352 research outputs found
Dynamics of rod and cone photoreceptor interactions under mesopic light levels
No full textVisual adaptation regulates contrast sensitivity during dynamically changing light conditions (Crawford, 1947; Hecht, Haig & Chase, 1937). These adaptation dynamics are unknown under dim (mesopic) light levels when the rod (R) and long (L), medium (M) and short (S) wavelength cone photoreceptor classes contribute to vision via interactions in shared non-opponent Magnocellular (MC), chromatically opponent Parvocellular (PC) and Koniocellular (KC) visual pathways (Dacey, 2000). This study investigated the time-course of adaptation and post-receptoral pathways mediating receptor specific rod and cone interactions under mesopic illumination. A four-primary photostimulator (Pokorny, Smithson & Quinlan, 2004) was used to independently control the activity of the four photoreceptor classes and their post-receptoral visual athways in human observers.\ud
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In the first experiment, the contrast sensitivity and time-course of visual adaptation under mesopic illumination were measured for receptoral (L, S, R) and post-receptoral (LMS, LMSR, L-M) stimuli. An incremental (Rapid-ON) sawtooth conditioning pulse biased detection to ON-cells within the visual pathways and sensitivity was assayed relative to pulse onset using a briefly presented incremental probe that did not alter adaptation. Cone.Cone interactions with luminance stimuli (L cone, LMS, LMSR) reduced sensitivity by 15% and the time course of recovery was 25± 5ms-1 (μ ± SEM). PC mediated (+L-M) chromatic stimuli sensitivity loss was less (8%) than for luminance and recovery was slower (μ = 2.95 ± 0.05 ms-1), with KC mediated (S cone) chromatic stimuli showing a high sensitivity loss (38%) and the slowest recovery time (1.6 ± 0.2 ms-1). Rod-Rod interactions increased sensitivity by 20% and the time course of recovery was 0.7 ± 0.2 ms-1 (μ ± SD). Compared to these interaction types, Rod-Cone interactions reduced sensitivity to a lesser degree (5%) and showed the fastest recovery (μ = 43 ± 7 ms-1).\ud
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In the second experiment, rod contribution to the magnocellular, parvocellular and koniocellular post-receptoral pathways under mesopic illumination was determined as a function of incremental stimulus duration and waveform (rectangular; sawtooth) using a rod colour match procedure (Cao, Pokorny & Smith, 2005; Cao, Pokorny, Smith & Zele, 2008a). For a 30% rod increment, a cone match required a decrease in [L/(L+M)] and an increase in [L+M] and [S/(L+M)], giving a greenish-blue and brighter appearance for probe durations of 75 ms or longer. Probe durations less than 75 ms showed an increase in [L+M] and no change in chromaticity [L/(L+M) or S/(L+M)], uggesting mediation by the MC pathway only for short duration rod stimuli.\ud
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s We advance previous studies by determining the time-course and nature of photoreceptor specific retinal interactions in the three post-receptoral pathways under mesopic illumination. In the first experiment, the time-course of adaptation for ON cell processing was determined, revealing opponent cell facilitation in chromatic PC and KC pathways. The Rod-Rod and Rod-Cone data identify previously unknown interaction types that act to maintain contrast sensitivity during dynamically changing light conditions and improve the speed of light adaptation under mesopic light levels. The second experiment determined the degree of rod contribution to the inferred post-eceptoral pathways as a function of the temporal properties of the rod signal.\ud
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r The understanding of the mechanisms underlying interactions between photoreceptors under mesopic illumination has implications for the study of retinal disease. Visual function has been shown to be reduced in persons with age-related maculopathy (ARM) risk genotypes prior to clinical signs of the disease (Feigl, Cao, Morris & Zele, 2011) and disturbances in rod-mediated adaptation have been shown in early phases of ARM (Dimitrov, Guymer, Zele, Anderson & Vingrys, 2008; Feigl, Brown, Lovie-Kitchin & Swann, 2005). Also, the understanding of retinal networks controlling vision enables the development of international lighting standards to optimise visual performance nder dim light levels (e.g. work-place environments, transportation)
Rod and cone pathway signaling and interaction under\ud mesopic illumination
No full textThis study investigates the time-course and post-receptoral pathway signaling of photoreceptor interactions when the rod (R) and three cone (L, M, S) photoreceptor classes contribute to mesopic vision. A four-primary photostimulator independently controls photoreceptor activity in human observers. \ud
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The first experiment defines the temporal adaptation response of receptoral (L-, S-cone, rod) and post-receptoral (LMS, LMSR,+L-M) signaling and interactions. Here we show that nonopponent cone-cone interactions (L-cone, LMS, LMSR) have monophasic temporal response patterns whereas opponent signals (+L-M, S-cone) show biphasic response patterns with slower recovery. By comparison, rod-cone interactions with nonopponent signals have faster adaptation responses and reduced sensitivity loss whereas opponent rod-cone interactions are small or absent. Additionally, the rod-rod interaction differs from these interaction types and acts to increase rod sensitivity due to temporal summation but with a slower time course. \ud
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The second experiment shows that the temporal profile of the rod signal alters the relative rod contributions to the three primary post-receptoral pathways. We demonstrate that rod signals generate luminance (þLþM) signals mediated via the MC pathway with all rod temporal profiles and chromatic signals (L/LþM, S/LþM) in both the PC and KC pathways with durations .75 ms. Thus, we propose that the change in relative weighting of rod signals within the post-receptoral pathways contributes to the sensitivity and temporal response of rod and cone pathway signaling and interactions
Earth scenes and space life : poems with illustrations / By A. Maynard Lyon.
