Basic visual capacities and shape discrimination after lesions of extrastriate area V4 in macaques

1996 ◽  
Vol 13 (1) ◽  
pp. 51-60 ◽  
Author(s):  
William H. Merigan
Keyword(s):  
Contrast Sensitivity ◽  
Luminance Contrast ◽  
Form Discrimination ◽  
Chromatic Contrast ◽  
Lower Quadrant ◽  
Line Segments ◽  
Area V4 ◽  
Fold Reduction ◽  
Visual Testing ◽  
Made In

Abstractlbotenic acid lesions were made in four macaque monkeys in a region of cortical area V4 that corresponds to the lower quadrant of one hemifield. For visual testing, fixation locus was monitoredwith scleral search coils and controlled behaviorally to place test stimuli either in the lesionedquadrant or in a control location in the opposite hemifield. Some basic visual capacities were slightly altered by the lesions; there was a two-fold reduction of luminance contrast sensitivity as well as red-green chromatic contrast sensitivity, both tested with stationary gratings. On the other hand, little or no loss was found when contrast sensitivity for detection or direction discrimination was tested with 10–Hz drifting gratings nor was there a reliable change in visual acuity. Hue and luminance matching were tested with a spatially more complex matching-to-sample task, but monkeys could not learn this task in the visual field locus of a V4 lesion. If previously trained at this locus, performance was not affected by the lesion. In contrast to the small effects on basic visual capabilities, performance on two form discrimination tasks was devastated by V4 lesions. The first involved discriminating the orientation of colinear groups of dots on a background of randomly placed dots. The second involved discriminating the orientation of a group of three line segments surrounded by differently oriented line segments. Some selectivity of the deficitsfor form discrimination was shown by the lack of an effect of the lesions on a global motion discrimination. These results show that while V4 lesions cause only slight disruptions of basic visual capacities, they profoundly disrupt form discriminations.

The Binocular Summation of Chromatic Contrast

Perception ◽  
1996 ◽  
Vol 25 (1_suppl) ◽  
pp. 145-145 ◽  
Author(s):  
D R Simmons ◽  
F A A Kingdom
Keyword(s):  
Contrast Sensitivity ◽  
Detection Threshold ◽  
Luminance Contrast ◽  
Binocular Summation ◽  
Chromatic Contrast ◽  
Probability Summation ◽  
Investigative Ophthalmology ◽  
Contrast Thresholds ◽  
Detection Mechanisms ◽  
Neural Summation

The level of binocularity possessed by mechanisms sensitive to chromatic contrast is still unclear. Recent studies of stereopsis and chromatic contrast have suggested that stereopsis is maintained at isoluminance, although the contrast sensitivity and disparity ranges of chromatic stereopsis mechanisms are reduced compared to luminance stereopsis mechanisms. Rose, Blake, and Halpern (1988 Investigative Ophthalmology and Visual Science29 283 – 290) hypothesised a link between binocular summation (ie the superiority of binocular detection over monocular detection) and stereopsis. Is this link maintained with heterochromatic isoluminant stimuli? To address this question, the binocular and monocular contrast thresholds for the detection of 0.5 cycle deg−1 Gabor patches were measured. The stimuli possessed different relative amounts of colour and luminance contrast ranging from isoluminance (red/green) to isochrominance (yellow/black) through intermediate values. It was found that, with these stimuli, binocular detection was well modelled by assuming independent mechanisms sensitive to chromatic contrast and luminance contrast. Furthermore, with isoluminant stimuli, levels of binocular summation were above those expected from probability summation between the eyes, thus providing evidence for binocular neural summation within chromatic detection mechanisms. Given that stereoscopic depth identification is impossible at contrast detection threshold with isoluminant heterochromatic stimuli, these results suggest that the link between stereopsis and levels of binocular neural summation may not be a particularly strong one. These results also provide clear evidence for the binocularity of chromatic detection mechanisms.

Development of face discrimination abilities, and relationship to magnocellular pathway development, between childhood and adulthood

2013 ◽  
Vol 30 (5-6) ◽  
pp. 251-262 ◽  
Author(s):  
PAMELA M. PALLETT ◽  
KAREN R. DOBKINS
Keyword(s):  
Spatial Frequency ◽  
Contrast Sensitivity ◽  
Face Processing ◽  
Luminance Contrast ◽  
Object Discrimination ◽  
Chromatic Contrast ◽  
Object Processing ◽  
Age Related ◽  
Visual Characteristics ◽  
Age Related Changes

