Complex Working Memory Span in Cochlear Implanted and Normal Hearing Teenagers

The individual’s capacity to maintain attention and process new information in the face of distraction is known in the literature as working memory (WM). Short term memory (STM) is used to encode and retain information for a short period of time. WM tasks are functionally distinct from STM tasks because they require not only information encoding, storage and rehearsal, but also include a processing/manipulation component requiring a dual task load, such as judging semantic acceptability of a sentence. STM tasks, such as word span or digit span, may be considered a subset of WM. STM requires simple storage, whereas WM requires a storage component as well as an active attention and control process. WM tasks have been found to differ from simple span tasks in their predictive validity, measuring variance that is unique from STM 1. The current model of working memory developed by Baddeley and his colleagues consists of four components2, (1) a domain-general central executive that controls attention and processing activities and regulates the flow of information in the processing system, (2) the phonological loop that is used for the temporary storage of verbal phonological memory codes, (3) the visual-spatial sketchpad that maintains and processes visual and spatial representations, and (4) the episodic buffer that is used to integrate and bind memory codes from different processing domains into larger chunks of information. The complex reading span task developed by Daneman & Carpenter 3 is among the most widely used tools for measuring the central executive function. The reading span task requires the participant to perform two operations at once: 1) read a series of sentences aloud and make a semantic acceptability judgment about the sentence and 2) keep track of the last word of each sentence so that the words can be recalled later. Reading span tasks have been found to have good reliability (i.e., .70 to .90) across a number of studies. Furthermore, performance on reading span tasks has been found to predict complex cognitive processes such as comprehension, problem solving and reasoning – all tasks that require “executive attention” 1. Reading span is thought to measure the capacity of the central executive because it requires simultaneous storage and processing of phonological and lexical information. Verbal storage uses a phonological loop, composed of a short-term phonological store subject to rapid decay plus a subvocal rehearsal process that can be used to refresh decaying representations within the store. Individuals with normal hearing perform similarly whether the task is presented through listening or through reading 3. However, WM estimates might be expected to differ considerably for reading and listening tasks in populations with significant hearing loss. Memory skills in Children with Hearing Loss Memory studies of children with hearing loss have primarily used STM tasks. Stiles et al, 4 compared performance of 6-9 year olds with mild to moderate HL with NH age mates on both phonological and visuospatial STM tasks. Although articulation rate and vocabulary were lower in children with hearing loss than in age-mates with normal hearing, there was no significant effect of hearing loss on memory performance,. This stands in contrast to results for children with greater hearing losses who use CIs. Watson, et al, 5 found a marked impairment on digit span and non-word repetition measures for children with CIs compared to NH children. Similar results were reported by Pisoni6 for digit span results obtained in CI users tested in both elementary grades and high school. When WM processes rely on verbal rehearsal and serial scanning of phonological information in STM, early severe-profound auditory deprivation seems to impair normal development. Reinstatement of auditory sensation in children with CIs was not sufficient to enable adequate development. Further evidence of this impairment is provided by examining the relationship between mismatch negativity activation and memory span. Connections between pre-attentive auditory sensory memory and “higher language functions” were apparent in NH children but not in age-matched CI users 5.