No full text3 p. l., [5]-71 p. incl. 21 pl.
Mesopic Pelli-Robson contrast sensitivity and MP-1 microperimetry in healthy ageing and age-related macular degeneration
No full text<b>Purpose</b>\ud
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- To determine whether decreasing illumination of the Pelli-Robson contrast sensitivity (CS) chart and MP-1 microperimeter to low mesopic conditions is more sensitive to vision changes occurring with healthy ageing and in early and intermediate age-related macular degeneration (AMD) and whether these mesopic tests can differentiate visual function between healthy older participants with and without AMD risk genotypes.\ud
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<b>Methods</b>\ud
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- Retinal sensitivity was measured in 98 healthy participants (19-85 years) and 21 AMD (AREDS Grade 2/3) patients (73.9±6.5 years) using the Pelli-Robson CS chart and MP-1 microperimeter under low mesopic and standard illumination. The effect of ageing and AMD on retinal sensitivity was estimated using regression analysis. Healthy older participants (>50 years; <i>n</i>=24) were genotyped for AMD risk genes <i>CFH</i> and/or <i>ARMS2</i> and retinal sensitivity was compared between genotypes. \ud
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<b>Results</b>\ud
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- With healthy ageing, photopic and mesopic Pelli-Robson CS showed a similar decline (-0.004 log CS/year). In AMD, photopic CS showed a similar decline to healthy ageing (-0.004 log CS/year) while mesopic CS was significantly reduced (-0.007 log CS/year). Both standard and low mesopic microperimetry showed a significant decline (-0.51 and -0.73 % contrast/year) with healthy ageing and greater decline (-0.73 and -0.99 % contrast/year) with AMD onset. Pelli-Robson CS and microperimetry sensitivity did not differ between AMD risk genotypes. \ud
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<b>Conclusions</b>\ud
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- Mesopic Pelli-Robson CS detects functional deficits before photopic CS in early and intermediate AMD that can be differentiated from normal ageing. This test can be easily administered in clinical practice and may provide a means for early detection of retinal dysfunction
Melanopsin mediated post-illumination pupil response in early age-related macular degeneration
No full textPurpose\ud
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To determine whether melanopsin expressing intrinsically photosensitive Retinal Ganglion Cell (ipRGC) inputs to the pupil light reflex (PLR) are affected in early age-related macular degeneration (AMD). \ud
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Methods\ud
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The PLR was measured in 40 participants (20 early AMD and 20 age-matched controls) using a custom-built Maxwellian-view pupillometer. Sinusoidal stimuli (0.5 Hz, 11.9 s duration, 35.6° diameter) were presented to the study eye and the consensual pupil response was measured for stimuli with high melanopsin excitation (464nm; blue) and with low melanopsin excitation (638 nm; red) that biased activation to the outer retina. Two melanopsin PLR metrics were quantified: the Phase Amplitude Percentage (PAP) during the sinusoidal stimulus presentation and the Post-Illumination Pupil Response (PIPR). The PLR during stimulus presentation was analyzed using latency to constriction, transient pupil response and maximum pupil constriction metrics. Diagnostic accuracy was evaluated using receiver operating characteristic (ROC) curves.\ud
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Results\ud
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The blue PIPR was significantly less sustained in the early AMD group (p<0.001). The red PIPR was not significantly different between groups (p>0.05). The PAP and blue stimulus constriction amplitude were significantly lower in the early AMD group (p < 0.05). There was no significant difference between groups in the latency or transient amplitude for both stimuli (p>0.05). ROC analysis showed excellent diagnostic accuracy for the blue PIPR metrics (AUC>0.9). \ud
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Conclusions\ud
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This is the initial report that the melanopsin controlled PIPR is dysfunctional in early AMD. The non-invasive, objective measurement of the ipRGC controlled PIPR has excellent diagnostic accuracy for early AMD
Connecting workplace attachment and pro-environmental behaviors in zoo and aquarium professionals
No full textThis is the peer reviewed version of the following article: Murphy, B., Maynard, L. (2022). Connecting workplace attachment and pro-environmental behaviors in zoo and aquarium professionals. Zoo Biology, 1– 9. https://doi.org/10.1002/zoo.21703, which has been published in final form at https://doi.org/10.1002/zoo.21703. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions: https://authorservices.wiley.com/author-resources/Journal-Authors/licensing/self-archiving.html#3.