AbstractThe current study tested the development of face and object processing in young children (mean age = 5.24 years), adolescents (mean age = 15.8 years), and adults (mean age = 21.1 years) using stimuli that were equated for low-level visual characteristics (luminance, contrast, and spatial frequency make-up) and methods that equate for difficulty across ages. We also tested sensitivity to luminance and chromatic contrast (i.e., thought to be mediated primarily by the subcortical Magnocellular (M) and Parvocellular (P) pathways, respectively) to determine whether age-related improvements in face or object discrimination were driven by age-related changes in the M and/or P pathways. Results showed a selective age-related improvement in face sensitivity and a relationship between age-related increases in face sensitivity and luminance contrast sensitivity. These results add to the mounting evidence that the M pathway may influence face processing.

scholarly journals Spatio-chromatic contrast sensitivity under mesopic and photopic light levels

2020 ◽  
Vol 20 (4) ◽  
pp. 23
Author(s):  
Sophie Wuerger ◽  
Maliha Ashraf ◽  
Minjung Kim ◽  
Jasna Martinovic ◽  
María Pérez-Ortiz ◽  
...  
Keyword(s):  
Contrast Sensitivity ◽  
Chromatic Contrast ◽  
Light Levels ◽  
Chromatic Contrast Sensitivity

Color and Luminance Contrast Sensitivity Changes in Early- and Late-Onset Strabismic Amblyopia

2006 ◽  
Vol 10 (1) ◽  
pp. 81
Author(s):  
John J. Sloper ◽  
Alison R. Davis ◽  
Majella M. Neveu ◽  
Chris R. Hogg ◽  
Michael J. Morgan ◽  
...  
Keyword(s):  
Contrast Sensitivity ◽  
Late Onset ◽  
Luminance Contrast ◽  
Strabismic Amblyopia ◽  
Sensitivity Changes

scholarly journals Psychophysical Measurements of Luminance Contrast Sensitivity and Color Discrimination with Transparent and Blue-Light Filter Intraocular Lenses

2017 ◽  
Vol 6 (2) ◽  
pp. 301-312 ◽  
Author(s):  
Marcelo Fernandes da Costa ◽  
Augusto Paranhos Júnior ◽  
Claudio Luiz Lottenberg ◽  
Leonardo Cunha Castro ◽  
Dora Fix Ventura
Keyword(s):  
Contrast Sensitivity ◽  
Blue Light ◽  
Color Discrimination ◽  
Luminance Contrast ◽  
Light Filter ◽  
Intraocular Lenses ◽  
Blue Light Filter

scholarly journals Luminance and chromatic contrast sensitivity at high light levels

2019 ◽  
Vol 19 (10) ◽  
pp. 70b ◽  
Author(s):  
Sophie Wuerger ◽  
Rafal Mantiuk ◽  
Maria Perez-Ortiz ◽  
Jasna Martinovic
Keyword(s):  
Contrast Sensitivity ◽  
High Light ◽  
Chromatic Contrast ◽  
Light Levels ◽  
Chromatic Contrast Sensitivity

Investigation of Chromatic Contrast Sensitivity Based on Different Color Directions and Spatial Frequencies

2011 ◽  
Vol 31 (1) ◽  
pp. 0133002 ◽  
Author(s):  
吕玮阁 Lü Weige ◽  
徐海松 Xu Haisong ◽  
汪哲弘 Wang Zhehong ◽  
M. Ronnier Luo M. Ronnier Luo
Keyword(s):  
Contrast Sensitivity ◽  
Chromatic Contrast ◽  
Spatial Frequencies ◽  
Different Color ◽  
Chromatic Contrast Sensitivity

scholarly journals Analysis of the Two-Peptide Bacteriocins Lactococcin G and Enterocin 1071 by Site-Directed Mutagenesis

2007 ◽  
Vol 73 (9) ◽  
pp. 2931-2938 ◽  
Author(s):  
Camilla Oppegård ◽  
Gunnar Fimland ◽  
Lisbeth Thorbæk ◽  
Jon Nissen-Meyer
Keyword(s):  
Specific Interaction ◽  
Site Directed Mutagenesis ◽  
Target Cells ◽  
Directed Mutagenesis ◽  
Hybrid Combination ◽  
Fold Reduction ◽  
Α Helix ◽  
Relative Potencies ◽  
Sequence Similarities ◽  
Made In

