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K C Scott-Brown

Publications and source records attributed to K C Scott-Brown.

5 recordsLinked to original sources
PubMed2003

Interocular orientation disparity and the stereoscopic perception of slanted surfaces.

The orientation threshold for two-dimensional filtered noise stimuli was estimated using forced-choice procedures with both dioptic and dichoptic viewing. In the dioptic case the two patterns were co-rotated. In the dichoptic case the stimuli were counter-rotated to produce an orientation disparity, which yields a percept of slant about the horizontal axis orthogonal to the cyclopean line of sight. Dioptic thresholds increased with the orientation bandwidth of the stimuli. In contrast, dichoptic thresholds were essentially constant across a wide range of conditions. In all cases, dichoptic orientation acuity was much finer than conventional estimates. In a second experiment, the dichoptic threshold was estimated for patterns superimposed on a depth pedestal. Acuity was affected significantly by the presence of the pedestal, and was an inverse function of pedestal amplitude. The results suggest that stereoscopic slant caused by dichoptic counter-rotation arises because of neural processing of the overall pattern of disparities of position produced by counter-rotation, rather than specialised encoding of orientation disparity.

Depth Perception↗
PubMed2001

The effect of the spatial arrangement of target lines on perceived speed.

Drifting lines that are not orthogonal to their direction of motion appear to travel more slowly than those that are, resulting in a "speed reduction" illusion. It has been shown that several factors affect the strength of this illusion such as the angle of tilt, the stimulus contrast and the line length [Castet, Lorenceau, Shiffrar, & Bonnet, Vision Research 33 (1993) 1921-1936]. We show here that the illusion is also affected strongly by other factors, notably the spatial arrangement of multi-element displays and whether there is a random component to the image motion. An array of short lines that are co-linear is processed in a manner similar to a continuous long line, whereas the same array distributed randomly in space is treated by the visual system as a group of independent short lines. Random variation of the length or position of a line as it is drifting abolishes the speed reduction illusion completely. The data indicate that even for simple stimuli, vector summation of local motion components with velocity signals arising at the line ends cannot, on its own, account for perceived speed.

Humans↗
PubMed2000

A low-cost, accurate method of producing large quantities of digitally filtered images.

We demonstrate how to produce complex image transformations of bitmap files for vision experiments using the Cogimatic Vision Starter Kit (VSK) library of mathematical routines along with Visual Basic, C++, or the Delphi Pascal compiler. Implementing this system on an IBM-compatible PC running Windows 95, 98, or NT4 enables researchers to quickly and economically manipulate images for vision research. The VSK includes a simple stand-alone image-processing application. In addition, VSK has the ability to automate image transformations and to fully integrate image processing into new experimental software on the PC platform.

Costs and Cost Analysis↗
PubMed1998

Contrast discrimination, non-uniform patterns and change blindness.

Change blindness--our inability to detect large changes in natural scenes when saccades, blinks and other transients interrupt visual input--seems to contradict psychophysical evidence for our exquisite sensitivity to contrast changes. Can the type of effects described as 'change blindness' be observed with simple, multi-element stimuli, amenable to psychophysical analysis? Such stimuli, composed of five mixed contrast elements, elicited a striking increase in contrast increment thresholds compared to those for an isolated element. Cue presentation prior to the stimulus substantially reduced thresholds, as for change blindness with natural scenes. On one hand, explanations for change blindness based on abstract and sketchy representations in short-term visual memory seem inappropriate for this low-level image property of contrast where there is ample evidence for exquisite performance on memory tasks. On the other hand, the highly increased thresholds for mixed contrast elements, and the decreased thresholds when a cue is present, argue against any simple early attentional or sensory explanation for change blindness. Thus, psychophysical results for very simple patterns cannot straightforwardly predict results even for the slightly more complicated patterns studied here.

Adult↗