Table 2.
Summary of representative studies of degraded speech processing in clinical populations.
| Population | Study, Degradation | Participants | Methodology | Major Findings |
|---|---|---|---|---|
| Traumatic brain injury | Gallun et al. [80]: Central auditory processing | 36 blast-exposed military veterans (age: 32.8); 29 controls (age: 32.1) | Participants went through a battery of standardised behavioural tests of central auditory function: temporal pattern perception, GIN, MLD, DDT, SSW, and QuickSIN. | While no participant performed poorly on all behavioural testing, performance was impaired in central auditory processing for the blast-exposed veterans in comparison to matched-controls. |
| Saunders et al. [81]: Central auditory processing | 99 military veterans (age: 34.1) | Participants went through self-reported measures as well as a battery of standardised behavioural measures: HINT, NA LiSN-S, ATTR, TCST, and SSW. | Participants in this study showed measurable performance deficits on speech-in-noise perception, binaural processing, temporal resolution, and speech segregation. | |
| Gallun et al. [82]: Central auditory processing | 30 blast-exposed military veterans, with a least one blast occurring 10 years prior to study (age: 37.3); 29 controls (age: 39.2) | Participants went through a battery of standardised behavioural tests of central auditory function: GIN, DDT, SSW, FPT, and MLD. | Replicating the findings from Gallun et al., 2012, this study found that the central auditory processing deficits persisted in individuals tested an average of more than 7 years after blast exposure. | |
| Papesh et al. [83]: Central auditory processing | 16 blast-exposed veterans (age 36.9); 13 veteran controls (age 38) with normal peripheral hearing | Participants competed self-reported measures and standardised tests of speech-in-noise perception, DDT, SSW, TCST, plus auditory event-related potential studies. | Impaired cortical sensory gating was primarily influenced by a diagnosis of TBI and reduced habituation by a diagnosis of post-traumatic stress disorder. Cortical sensory gating and habituation to acoustic startle strongly predicted degraded speech perception | |
| Stroke aphasia | Bamiou et al. [84]: Dichotic listening | 8 patients with insular strokes (age: 63); 8 control participants (age: 63) | Participants heard pairs of spoken digits presented simultaneously to each ear, and were asked to repeat all four digits. | Dichotic listening was abnormal in five of the eight stroke patients. |
| Dunton et al. [85]: Accents | 16 participants with aphasia (age: 59); 16 controls (age: 59; English) | Participants heard English sentences spoken with a familiar (South-East British England) or unfamiliar (Nigerian) accent. | Aphasia patients made more errors in comprehending sentences spoken in an unfamiliar accent vs. a familiar accent. | |
| Jacks and Haley [86]: AAF (MAF) | 10 aphasia patients (age: 53.1); 10 controls (age: 63.1; English) | Participants produced spoken sentences with no feedback, DAF, FAF or noise-masked auditory feedback (MAF). | Speech rate increased under MAF but decreased with DAF and FAF in most participants with aphasia. | |
| Parkinson’s disease | Liu et al. [87]: AAF (MAF and FAF) | 12 PD participants (ge: 62.3); 13 control participants (age: 68.7) | Participants sustained a vowel whilst receiving changes in feedback of loudness (±3/4 dB) or pitch (±100 cents). | All participants produced compensatory responses to AAF, but response sizes were larger in PD than controls. |
| Chen et al. [88]: AAF (FAF) | 15 people with PD (age: 61); 15 control participants (age 61; Cantonese) | Participants were asked to vocalize a vowel sound with AAF pitch-shifted upwards or downwards. | PD participants produced larger magnitudes of compensation. | |
| Alzheimer’s disease | Gates et al. [89]: Dichotic digits | 17 ADs (age: 84); 64 MCI (age: 82.3); 232 controls (age: 78.8) | Participants listened to 40 numbers presented in pairs to each ear simultaneously. | AD patients scored the worst in the dichotic digits, followed by the MCI group and then the controls. |
| Golden et al. [90]: Auditory scene analysis | 13 AD participants (age: 66); 17 control participants (age: 68) | In fMRI, participants listened to their own name interleaved with or superimposed on multi-talker babble. | Significantly enhanced activation of right supramarginal gyrus in the AD vs. control group for the cocktail party effect. | |
| Ranasinghe et al. [91]: AAF (FAF) | 19 AD participants; 16 control participants | Participants were asked to produce a spoken vowel in context of AAF, with perturbations of pitch. | AD patients showed enhanced compensatory response and poorer pitch-response persistence vs. controls. | |
| Primary progressive aphasia | Hailstone et al. [92]: Accents | 20 ADs (age: 66.4); 6 nfvPPA (age: 66); 35 controls (age: 65); British English | Accent comprehension and accent recognition was assessed. VBM examined grey matter correlates. | Reduced comprehension for phrases in unfamiliar vs. familiar accents in AD and for words in nfvPPA; in AD group, grey matter associations of accent comprehension and recognition in anterior superior temporal lobe |
| Cope et al. [93]: Noise-vocoding | 11 nfvPPA (age: 72); 11 control participants (age: 72) | During MEG, participants listened to vocoded words presented with written text that matched/mismatched. | People with nfvPPA compared to controls showed delayed resolution of predictions in temporal lobe, enhanced frontal beta power and top-down fronto-temporal connectivity; precision of predictions correlated with beta power across groups | |
| Hardy et al. [94]: SWS | 9 nfvPPA (age: 69.6); 10 svPPA (age: 64.9); 7 lvPPA (age: 66.3); 17 control (age: 67.7) | Participants transcribed SWS of numbers/locations. VBM examined grey matter correlates in combined patient cohort. | Variable task performance groups; all showed spontaneous perceptual learning effects for SWS numbers; grey matter correlates in a distributed left hemisphere network extending beyond classical speech-processing cortices, perceptual learning effect in left inferior parietal cortex |
Information in the Participants column is based on available information from the original papers; age is given as a mean or range and language refers to participants’ native languages. Abbreviations: AAF, altered auditory feedback; AD, Alzheimer’s disease; ATTR, Adaptive Tests of Temporal Resolution; DAF, delayed auditory feedback; dB, decibels; DDT, Dichotic Digits Test; FAF; frequency altered feedback; fMRI, functional magnetic resonance imaging; FPT, Frequency Patterns Tests (FPT); GIN, Gaps-In-Noise test; HINT, Hearing in Noise Test; lvPPA, logopenic variant primary progressive aphasia; MAF, masked/masking auditory feedback; MCI, mild cognitive impairment; MEG, magnetoencephalography; MLD, The Masking Level Difference; NA LiSN-S, North American Listening in Spatialised Noise-Sentence test; nfvPPA, nonfluent primary progressive aphasia; PD, Parkinson’s disease; PR, perceptual restoration; QuickSIN, Quick Speech in Noise; SSW, Staggered Spondaic Words; SWS, sinewave speech; svPPA, semantic variant primary progressive aphasia; TBI, traumatic brain injury; TCST, Time Compressed Speech Test; VBM, voxel based morphometry.