Contrast-coding in amblyopia. I. Differences in the neural basis of human amblyopia

1983 ◽  
Vol 217 (1208) ◽  
pp. 309-330 ◽  
Keyword(s):  
Visual Development ◽  
Neural Basis ◽  
Physiological Basis ◽  
Low Contrast ◽  
Spatial Frequencies ◽  
Matching Procedure ◽  
Contrast Perception ◽  
Contrast Matching ◽  
Contrast Range ◽  
Shed Light

To shed light on the basis of normal contrast perception in general and its susceptibility during early visual development in particular the contrast-coding deficit of amblyopic eyes was investigated. This was accomplished by using two different but complementary paradigms, one involving equating the contrast sensations between the amblyopic and normal fellow eye and the other involving the assessment of incremental sensitivity at different contrast levels. Since human amblyopia is known to have three different forms, representatives of each were tested. These include strabismics, anisometropes and astigmats. The results of the contrast-matching approach suggest that (i) strabismic and anisometropic (including meridional) amblyopes show important differences in supra-threshold contrast matching (this difference, which occurs across different spatial frequencies, at different luminances and for different field sizes, suggests a different neural basis for the two main forms of human amblyopia); (ii) all forms of amblyopia share one common feature, that of large threshold losses relative to the extent of the suprathreshold anomaly; (iii) the accelerating growth in subjective contrast above the raised threshold shown by the matching procedure is not evident in the assessment of incremental contrast sensitivity. From these results it is argued that, although contrast perception (in the low contrast range) is disturbed in amblyopia, amblyopia cannot be adequately understood in these terms alone. This raises important questions for our understanding of the physiological basis of contrast-coding in normal vision and its perceptual importance.

Contrast-coding in amblyopia. II. On the physiological basis of contrast recruitment

1983 ◽  
Vol 217 (1208) ◽  
pp. 331-340 ◽  
Keyword(s):  
Psychological Adaptation ◽  
Visual Development ◽  
Threshold Function ◽  
High Threshold ◽  
Physiological Basis ◽  
Contrast Mechanism ◽  
Anomalous Threshold ◽  
Band Limited ◽  
Contrast Perception ◽  
Contrast Thresholds

The perceptual compensations that result from a disruption to early visual development (amblyopia) were investigated to highlight the adaptative capabilities of normal contrast-coding. In anisometropic and meridional ambylopia, contrast thresholds may be raised without sub­stantial impairment to the perception of high contrasts. This accelerating response linking the anomalous threshold function with normal suprathreshold behaviour is similar to that observed for loudness perception in cases of inner ear damage and termed recruitment. This phenomenon is not purely psychological adaptation to amblyopia because magnitude estimation of contrast change within the ‘recruiting range’ is not disturbed. Three possible physiological explanations for contrast recruit­ment are examined, namely (i) recruitment of different-frequency neu­rons, (ii) recruitment of different-threshold neurons and (iii) a gain change in the response–contrast function of individual neurons. Since contrast­-matching in the presence of band-limited noise designed to raise artificially the threshold of adjacent detectors does not alter the recruiting response, it is unlikely that ‘across-frequency’ recruiting represents an adequate explanation. Similarly, it is argued that since the incremental sensitivity to contrast change is not enhanced in the recruiting region it is also unlikely the amblyopic neurons have steeper response–contrast relations (gain) than normal. The remaining and more likely possibility, in the light of recent neurophysiological findings of separate low and high threshold systems in the primate, is that recruitment in amblyopia occurs across neurons with the same spatial but different threshold characteristics. This suggests that normal contrast perception is subserved by more than one contrast mechanism and that in amblyopia the more sensitive contrast channel (lower threshold) is selectively affected.

scholarly journals Preliminary photographs and improved positives: discovering the New York Public Library’s Arctic Exploration album

2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Elena Basso ◽  
Federica Pozzi ◽  
Jessica Keister ◽  
Elizabeth Cronin
Keyword(s):  
New York ◽  
Fiber Optics ◽  
Public Library ◽  
Extreme Environment ◽  
The Arctic ◽  
Low Contrast ◽  
X Ray ◽  
Full Characterization ◽  
New York Public Library ◽  
Shed Light

