scholarly journals Effects of flanking patterns on contrast detection and contrast discrimination

2010 ◽  
Vol 3 (9) ◽  
pp. 345-345 ◽  
Author(s):  
S. L Varadharajan ◽  
J. M Foley
Keyword(s):  
Contrast Detection ◽  
Contrast Discrimination

Representing contrast detection as an eigenvalue problem

1999 ◽  
Vol 12 (4) ◽  
pp. 397-419 ◽  
Author(s):  
Alan L. Stewart ◽  
Phyllis A. Mancino ◽  
Roger S. Pinkham ◽  
John M. Chomak
Keyword(s):  
Eigenvalue Problem ◽  
Contrast Detection

Contrast adaptation may enhance contrast discrimination

2002 ◽  
Vol 16 (1) ◽  
pp. 45-58 ◽  
Author(s):  
Giulia Abbonizio ◽  
Colin Clifford ◽  
Keith Langley
Keyword(s):  
Contrast Adaptation ◽  
Contrast Discrimination

Encoding of graded changes in spatial specificity of prior cues in human visual cortex

2014 ◽  
Vol 112 (11) ◽  
pp. 2834-2849 ◽  
Author(s):  
Yuko Hara ◽  
Justin L. Gardner
Keyword(s):  
Prior Information ◽  
Prior Probability ◽  
Blood Oxygenation ◽  
Response Magnitude ◽  
Behavioral Performance ◽  
Significant Difference ◽  
Cortical Responses ◽  
Sensory Responses ◽  
Contrast Discrimination ◽  
Spatial Specificity

Prior information about the relevance of spatial locations can vary in specificity; a single location, a subset of locations, or all locations may be of potential importance. Using a contrast-discrimination task with four possible targets, we asked whether performance benefits are graded with the spatial specificity of a prior cue and whether we could quantitatively account for behavioral performance with cortical activity changes measured by blood oxygenation level-dependent (BOLD) imaging. Thus we changed the prior probability that each location contained the target from 100 to 50 to 25% by cueing in advance 1, 2, or 4 of the possible locations. We found that behavioral performance (discrimination thresholds) improved in a graded fashion with spatial specificity. However, concurrently measured cortical responses from retinotopically defined visual areas were not strictly graded; response magnitude decreased when all 4 locations were cued (25% prior probability) relative to the 100 and 50% prior probability conditions, but no significant difference in response magnitude was found between the 100 and 50% prior probability conditions for either cued or uncued locations. Also, although cueing locations increased responses relative to noncueing, this cue sensitivity was not graded with prior probability. Furthermore, contrast sensitivity of cortical responses, which could improve contrast discrimination performance, was not graded. Instead, an efficient-selection model showed that even if sensory responses do not strictly scale with prior probability, selection of sensory responses by weighting larger responses more can result in graded behavioral performance benefits with increasing spatial specificity of prior information.

scholarly journals Dual-rotation C-arm cone-beam computed tomography to increase low-contrast detection

2017 ◽  
Vol 44 (9) ◽  
pp. e164-e173
Author(s):  
Aymeric Reshef ◽  
Cyril Riddell ◽  
Yves Trousset ◽  
Saïd Ladjal ◽  
Isabelle Bloch
Keyword(s):  
Computed Tomography ◽  
Cone Beam Computed Tomography ◽  
Cone Beam ◽  
Low Contrast ◽  
Contrast Detection ◽  
Dual Rotation

Electrophysiological and Psychophysical Responses to Modulation of Contrast of a Grating Pattern

Perception ◽  
1972 ◽  
Vol 1 (3) ◽  
pp. 341-349 ◽  
Author(s):  
I Bodis-Wollner ◽  
C D Hendley ◽  
J J Kulikowski
Keyword(s):  
Visual System ◽  
Human Visual System ◽  
Just Noticeable Difference ◽  
Evoked Responses ◽  
Successive Presentation ◽  
Electrophysiological Data ◽  
Grating Pattern ◽  
Modulation Rate ◽  
Contrast Discrimination ◽  
Lower Contrast

Contrast-modulated grating patterns were used to compare evoked responses and psychophysical thresholds of contrast modulation. The stimulus consisted of the successive presentation of a grating pattern at a higher and lower contrast. At a modulation rate of 8 Hz it was found that there is correspondence between the two kinds of data for a 6 cycle/degree grating. The just noticeable difference was not constant, and data approximated a Weber's law of contrast discrimination. However, it was found that there is a slight departure from this law, in that the ratio decreases with mean contrast. Both psychophysical and electrophysiological data exclude a model of simple luminance detection and are consistent with the operation of spatial contrast detectors in the human visual system.

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