Visual requirements for reading: The importance of a large field of view in reading with a magnifier

Abstract

It is assumed that too low values for optimal field of view in magnifier reading were obtained in the past by applying the 'Drifting Text' Technique [1,3,4] in which the subjects had no control of the movements of the magnified image. On the basis of the view that reading involves alternating sequences of locating and recognizing textual information [9], it is argued that part of the magnified image is required for the movement control of the visual display. Higher values are predicted than the 1-6 characters proposed in the model of Whittaker and Lovie- Kitchin [1]. 14 Male and female subjects with a macular degeneration ranging in age from 20 to 82 years of age participated in an experiment to determine the optimal field of view in CCTV-magnifier reading. Large effects of width and height are found on reading rate and the data suggest that the optimal values are even higher than the maximum value of 12 characters that could be technically realized in the present experiment. Large age effects are found in both reading rate and smoothness of control of the platform. The data on the movements of the platform and the eyes are discussed. It is concluded that the elderly subject applied another strategy to move the platform than the other subjects. In all subjects large variations are observed in the velocity of transportation of the platform. It is assumed that these variations signal the flexibility of the motor control process that is required to adapt the reading process as a whole to fluctuations in the comprehension process.