REHABILITATING LANGUAGE DISORDERS BY IMPROVING SEQUENTIAL PROCESSING: A REVIEW

Recent research suggests that language processing (LP) may rely heavily on sequential processing (SP), a cognitive ability that allows people to process the patterns of environmental stimuli that unfold in time, such as spoken language or music. Indeed, spoken language corresponds to a set of linguistic units (e.g., phonemes, syllables, words) that are organized in time in a non-random way, according to phonotactic and syntactic rules. In this review, we discuss recent research highlighting the importance of SP for learning and processing such linguistic regularities and argue that interventions focused on improving SP may provide a potentially effective way to rehabilitate language impairments. The first part of this review presents a series of findings showing that LP is intimately related to SP. We review the literature on populations with normal LP performance suggesting that LP relies upon SP. We then report two recent studies from our lab that demonstrated a direct link between LP and SP: (1) a behavioral study showing that variations on a non-linguistic SP task are significantly associated with LP, and (2) an event-related potential study showing that the neural correlates of SP interact with LP abilities in healthy adults. The second part of this review summarizes the literature suggesting that populations with LP impairments (such as language delays due to hearing loss, dyslexia, specific language impairment, and aphasia) also display SP impairments. Thus, disturbances to SP appear to be a commonality among what appears to be very different types of LP impairments, suggesting that impaired SP causes or exacerbates LP impairment. This leads to the third part of this review, where we first summarize recent findings from brain plasticity showing that: (1) cognitive training can improve cognitive processing, and that (2) increasing cognitive processing performance through training can result in a cognitive "transfer" by also increasing performance on other related cognitive skills. We then present a potentially new method for LP remediation that is based on the idea that some LP impairments might stem directly from SP disturbances and that improving SP processing will, via transfer, result in increased LP performance. This method was applied by our research team to conduct a study aimed at improving SP and LP mechanisms. To our knowledge, the SP training study presented here shows the first evidence that SP performance can be improved and therefore has strong clinical implications as a potentially effective and novel intervention to treat LP impairments.