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Biomedical subjects

P Cavanagh

Publications and source records attributed to P Cavanagh.

At least 109 records · Page 6Linked to original sources
PubMed1984

Screening for color blindness using optokinetic nystagmus.

Red/green luminosity ratios were determined by a new method. A special colored grating of red and green bars appeared to move to the left (or right) when the red bars were darker (or lighter) than the green bars. Optokinetic nystagmic eye movements (OKN) elicited by this stimulus could be measured photoelectrically, or by directly watching the subject's eyes. When the red/green ratio passed through equiluminance, the direction of apparent movement (AM) and of OKN reversed in direction. Protans needed more red than normals to reach equiluminance, and deutans needed more green. This OKN method might be applied to nonverbal subjects such as infants and animals.

Color Vision Defects↗
PubMed1983

Interocular transfer of a chromatic frequency shift.

Interocular transfer of a spatial frequency shift was obtained with equiluminous color gratings. Gratings which combined both color and luminance contrast yielded small aftereffects and no interocular transfer. Recent electrophysiological work has uncovered color-sensitive binocularly driven cells in visual cortex. These cells are transient and often respond to color contrast in the absence of luminance contrast. The stimulus parameters associated with successful interocular transfer, equiluminous colors and brief test, matched the properties of these cells. Previous failure to induce interocular transfer of color effects may be explained by inappropriate stimulus parameters.

Adaptation, Ocular↗
PubMed1981

Color and luminance: independent frequency shifts.

Simultaneous opposite spatial frequency shifts can be obtained in chrominance and luminance channels. The chrominance shift cannot be transferred interocularly. Chrominance and luminance channels seem to perform similar but independent spatial frequency analyses.

Color Perception↗
PubMed1981

Isolation of Legionella pneumophila (serogroup one) from shower-water in Ballarat.

Five non-fatal cases of Legionnaires' disease occurred during 1979 and 1980 among patients living in Ballarat. The distribution of the dates of onset was sporadic, and no patient could be considered to have been at risk from faulty air-conditioning equipment; however, two of these patients, both female, had been resident, on separate occasions, in the reception ward of a long-stay institution during the incubation period of their illnesses. A fourfold rise in antibodies to the Philadelphia strain of Legionella pneumophila (serogroup 1) was demonstrated in all five of these patients, and subsequent examination of water in the shower block of the reception ward yielded a strain of the same serotype of L. pneumophila.

Australia↗
PubMed1980

Motion aftereffect: a global mechanism for the perception of rotation.

Observers adapted to motion by looking at rotating logarithmic spirals. They were tested with a stationary mirror image of the adapting spiral in which all contours were at 90 degrees to those of the first spiral. Motion aftereffects were reported in the contrarotational direction--that is, observers who had seen clockwise rotating motion reported seeing counterclockwise aftereffects. These aftereffects lasted one-third as long as the aftereffects obtained when the adapting spiral was used as the test figure. These two aftereffects were shown to have different storage properties, thereby indexing the operation of at least two different mechanism. We interpret the motion aftereffect that is obtained with the mirror-image stimulus as indicative of the existence of global rotation detectors.

Figural Aftereffect↗
PubMed1980

Genetic studies in human and murine giardiasis.

Genetic markers were analysed in 48 adults who appeared to have a prolonged infection with Giardia lamblia. The frequency of ABO blood groups, Rhesus blood groups, and Gm phenotypes was similar to that in control subjects. However, there was a higher than expected frequency of HLA antigens A1 (observed 46 . 7%, expected 32%) and B12 (observed 47 . 8%, expected 25 . 8%) and a higher than expected frequency of the phenotypes A1/A2 and B12/B27. Genetic studies were also performed with inbred strains of mice showing relatively rapid (BALB/c) and defective (C3H/He) spontaneous elimination of Giardia muris. From analysis in backcross mice several genes appeared to influence susceptibility to prolonged infection with G. muris.

Adolescent↗
PubMed1978

Campylobacter.

Explore the source record for details and available documents.

Animals↗
PubMed1978

Size and position invariance in the visual system.

The encoding of simple features such as lines and angles leads naturally to size and position invariance when these features are analyzed symbolically in terms of structure and connectedness. No such analysis is possible for a spatial frequency encoding, however, as all a priori indications of pattern unity are lost. An additional transformation of spatial frequency information is therefore demonstrated that automatically derives a size invariant representation of form. The feasibility of the transform scheme in the visual system is outlined with a hypothetical processing sequence. It is found that the organization of cells in the striate cortex shows a marked similarity to an intermediate stage of the proposed sequence.

Fourier Analysis↗