ABSTRACT The two peptides (Lcn-α and Lcn-β) of the two-peptide bacteriocin lactococcin G (Lcn) were changed by stepwise site-directed mutagenesis into the corresponding peptides (Ent-α and Ent-β) of the two-peptide bacteriocin enterocin 1071 (Ent), and the potencies and specificities of the various hybrid constructs were determined. Both Lcn and, to a lesser extent, Ent were active against all the tested lactococcal strains, but only Ent was active against the tested enterococcal strains. The two bacteriocins thus differed in their relative potencies to various target cells, despite their sequence similarities. The hybrid combination Lcn-α+Ent-β had low potency against all strains tested, indicating that these two peptides do not interact optimally. The reciprocal hybrid combination (i.e., Ent-α+Lcn-β), in contrast, was highly potent, indicating that these two peptides may form a functional antimicrobial unit. In fact, this hybrid combination (Ent-α+Lcn-β) was more potent against lactococcal strains than wild-type Ent was (i.e., Ent-α+Ent-β), but it was inactive against enterococcal strains (in contrast to Ent but similar to Lcn). The observation that Ent-α is more active against lactococci in combination with Lcn-β and more active against enterococci in combination with Ent-β suggests that the β peptide is an important determinant of target cell specificity. Especially the N-terminal residues of the β peptide seem to be important for specificity, since Ent-α combined with an Ent-β variant with Ent-to-Lcn mutations at positions 1 to 4, 7, 9, and 10 was >150-fold less active against enterococcal strains but one to four times more active against lactococcal strains than Ent-α+Ent-β. Moreover, Ent-to-Lcn single-residue mutations in the region spanning residues 1 to 7 in Ent-β had a more detrimental effect on the activity against enterococci than on that against lactococcal strains. Of the single-residue mutations made in the N-terminal region of the α peptide, the Ent-to-Lcn mutations N8Q and P12R in Ent-α influenced specificity, as follows: the N8Q mutation had no effect on activity against tested enterococcal strains but increased the activity 2- to 4-fold against the tested lactococcal strains, and the P12R mutation reduced the activity >150-fold and only ∼2-fold against enterococcal and lactococcal strains, respectively. Changing residues in the C-terminal half/part of the Lcn peptides (residues 20 to 39 and 25 to 35 in Lcn-α and Lcn-β, respectively) to those found in the corresponding Ent peptides did not have a marked effect on the activity, but there was an ∼10-fold or greater reduction in the activity upon also introducing Lcn-to-Ent mutations in the mid-region (residues 8 to 19 and 9 to 24 in Lcn-α and Lcn-β, respectively). Interestingly, the Lcn-to-Ent F19L+G20A mutation in an Lcn-Ent-β hybrid peptide was more detrimental when the altered peptide was combined with Lcn-α (>10-fold reduction) than when it was combined with Ent-α (∼2-fold reduction), suggesting that residues 19 and 20 (which are part of a GXXXG motif) in the β peptide may be involved in a specific interaction with the cognate α peptide. It is also noteworthy that the K2P and A7P mutations in Lcn-β reduced the activity only ∼2-fold, suggesting that the first seven residues in the β peptides do not form an α-helix.

scholarly journals Visual performance in a flight simulator: multifocal intraocular lenses in pilots

2018 ◽  
Vol 3 (1) ◽  
pp. e000139
Author(s):  
Lee Lenton
Keyword(s):  
Visual Acuity ◽  
Contrast Sensitivity ◽  
Luminance Contrast ◽  
Intraocular Lenses ◽  
Visual Performance ◽  
Flight Simulator ◽  
Night Time ◽  
Multifocal Intraocular Lenses ◽  
Low Luminance ◽  
Visual Tasks

ObjectiveTo compare the performance of adults with multifocal intraocular lenses (MIOLs) in a realistic flight simulator with age-matched adults with monofocal intraocular lenses (IOLs).Methods and AnalysisTwenty-five adults ≥60 years with either bilateral MIOL or bilateral IOL implantation were enrolled. Visual function tests included visual acuity and contrast sensitivity under photopic and mesopic conditions, defocus curves and low luminance contrast sensitivity tests in the presence and absence of glare (Mesotest II), as well as halo size measurement using an app-based halometer (Aston halometer). Flight simulator performance was assessed in a fixed-based flight simulator (PS4.5). Subjects completed three simulated landing runs in both daytime and night-time conditions in a randomised order, including a series of visual tasks critical for safety.ResultsOf the 25 age-matched enrolled subjects, 13 had bilateral MIOLs and 12 had bilateral IOLs. Photopic and mesopic visual acuity or contrast sensitivity were not significantly different between the groups. Larger halo areas were seen in the MIOL group and Mesotest values were significantly worse in the MIOL group, both with and without glare. The defocus curves showed better uncorrected visual acuity at intermediate and near distances for the MIOL group. There were no significant differences regarding performance of the vision-related flight simulator tasks between both groups.ConclusionsThe performance of visually related flight simulator tasks was not significantly impaired in older adults with MIOLs compared with age-matched adults with monofocal IOLs. These findings suggest that MIOLs do not impair visual performance in a flight simulator.

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