Biomedical subjects

Lothar Spillmann

Publications and source records attributed to Lothar Spillmann.

22 records · Page 2Linked to original sources

PubMed2002

Scintillating lustre and brightness induced by radial lines.

Gray disks inserted into the central gaps of an Ehrenstein pattern appear to lighten up and scintillate with each movement of the eye or stimulus pattern. We call this phenomenon scintillating lustre. Both phenomena-illusory brightness and scintillating lustre-depend on the presence of the radial inducing lines converging onto the gaps. Without the radii the gray disks appear matte. Using parametric stimulus variation, we show that the strength of scintillating lustre covaries with line-induced brightness enhancement when the length, width, number, and contrast of the radial lines, as well as the size of the gaps in the Ehrenstein figure, are varied. Following the proposal by Anstis (2000, Vision Research 40 2551-2556), we suggest that lustre results from a competition between the ON and OFF visual pathways. Whereas Helmholtz's binocular gloss is elicited by stereoscopically fused incremental and decremental stimuli, the present study demonstrates that lustre can also arise from the interaction between line-induced brightness (illusory increment) and a dark gray disk (physical decrement).

Adult↗

PubMed2000

Stroke-blind for colors, faces and locations: Partial recovery after three years.

Purpose. To study and follow-up achromatopsia, prosopagnosia, and topographagnosia in a patient who suffered a bilateral stroke of the posterior cerebral arteries. Methods. Ophthalmological, neuropsychological and neuroradiological examinations were conducted over a span of 3 years to assess the amount of brain damage and look for signs of functional recovery. Results. After the onset of achromatopsia, perception of the color green re-appeared first, followed by red, yellow, and brown. Blue which had appeared entirely black was last to return. While reading and color naming have largely recovered, color discrimination after three years remains poor especially in dim lighting. Similarly, with prosopagnosia, while the patient has learn to identify people (including photographs) by individual features, his ability to perceive and recognize faces and facial expressions holistically remains severely impaired. Recognition of streets, houses, and topographical layouts also continues to be affected, while the perception of speed and distance has somewhat improved. Perimetry further suggests a mild improvement of the superior hemianopia in his visual fields. Conclusions. Although major deficits in color, face and place perception remain, some functions impaired by the stroke have returned par-alleling a partial recovery from the brain lesion as demonstrated by NMR.

Journal Article↗

PubMedDate not supplied

Flashing anomalous color contrast.

A new visual phenomenon that we call flashing anomalous color contrast is described. This phenomenon arises from the interaction between a gray central disk and a chromatic annulus surrounded by black radial lines. In an array of such figures, the central gray disk no longer appears gray, but assumes a color complementary to that of the surrounding annulus. The induced color appears: (1) vivid and saturated; (2) self-luminous, not a surface property; (3) flashing with eye or stimulus movement; (4) floating out of its confines; and (5) stronger in extrafoveal than in foveal vision. The strength of the effect depends on the number, length, width, and luminance contrast of the radial lines. The results suggest that the chromatic ring bounding the inner tips of the black radial lines induces simultaneous color contrast, whereas the radial lines elicit, in conjunction with the gray disk and the ring, the flashing, vividness, and high saturation of the effect. The stimulus properties inducing the illusion suggest that flashing anomalous color contrast may be based on asynchronous interactions among multiple visual pathways.

Adaptation, Ocular↗

PubMedDate not supplied

Spatial profile of contours inducing long-range color assimilation.

Color induction was measured using a matching method for two spatial patterns, each composed of double contours. In one pattern (the standard), the contours had sharp edges to induce the Watercolor Effect (WCE); in the other, the two contours had a spatial taper so that the overall profile produced a sawtooth edge, or ramped stimulus. These patterns were chosen based on our previous study demonstrating that the strength of the chromatic WCE depends on a luminance difference between the two contours. Low-pass chromatic mechanisms, unlike bandpass luminance mechanisms, may be expected to be insensitive to the difference between the two spatial profiles. The strength of the watercolor spreading was similar for the two patterns at narrow widths of the contour possibly because of chromatic aberration, but with wider contours, the standard stimulus produced stronger assimilation than the ramped stimulus. This research suggests that luminance-dependent chromatic mechanisms mediate the WCE and that these mechanisms are sensitive to differences in the two spatial profiles of the pattern contours only when they are wide.

Adult↗