Extrinsic Cognitive Load Impairs Spoken Word Recognition in High- and Low-Predictability Sentences

Abstract

Objectives: Listening effort (LE) induced by speech degradation reduces performance on concurrent cognitive tasks. However, a converse effect of extrinsic cognitive load on recognition of spoken words in sentences has not been shown. The aims of the present study were to (a) examine the impact of extrinsic cognitive load on spoken word recognition in a sentence recognition task and (b) determine whether cognitive load and/or LE needed to understand spectrally degraded speech would differentially affect word recognition in high- and low-predictability sentences. Downstream effects of speech degradation and sentence predictability on the cognitive load task were also examined.

Design: One hundred twenty young adults identified sentence-final spoken words in high- and low-predictability Speech Perception in Noise sentences. Cognitive load consisted of a preload of short (low-load) or long (high-load) sequences of digits, presented visually before each spoken sentence and reported either before or after identification of the sentence-final word. LE was varied by spectrally degrading sentences with four-, six-, or eight-channel noise vocoding. Level of spectral degradation and order of report (digits first or words first) were between-participants variables. Effects of cognitive load, sentence predictability, and speech degradation on accuracy of sentence-final word identification as well as recall of preload digit sequences were examined.

Results: In addition to anticipated main effects of sentence predictability and spectral degradation on word recognition, we found an effect of cognitive load, such that words were identified more accurately under low load than high load. However, load differentially affected word identification in high- and low-predictability sentences depending on the level of sentence degradation. Under severe spectral degradation (four-channel vocoding), the effect of cognitive load on word identification was present for high-predictability sentences but not for low-predictability sentences. Under mild spectral degradation (eight-channel vocoding), the effect of load was present for low-predictability sentences but not for high-predictability sentences. There were also reliable downstream effects of speech degradation and sentence predictability on recall of the preload digit sequences. Long digit sequences were more easily recalled following spoken sentences that were less spectrally degraded. When digits were reported after identification of sentence-final words, short digit sequences were recalled more accurately when the spoken sentences were predictable.

Conclusions: Extrinsic cognitive load can impair recognition of spectrally degraded spoken words in a sentence recognition task. Cognitive load affected word identification in both high- and low-predictability sentences, suggesting that load may impact both context use and lower-level perceptual processes. Consistent with prior work, LE also had downstream effects on memory for visual digit sequences. Results support the proposal that extrinsic cognitive load and LE induced by signal degradation both draw on a central, limited pool of cognitive resources that is used to recognize spoken words in sentences under adverse listening conditions.

Figure 1. Accuracy of sentence-final word recognition

Note. A. Accuracy of sentence-final word recognition as a function of sentence predictability and cognitive load. B. Contextual facilitation effect, i.e., the difference in word recognition accuracy between high- and low-predictability sentences, shown as a function of cognitive load. C. Cognitive load effect, i.e., the difference in word recognition accuracy under high versus low cognitive load, shown as a function of sentence predictability. Separate panels show the spectral degradation conditions: 4 Ch, highly degraded 4-channel vocoding; 6 Ch, moderately degraded 6-channel vocoding; 8 Ch, mildly degraded 8-channel vocoding. Data are collapsed across order of report (words first or digits first). Error bars show plus or minus one standard error (SE) from the mean.

Figure 2. Load cost as a function of accuracy for words

Note. Scatterplots of Load Cost (low load accuracy minus high load accuracy) as a function of word identification accuracy per condition (mean accuracy for high and low load conditions). Top panel, high-predictability (HP) sentences; bottom panel, low-predictability (LP) sentences HP 4ch, highly degraded 4-channel vocoding; 6ch, moderately degraded 6-channel vocoding; 8ch, mildly degraded 8-channel vocoding. Data are collapsed across order of report (words first or digits first). Note that a positive value for “load cost” indicates the expected direction of the difference, with higher accuracy of word identification under low than high load.

Figure 3. Accuracy of digit recall

Note. D/W, digits reported first; W/D, words reported first. Separate panels show the spectral degradation conditions: 4 Ch, highly degraded 4-channel vocoding; 6 Ch, moderately degraded 6-channel vocoding; 8 Ch, mildly degraded 8-channel vocoding. Error bars show plus or minus one standard error (SE) from the mean.