The chicken has been extensively studied as an animal model for myopia because its eye growth is tightly controlled by visual experience. It has been found that the retina controls the axial eye growth rates depending on the amount and the sign of defocus imposed in the projected image. Glucagonergic amacrine cells were discovered that appear to encode for the sign of imposed defocus. It is not clear whether the downstream neurons, the retinal ganglion cells, still have access to this information-and whether it ultimately reaches the brain. We have analyzed the spike rates of chicken retinal ganglion cells in vitro using a microelectrode array. For this purpose, we initially defined spatial resolution and contrast sensitivity in vitro. Two classes of chicken retinal ganglions were found, depending on the linearity of their responses with increasing contrast. Responses generally declined with increasing defocus of the visual stimulus. These responses were well predicted by the modulation transfer function for a diffraction-limited defocused optical system, the first Bessel function. Thus, the studied retinal ganglion cells did not distinguish between a loss of contrast at a given spatial frequency due to reduced contrast of the stimulus pattern or because the pattern was presented out of focus. Furthermore, there was no indication that the retinal ganglion cells responded differently to defocus of either sign, at least for the cells that were recorded in this study.

The temperature dependence of planar channeling radiation of 62.8 MeV electrons has been studied for silicon, germanium, and beryllium. The measurements have been performed using an uncollimated lowemittance cw beam from the superconducting electron linac S-DALINAC at the Technische Hochschule Darmstadt. Energies and linewidths of transitions between transverse bound states have been determined in the energy range between 40 and 230 keV for silicon and beryllium at temperatures between 12 and 330 K, and for germanium between 12 and 223 K. From the shift of the transition energies with temperature the mean thermal vibrational amplitudes of the atoms transverse to the channeling planes are determined by comparison with calculations using the many-beam formalism. Within experimental errors no directional dependence of the vibrations is observed. For silicon a Debye temperature of ͑535.2Ϯ8.5͒ K at 12 K and ͑519.0Ϯ10.8͒ K at 300 K has been derived. For germanium an increase from ͑232.7Ϯ12.8͒ K at 12 K to ͑292.0Ϯ16.4͒ K at 223 K is observed. Planar channeling radiation spectra from a beryllium crystal taken at 12, 220, and 300 K have been analyzed the same way yielding a Debye temperature of

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