Biomedical subjects

Walter H Ehrenstein

Publications and source records attributed to Walter H Ehrenstein.

5 recordsLinked to original sources

PubMed2005

Eye preference within the context of binocular functions.

BACKGROUND: Eye preference refers to an asymmetric use of the two eyes, but it does not imply a unitary asymmetry between the eyes. Many different methods are used to assess eye preference, including eyedness questionnaires and sighting tasks that require binocular and monocular alignment of a target through a hole in the middle of a card or funnel. The results of these coarse accounts of eye preference are useful as a first screening, but do not allow for graded quantification of the manifested asymmetry in binocular vision. Moreover, they often concern only a rather selective range of binocular functions. The aim of the present study was to further differentiate eye preference within the context of other binocular functions as measured in standard optometric tests, and to validate their relation to questionnaire data of eyedness. METHODS: Conventional accounts of eye preference (German adaptation of Coren's questionnaire and a sighting task) were compared with various optometric tests of binocular function within a sample of 103 subjects. Examination included visual acuity and accommodation in each eye, stereoscopic prevalence, suppression due to binocular rivalry, fixation disparity (Mallett test). RESULTS: Sighting dominance was leftward in 32% and rightward in 68% of the cases and was highly correlated (Kendall's tau(b)=0.70) with eyedness. Further significant associations were restricted to stereoscopic prevalence which correlated with sighting dominance (tau(b)=0.55), eyedness (tau(b)=0.50), and rivalry dominance (tau(b)=0.28). CONCLUSION: Eye preference seems to be essentially reflected by eyedness, sighting dominance, and stereoscopic prevalence, but largely unrelated to fixation disparity, accommodation, and visual acuity.

Accommodation, Ocular↗

PubMed2005

Comparing endoscopic systems on two simulated tasks.

Endoscopes are slender instruments for performing medical procedures through small incisions or natural body orifices. Three experiments examined the performance effects of various endoscope systems when naive participants executed tasks in a bladder-like environment. The systems involved a direct endoscope, requiring the user to look through a lens at the outer part of the endoscope, and a video endoscope that picks up the image via a camera attached to the endoscope and displays it on a video monitor. The results indicate that the participants performed the tasks better with video than with direct endoscopes, and showed more transfer of practice with video endoscopic surgery from a small to a large task environment than vice versa. The optimal position of the monitor with video endoscopic surgery appeared to involve a reasonable angle relative to the operating area (45 degrees was used). Performance was less at a greater angle (90 degrees), but also at a small angle (10 degrees). It did not matter whether the monitor was located left, right or above the operating area. As performance did not fully transfer to differently sized task environments, endoscopists should initially train with task environments of different, and especially small, sizes.

Adult↗

PubMed2004

Illusory contours and surfaces without amodal completion and depth stratification.

Cognitive and figural cues were studied in modified Ehrenstein figures made from letters of the alphabet instead of radial lines. Capital letters with and without terminators (L, J vs O, D) were used, oriented towards or away from the central gap. Three groups, of 14 subjects each, estimated the magnitude of either (i) the illusory contour, (ii) brightness enhancement, or (iii) apparent depth. Strong illusory contour formation and brightness enhancement, but no depth stratification, were perceived in figures devoid of apparent occlusion and amodal completion. These results demonstrate that the Ehrenstein illusion can arise from line ends--with no need for perceptual completion, showing that illusory boundaries and surfaces can be dissociated from apparent depth. Results support a bottom-up explanation in terms of end-stopped neurons in the visual cortex. Conversely, top-down processes appear to be responsible for depth stratification.

Cognition↗

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↗

PubMed2002

[Apparent size and judgment-order effect: a magnitude estimation study of the Delboeuf illusion].

Apparent sizes of circles in the Delboeuf figure were measured by magnitude estimation without modulus. The purpose was to investigate the Delboeuf illusion and the effect of judgment order on perceived size. Contrary to the conventional Delboeuf illusion, overestimation effects appeared for outer circles at small diameter differences. The illusory magnitude depended on the diameter ratio and diameter difference of the constituent circles. The maximum magnitude of the illusion did not always appear at the diameter ratio, 0.67 (as found before by the method of limits). The circle judged first had an assimilative effect on the apparent size of the subsequently judged circle. The time-order dependency of assimilation was more pronounced for the inner than for the outer circle. The judgment-order effect may be accounted for by the attention mechanism.

Attention↗