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Temporal dynamics of rod and cone photoreceptor interactions under mesopic illumination
No full text<B>This article is free to read on the publisher's website</B>\ud
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<b>Purpose</b>\ud
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- Photoreceptor interactions reduce the temporal bandwidth of the visual system under mesopic illumination. The dynamics of these interactions are not clear. This study investigated cone-cone and rod-cone interactions when the rod (R) and three cone (L, M, S) photoreceptor classes contribute to vision via shared post-receptoral pathways.\ud
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<b>Methods</b>\ud
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- A four-primary photostimulator independently controlled photoreceptor activity in human observers. To determine the temporal dynamics of receptoral (L, S, R) and post-receptoral (LMS, LMSR, +L-M) pathways (5 Td, 7° eccentricity) in Experiment 1, ON-pathway sensitivity was assayed with an incremental probe (25ms) presented relative to onset of an incremental sawtooth conditioning pulse (1000ms). To define the post-receptoral pathways mediating the rod stimulus, Experiment 2 matched the color appearance of increased rod activation (30% contrast, 25-1000ms; constant cone excitation) with cone stimuli (variable L+M, L/L+M, S/L+M; constant rod excitation).\ud
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<b>Results</b>\ud
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- Cone-cone interactions with luminance stimuli (LMS, LMSR, L-cone) reduced Weber contrast sensitivity by 13% and the time course of adaptation was 23.7±1ms (μ±SE). With chromatic stimuli (+L-M, S), cone pathway sensitivity was also reduced and recovery was slower (+L-M 8%, 2.9±0.1ms; S 38%, 1.5±0.3ms). Threshold patterns at ON-conditioning pulse onset were monophasic for luminance and biphasic for chromatic stimuli. Rod-rod interactions increased sensitivity(19%) with a recovery time of 0.7±0.2ms. Compared to cone-cone interactions, rod-cone interactions with luminance stimuli reduced sensitivity to a lesser degree (5%) with faster recovery (42.9±0.7ms). Rod-cone interactions were absent with chromatic stimuli. Experiment 2 showed that rod activation generated luminance (L+M) signals at all durations, and chromatic signals (L/L+M, S/L+M) for durations >75ms.\ud
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<b>Conclusions</b>\ud
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- Temporal dynamics of cone-cone interactions are consistent with contrast sensitivity loss in the MC pathway for luminance stimuli and chromatically opponent responses in the PC and KC pathway with chromatic stimuli. Rod-cone interactions limit contrast sensitivity loss during dynamic illumination changes and increase the speed of mesopic light adaptation. The change in relative weighting of the temporal rod signal within the major post-receptoral pathways modifies the sensitivity and dynamics of photoreceptor interactions
The Maynard, J. L., & Haas, M. L. (Eds.). 2022. The Routledge Handbook of Ideology and International Relations. Taylor & Francis.
No full textThe Routledge Handbook of Ideology and International Relations is part of the “Routledge Handbooks on Political Ideologies, Practices, and Interpretations” series, and has been written by two authors and various contributors. The main author is Jonathan Leader Maynard, a lecturer at King's College London, one of the 10 leading universities in the United Kingdom, and the second author is Professor Mark L. Haas, a lecturer at Duquesne University in the United States. In the book, which examines the effect of ideology on international relations, both authors critically address the issues of ideological polarization, ideological disagreements, and conflicts of interest between countries in foreign policy matters. The content of the book comprises four main chapters. The first chapter analyses the relationship between ideology, nation, and state; the second addresses the issues of ideology and conflict; the third reviews the transnational dimension of ideology; and the final presents an evaluation of the ideological strategies and transnational relations of such countries and regions as India, Latin America, Central Asia, China, Africa, Russia, United States, Europe and the European Union and South Korea
Intrinsically photosensitive retinal ganglion cell function, sleep efficiency and depression in advanced age-related macular degeneration
No full textPURPOSE. Melanopsin expressing intrinsically photosensitive retinal ganglion cells (ipRGC) input to multiple brain regions including those for pupil control, circadian rhythms, sleep and mood regulation. Here we measured ipRGC function and its relationship to sleep quality and depression in patients with advanced AMD. METHODS. The melanopsin-mediated post-illumination pupil response (PIPR) was measured in 53 patients with advanced AMD (age 78.8 ± 8.8 years) and in 20 healthy controls (age 72.5 ± 3.3 years). Sleep quality and efficiency was assessed using the Pittsburgh Sleep Quality Index (PSQI). Risk of depression was determined using the Center for Epidemiologic Studies Depression questionnaire. RESULTS. The group with AMD showed significantly reduced pupil constrictions (P = 0.039); PIPR amplitudes (P = 0.003); global sleep scores (P = 0.01); and higher levels of depression (P < 0.001) than the control group. There was a significant correlation between the PIPR amplitude and global sleep score in the AMD group (P = 0.01). The amplitude of PIPR significantly correlated with sleep efficiency (P = 0.008; regression, P = 0.01, R = 0.13), but not sleep quality (P = 0.23) in the AMD group. There was no correlation between PIPR and depression scores. CONCLUSIONS. Intrinsically photosensitive RGC dysfunction in advanced AMD contributes to the observed reduction in sleep efficiency. The correlation between the melanopsin-mediated PIPR and sleep may indicate reduced photic input to the suprachiasmatic nucleus and ventrolateral preoptic area due to ipRGC dysfunction in AMD
