scholarly journals Perceptual averaging of dichoptic mixtures of colour contrast promoted by task-irrelevant luminance contrast

2014 ◽  
Vol 14 (10) ◽  
pp. 963-963
Author(s):  
L. Libenson ◽  
F. Kingdom
Keyword(s):  
Luminance Contrast ◽  
Colour Contrast ◽  
Task Irrelevant

scholarly journals Luminance contrast and colour contrast related errors in pseudoisochromatic plate identification

Eye ◽  
1997 ◽  
Vol 11 (5) ◽  
pp. 713-716
Author(s):  
Michael Wall ◽  
Paul B Donzis
Keyword(s):  
Luminance Contrast ◽  
Colour Contrast

Texture Segregation by Orientation Differences: Colour Sensitive but Not Hue Specific?

Perception ◽  
1996 ◽  
Vol 25 (1_suppl) ◽  
pp. 98-98
Author(s):  
U Leonards ◽  
W Singer
Keyword(s):  
Experimental Psychology ◽  
Human Perception ◽  
Luminance Contrast ◽  
Texture Element ◽  
Feature Maps ◽  
Texture Segregation ◽  
Colour Contrast

Segregation of textures on the basis of orientation differences between texture elements is achieved even when these texture elements differ from their surround only by colour (McIlhagga et al, 1990 Vision Research30 489 – 495). This finding seems to contradict the assumption that colour and orientation are extracted in separate feature maps (eg Treisman and Sato, 1990 Journal of Experimental Psychology: Human Perception and Performance16 459 – 478). To examine whether colour information is evaluated in parallel in different processing streams for the assessment of hue and form, we tested whether texture elements can be segregated if they differ only by specific conjunctions of colour and orientation; texture elements consisted of crosses with their two crossing lines differing in colour. Texture elements defining figure and background had the same coloured composition but the conjunction of colour with the two crossing lines was reversed. Different colour combinations were tested under various luminance contrast conditions, irrespective of the colour combination, segmentation was achieved as long as the two crossing lines of the texture elements differed in luminance. If, however, the different colours of the two crossing lines were approximately equiluminant, segmentation was reduced or impossible. Thus, subjects were able to use for texture segregation conjunctions between luminance and orientation but not between colour and orientation. Our results suggest that colour cannot be associated selectively with differently oriented components of the same texture element. This supports the hypothesis that colour contrast is used in parallel by different processing streams to assess the orientation and hue of contours and reveals limitations in the selectivity with which features are subsequently bound together.

Isoluminant Colour Contrast Does Not Fill in Surfaces

Perception ◽  
1996 ◽  
Vol 25 (1_suppl) ◽  
pp. 40-40
Author(s):  
B Dresp ◽  
C Wehrhahn
Keyword(s):  
Luminance Contrast ◽  
Opposite Polarity ◽  
The Other ◽  
Test Surface ◽  
Colour Contrast ◽  
Mixed Polarity ◽  
Polarity Condition ◽  
Matching Procedure ◽  
The Mean ◽  
Neurophysiological Basis

It has been suggested (Livingstone and Hubel, 1988 Science240 740 – 749) that the ‘colour-blind’ magnocellular pathways generate the neurophysiological basis of surfaces with illusory contours since the latter do not seem to be perceived in inducing configurations of a given colour which is isoluminant with regard to the colour of the background (equiluminant colour contrast). However, psychophysical data allowing us to assess the relative visibility of illusory surfaces in coloured stimuli with luminance contrast compared to configurations with equiluminant colour contrast are not yet available. We designed a colour-matching experiment where ten naive observers had to adjust the intensity of a red illusory surface so that it appeared to match the intensity of the red background. The configurations used were Kanizsa squares with green inducing elements, isoluminant or not with regard to the background. Isoluminance was assessed individually for each observer by means of a classical flicker test. A brightness-matching procedure was applied to configurations of achromatic inducers on a grey background. In this case, the inducers had either all the same contrast polarity (light), or both polarities (light and dark) within a given configuration. Luminance contrast in the achromatic configuration with only one polarity was the same as in the non-isoluminant colour condition. Luminance contrasts of light and dark inducers in the mixed-polarity condition were physically balanced. The results show that the mean point of subjective equality (PSE) of the test surface corresponds to the physical intensity of the background with equiluminant colour contrast only, indicating the absence of an apparent surface in this condition. This result supports the idea that magnocellular pathways in the human visual system mediate the neurophysiological genesis of illusory surfaces. In all the other stimulus conditions, the PSE does not correspond to the physical intensity of the background. Matching ‘errors’ are significantly stronger in the achromatic conditions, but, paradoxically, strongest in the condition with balanced contrasts of opposite polarity. This finding suggests that luminance contrast is not the only determinant of the perceived strength of illusory surfaces.

Neglect for low luminance contrast stimuli but not for high colour contrast stimuli

Neuroreport ◽  
1996 ◽  
Vol 7 (8) ◽  
pp. 1360-1364 ◽  
Author(s):  
Fabrizio Doricchi ◽  
Paola Angelelli ◽  
Maria De Luca ◽  
Donatella Spinelli
Keyword(s):  
Luminance Contrast ◽  
Colour Contrast ◽  
Low Luminance

Effects of Awareness on the Control of Attention

2016 ◽  
Vol 28 (6) ◽  
pp. 842-851 ◽  
Author(s):  
Taylor W. Webb ◽  
Hope H. Kean ◽  
Michael S. A. Graziano
Keyword(s):  
Body Schema ◽  
Irrelevant Stimulus ◽  
Luminance Contrast ◽  
Schema Theory ◽  
The Body ◽  
Attention Task ◽  
Metacontrast Masking ◽  
Task Irrelevant ◽  
The Relationship ◽  
The Brain

