Some measures of verbal and spatial working memory in eight- and nine-year-old hearing-impaired children with cochlear implants

Abstract

Objective: The purpose of this study was to examine working memory for sequences of auditory and visual stimuli in prelingually deafened pediatric cochlear implant users with at least 4 yr of device experience.

Design: Two groups of 8- and 9-yr-old children, 45 normal-hearing and 45 hearing-impaired users of cochlear implants, completed a novel working memory task requiring memory for sequences of either visual-spatial cues or visual-spatial cues paired with auditory signals. In each sequence, colored response buttons were illuminated either with or without simultaneous auditory presentation of verbal labels (color-names or digit-names). The child was required to reproduce each sequence by pressing the appropriate buttons on the response box. Sequence length was varied and a measure of memory span corresponding to the longest list length correctly reproduced under each set of presentation conditions was recorded. Additional children completed a modified task that eliminated the visual-spatial light cues but that still required reproduction of auditory color-name sequences using the same response box. Data from 37 pediatric cochlear implant users were collected using this modified task.

Results: The cochlear implant group obtained shorter span scores on average than the normal-hearing group, regardless of presentation format. The normal-hearing children also demonstrated a larger "redundancy gain" than children in the cochlear implant group-that is, the normal-hearing group displayed better memory for auditory-plus-lights sequences than for the lights-only sequences. Although the children with cochlear implants did not use the auditory signals as effectively as normal-hearing children when visual-spatial cues were also available, their performance on the modified memory task using only auditory cues showed that some of the children were capable of encoding auditory-only sequences at a level comparable with normal-hearing children.

Conclusions: The finding of smaller redundancy gains from the addition of auditory cues to visual-spatial sequences in the cochlear implant group as compared with the normal-hearing group demonstrates differences in encoding or rehearsal strategies between these two groups of children. Differences in memory span between the two groups even on a visual-spatial memory task suggests that atypical working memory development irrespective of input modality may be present in this clinical population.

Figure 1

Diagram of memory game apparatus and experimental conditions given a list length of two items. Each shaded hexagon represents a large colored button back-lit by a light. All auditory stimuli were presented via a loudspeaker located just behind the memory game response box. The verbal labels simply illustrate the consistent mapping between a particular auditory stimulus and a given button location. “A_C+L” = auditory color-names-plus-lights; “A_D+L” = auditory digit-names-plus-lights; “L” = lights-only.

Figure 2

Comparison of performance on the memory game task across different presentation conditions in the normal-hearing (NH) and pediatric cochlear implant (CI) groups. Mean span scores from the NH group are shown on the left, mean span scores from the CI group on the right. “A_C+L” = auditory color-names-plus-lights; “A_D+L” = auditory digit-names-plus-lights; “L” = lights-only. Mean scores from all participants in each group are shown in the top panel (a). Mean scores from the subset of 22 CI participants who made no errors on the color-name identification pretest and the 22 normal-hearing children with whom they were matched are shown in (b). Positive error bars indicate 1 SD from the mean. Error bars in the negative direction indicate 1 standard error.

Figure 3

Memory game task group means for the color-names-plus-lights presentation condition (“A_C+L”), the lights-only presentation condition (“L”), and the auditory-only presentation condition using color-name stimuli (“A_C”). Results from the 27 normal-hearing children in Experiment 2 are shown in the left-hand panel. Results from the cochlear implant group in Experiment 3 are shown in the right-hand panel (N = 37). Positive error bars indicate 1 SD from the mean. Error bars in the negative direction indicate 1 standard error. (The two leftmost bars representing the “A_C+L” and “L” conditions are a subset of the data reported in Experiment 1 for the normal-hearing children.)

Figure 4

Histograms showing the distribution of scores obtained in Experiments 2 and 3 using the auditory-only presentation condition of the memory game task. Normal-hearing (NH) children are shown in the top panel, pediatric cochlear implant (CI) users are shown in the bottom panel.