Biomedical subjects

J Hegdé

Publications and source records attributed to J Hegdé.

3 recordsLinked to original sources

PubMed2000

Selectivity for complex shapes in primate visual area V2.

To explore the role of visual area V2 in shape analysis, we studied the responses of neurons in area V2 of the alert macaque using a set of 128 grating and geometric line stimuli that varied in their shape characteristics and geometric complexity. Simple stimuli included oriented bars and sinusoidal gratings; complex stimuli included angles, arcs, circles, and intersecting lines, plus hyperbolic and polar gratings. We found that most V2 cells responded well to at least some of the complex stimuli, and in many V2 cells the most effective complex stimulus elicited a significantly larger response than the most effective bar or sinusoid. Approximately one-third of the V2 cells showed significant differential responsiveness to various complex shape characteristics, and many were also selective for the orientation, size, and/or spatial frequency of the preferred shape. These results indicate that V2 cells explicitly represent complex shape information and suggest specific types of higher order visual information that V2 cells extract from visual scenes.

Animals↗

PubMed1999

The popout in some conjunction searches is due to perceptual grouping.

The target in a visual search task usually pops out if it can be distinguished from its background on the basis of only one visual feature but not if the target represents a conjunction of two or more features. However, several recent reports suggest that in certain cases, search targets defined by a conjunction of two features also pop out. We have reinvestigated three pairs of such features to determine whether the popout in these cases can be attributed to perceptual grouping. We find that that in all three cases, popout no longer occurs when perceptual grouping is degraded, suggesting that the popout is the result of perceptual grouping and not of novel mechanism/s of conjunction search.

Depth Perception↗

PubMed1993

Distribution of swallow protein in egg chambers and embryos of Drosophila melanogaster.

The Drosophila maternal effect gene swallow has a role in localizing bicoid mRNA at the anterior margin of the oocyte during oogenesis, and a poorly characterized role in nuclear divisions in early embryogenesis. We have examined the distribution of swallow protein during oogenesis and embryogenesis using anti-swallow antibodies. During oogenesis, high levels of swallow protein are present in basal nurse cell cytoplasm, although small amounts are also present at the anterior oocyte margin, the site of bicoid RNA localization. Only a small fraction of swallow protein is in a position to interact directly with bicoid RNA during localization. The asymmetric distribution of swallow protein is disrupted in swallow ovaries, in which bicoid RNA becomes unlocalized late in oogenesis. swallow protein is uniformly distributed in eggs, but becomes localized to nuclei during early mitotic divisions in early embryogenesis. swallow protein enters each nucleus at the beginning of mitosis, occupies a position complementary to that of condensed chromatin, and leaves each nucleus at the end of mitosis. We show examples of nuclear division defects in swallow mutant embryos, and suggest that the abnormal nuclear divisions in early swallow embryos reflect a second function for swallow protein that contributes to abdominal segmentation defects common in swallow embryos.

Animals↗