Communication under sharply degraded auditory input and the “2-sentence” problem

Abstract

ABSTRACTIntroductionMany cochlear implant (CI) users who do quite well in standard clinical tests of speech perception report that a great amount of effort is required when listening in real-world situations. We hypothesize that the combined constraints of the sharply degraded signal provided by a CI and finite cognitive resources may lead to a “tipping point” when listeners are confronted with speech material that is more complex than the single words or single sentences that are used in clinical tests. Beyond this tipping point, communication may become too difficult, even for CI users whose standard speech intelligibility scores are above average.MethodsHere, we investigate whether speech identification performance and processing effort (indexed by pupil dilation measures) are affected when CI users or normal hearing control subjects are asked to repeat two sentences presented sequentially instead of just one sentence.ResultsResponse accuracy was minimally affected in normal hearing listeners, but CI users showed a wide range of outcomes, from no change to decrements of up to 45 percentage points. The amount of decrement was not predictable from the CI users’ performance in standard clinical tests. Pupillometry measures tracked closely with effort in both the CI group and the normal hearing group, even though the latter had speech perception scores near ceiling levels for all conditions.DiscussionA communicative tipping point may be reached in many (but not all) CI users in response to input that is only minimally more challenging than standard clinical tests; specifically, when two sentences are presented sequentially before requesting a response, instead of presenting just a single sentence at a time. This potential “2-Sentence Problem” represents one of the simplest possible scenarios that go beyond presentation of a single word or sentence, and it raises the possibility that even good performers in clinical tests of speech perception may be brought beyond the tipping point by other ecologically relevant manipulations. The present findings also raise the possibility that a clinical version of a 2-sentence test may provide actionable information for counseling and rehabilitating CI users.