In an attempt to control the initial stage of perceptual filtering or feature extraction, 7 homographs or ambiguous characters were generated, each having identical physical attributes and thus identical retinal stimulations, may it be processed as a letter or a digit. Expressed in a block style, e.g. Letter 0 (oh) was exactly the same as Digit 0 (zero) in all physical dimensions. Each homograph (target) was presented among the two unambiguous nontargets, consisting of letters only (letter context), a letter and a digit (mixed context), and digits only (digit context). In spite of the strong digit bias inherent to the block style representation of characters, the context did exert large effects, presumed to occur in a later stage of information processing, i.e. the decision or interpretation stage. Context effects were generally greater with the whole report (all three characters were reported) than with the cued report (only the cued target was reported). The attention factor, as revealed by the differences between whole and cued reports, seems generally large with the letter context but negligible with the digit context. Differential context effects may, in part, be attributable to familiarity. Physical properties of nontargets as well as those of targets seem to control visual information processing to a substantial degree.