Biomedical subjects

R S Pinkham

Publications and source records attributed to R S Pinkham.

3 recordsLinked to original sources

PubMed1999

Representing contrast detection as an eigenvalue problem.

Contrast detection can be formulated as an eigenvalue problem. One of the simplest resulting models has only two parameters. The model is space variant and employs the Hermite functions as eigenfunctions. Computing the response to a sinusoidal acuity grating yields the observer's contrast response. The model itself, however, is developed within an abstract mathematical framework which is general enough to include Fourier analysis as a special case. Consequently, the methods of Fourier analysis are generalized to those of eigenfunction expansion and the spectral theory of linear operators.

Contrast Sensitivity↗

PubMed1998

A word-superiority effect in the presence of foveal load.

Foveal stimuli have been shown to disrupt visual information processing in the parafovea and periphery by their mere presence. In the present study, 6 subjects were presented letter triads 3.58 degrees to the right or left of the point of fixation. At the same time, a single letter was presented at the point of fixation that was either the same as the middle letter in the triad or different from any of the triad letters. On other trials, no letter was presented at the point of fixation. Analysis indicated a word superiority effect when a foveal letter was presented that was the same as the letter in the triad. Performance between words and nonwords did not differ significantly when the foveal letter was different or absent. It was concluded that the mere presence of foveal load alone is not disruptive to performance. Depending on the visual context of the target to be reported, the presence of a foveal stimulus may improve performance.

Discrimination, Psychological↗

PubMed1994

Space-variant models of visual acuity using self-adjoint integral operators.

The purpose of this paper is to outline a more general approach to visual acuity experiments than the classical methods borrowed from the optical sciences. A theory based on integral operators with symmetric kernels replaces the standard use of filters constructed from windowed sines and cosines. This more general approach allows greater latitude in the range of phenomena to be modelled. It also permits all the standard techniques used in Fourier expansion of a stimulus and response to be generalized to a space-variant system such as the human visual field.

Cybernetics↗