The Relationship between Language Production and Verbal Short-Term Memory: The Role of Stress Grouping

Nonword repetition in adults who stutter: The effects of stimuli stress and auditory-orthographic cues

Purpose

Adults who stutter (AWS) are less accurate in their immediate repetition of novel phonological sequences compared to adults who do not stutter (AWNS). The present study examined whether manipulation of the following two aspects of traditional nonword repetition tasks unmask distinct weaknesses in phonological working memory in AWS: (1) presentation of stimuli with less-frequent stress patterns, and (2) removal of auditory-orthographic cues immediately prior to response.

Method

Fifty-two participants (26 AWS, 26 AWNS) produced 12 bisyllabic nonwords in the presence of corresponding auditory-orthographic cues (i.e., immediate repetition task), and the absence of auditory-orthographic cues (i.e., short-term recall task). Half of each cohort (13 AWS, 13 AWNS) were exposed to the stimuli with high-frequency trochaic stress, and half (13 AWS, 13 AWNS) were exposed to identical stimuli with lower-frequency iambic stress.

Results

No differences in immediate repetition accuracy for trochaic or iambic nonwords were observed for either group. However, AWS were less accurate when recalling iambic nonwords than trochaic nonwords in the absence of auditory-orthographic cues.

Conclusions

Manipulation of two factors which may minimize phonological demand during standard nonword repetition tasks increased the number of errors in AWS compared to AWNS. These findings suggest greater vulnerability in phonological working memory in AWS, even when producing nonwords as short as two syllables.

A matter of emphasis: Linguistic stress habits modulate serial recall

Models of short-term memory for sequential information rely on item-level, feature-based descriptions to account for errors in serial recall. Transposition errors within alternating similar/dissimilar letter sequences derive from interactions between overlapping features. However, in two experiments, we demonstrated that the characteristics of the sequence are what determine the fates of items, rather than the properties ascribed to the items themselves. Performance in alternating sequences is determined by the way that the sequences themselves induce particular prosodic rehearsal patterns, and not by the nature of the items per se. In a serial recall task, the shapes of the canonical “saw-tooth” serial position curves and transposition error probabilities at successive input–output distances were modulated by subvocal rehearsal strategies, despite all item-based parameters being held constant. We replicated this finding using nonalternating lists, thus demonstrating that transpositions are substantially influenced by prosodic features—such as stress—that emerge during subvocal rehearsal.

Language Experience Affects Grouping of Musical Instrument Sounds

Language experience clearly affects the perception of speech, but little is known about whether these differences in perception extend to non-speech sounds. In this study, we investigated rhythmic perception of non-linguistic sounds in speakers of French and German using a grouping task, in which complexity (variability in sounds, presence of pauses) was manipulated. In this task, participants grouped sequences of auditory chimeras formed from musical instruments. These chimeras mimic the complexity of speech without being speech. We found that, while showing the same overall grouping preferences, the German speakers showed stronger biases than the French speakers in grouping complex sequences. Sound variability reduced all participants' biases, resulting in the French group showing no grouping preference for the most variable sequences, though this reduction was attenuated by musical experience. In sum, this study demonstrates that linguistic experience, musical experience, and complexity affect rhythmic grouping of non-linguistic sounds and suggests that experience with acoustic cues in a meaningful context (language or music) is necessary for developing a robust grouping preference that survives acoustic variability.

Metrical Encoding in Adults Who Do and Do Not Stutter

PURPOSE

The purpose of this study was to explore metrical aspects of phonological encoding (i.e., stress and syllable boundary assignment) in adults who do and do not stutter (AWS and AWNS, respectively).

METHOD

Participants monitored nonwords for target sounds during silent phoneme monitoring tasks across two distinct experiments. For Experiment 1, the 22 participants (11 AWNS, 11 AWS) silently monitored target phonemes in nonwords with initial stress. For Experiment 2, an additional cohort of 22 participants (11 AWNS, 11 AWS) silently monitored phonemes in nonwords with noninitial stress.

RESULTS

In Experiment 1, AWNS and AWS silently monitored target phonemes in initial stress stimuli with similar speed and accuracy. In Experiment 2, AWS demonstrated a within-group effect that was not present for AWNS. They required additional time when monitoring phonemes immediately following syllable boundary assignment in stimuli with noninitial stress. There was also a between-groups effect, with AWS exhibiting significantly greater errors identifying phonemes in nonwords with noninitial stress than AWNS.

CONCLUSIONS

Findings suggest metrical properties may affect the time course of phonological encoding in AWS in a manner distinct from AWNS. Specifically, in the absence of initial stress, metrical encoding of the syllable boundary may delay speech planning in AWS and contribute to breakdowns in fluent speech production.