The just noticeable deviation (jnd) of the position of light points in the grid structure of matrix signs was determined in a laboratory experiment. The stimuli, consisting of either lines (10 light points) or areas (10x10 light points), were presented on a colour VDU-screen. The variables tested were light point distance (2.75, 1.38 or 0.688 min of arc), spatial location (centre or edge of an area), direction of dislocation (crosswise or length-wise in a line), colour (white, red, green, or blue), luminance ratio (1:560 or 1:10) and presentation time (1 or 5s). Neither a difference between lines and areas, nor an effect of spatial location, direction of dislocation and presentation time was found. For blue light points the jnd was twice as large as for white, green and red. For the lower luminance ratio the jnd appeared to be 20% larger. The maximum allowable deviation in mm (85% criterion) for white, red and green light points can be described by 0.081R^1.71.d^-0.71, where d is the average light point distance in mm and R the viewing distance in m.
Samenvatting