Lothar Spillmann

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Psychophysical research on the Hermann grid illusion is reviewed and possible neurophysiological mechanisms are discussed. The illusion is most plausibly explained by lateral inhibition within the concentric receptive fields of retinal and/or geniculate ganglion cells, with contributions by the binocular orientation-specific cortical cells. Results may be(More)
Classical receptive-field concepts have been used to explain local perceptual effects such as border contrast and Mach bands, but are not sufficient to explain global perceptual effects. Examples are the perception of illusory contours, area contrast, color constancy, depth planes, coherent motion and texture contrast. These diverse effects require(More)
Two line gratings abutting each other with a phase shift of half a cycle elicit the perception of an illusory line running orthogonally between the two sets of grating lines. We found that rating strength increases with increasing number of lines, line length, and phase angle. In contrast, rating strength decreases with increasing spacing of lines, lateral(More)
We have measured the perceptive field, the psychophysical correlate of the physiologically determined receptive field, in man and monkey. Measurements were made using the Hermann grid illusion and the Westheimer paradigm. The following results were found: First, in both man and monkey, the size of perceptive fields and field centers increases from the fovea(More)
A colored line flanking a darker border will appear to assimilate its color onto the enclosed white area over distances of up to 45 deg (the Watercolor Effect). This coloration is uniform and complete within 100 ms. We found that thin (6 arcmin), winding inducing lines with different contrasts to the ground are generally more effective than thick, straight,(More)
A pincushion formed by four arcs on a gray background looks darker when the arcs are black, and lighter when the arcs are white. Yet, a matching-experiment shows that this difference is relative. Whereas the apparently darker pincushion requires a matching luminance that is lower than the background luminance (i.e. assimilation), the apparently lighter(More)
The study of illusory brightness and contour phenomena has become an important tool in modern brain research. Gestalt, cognitive, neural, and computational approaches are reviewed and their explanatory powers are discussed in the light of empirical data. Two well-known phenomena of illusory form are dealt with, the Ehrenstein illusion and the Kanizsa(More)
With strict fixation, a flickering light spot smaller than 3 deg presented to the peripheral retina will rapidly appear to lose contrast and stop flickering within 35 s, before fading away completely. The time required for this adaptation to occur decreases with: decreasing depth of modulation (97-9%); decreasing stimulus diameter (2 deg-7 min arc);(More)
Psychophysical tests of S-cone contributions to temporal ON- and OFF-channels were conducted. Detection thresholds for S-cone modulation were measured with two kinds of test stimuli presented on a CRT: a rapid-on sawtooth test and a rapid-off sawtooth test, assumed to be detected differentially by temporal ON- and OFF-channels, respectively. S-cone related(More)