Interactions Between Item Set and Vocoding in Serial Recall.
Adam K Bosen, Mary C Luckasen
PMID 31033634WHAT IT FOUND
Vocoding degraded speech significantly reduced serial recall for words and non-words but had little impact on digit span.
This suggests digit span measures core memory capacity, while word span reflects the combined load of memory and auditory processing difficulty.
Key findings
01Vocoding had little impact on correct response rate for digits, with the largest difference for six-item lists not reaching significance.
02Correct response rate was significantly worse for lists of words and non-words in the vocoded condition compared to unprocessed.
03Principal components analysis showed that most variability in memory span was explained by a single underlying memory capacity factor, while sensitivity to vocoding for words and non-words was a separate, orthogonal factor.
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
Participants were young adults with normal hearing, so results may not generalize to children or older adults with hearing loss. Participants were not extensively trained on the vocoded speech, which may represent a worst-case scenario for the impact of degradation. The study used a specific 8-channel vocoder, which mimics but does not exactly replicate the auditory experience of cochlear implant users. The word and non-word sets were closed sets (60 and 50 items respectively), though larger than digits, which may still allow some strategic learning.
Declared interests
Research supported by N.I.H. Extramural and Non-U.S. Gov't grants. No other conflicts declared.
The easy way to misread this
Do not assume that a patient's poor performance on word span tasks is solely due to low memory capacity. The study shows that degraded auditory input significantly impacts word span but not digit span, meaning word span scores are confounded by the patient's ability to identify the speech sounds.