Thus, a capital letter and a lowercase letter seem to be allographs of a single grapheme in English, but probably not in German, where capitalization distinguishes between grammatically derived morphemes ( Wissen as noun vs. What counts as a grapheme is language-dependent even within a writing system. This technical definition of grapheme also includes nonletter graphemes such as the apostrophe, which distinguishes teacher’s from teachers. According to this definition, the functional role of graphemes does not depend on mapping to phonemes, as attested by the contrast between homophonic morphemes such as buy/bye and reel/real. For example, in English all letters are graphemes as well as graphs, because all letters distinguish among written English morphemes. The unit is functional in that the grapheme is the minimal graphic unit distinguishing two written morphemes, thus analogous to the phoneme, which distinguishes two spoken morphemes. A definition of grapheme that conforms to linguistic analysis by being parallel to descriptions of phoneme and morpheme is this: a grapheme is a functional unit of writing that abstracts over variations in graphs-allographs for instance, all the fonts for the letter b that exist at in a given language. Such a definition lacks both universality (e.g., Chinese characters do not map to phonemes) and also departs from the logic of linguistic descriptions. It is common in alphabetic reading research to refer to a grapheme as the basic unit of writing-in particular, one or more letters that map onto a single phoneme. However, the visual forms of graphs-reflecting their visual complexity and discriminability-have the potential to affect the identification of both individual graphs and graph combinations (e.g., single letters and letter combinations in alphabets and abjads, akshara in alphasyllabaries, syllables in syllabaries, and characters in morphosyllabaries Pelli, Burns, Farell, & Moore-Page, 2006), and thus to affect learning to read. The actual forms of the graphic units have received less attention. This mapping variety has been the focus of comparative reading research (e.g., universal grammar of reading, Perfetti, 2003 phonological grain size, Ziegler & Goswami, 2005 orthographic depth, Katz & Frost, 1992 semantic transparency, Wydell, 2012 for reviews, see Frost, 2012 Perfetti & Harris, 2013 Seidenberg, 2011). Much of this variety is associated with variable mappings that graphic units can have to linguistic units (abjad, alphabetic, syllabary, alphasyllabary, and morphosyllabary). The world’s writing systems contain graphs that span a wide variety of visual forms. The measure can be universally applied across writing systems, providing a research tool for studies of reading and writing. The results from the computational and experimental comparisons showed that GraphCom provides a measure of graphic complexity that exceeds previous measures in its empirical validation. In our analysis of the complexity of 21,550 graphs, we (a) determined the complexity variation across writing systems along each dimension, (b) examined the relationships among complexity patterns within and across writing systems, and (c) compared the dimensions in their abilities to differentiate the graphs from different writing systems, in order to predict human perceptual judgments ( n = 180) of graphs with varying complexity. The measure includes four dimensions whose value in capturing the different visual properties of graphs had been demonstrated in prior reading research-(1) perimetric complexity, sensitive to the ratio of a written form to its surrounding white space (Pelli, Burns, Farell, & Moore-Page, 2006) (2) number of disconnected components, sensitive to discontinuity (Gibson, 1969) (3) number of connected points, sensitive to continuity (Lanthier, Risko, Stolz, & Besner, 2009) and (4) number of simple features, sensitive to the strokes that compose graphs (Wu, Zhou, & Shu, 1999). We applied the measure to 131 written languages, allowing comparisons of complexity and providing a basis for empirical testing of GraphCom. We report a new multidimensional measure of visual complexity (GraphCom) that captures variability in the complexity of graphs within and across writing systems.
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