Representation of letter position in single-word reading: evidence from acquired dyslexia.

Visual word recognition requires information about the positions as well as the identities of the letters in a word. This study addresses representation of letter position at prelexical levels of the word recognition process. We present evidence from an acquired dyslexic patient, L.H.D., who perseverates letters in single-word reading tasks: Far more often than expected by chance, L.H.D.'s reading responses include letters from preceding responses (e.g., SAILOR read as SAILOG immediately after FLAG was read correctly). Analyses carried out over two large data sets compared the positions of perseverated letters (e.g., the G in SAILOG) with the positions of the corresponding "source" letters (e.g., the G in FLAG). The analyses assessed the extent to which the perseverations preserved source position as defined by various theories of letter position representation. The results provided strong evidence for graded both-edges position representations, in which the position of each letter is encoded coarsely relative to both the beginning and the end of the word. Alternative position representation schemes, including letter-context and orthosyllabic schemes, were not supported.