PURPOSE: Most studies of visual development have concentrated on visual development of infants. Only a few studies have extended this to children and determined the point at which visual function becomes truly adult-like. Yet from a clinical and research perspective it is important to know this. This review paper is a discussion of the development of visual acuity and contrast sensitivity into childhood. METHODS:The literature on subjective (measured with preferential looking or psychophysical methods) and objective (visually-evoked potential) measures of visual acuity and contrast sensitivity was examined with particular emphasis on studies of children over the age of 5 years and those articles that compared different age groups and those that made a comparison with adults. RESULTS: Visual acuity was found to be fully mature between the ages of 5 and the mid teenage years, while contrast sensitivity was found to mature fully between the ages of 8 to 19 years. Thus, there is still no clear answer to the fundamental question of when these basic aspects of visual function mature, but it may be later than previously thought. CONCLUSIONS: Further studies are needed to answer this basic question more precisely and objective measures, such as VEP, may be able to answer this question better than psychophysical methods. KEY WORDS: visual development; visual acuity; contrast sensitivity; critical period; visually-evoked potential. RESUMEN OBJETIVO: La mayoría de los estudios sobre desarrollo visual se han centrado en el desarrollo visual de bebés. Sólo unos pocos estudios han ampliado el intervalo de edades estudiadas para incluir a niños y han determinado en qué momento la función visual alcanza un estado verdaderamente equiparable al de un adulto. Sin embargo, desde una perspectiva clínica y de interés científico, es importante conocer este dato. En este artículo de revisión se analiza el desarrollo de la agudeza visual y de la sensibilidad al contraste a lo largo de la infancia. MÉTODOS: Se analizaron los artículos científicos existentes sobre medidas de agudeza visual y de sensibilidad al contraste, tanto subjetivas (medidas con la técnica de mirada preferencial o por métodos psicofísicos) como objetivas (potenciales visuales evocados), centrándonos particularmente en aquellos estudios realizados en niños mayores de 5 años y en aquellos artículos donde se compararon diversos grupos de edad entre sí o con un grupo de adultos. RESULTADOS: Se encontró que para la agudeza visual el ojo alcanza un estado plenamente maduro a una edad comprendida entre los 5 y los 15-16 años, mientras que para la sensibilidad al contraste el ojo alcanza la madurez plena a una edad comprendida entre los 8 y los 19 años. Así, todavía no disponemos de una respuesta clara a la pregunta fundamental de cuándo estos aspectos de la función visual acaban de madurar, pero es posible que esto suceda a una edad más tardía de la que se creía hasta ahora. CONCLUSIONES: Es necesario realizar más estudios para poder dar una respuesta más precisa a...

To date, modern three-dimensional (3D) supernova (SN) simulations have not demonstrated that explosion energies of 1051 erg (=1 bethe=1 B) or more are possible for neutrino-driven SNe of non/slow-rotating M < 20 M ⊙ progenitors. We present the first such model, considering a nonrotating, solar-metallicity 18.88 M ⊙ progenitor, whose final 7 minutes of convective oxygen-shell burning were simulated in 3D and showed a violent oxygen–neon shell merger prior to collapse. A large set of 3D SN models was computed with the Prometheus-Vertex code, whose improved convergence of the two-moment equations with Boltzmann closure allows now to fully exploit the implicit neutrino-transport treatment. Nuclear burning is treated with a 23-species network. We vary the angular grid resolution and consider different nuclear equations of state and muon formation in the proto-neutron star (PNS), which requires six-species transport with coupling of all neutrino flavors across all energy–momentum groups. Elaborate neutrino transport was applied until ∼2 s after bounce. In one case, the simulation was continued to >7 s with an approximate treatment of neutrino effects that allows for seamless continuation without transients. A spherically symmetric neutrino-driven wind does not develop. Instead, accretion downflows to the PNS and outflows of neutrino-heated matter establish a monotonic rise of the explosion energy until ∼7 s post-bounce, when the outgoing shock reaches ∼50,000 km and enters the He layer. The converged value of the explosion energy at infinity (with overburden subtracted) is ∼1 B and the ejected 56Ni mass ≲0.087 M ⊙, both within a few 10% of the SN 1987A values. The final NS mass and kick are ∼1.65 M ⊙ and >450 km s−1, respectively.

Primary objective The purpose of this study was to develop an objective way to assess human visual attention using the alpha band component of the visual-evoked potential (VEP). Design and methods Six different attentional conditions were tested: eyes-open, eyes-closed, eyes-closed with backwards number counting, and three rapid serial visual presentation (RSVP) tasks. 18 visually-normal, young-adult subjects (ages 21 to 28 years) were tested binocularly at 1 meter for each condition on two separate days. The Diopsys™ NOVA-TR system was used to obtain the visual-evoked potential (VEP) and extracted alpha-wave and its related power spectrum. Additionally, the Visual Search and Attention Test (VSAT) was administered as a subjective measure of visual attention. Results Subjects exhibited significant decreases in power in the alpha band when comparing the eyes-closed to the eyes-open conditions, with power in the eyes-closed condition being, on average, twice as large. The response from the other four conditions did not reflect the differential attentional demands. The ratio of the power in the eyes-closed condition to the eyes open condition in the lower alpha frequencies (8–10 Hz) was found to be significantly correlated to the group’s performance on the VSAT, especially the 10 Hz component. Conclusions An individual’s ability to attenuate their alpha-component during visual processing may be a predictor of their visual attentional state. These findings solidify the role of the VEP alpha subcomponent as an objective electrophysiological correlate of visual attention, which may be useful in the diagnosis and treatment of human visual-attention disorders in the future.

We explore the formation of superbubbles through energy deposition by multiple supernovae (SNe) in a uniform medium. We use total energy conserving, 3-D hydrodynamic simulations to study how SNe correlated in space and time create superbubbles. While isolated SNe fizzle out completely by ∼ 1 Myr due to radiative losses, for a realistic cluster size it is likely that subsequent SNe go off within the hot/dilute bubble and sustain the shock till the cluster lifetime. For realistic cluster sizes, we find that the bubble remains overpressured only if, for a given n g0 , N OB is sufficiently large. While most of the input energy is still lost radiatively, superbubbles can retain up to ∼ 5 − 10% of the input energy in form of kinetic+thermal energy till 10 Myr for ISM density n g0 ≈ 1 cm −3 . We find that the mechanical efficiency decreases for higher densities (η mech ∝ n −2/3 g0 ). We compare the radii and velocities of simulated supershells with observations and the classical adiabatic model. Our simulations show that the superbubbles retain only 10% of the injected energy, thereby explaining the observed smaller size and slower expansion of supershells. We also confirm that a sufficiently large ( 10 4 ) number of SNe is required to go off in order to create a steady wind with a stable termination shock within the superbubble. We show that the mechanical efficiency increases with increasing resolution, and that explicit diffusion is required to obtain converged results.