Ageing and Noise in the Visual System

Abstract

THE differential visual thresholds of a group of children aged 8–10 years and a group of adults aged 18–22 years have been compared using a technique similar to that used by Gregory and Kendon¹. Subjects were asked to vary the intensity of a test spot 3 mm in diameter in a field 100 mm long by 25 mm high at a distance of 2.5 m. A series of eight different intensities of the background field was used and each subject was given one series with the background intensity increasing and one series decreasing. The results of these experiments for the two groups of ten subjects are shown in Fig. 1 by plotting δI against I, where δI is the difference between the intensity of the background and of the test spot for the spot to be correctly located and I is the intensity of the background field. The results of trials with the background intensity increasing and decreasing are pooled, the justification for this being that the same result is achieved by plotting the results from the two series of trials separately. It will be seen that at every level of illumination used the adults had a lower threshold than the children.