Blind Spots: Examining Political Advertising Misinformation and How U.S. News Media Hold Political Actors Accountable
No full textWhile conventional wisdom suggests political ads are often misleading, this is the first known study to quantify the prevalence of inaccuracies in political advertising. This study also examines how and explains why the U.S. news media provide coverage of political advertising in the manner that they do. A multi-method research design includes a content analysis of the television ads from the 2008 presidential election, secondary data analysis of the National Annenberg Election Survey 2008, semantic network analysis of press coverage of political television ads from the 2008 election, as well as in-depth interviews with scholars, practitioners, journalists and lawyers having expertise in the issues surrounding political advertising. Of all the English-language paid political ads that aired on television during the 2008 general election, just under 30% contained at least one inaccuracy based upon the ratings of FactCheck.org and PolitiFact.com. This figure, however, is likely a gross under representation of the prevalence of inaccuracies in political ads from 2008 because most of the ads (70%) were never evaluated by these purportedly elite fact-checkers. Among ads assessed, however, more than three out of four of the evaluated claims had some degree of inaccuracy. Furthermore, ads containing at least one inaccuracy aired twice as often on television as the ads that were never evaluated. To the degree inaccurate ads air on television more frequently, then, there is cause for concern particularly given the broadcasters' mandate to serve the public interest. Moreover, while political interest supporters were one of the groups most likely to have inaccuracies in their ads, nearly half of their spending was in the last weeks of the election contributing to most of their ads going without evaluation. Thus, in a post-Citizens United world, attempts by fact-checkers to review the onslaught of PAC ads during the final weeks of the 2012 election (and the final weeks of future elections) will be crucial in combating inaccuracies. This study also extends the work of Geer (2006) who offered an organized review of negativity in political advertising. Rather than finding support for the hypothesis that negative attack ads are more accurate than advocacy ads, the evidence challenges Geer's defense of negativity. Among the ads evaluated by the fact-checkers, inaccuracies were significantly more likely to be present in attack rather than either advocacy or contrast ads. While Geer may have demonstrated that negative ads offer more substantive evidence, simply because evidence is presented does not mean the evidence is accurate. In the more provocative ads of 2008 designed to gain attention, inaccuracies were rife. Moreover, rather than the mainstream news media fixation on political ad negativity, the evidence in the forthcoming pages suggests attention is more warranted concerning the accuracy of the claims within the ads regardless of the ad's tone. A first step toward a theory of strategic misinformation is also offered by demonstrating that it is possible to predict which political ads were more likely to draw an inaccurate rating from the fact-checkers. Holding all other variables constant, it was attack ads that had the highest odds of being evaluated as inaccurate with contrast ads also having a high likelihood. These predictions also confirmed that as the campaign progressed, the odds of an ad being rated inaccurate declined which was a function of ads not being evaluated. Furthermore, it was revealed that a loss of momentum or a decline in public perceptions of candidate characteristics increased the odds of candidates drawing inaccurate ratings in their attack ads. In extending understanding of how news media cover candidate campaigns when political advertising is referenced, a plurality of media outlets from the over two dozen in the study were characterized foremost by their focus on campaign strategy rather than fact-checking. One cluster, however, emerged as AdWatchers - those committed to using political ads to scrutinize the accuracy of what candidates and their surrogates were claiming. Nonetheless, the economic realities of adwatching are that there is a so called "chilling effect" because it is expensive, time-consuming, and divisive. Furthermore, the dearth of watchdog ad reporting enables broadcast stations to continue airing ads that may be false while preserving their ability to claim ignorance about the content when faced with regulatory compliance issues. Thus, the political ads most likely to air are the ones with inaccuracies. Chances are the ads will go unscrutinized by the mainstream news media while television stations profit from their proliferation.Mass Media and Communicatio
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