buildings

By defining the role of service life within a LCA and indicating what can be achieved by a sound service life prediction, the environmental assessment of buildings can be more accurate. Aspects that will be looked in this paper at are the fixed service life within the current assessments, the different phases within service life and the rate of replacement of components. A description is given of preliminary results of research undertaken to develop a life cycle assessment method specifically for "flexible" buildings. This paper describes different aspects of the way to execute such an environmental calculation. The link between environmental load and the building sector is elaborated and emphasis is placed on the differences between the environmental load in the building sector and other sectors. Certain aspects related to environmental calculations are important when determining the environmental load of a building are reviewed and further illustrated using three examples of LCA for a building. The use of the factor method is described when undertaking environmental calculations and additional information is given for enhanced calculations suggesting that the proposed changes make LCA calculations in the building sector more accurate

A single motion system suffices for global-motion perception

AbstractGlobal-motion perception is the perception of coherent motion in a noisy motion stimulus. Thresholds for coherent motion perception were measured for different combinations of signal and noise speeds. Previous research [Edwards, M., Badcock, D. R., & Smith, A. T. (1998). Independent speed-tuned global-motion systems. Vision Research, 38 (11), 1573–1580; Khuu, S. K., & Badcock, D. R. (2002). Global speed processing: evidence for local averaging within, but not across two speed ranges. Vision Research, 42 (28), 3031–3042.] showed that thresholds were elevated when signal and noise speeds were similar, but not when they were different. The regions of increased threshold values for low and high signal speeds showed little overlap. On the basis of this evidence two independent speed-tuned systems were proposed: one for slow and one for fast-motion. However, in those studies only two signal speeds were used. We expanded the results by measuring threshold-curves for four different signal speeds. Considerable overlap of the threshold-curves was found between conditions. These results speak against a bipartite global-motion system. Model simulations indicate that present and previous experimental results can be produced by a single motion system providing that the mechanisms within it are speed-tuned