An important element in the microgenetic theory of language processing concerns the prediction of semantic to phonological flow. This prediction has found support in studies of deep dyslexia ( Coltheart, Patterson, & Marshall, 1980), where patients with generally large left hemisphere lesions, who are unable to derive phonology from print, show semantic errors in reading, especially for concrete nouns. Such patients extract meaning from the word form even though they cannot process the word phonetically, suggesting a prephonological stage of lexical meaning. Similar phenomena in the auditory modality have been reported ( Morton, 1980). There are reports of ability to point to semantic associates of an orally presented target on a forced-choice paradigm in patients with cortical or word deafness who are otherwise unable to point to the correct object.
Not only is word meaning extracted prior to phonology, it may be extracted prior to the conscious perception of the word. One well-known study showing semantic priming for backward-masked (and not consciously perceived) words provided important early support ( Marcel, 1983a; See Holender, 1986). There are also reports of cross-field semantic priming in cases of callosal section ( Gazzaniga, 1980). In our lab, we have noted that semantic priming is most pronounced in cases of severe aphasia, even when the subject has difficulty reading the target words, again suggesting that semantic processing is a preliminary stage in cognition prior to phonological analysis, prior even to conscious object or word perception.
Converging information comes from studies of pure alexia, letter-by-letter reading associated with a left occipital and, usually, splenial lesion. Recent studies suggest depressed function in the mirror right occipital area. Wordevoked potentials may be flattened over the right posterior region -- in spite of normal late potentials associated with meaning -- suggesting mirror diaschisis ( Neville, Snyder, Knight, & Galambos, 1979). In a related study of nonalexic patients with left and right hemisphere lesions, elevated thresholds for the____________________