Illuminant and Viewpoint Biases from Embossed Surfaces

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 248-248 ◽  
Author(s):  
P Mamassian ◽  
M S Landy
Keyword(s):  
Human Visual System ◽  
A Priori ◽  
Reaction Times ◽  
Indirect Evidence ◽  
Shape From Shading ◽  
Judgment Task ◽  
Surface Shape ◽  
Oriented Stimulus ◽  
Depth Cue ◽  
Image Contour

The human visual system uses a-priori constraints for the estimation of surface shape from images. We propose here a robust paradigm to study individual observers' assumptions about the illuminant and viewpoint positions. In the study of illumination, the stimuli consisted of parallel, sinusoidally shaped, striped regions, alternating between wide and narrow. Narrow stripes alternating between white and black separated the uniform grey stripes, representing slanted edges in light and in shadow. The stimulus had the shape-from-shading ambiguity: either the wide or the narrow stripes could be seen as ‘in-front’, consistent with different assumed tilts of the illuminant. In a brief flash of a randomly oriented stimulus, observers stated whether the narrow or wide stripes appeared in the foreground. The results showed a strong bias for a light-from-above-left assumption (as in Howard et al, 1990 Perception19 523 – 530; Sun and Perona, 1996 Investigative Ophthalmology and Visual Science37 935). This bias was 20 to 30 deg to the left of vertical. Slower reaction times were obtained for more ambiguous figures. The same shape judgment task was used with an unshaded stimulus where the only depth cue was image contour. The same curvy, striped figure was portrayed with image contours at the edges of the stripes, as well as surface markings orthogonal to the depth variation, resulting in a shape-from-contour cue. We have previously reported indirect evidence for a bias of viewpoint above the object, that is observers interpret surface normals as pointing upward (Mamassian, 1995 Perception24 Supplement, 35). Our observers' shape judgments were consistent with this bias.

Shape from Shading. I: Surface Curvature and Orientation

Perception ◽  
1994 ◽  
Vol 23 (2) ◽  
pp. 169-189 ◽  
Author(s):  
Alan Johnston ◽  
Peter J Passmore
Keyword(s):  
Visual System ◽  
Light Source ◽  
Human Visual System ◽  
Three Dimensional ◽  
Shape Index ◽  
Shape From Shading ◽  
Surface Curvature ◽  
Surface Shape ◽  
Alignment Task ◽  
Band Limited

The human visual system makes effective use of shading alone in recovering the shape of objects. Pictures of sculptures are readily interpreted—a situation where shading provides virtually the sole cue to shape. However, shading has been considered a poor cue to depth in comparison with retinal disparity and kinetic cues. Curvature discrimination thresholds were measured with the use of a surface-alignment task for a range of surface curvatures from 0.16 cm−1 to 1.06 cm−1. Weber fractions were around 0.1, demonstrating considerable precision in this task. Weber fractions did not vary substantially as a function of surface curvature. Rotation of the light source around the line of sight had no effect on curvature discrimination but rotation towards the viewer increased discrimination thresholds. In contrast, slant discrimination declined with rotation of the light-source vector towards the viewpoint. When a band-limited random grey-level texture was mapped onto the sphere, curvature discrimination thresholds increased gradually as a function of texture contrast, even though texture and shading provided consistent cues to depth. Adding texture also increased slant discrimination thresholds, demonstrating that texture can act as a source of noise in shape-from-shading tasks. The psychophysical findings have been used to evaluate whether current algorithms for shape from shading in computer vision could serve as models of human three-dimensional shape analysis and to highlight low-level intramodular interactions between depth cues. It is demonstrated that, in the case of surfaces defined by shading, curvature descriptions are primary and do not depend upon the prior encoding of surface orientation, and Koenderink's local-shape index is suggested as an alternative intermediate representation of surface shape in the human visual system.

scholarly journals Corroborating behavioral evidence for the interplay of representational richness and semantic control in semantic word processing

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Laura Bechtold ◽  
Christian Bellebaum ◽  
Paul Hoffman ◽  
Marta Ghio
Keyword(s):  
Word Processing ◽  
Context Effects ◽  
Reaction Times ◽  
Abstract Word ◽  
Judgment Task ◽  
Healthy Adults ◽  
Control Mechanisms ◽  
Contextual Cues ◽  
Semantic Judgment ◽  
Behavioral Evidence