AbstractIn the late 19th and early 20th centuries, original photographs were sent to publishers so that they could be reproduced in print. The photographs often needed to be reworked with overpainting and masking, and such modifications were especially necessary for low-contrast photographs to be reproduced as a letterpress halftone. As altered objects, many of these marked-up photographs were simply discarded after use. An album at The New York Public Library, however, contains 157 such photographs, all relating to the Jackson–Harmsworth expedition to Franz Josef Land, from 1894 to 1897. Received as gifts from publishers, the photographs are heavily retouched with overpainting and masking, as well as drawn and collaged elements. The intense level of overpainting on many of the photographs, but not on others, raised questions about their production and alteration. Jackson’s accounts attested to his practice of developing and printing photographs on site, testing different materials and techniques—including platino-bromide and silver-gelatin papers—to overcome the harsh environmental conditions. In this context, sixteen photographs from the album were analyzed through a combination of non-invasive and micro-invasive techniques, including X-ray fluorescence (XRF) spectroscopy, fiber optics reflectance spectroscopy (FORS), Raman and Fourier-transform infrared (FTIR) spectroscopies, and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDS). This analytical campaign aimed to evaluate the possible residual presence of silver halides in any of the preliminary and improved photographs. The detection of these compounds would be one of several factors supporting a hypothesis that some of the photographs in the album were indeed printed on site, in the Arctic, and, as a result, may have been impacted by the extreme environment. Additional goals of the study included the evaluation of the extent of retouching, providing a full characterization of the pigments and dyes used in overpainted prints, and comparing the results with contemporaneous photographic publications that indicate which coloring materials were available at the time. Further analyses shed light on the organic components present in the binders and photographic emulsions. This research has increased our knowledge of photographic processes undertaken in a hostile environment such as the Arctic, and shed light on the technical aspects of photographically illustrating books during the late 19th and early 20th centuries.

scholarly journals Breathing-driven prefrontal oscillations regulate maintenance of conditioned-fear evoked freezing independently of initiation

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Sophie Bagur ◽  
Julie M. Lefort ◽  
Marie M. Lacroix ◽  
Gaëtan de Lavilléon ◽  
Cyril Herry ◽  
...  
Keyword(s):  
Functional Role ◽  
Population Analysis ◽  
Conditioned Fear ◽  
Stable State ◽  
Network Activity ◽  
Power Dynamics ◽  
Potential Mechanism ◽  
Physiological Basis ◽  
Dorsomedial Prefrontal Cortex ◽  
Shed Light

AbstractBrain–body interactions are thought to be essential in emotions but their physiological basis remains poorly understood. In mice, regular 4 Hz breathing appears during freezing after cue-fear conditioning. Here we show that the olfactory bulb (OB) transmits this rhythm to the dorsomedial prefrontal cortex (dmPFC) where it organizes neural activity. Reduction of the respiratory-related 4 Hz oscillation, via bulbectomy or optogenetic perturbation of the OB, reduces freezing. Behavioural modelling shows that this is due to a specific reduction in freezing maintenance without impacting its initiation, thus dissociating these two phenomena. dmPFC LFP and firing patterns support the region’s specific function in freezing maintenance. In particular, population analysis reveals that network activity tracks 4 Hz power dynamics during freezing and reaches a stable state at 4 Hz peak that lasts until freezing termination. These results provide a potential mechanism and a functional role for bodily feedback in emotions and therefore shed light on the historical James–Cannon debate.

scholarly journals Similar levels of emotional contagion in male and female rats

2019 ◽  
Author(s):  
Yingying Han ◽  
Bo Sichterman ◽  
Maria Carrillo ◽  
Valeria Gazzola ◽  
Christian Keysers
Keyword(s):  
Sex Differences ◽  
Social Life ◽  
Emotional Contagion ◽  
Female Rats ◽  
Male Rats ◽  
Neural Basis ◽  
Male And Female Rats ◽  
Danger Detection ◽  
Rats And Mice ◽  
Shed Light

AbstractEmotional contagion, the ability to feel what other individuals feel, is thought to be an important element of social life. In humans, emotional contagion has been shown to be stronger in women than men. Emotional contagion has been shown to exist also in rodents, and a growing number of studies explore the neural basis of emotional contagion in male rats and mice. These studies promise to shed light on the mechanisms that might go astray in psychiatric disorders characterized by dysfunctions of emotional contagion and empathy. Here we explore whether there are sex differences in emotional contagion in rats. We use an established paradigm in which a demonstrator rat receives footshocks while freezing is measured in both the demonstrator and an observer rat, which can hear, smell and see each other. By comparing pairs of male rats with pairs of female rats, we find (i) that female demonstrators freeze less when submitted to footshocks, but that (ii) the emotional contagion response, i.e. the degree of influence across the rats, does not depend on the sex of the rats. This was true whether emotional contagion was quantified based on the slope of a regression linking demonstrator and observer average freezing, or on Granger causality estimates of moment-to-moment freezing. The lack of sex differences in emotional contagion is compatible with an interpretation of emotional contagion as serving selfish danger detection.

