Object distance scaling in real space is preserved in low vision subjects

Abstract

Purpose: We investigate the ability of adults with and without visual impairment estimate distances between stimuli in real environment. Methods: W=e evaluated 12 subjects aged between 20 and 40 years in which 6 subjects with normal vision (mean age=31.0, SD=6.5), and 6 subjects with visual impairment (mean age=27.7, SD=7.8). Two styrofoam balls of 10cm in diameter were used, painted in black and a line of white velcro of 3.5 meters was fixed in the floor of a hallway without lateral references. Psychophysical scaling was evaluated by magnitude estimation and the exponent of the Stevens' law was calculated. Results: The calculated exponent for the controls was 1.13 for near judgment and 1.11 for far distances. The low vision group showed exponent values of 1.01 for near and 0.96 for far distances judgment. There was a statistical difference for 120cm of distance between balls for near (F 10 =88.21, p<0.001) and a tendency to difference for 200cm (F 10 =3.81, p=0.079) between groups. Conclusions: Our scaling procedure shows that despite the reduction in the distance judged by the low vision subjects, their internal representation of space is preserved. Similar exponent values indicates that their suprathreshold impression of the distance follow the same rules of the normal subject.