Linear Relationship of Motion Displacement Threshold with Stimulus Energy (calculated as a function of Contrast and Line Length)

Abstract

Abstract: : Purpose: to explore the relationship between motion displacement threshold (MDT) and stimulus energy, calculated as a function of contrast and line length. Methods: A video display under PC control was used to present a horizontal line stimulus in the nasal field at –27,3 degrees at a test distance of 30cm. The right eye of two experienced normal subjects (47 and 31 years) was tested with peripheral refraction corrected. A central target was fixated and the line stimulus (randomized presentation order of lengths 11, 22, 43, 86 or 128 min arc and contrast 25%, 40%, 55%, 60% or 85%) was programmed to pass through 5 presentations of displacements ranging 0–40 min arc. Stimulus presentation consisted of 3 oscillations of 200 msec per cycle duration. Each parameter was tested 3 times, frequency of seeing curves (FOS) were obtained and 50% seen threshold calculated by probit analysis. Results: There was a linear correlation of MDT with stimulus energy [stimulus area (min arc²) x luminance (cdm²)] when plotted as a log log function. The slope approximated –1 (–0.93 and –0.94 for each subject).  

Conclusions: A linear relationship of MDT with stimulus energy is demonstrated. These results suggest that the stimulus parameters tested lie within the area of linear summation at this peripheral location. This information will be applied to the development of a new multi–location MDT test for the early diagnosis of glaucoma. Supported by unrestricted grant from Pfizer.

Keywords: contrast sensitivity • motion–2D • perimetry