AbstractThis study aimed to replicate and validate concreteness and context effects on semantic word processing. In Experiment 1, we replicated the behavioral findings of Hoffman et al. (Cortex 63,250–266, https://doi.org/10.1016/j.cortex.2014.09.001, 2015) by applying their cueing paradigm with their original stimuli translated into German. We found concreteness and contextual cues to facilitate word processing in a semantic judgment task with 55 healthy adults. The two factors interacted in their effect on reaction times: abstract word processing profited more strongly from a contextual cue, while the concrete words’ processing advantage was reduced but still present. For accuracy, the descriptive pattern of results suggested an interaction, which was, however, not significant. In Experiment 2, we reformulated the contextual cues to avoid repetition of the to-be-processed word. In 83 healthy adults, the same pattern of results emerged, further validating the findings. Our corroborating evidence supports theories integrating representational richness and semantic control mechanisms as complementary mechanisms in semantic word processing.

The myth of visual depth cues IV: Shape-from-shading

2021 ◽  
Author(s):  
Lydia Maniatis
Keyword(s):  
Visual Experience ◽  
Shape From Shading ◽  
Visual Depth ◽  
Depth Cues ◽  
Depth Cue ◽  
Physical Fact

The popular idea that “shading” is a shape and depth “cue” is the result of a failure to appreciate that neither shading as a physical fact nor shading as a perceptual fact can serve to explain the process leading to visual experience, because the description “shading” does not apply to the proximal stimulation, where this process begins. Both perceived shape and perceived illumination are products of figural constraints.

AGE OF ONSET, TYPE OF EXPOSURE, AND ULTIMATE ATTAINMENT OF L2 MORPHO-SYNTACTIC SENSITIVITY

2019 ◽  
Vol 42 (4) ◽  
pp. 801-823
Author(s):  
Eun-Kyoung Rosa Lee
Keyword(s):  
Language Learning ◽  
Native Speakers ◽  
Age Of Onset ◽  
Reaction Times ◽  
Foreign Language Learning ◽  
Judgment Task ◽  
Control Group ◽  
Learning Context ◽  
Grammaticality Judgment ◽  
Third Person

AbstractThe present study examined whether early immersive L2 exposure in a foreign language learning context can yield long-term advantages in L2 morpho-syntactic sensitivity. Participants were 40 Korean university students with high English proficiency, who had either attended an English kindergarten or begun learning English in a classroom, and a control group of native English speakers. All participants performed a speeded aural grammaticality judgment task that included the following features: articles, subcategorization, plural -s, third-person -s. Results showed that the English-kindergarten group outperformed the late-classroom group in terms of accuracy for ungrammatical sentences, while the two groups did not differ significantly on grammatical sentences and in reaction time measures. The learners altogether scored higher in plural -s and third-person -s compared to articles. While the native speakers showed near-perfect accuracy and fast reaction times, the highly proficient learners were at near-chance level in detecting morpho-syntactic errors during online L2 aural processing.

Parallel Processing of Luminance Steps in the Presence of Luminance Gradients

Perception ◽  
1996 ◽  
Vol 25 (1_suppl) ◽  
pp. 62-62 ◽  
Author(s):  
A Grodon ◽  
M Fahle
Keyword(s):  
Parallel Processing ◽  
Visual System ◽  
Human Visual System ◽  
Reaction Times ◽  
Step Size ◽  
Detection Thresholds ◽  
Imaginary Circle ◽  
Staircase Procedure ◽  
Dark Background ◽  
Spatial Changes

Some features of complex visual displays are analysed effortlessly and in parallel by the human visual system, without requiring scrutiny. Examples for such features are changes of luminance, colour, orientation, and movement. We measured thresholds as well as reaction times for the detection of abrupt spatial changes in luminance in the presence of luminance gradients, in order to evaluate the ability of the system to ignore such gradients. Stimuli were presented on a 20 inch monitor under control of a Silicon Graphics workstation. Luminance was calibrated by means of a photometer (Minolta). We presented between 4 and 14 rectangles simultaneously on a homogeneous dark background. Rectangles were arranged on an incomplete, imaginary circle around the fixation point and luminance changed stepwise from one rectangle to the next. Five observers had to indicate whether all luminance steps between the rectangles were subjectively equal or whether one luminance step was larger. Detection thresholds were determined for the larger step as a function of the small steps (‘base step size’) by means of an adaptive staircase procedure. The smallest luminance steps were detected when the base step size was zero and when only few rectangles were presented. Thresholds increased slightly with the number of rectangles displayed simultaneously, and to a greater extent (by up to a factor of 2) with increasing base step size. The results of all observers improved significantly through practice, by about a factor of 2. We conclude that the visual system is unable to completely eliminate gradients of luminance and to isolate sharp transitions in luminance.

