PubMed · 7269298
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
J Nachmias. 1981. On the psychometric function for contrast detection.. https://doi.org/10.1016/0042-6989(81)90115-2
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
Projective geometry determines how the retinal image of an object deforms as it moves through three-dimensional space. Does the visual system use constraints derived from this information, such as rigidity, to aid the tracking of moving objects? A novel psychophysical technique is introduced for assessing which of two competing motion transformations is 'preferred' by the visual system, in a two-frame sequence. In the first experiment, relative preference strengths for translations parallel and perpendicular to the major axis of a wire-frame object were measured by pitting the two against each other. It was found that parallel translations were preferred to perpendicular ones. On the basis of these data a proximity measure for normalising different transformations, independent of any effects of figural similarity, was developed. In the second experiment, two wire-frame planar structures were used to pit one of five transformations (rotation, expansion, vertical expansion, shear and random jitter) against a translation. Preference strength was measured as the translation distance at which the transformation and the translation were perceived with equal frequency. The PSEs were found to collapse on to a single line when plotted against the proximity magnitude, with the exception of a residual preference for pure translation over all other transformations. In general, these results suggest that preference strength for moving wire-frame figures is determined primarily by the proximity of local features on the displacing contour, with little regard for the projective shape transformation.
When a texture pattern was briefly presented followed by a small annular mask, it was found that the central area of the texture was strongly suppressed within the mask. Analogous to filling-in of brightness in a uniform luminance area (Paradiso, M. A. & Nakayama, K. (1991) Vision Research, 31, 1221-1236), this phenomenon demonstrates filling-in of texture; the texture area was unperceived because filling-in of the texture area was interrupted by the contour in the mask. However, odd local features within the texture, which were assumed to pop out, were selectively perceived while other features were suppressed within the mask. These results suggest that: (1) rapid pattern segregation occurs before and/or separately from texture filling-in, and that (2) filling-in is initiated at boundaries between surfaces rather than at luminance gradients.
We assessed the influence of dioptric and diffusive blur on normal subjects' letter and Vernier acuity in two experiments. In the first experiment, letter acuity was measured for isolated black Sloan letters and Vernier acuity was determined for a pair of black vertical abutting or nonabutting lines. Targets were viewed through plus lenses that produced 0, 1, 2, 4, and 8 D of dioptric blur. In the second experiment, letter acuity was determined for bright 4-position Ts and Vernier acuity was measured for a pair of bright abutting vertical lines. Six levels of imposed diffusive blur were produced by varying the distance between a ground glass screen and the oscilloscope on which the targets were presented. The results of both experiments indicate that letter and Vernier acuity for abutting or closely separated lines worsen in parallel curvilinear fashion, as long as the lines comprising the Vernier targets remain equally detectable when various amounts of dioptric and diffusive blur are imposed. We conclude that both dioptric and diffusive blur introduce common processing limitations for letter and Vernier acuity.