Quantifying interactions between accommodation and vergence in a binocularly normal population

AbstractStimulation of the accommodation system results in a response in the vergence system via accommodative vergence cross-link interactions, and stimulation of the vergence system results in an accommodation response via vergence accommodation cross-link interactions. Cross-link interactions are necessary in order to ensure simultaneous responses in the accommodation and vergence systems. The crosslink interactions are represented most comprehensively by the response AC/A (accommodative vergence) and CA/C (vergence accommodation) ratios, although the stimulus AC/A ratio is measured clinically, and the stimulus CA/C ratio is seldom measured in clinical practice. The present study aims to quantify both stimulus and response AC/A and CA/C ratios in a binocularly normal population, and determine the relationship between them. 25 Subjects (mean±SD age 21.0±1.9years) were recruited from the university population. A significant linear relationship was found between the stimulus and response ratios, for both AC/A (r2=0.96, p<0.001) and CA/C ratios (r2=0.40, p<0.05). Good agreement was found between the stimulus and response AC/A ratios (95% CI −0.06 to 0.24MA/D). Stimulus and response CA/C ratios are linearly related. Stimulus CA/C ratios were higher than response ratios at low values, and lower than response ratios at high values (95% CI −0.46 to 0.42D/MA). Agreement between stimulus and response CA/C ratios is poorer than that found for AC/A ratios due to increased variability in vergence responses when viewing the Gaussian blurred target. This study has shown that more work is needed to refine the methodology of CA/C ratio measurement

The use of cues to convergence and accommodation in naive, uninstructed participants

A remote haploscopic video refractor was used to assess vergence and accommodation responses in a group of 32 emmetropic, orthophoric, symptom free, young adults naïve to vision experiments in a minimally instructed setting. Picture targets were presented at four positions between 2 m and 33 cm. Blur, disparity and looming cues were presented in combination or separately to asses their contributions to the total near response in a within-subjects design. Response gain for both vergence and accommodation reduced markedly whenever disparity was excluded, with much smaller effects when blur and proximity were excluded. Despite the clinical homogeneity of the participant group there were also some individual differences

Institutional infrastructure and economic performance: Levels versus catching up and frontier shifts.

We analyze the relationship between institutional infrastructure (capturing political stability, quality of government and social infrastructure) and overall country productivity for a sample of 57 (OECD and non-OECD) countries. Specifically, we compare empirical results for alternative productivity measures: output per worker and total factor productivity (TFP); in addition, we consider both levels and changes, where we decompose TFP changes into efficiency changes and technical changes. This gives us insight into the different channels through which the institutional infrastructure impacts on overall productivity performance: the 'accumulation' of production factors versus the 'accommodation' of production factors, and the 'shifting' of the world productivity frontier versus the 'catching up' with this frontier. In line with the existing literature, our results suggest a substantial accumulation effect: good institutions enhance capital accumulation. In addition, we find significant evidence in favor of an accommodation effect (in terms of both levels and changes), which elicits institutional quality as a 'lubricant' of the economic system: good institutions facilitate complex transactions, specialization and flexibility while reducing transaction costs. Interestingly, we find that good institutions enhance technical change as well as efficiency change. Conveniently, the decomposition of TFP change also allows us to interpret the convergence issue, for which largely inconclusive evidence is obtained on the basis of a combined TFP measure. Our findings reveal that efficiency change is associated with convergence, i.e., countries with lower initial productivity realize higher productivity growth through catching up. By contrast, technical change corresponds to divergence, i.e., countries with higher initial productivity succeed in higher productivity growth through shifts of the technological frontier. One possible rationalization is that greater experience with technological innovation (i.e., a closer situation to the world technology frontier) benefits the implementation of new products and processes (i.e., the cost of additional innovations falls).Performance;

Engineering data compendium. Human perception and performance. User's guide

The concept underlying the Engineering Data Compendium was the product of a research and development program (Integrated Perceptual Information for Designers project) aimed at facilitating the application of basic research findings in human performance to the design and military crew systems. The principal objective was to develop a workable strategy for: (1) identifying and distilling information of potential value to system design from the existing research literature, and (2) presenting this technical information in a way that would aid its accessibility, interpretability, and applicability by systems designers. The present four volumes of the Engineering Data Compendium represent the first implementation of this strategy. This is the first volume, the User's Guide, containing a description of the program and instructions for its use