City University London

About: City University London is a education organization based out in London, United Kingdom. It is known for research contribution in the topics: Population & Context (language use). The organization has 5735 authors who have published 17285 publications receiving 453290 citations.

A 'dipper' function for texture discrimination based on orientation variance.

Abstract: We measured the just-noticeable difference (JND) in orientation variance between two textures (Figure 1) as we varied the baseline (pedestal) variance present in both textures. JND's first fell as pedestal variance increased and then rose, producing a 'dipper' function similar to those previously reported for contrast, blur, and orientation-contrast discriminations. A dipper function (both facilitation and masking) is predicted on purely statistical grounds by a noisy variance-discrimination mechanism. However, for two out of three observers, the dipper function was significantly better fit when the mechanism was made incapable of discriminating between small sample variances. We speculate that a threshold nonlinearity like this prevents the visual system from including its intrinsic noise in texture representations and suggest that similar thresholds prevent the visibility of other artifacts that sensory coding would otherwise introduce, such as blur.

Cost and cost-effectiveness of nationwide school-based helminth control in Uganda: intra-country variation and effects of scaling-up.

Abstract: Estimates of cost and cost-effectiveness are typically based on a limited number of small-scale studies with no investigation of the existence of economies to scale or intra-country variation in cost and cost-effectiveness. This information gap hinders the efficient allocation of health care resources and the ability to generalize estimates to other settings. The current study investigates the intra-country variation in the cost and cost-effectiveness of nationwide school-based treatment of helminth (worm) infection in Uganda. Programme cost data were collected through semi-structured interviews with district officials and from accounting records in six of the 23 intervention districts. Both financial and economic costs were assessed. Costs were estimated on the basis of cost in US$ per schoolchild treated, and an incremental cost-effectiveness ratio (cost in US$ per case of anaemia averted) was used to evaluate programme cost-effectiveness. Sensitivity analysis was performed to assess the effect of discount rate and drug price. The overall economic cost per child treated in the six districts was US$0.54 and the cost-effectiveness was US$3.19 per case of anaemia averted. Analysis indicated that estimates of both cost and cost-effectiveness differ markedly with the total number of children who received treatment, indicating economies of scale. There was also substantial variation between districts in the cost per individual treated (US$0.41-0.91) and cost per anaemia case averted (US$1.70-9.51). Independent variables were shown to be statistically associated with both sets of estimates. This study highlights the potential bias in transferring data across settings without understanding the nature of observed variations.

The spectral transmission of ocular media suggests ultraviolet sensitivity is widespread among mammals

Abstract: Although ultraviolet (UV) sensitivity is widespread among animals it is considered rare in mammals, being restricted to the few species that have a visual pigment maximally sensitive (λmax) below 400 nm. However, even animals without such a pigment will be UV-sensitive if they have ocular media that transmit these wavelengths, as all visual pigments absorb significant amounts of UV if the energy level is sufficient. Although it is known that lenses of diurnal sciurid rodents, tree shrews and primates prevent UV from reaching the retina, the degree of UV transmission by ocular media of most other mammals without a visual pigment with λmax in the UV is unknown. We examined lenses of 38 mammalian species from 25 families in nine orders and observed large diversity in the degree of short-wavelength transmission. All species whose lenses removed short wavelengths had retinae specialized for high spatial resolution and relatively high cone numbers, suggesting that UV removal is primarily linked to increased acuity. Other mammals, however, such as hedgehogs, dogs, cats, ferrets and okapis had lenses transmitting significant amounts of UVA (315–400 nm), suggesting that they will be UV-sensitive even without a specific UV visual pigment.

Examining the relationship between free recall and immediate serial recall: the effects of list length and output order

Abstract: In 4 experiments, participants were presented with lists of between 1 and 15 words for tests of immediate memory. For all tasks, participants tended to initiate recall with the first word on the list for short lists. As the list length was increased, so there was a decreased tendency to start with the first list item; and, when free to do so, participants showed an increased tendency to start with one of the last 4 list items. In all tasks, the start position strongly influenced the shape of the resultant serial position curves: When recall started at Serial Position 1, elevated recall of early list items was observed; when recall started toward the end of the list, there were extended recency effects. These results occurred under immediate free recall (IFR) and different variants of immediate serial recall (ISR) and reconstruction of order (RoO) tasks. We argue that these findings have implications for the relationship between IFR and ISR and between rehearsal and recall.