Enhancing visual performance for people with central vision loss

Abstract

People with central vision loss must use peripheral vision for visual tasks. It is well known that performance for almost all spatial tasks is worse in the normal periphery than in the normal fovea. The primary goal of my ongoing research is to understand the limiting factors and the potential for enhancing vision for people with central vision loss. Here I review my previous work related to understanding the limiting factors on reading, a task that is the primary complaint of many patients with age-related macular degeneration, the leading cause of visual impairment in the elderly. I also review my work related to enhancing visual functions in the normal periphery and how it may be applied to people with central vision loss.

Figure 1

Reading speed (wpm) is plotted as a function of print size (deg) for (a) an observer with normal vision, tested at the fovea and five other eccentricities (2.5 – 20°) in the inferior visual field; and (b) an observer with AMD whose preferred retinal locus was 7° directly below the anatomical fovea (in the visual field domain). For each set of reading speed vs. print size data, a two-line fit (on log-log axes) was used to fit the data where the intersection of the two lines represents the critical print size, the smallest print size that can be read at the maximum reading speed. In (b), we included the maximum reading speeds, averaged across six young adults with normal vision, at 5 (upper dotted line) and 10° (lower dashed line) eccentricity for comparison. The left starting point of each of these two lines represents the averaged critical print size at the respective eccentricity in the normal periphery. Error bars represent ± 1 S.E.M and are smaller than the size of the symbols when not shown. Panel (a) was modified from Chung et al.

Figure 2

The word “common” rendered at the five letter spacings used in Chung. The illustration was modified from Chung.

Figure 3

Reading speed (wpm) is plotted as a function of letter spacing (see Figure 2), expressed as multiples of the standard letter spacing used for Courier font (the font used in the study). Panel (a) shows the averaged reading speed for six young adults with normal vision tested at the fovea and 5 and 10° in the inferior visual field. Panel (b) shows the reading speed for an observer with AMD. In all cases, the “critical spacing” was close to the standard letter spacing. Error bars represent ± 1 S.E.M. Panel (a) was modified from Chung.

Figure 4

Panel (a) shows how the spatial extent of crowding (deg) varies as a function of stimulus duration (msec). The spatial extent of crowding was defined as the separation between a target letter T and one of its four flanking Ts that allowed observers to identify the orientation of the target T at an accuracy of 62.5%. The contrast polarity of the target could be the same as, or opposite to that of the flankers. Panel (b) plots reading speed (wpm) as a function of eccentricity (deg), for text rendered as all white letters, all black letters, or interleaved white and black letters. Data shown in both panels represent the averaged values for the same three observers and are modified from Chung & Mansfield. Error bars represent ± 1 S.E.M.

Figure 5

Proportion-correct of identifying crowded letters is plotted as a function of training block for an observer in Chung in panel (a). Each symbol represents the averaged performance for a block of 100 trials. His reading speeds (wpm) for different print sizes (deg), determined before (pre-test) and after (post-test) training, are plotted in panel (b). The presentation of these data is modified from Chung.

Figure 6

The different vertical word spacings (expressed as multiples of the standard line spacing for the Courier font used) used in the studies of Chung and Chung et al. are shown in (a). Reading speeds measured for the conditions illustrated in (a) are plotted as average values for (b) a group of five young adults with normal vision tested at the fovea and 5 and 10° in the inferior visual field and (c) a group of four AMD observers. The infinity symbol on the abscissa represents the unflanked condition. Error bars represent ± 1 S.E.M. Panel (a) was modified from Chung and panel (b) was modified from Chung et al.

Figure 7

Reading speed (wpm) for 100-word passages, averaged across eight AMD observers, is plotted as a function of line spacing (multiples of “standard”), for two print sizes — 1× and 2× the critical print size (CPS). Error bars represent ± 1 S.E.M. Data were from Chung et al.

Figure 8

A comparison of the size of the visual span and maximum reading speed before and after perceptual learning of a letter-recognition task designed to expand the visual span. Panel (a) plots the difference in the size of the visual span, expressed as bits of information transmitted, for the no-training control group, and at the transferred (untrained) and trained retinal locations. Panel (b) plots the ratio of the maximum reading speed before and after training. Values plotted are averaged across the observers. Error bars represent ± 1 S.E.M. Pairwise comparisons among the three categories that are statistically significant are listed in the corresponding histogram. The presentation of these data is modified from Chung et al.