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. Author manuscript; available in PMC: 2009 Feb 1.
Published in final edited form as: Vision Res. 2008 Jan 14;48(4):577–588. doi: 10.1016/j.visres.2007.11.022

Figure 1.

Figure 1

Measurement of Visual-Span Profiles: Trigrams (strings of 3-letters) for measuring the visual span were presented at various positions left or right of fixation. Subjects were instructed to use either their preferred retinal locus (for AMD subjects with central scotomas) or central vision (for AMD subjects without scotomas or normal vision subjects) to fixate the mid point between two vertically separated green fixation dots (shown as grey dots in this figure). Subjects reported aloud all 3 letters of the trigram from left to right. The lower panel shows a sample visual-span profile in which proportion correct (left vertical scale) is plotted as a function of letter position for a normally sighted subject. The right vertical scale shows an approximately linear transformation from percent correct to information transmitted in bits, where 100% correct for identifying 1 of 26 letters corresponds to 4.7 bits of information. The size of the visual span was quantified by summing across the information transmitted in each slot (from letter position -5 to +5).