scholarly journals Cognitive processes behind the shooter bias: Dissecting response bias, motor preparation and information accumulation

2021 ◽  
Author(s):  
Marius Frenken ◽  
Wanja Hemmerich ◽  
David Izydorczyk ◽  
Sophie Elisabeth Scharf ◽  
Roland Imhoff
Keyword(s):  
Response Bias ◽  
Cognitive Processes ◽  
A Priori ◽  
Reaction Times ◽  
Motor Preparation ◽  
Total N ◽  
The Public ◽  
Decision Bias ◽  
Model Study ◽  
Racial Biases

A rich body of research points to racial biases in so-called police officer dilemma tasks: participants are generally faster and less error-prone to “shoot” (vs. not “shoot”) Black (vs. White) targets. In three experimental (and two supplemental) studies (total N = 914), we aimed at examining the cognitive processes underlying these findings under fully standardized conditions. To be able to dissect a-priori decision bias, biased information processing and motor preparation, we rendered video sequences of virtual avatars that differed in nothing but the tone of their skin. Modeling the data via drift diffusion models revealed that the threat of a social group can be explicitly learned and mapped accordingly on an a-priori response bias within the model (Study 1). Studies 2 and 3 replicated the racial shooter bias as apparent in faster reaction times in stereotype-consistent trials. This, however, appears to result from stereotype-consistent motoric preparations and execution readiness, but not from pre-judicial threat biases. The results have implications especially for automatic stereotypes in the public.

Immediate-term chemotherapy-related cognitive impairment (CRCI) following administration of intravenous (IV) chemotherapy.

2017 ◽  
Vol 35 (15_suppl) ◽  
pp. 10084-10084
Author(s):  
Omar Farooq Khan ◽  
Ellen R. Cusano ◽  
Soundouss Raissouni ◽  
Mica Pabia ◽  
Johanna Haeseker ◽  
...  
Keyword(s):  
Reaction Time ◽  
Peripheral Neuropathy ◽  
A Priori ◽  
Reaction Times ◽  
Vigilance Task ◽  
Prior Chemotherapy ◽  
Chemotherapy Administration ◽  
Stanford Sleepiness Scale ◽  
Time Changes ◽  
Psychomotor Vigilance

10084 Background: The acute impact of chemotherapy on cognition is unknown. This study utilized performance on the psychomotor vigilance task (PVT) and trail-making test B (TMT) to assess CRCI immediately following chemotherapy administration. Methods: Patients aged 18-80 years receiving first-line IV chemotherapy for any stage of breast or colorectal cancer were eligible. Patients with brain metastases, neurologic disorders or allergic reactions to chemotherapy were excluded. Patient symptoms, peripheral neuropathy and Stanford Sleepiness Scale were assessed. A five-minute PVT and TMT were completed on a tablet computer pre-chemotherapy and immediately post-chemotherapy. Paired Wilcoxon Rank Sum tests were used to assess change in median PVT reaction time, TMT completion time, TMT errors and PVT lapses. A priori, an increase in median PVT reaction times by over 20 ms (approximating reaction time changes with blood alcohol concentrations of 0.04 to 0.05 g%) was considered a clinically relevant change. Results: 144 patients (74 breast, 70 colorectal, median age 55.5 years) were tested. Post-chemotherapy, median PVT reaction time slowed by an average of 12.4 ms ( p = 0.01). Post-chemotherapy median PVT times slowed by over 20 ms in 59 patients (40.9%). TMT completion post-chemotherapy was faster by an average of 6.1 seconds ( p < 0.001). No differences were seen in TMT errors ( p = 0.417) or PVT lapses ( p = 0.845). Change in median PVT reaction time was not associated with age, gender, number of prior chemotherapy cycles, peripheral neuropathy grade, self-reported symptoms (anxiety, fatigue or depression). Change in median PVT reaction time was also not significantly associated with use of any specific chemotherapeutic drug or class, including paclitaxel (which includes ethanol as an excipient). Conclusions: Median PVT reaction time was significantly slower immediately after chemotherapy compared to a pre-chemotherapy baseline, and impairment correlating to effects of alcohol was seen in 41% of patients. This effect appears independent of age, self-reported symptoms or prior chemotherapy cycles. Further studies assessing functional impact of immediate-term CRCI are warranted.

