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High temporal resolution event-related brain potential and electroencephalographic coherence studies of the neural substrate of short-term storage in working memory indicate that the sustained coactivation of both prefrontal cortex and the posterior cortical systems that participate in the initial perception and comprehension of the retained information are involved in its storage. These studies further show that short-term storage mechanisms involve an increase in neural synchrony between prefrontal cortex and posterior cortex and the enhanced activation of long-term memory representations of material held in short-term memory. This activation begins during the encoding/comprehension phase and evidently is prolonged into the retention phase by attentional drive from prefrontal cortex control systems. A parsimonious interpretation of these findings is that the long-term memory systems associated with the posterior cortical processors provide the necessary representational basis for working memory, with the property of short-term memory decay being primarily due to the posterior system. In this view, there is no reason to posit specialized neural systems whose functions are limited to those of short-term storage buffers. Prefrontal cortex provides the attentional pointer system for maintaining activation in the appropriate posterior processing systems. Short-term memory capacity and phenomena such as displacement of information in short-term memory are determined by limitations on the number of pointers that can be sustained by the prefrontal control systems.

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Prior probabilities of graphemes and conditional probabilities for their pronunciation as specific phonemes are given based on a corpus of 17,310 English words. Phonemes are as given in recent editions of Websters New Collegiate Dictionary, with minor revisions; graphemes are defined as letters or letter clusters corresponding to single phonemes. Grapheme-phoneme probabilities were derived from a revised table of frequency of occurrence of phoneme-to-grapheme correspondences generated in a study of spelling regularities (P. R. Hanna, J. S. Hanna, Hodges, & Rudorf, 1966). This quantitative descriptive information provides an index ofthe strength of particular graphemephoneme associations in English. Suggestions are made for the utilization of these probabilities as estimates of spelling/sound predictability in reading research.