A light gray square was displayed on a background of dynamic two-dimensional noise. After 10 sec of steady eccentric fixation, the square disappeared completely and the region corresponding to it was "filled in" by dynamic noise from the surround. Furthermore, when the whole display was switched off, a persisting patch of dynamic two-dimensional noise was seen in the region corresponding to the gray square. This persistent patch could be seen for almost 10 sec on some trials, suggesting that a dynamic neural representation of the surrounding "twinkle" is being created in this region. The fading of the square was especially pronounced in peripheral vision. Also, displacing the square by a small distance was usually sufficient to restore its visibility but this distance increased with eccentricity. This may be a consequence of the progressive increase of receptive field size with eccentricity that has been noted in both area 17 and MT. The perceptual fading and "filling in" that we report concurs with the recent physiological observations of Pettet and Gilbert [(1991) Society for Neuroscience Abstracts, 17, 1090] and Gilbert and Wiesel [(1992) Nature, 356, 150-152] in area 17 of cats and primates.

Fixation, Ocular↗

PubMedDate not supplied

Squeezing speech into the deaf ear.

Explore the source record for details and available documents.

Adult↗

PubMedDate not supplied

Real and apparent movement nulled.

It is a controversial issue whether 'real' movement, seen from the successive stimulation of retinal receptors by a moving image, and 'apparent' (phi) movement, which is produced by stimuli separated in space and time, are transmitted by the same or different neural channels. With this question in mind, we have devised ways to oppose real against opposite-direction apparent movement, to see whether they cancel. Cancelling, especially in a variety of conditions, would be expected for a single but not for separate neural movement channels. As we report here, we find that opposed-direction real and apparent movements will cancel, allowing null measurements to be made.

Humans↗

PubMedDate not supplied

Microbial ribosomal vaccines.

Ribosomal vaccines have been prepared from several different bacterial, fungal, and protozoan microorganisms. Most of these preparations offer a higher degree of protection than do vaccines made from the homologous whole cells, but the mode of protection is controversial. All of the reported ribosomal vaccines are contaminated with cell surface determinants. Antisera raised to ribosomal preparations are directed to innate ribosomal components as well as to surface antigens. Several hypotheses exist for the reported protection from disease: the cell surface contaminants serve as the protective moieties; ribosomes act as potent adjuvants for contaminating cell surface determinants; ribosomes innately contain antigenic determinants that cross-react with cell surface antigens; recently translated cell surface polypeptides are still attached to the ribosomal RNA in the ribosomes; ribosomes migrate from the cytoplasm of the microbe to the periphery of the cell, and ribosomal antigens are exposed on the cell surface; or ribosomes contain messenger RNA and produce microbial cell surface polypeptides in immunized individuals. A short description of the biochemical, biophysical, and structural characteristics of prokaryotic and eukaryotic ribosomes is presented, followed by a discussion of the ability of various ribosomal vaccines to protect against infectious agents.

Amino Acids↗