Some effects of inclination on elastohydrodynamic squeeze film problems

1976 ◽  
Vol 78 (2) ◽  
pp. 247-260 ◽  
Author(s):  
D. Whicker ◽  
A. L. Browne ◽  
S. M. Rohde
Keyword(s):  
Experimental Data ◽  
Viscous Fluid ◽  
Pressure Distribution ◽  
Slip Velocity ◽  
A Priori ◽  
Surface Shape ◽  
Time Dependent ◽  
Squeeze Film ◽  
Rigid Surface ◽  
Loading Function

An analysis is presented for the non-inertial descent of an inclined sinkage element (a rectangular prism) through a viscous fluid onto a rigid surface. The effects of sinkage-element deformability, slip velocity and time-dependent loading conditions are considered. Unlike previous analyses no assumptions are made a priori about the form of the pressure distribution during, or the effect of corners on, inclined sinkage. The results for rigid square plates are compared with those of previous analyses and with the limited amount of experimental data available. Results are also presented for a deformable sinkage element, which is used to model the action of an individual tyre tread element on a wet pavement. An inclination function based on available data on the tyre surface shape in the footprint region is used. The loading function for this case is based on measured values of tyre footprint pressure.

On Deposition and Build-Up Detachment in Compressor Fouling

2018 ◽  
Author(s):  
Nicola Casari ◽  
Michele Pinelli ◽  
Alessio Suman
Keyword(s):  
Gas Turbines ◽  
Particle Deposition ◽  
A Priori ◽  
A Priori Estimate ◽  
Major Effect ◽  
Surface Shape ◽  
Adhesion Forces ◽  
Severe Problem ◽  
Two Bodies ◽  
Uncontrolled Variation

Compressor fouling is a severe problem for both heavy-duty and aero-propulsion gas turbines. Particles can impinge on the blade and annulus surfaces, sticking there. The consequences of particle deposition are the increase of the roughness and an uncontrolled variation in the surface shape. These problems have a major effect on the performance of the compressor over time. Variations in the flow field can make the flow quantities close to the deposit to change, and it may happen that the conditions for the sticking do not hold any longer. If this is the case, the build-up detachment may happen. This occurrence can mitigate the fouling effects and may be exploited for keeping the performance of the compressor as high as possible over the operating period. In this work, an innovative model is proposed in order to evaluate the adhesion forces and the possible detachment. Particularly, the same forces that keep a gecko stuck to a surface are considered: the van der Waals forces (due to the proximity of the two bodies) and the Laplace force (due to the curvature of the liquid film related to the humidity). The so formulated model, named gecko-like for such a reason, is used for the numerical analyses of a deposition problem. Both the sticking and possible build-up detachment are considered. The outcome of this work can be regarded as an a-priori estimate of the forces to be kept into account when dealing with compressor fouling problems.

Development of Infants' Sensitivity to Surface Contour Information for Spatial Layout

Perception ◽  
10.1068/p2789 ◽  
2001 ◽  
Vol 30 (2) ◽  
pp. 167-176 ◽  
Author(s):  
Maya G Sen ◽  
Albert Yonas ◽  
David C Knill
Keyword(s):  
Age Groups ◽  
Spatial Layout ◽  
The Other ◽  
Surface Shape ◽  
Depth Information ◽  
Surface Contour ◽  
Depth Cue ◽  
Contour Information ◽  
Monocular Depth ◽  
Control Study

The development of sensitivity to a recently discovered static-monocular depth cue to surface shape, surface contours, was investigated. Twenty infants in each of three age groups (5, 5½, and 7 months) viewed a display that creates an illusion, for adult viewers, that what is in fact a frontoparallel cylinder is slanted away in depth, so that one end appears closer than the other. Preferential reaching was recorded in both monocular and binocular conditions. More reaching to the apparently closer end in the monocular than in the binocular condition is evidence of sensitivity. Infants aged 7 months responded to surface contour information, but infants aged 5 and 5 months did not. In a control study, twenty 5-month-old infants reached consistently for the closer ends of cylinders that were actually rotated in depth. As findings with other static-monocular depth information suggest, infants' sensitivity to surface contour information appears to develop at approximately 6 months.

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