Exposure Duration and Effective Figure-Ground Contrast

1965 ◽  
Vol 17 (4) ◽  
pp. 308-314 ◽  
Author(s):  
Daniel Kahneman
Keyword(s):  
Exposure Duration ◽  
Matching Method ◽  
Apparent Contrast ◽  
Post Exposure ◽  
Tachistoscopic Presentation ◽  
Matching Procedure ◽  
Contrast Matching

The pre-and post-exposure fields in the tachistoscopic presentation are assumed to reduce the apparent contrast of the figure by brightness summation. A matching procedure was used to measure this effect. Apparent contrast rises linearly with duration, but only in the upper range. Further observations confirm the suggestion that the pre-and post-exposure fields retard the formation of bounding contours with a further reduction of apparent contrast at short durations as a result. It is indicated that the contrast-matching method provides a short-cut technique for the measurement of the temporal range of brightness summation.

scholarly journals A roadmap for the study of conscious audition and its neural basis

2017 ◽  
Vol 372 (1714) ◽  
pp. 20160103 ◽  
Author(s):  
Andrew R. Dykstra ◽  
Peter A. Cariani ◽  
Alexander Gutschalk
Keyword(s):  
Auditory Perception ◽  
Neural Correlates ◽  
Scene Analysis ◽  
Conscious Perception ◽  
Neural Basis ◽  
Or Groups ◽  
Neural Processes ◽  
Auditory Scenes ◽  
Shed Light

How and which aspects of neural activity give rise to subjective perceptual experience—i.e. conscious perception—is a fundamental question of neuroscience. To date, the vast majority of work concerning this question has come from vision, raising the issue of generalizability of prominent resulting theories. However, recent work has begun to shed light on the neural processes subserving conscious perception in other modalities, particularly audition. Here, we outline a roadmap for the future study of conscious auditory perception and its neural basis, paying particular attention to how conscious perception emerges (and of which elements or groups of elements) in complex auditory scenes. We begin by discussing the functional role of the auditory system, particularly as it pertains to conscious perception. Next, we ask: what are the phenomena that need to be explained by a theory of conscious auditory perception? After surveying the available literature for candidate neural correlates, we end by considering the implications that such results have for a general theory of conscious perception as well as prominent outstanding questions and what approaches/techniques can best be used to address them. This article is part of the themed issue ‘Auditory and visual scene analysis’.

scholarly journals Contrast matching across spatial frequencies for isoluminant chromatic gratings

2000 ◽  
Vol 40 (16) ◽  
pp. 2159-2165 ◽  
Author(s):  
Kaisa Tiippana ◽  
Jyrki Rovamo ◽  
Risto Näsänen ◽  
David Whitaker ◽  
Pia Mäkelä
Keyword(s):  
Spatial Frequencies ◽  
Contrast Matching

Variable Density Linear Acoustic Inverse Problem

1993 ◽  
Vol 15 (3) ◽  
pp. 255-266 ◽  
Author(s):  
M. Moghaddam ◽  
W.C. Chew
Keyword(s):  
Inverse Problem ◽  
Variable Density ◽  
Diffraction Tomography ◽  
Frequency Diversity ◽  
Low Contrast ◽  
Spatial Frequencies ◽  
Basic Ideas ◽  
Measured Pressure ◽  
Density Linear ◽  
Wave Incidence

The linear acoustic inverse problem is solved simultaneously for density (ρ) and compressibility (κ) using the basic ideas of diffraction tomography (DT). The key to solving this problem is to utilize frequency diversity to obtain the required independent measurements. The receivers are assumed to be in the far field of the object, and plane wave incidence is also assumed. The Born approximation is used to arrive at a relationship between the measured pressure field and two terms related to the spatial Fourier transform of the two unknowns, ρ and κ. The term involving compressibility corresponds to monopole scattering and that for density to dipole scattering. Measurements at several frequencies are used and a least squares problem is solved to reconstruct ρ and κ at the same time. It is observed that the low spatial frequencies in the spectra of ρ and κ produce inaccuracies in the results. Hence, a regularization method is devised to remove this problem. Several results are shown. Low contrast objects for which the above analysis holds are used to show that good reconstructions are obtained for both density and compressibility after regularization is applied.

The Effect of Spatial Frequency and Contrast on Visual Persistence

Perception ◽  
1979 ◽  
Vol 8 (5) ◽  
pp. 529-539 ◽  
Author(s):  
Alison Bowling ◽  
William Lovegrove ◽  
Barry Mapperson
Keyword(s):  
Spatial Frequency ◽  
Visual Persistence ◽  
Published Data ◽  
High Contrast ◽  
Low Contrast ◽  
Spatial Frequencies ◽  
Sinusoidal Gratings

The visual persistence of sinusoidal gratings of varying spatial frequency and contrast was measured. It was found that the persistence of low-contrast gratings was longer than that of high-contrast stimuli for all spatial frequencies investigated. At higher contrast levels of 1 and 4 cycles deg−1 gratings, a tendency for persistence to be independent of contrast was observed. For 12 cycles deg−1 gratings, however, persistence continued to decrease with increasing contrast. These results are compared with recently published data on other temporal responses, and are discussed in terms of the different properties of sustained and transient channels.

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