Previous studies show that it is possible to attend to a stimulus without awareness of it. Whether attention and awareness are independent or have a specific relationship, however, remains debated. Here, we tested three aspects of visual attention with and without awareness of the visual stimulus. Metacontrast masking rendered participants either subjectively aware or not aware of the stimulus. Attention drawn to the stimulus was measured by using the stimulus as a cue in a spatial attention task. We found that attention was drawn to the stimulus regardless of whether or not people were aware of it. However, attention changed significantly in the absence of awareness in at least three ways. First, attention to a task-relevant stimulus was less stable over time. Second, inhibition of return, the automatic suppression of attention to a task-irrelevant stimulus, was reduced. Third, attention was more driven by the luminance contrast of the stimulus. These findings add to the growing information on the behavior of attention with and without awareness. The findings are also consistent with our recently proposed account of the relationship between attention and awareness. In the attention schema theory, awareness is the internal model of attention. Just as the brain contains a body schema that models the body and helps control the body, so it contains an attention schema that helps control attention. In that theory, in the absence of awareness, the control of attention should suffer in basic ways predictable from dynamical systems theory. The present results confirm some of those predictions.

Colour Inputs to Random-Dot Stereopsis

Perception ◽  
1992 ◽  
Vol 21 (6) ◽  
pp. 717-729 ◽  
Author(s):  
Geoffrey W Stuart ◽  
Mark Edwards ◽  
Michael L Cook
Keyword(s):  
Luminance Contrast ◽  
Stereoscopic Depth ◽  
Signal To Noise ◽  
Chromatic Contrast ◽  
Magnocellular System ◽  
Colour Contrast ◽  
Random Dot Stereograms ◽  
Photoreceptor Mosaic

Recently it has been claimed by Livingstone and Hubel that, of three anatomically and functionally distinct visual channels (the magnocellular, parvocellular interblob, and blob channels), only the magnocellular channel is involved in the processing of stereoscopic depth. Since the magnocellular system shows little overt colour opponency, the reported loss of the ability to resolve random-dot stereograms defined only by colour contrast seems consistent with this view. However, Julesz observed that reversed-contrast stereograms could be fused if correlated colour information was added. In the present study, ‘noise’ (non-corresponding) pixels were injected into random-dot stereograms in order to increase fusion time. All six subjects tested were able to achieve stereopsis in less than three minutes when there was only correspondence in colour and not in luminance, and three when luminance contrast was completely reversed. This ability depends on information about the direction of colour contrast, not just the presence of chromatic borders. When luminance and chromatic contrast are defined in terms of signal-to-noise ratios at the photoreceptor mosaic, chromatic information plays at least as important a role in stereopsis as does luminance information, suggesting that the magnocellular channel is not uniquely involved.

Road lighting: A pilot study investigating improvement of visual performance using light sources with a larger gamut area

2020 ◽  
Vol 52 (7) ◽  
pp. 895-905
Author(s):  
B Yang ◽  
M Wei
Keyword(s):  
Pilot Study ◽  
Reaction Times ◽  
Luminance Contrast ◽  
Visual Performance ◽  
Light Sources ◽  
Detection Rates ◽  
Road Lighting ◽  
Colour Contrast ◽  
Gamut Size ◽  
Colour Gamut

Many past studies investigating visual performance focused mainly on the effect of luminance contrast between the target and background. Other studies have suggested the importance of colour contrast on visual performance. This pilot study was designed to investigate whether visual performance in the context of road lighting can be improved by enhancing the chroma of targets. Observers were asked to detect an off-axis target with different levels of luminance, hue, and chroma on a uniform background at 1.5 cd/m2. When the target and the background were set to the same luminance, a zero luminance contrast, the detection rates were significantly lower and the reaction times were significantly longer. Enhancing the colour contrast between the target and the background by increasing the target chroma level, however, was found to improve visual performance to similar levels as those when the target was revealed by luminance contrast against the background. Such an enhancement on colour contrast can be achieved in practice using light sources with a greater colour gamut size.

scholarly journals Collinear search impairment is luminance contrast invariant

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Chia-huei Tseng ◽  
Hiu Mei Chow ◽  
Jiayu Liang ◽  
Satoshi Shioiri ◽  
Chien-Chung Chen
Keyword(s):  
Target Detection ◽  
Opposite Effect ◽  
Visual Display ◽  
Threshold Level ◽  
Luminance Contrast ◽  
Early Vision ◽  
Basic Features ◽  
Task Irrelevant ◽  
Collinear Facilitation ◽  
And Task

AbstractCollinear search impairment (CSI) is a phenomenon where a task-irrelevant collinear structure impairs a target search in a visual display. It has been suggested that CSI is monocular, occurs without the participants’ access to consciousness and is possibly processed at an early visual site (e.g. V1). This effect has frequently been compared with a well-documented opposite effect called attentional capture (AC), in which salient and task-irrelevant basic features (e.g. color, orientation) enhance target detection. However, whether this phenomenon can be attributed to non-attentional factors such as collinear facilitation (CF) has not yet been formally tested. Here we used one well-established property of CF, i.e. that target contrast modulates its effect direction (facilitation vs suppression), to examine whether CSI shared similar signature profiles along different contrast levels. In other words, we tested whether CSI previously observed at the supra-threshold level was reduced or reversed at near-threshold contrast levels. Our results showed that, regardless of the luminance contrast levels, participants spent a longer time searching for targets displayed on the salient singleton collinear structure than those displayed off the structure. Contrast invariance suggests that it is unlikely that CSI is exclusively sub-served by an early vision mechanism (e.g. CF).

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