PubMed · 14173415
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R A WEALE. 1964-09-11. HUMAN CONES.. https://doi.org/10.1126/science.145.3637.1205
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Theories of induction propose that the brightness of a test patch within a complex surround is explained by local contrast or by integrating contrasts from various regions within the surround, weighted inversely with the distance from the test. Results here corroborate that brightness induction from a patterned background depends on both contiguous and non-contiguous surrounding light, but the measurements were inconsistent with any linear integration of contrast at edges within the scene. In some conditions, assimilation rather than contrast to contiguous surrounding light was observed, depending on the luminance of the light in non-contiguous regions. This finding implies that brightness induction from patterned backgrounds depends on neural processes that can cause contrast and/or assimilation, depending on the luminance relation between contiguous and non-contiguous regions. A model in the literature postulating that the influence of a non-contiguous edge is regulated by the amount of contrast at the contiguous edge can accommodate brightness induced by these patterned backgrounds.
Variations in blur are present in retinal images of scenes containing objects at multiple depth planes. Here we examine whether neural representations of image blur can be recalibrated as a function of depth. Participants were exposed to textured images whose blur changed with depth in a novel manner. For one group of participants, image blur increased as the images moved closer; for the other group, blur increased as the images moved away. A comparison of post-test versus pre-test performances on a blur-matching task at near and far test positions revealed that both groups of participants showed significant experience-dependent recalibration of the relationship between depth and blur. These results demonstrate that blur adaptation is conditioned by 3D viewing contexts.
The absence of short-wave-sensitive (S-) cones in the human foveola normally goes unnoticed, but the resulting foveal S-cone, or blue, scotoma can be visualized as the negative afterimage of a short-wavelength adapting field on a larger white background. The afterimage has an annular shape with a lighter inner region that corresponds to Maxwell's spot, and a small bright spot in the center corresponding to the foveal blue scotoma. We have shown that the visibility of the center spot in the afterimage approximately follows the spectral sensitivity curve of the S-cones. We further demonstrate that the central bright spot subtends a retinal area that is coincident with the tritanopic region of the foveola. The macular pigment distribution measured for the same observers also peaks in the central fovea, but has a relatively high density over a broader retinal region than the bright spot in the negative afterimage, and more closely corresponds to the lighter annular region of the afterimage. The results support the hypothesis of an active post-receptoral process for filling-in of chromatic scotomas.