Sentence-Level Intonation in Acquired and Developmental Language Disorders: Acoustic and Hemispheric Perspectives

Cite this article as: Esan, B. O. (2026). Sentence-level intonation in acquired and developmental language disorders: Acoustic and hemispheric perspectives. Sokoto Journal of Linguistics and Communication Studies (SOJOLICS), 2(1), 507-520. https://doi.org/10.36349/sojolics.2026.v02i01.042

By

Bunmi Oluwaseun Esan
Department of Linguistics and Languages
Federal University Oye Ekiti
bunmi.esan@fuoye.edu.ng

Abstract

This study contrasts sentence-level intonation in Acquired Language Disorder (ALD) and Developmental Language Disorder (DLD) with a view to providing insight into differential hemispheric involvement and lateralisation patterns using Hemispheric Specialisation Theory. Intonation tune assignment and fundamental frequency (F0) realisation using SFS version 1.51 were analysed across declarative sentences, wh-questions, declarative-form statements, polar questions, and reanalysed interrogative sentences. Participants comprised 18 people with ALD and 17 people with DLD from two tertiary health facilities, one rehabilitation centre and two government special schools in Ekiti State, Nigeria who completed a set of perception and production tasks targeting sentence-level intonation. The findings reveal a clear contrast between the groups. ALDparticipants exhibited relatively higher accuracy in selecting intonation patterns, particularly falling contours for declaratives and wh-question, and rising contour for polar questions. In contrast, DLDparticipants demonstrated prevalent reliance on level and obscure tunes with marked deficits in interrogative and pragmatically marked sentence types. Acoustic analyses further specified wide and differentiated F0 ranges in ALD, whereas DLD was characterised by compacted pitch ranges for falling contours and inflated terminal rises for rising contours. The results suggest that ALD involves disordered but patterns consistent with partial preservation of NE prosodic features arising from neurological injury, while DLD exhibits impairment beyondNE prosodic features. The study found that prosodic processing is differently impaired in the groups. It recommends the inclusion of control groups in further studies.

Keywords: Prosody; Language impairment;Hemispheric specialisation; Prosodic lateralisation; Fundamental frequency (F0)

1. Introduction

Intonation refers to systematic variations in pitch across an utterance that signals grammatical structure, sentence modality, and communicative intent (Arvaniti, et al., 2025; Ladd, 2008). From a neurolinguistic perspective, sentence-level intonation requires the integration of pitch modulation, temporal sequencing and syntactic mapping across extended stretches of speech (Chien, et al., 2021; Pouw, et al., 2025). It constitutes a core neurolinguistic function through which the brain encodes sentence modality, grammatical structure, and communicative intent via systematic modulation of fundamental frequency (F0). Unlike segmental phonology, intonation requires the dynamic integration of pitch movement, linking acoustic realisation to syntactic and pragmatic interpretation of utterances (Ladd, 2008). Neurocognitive models of speech processing therefore regard intonation as a higher-order prosodic computation that emerges from coordinated activity across distributed cortical networks. Disruption of these networks has been shown to be associated with communicative impairment, even when segmental production remains relatively intact, underscoring the importance of intonation as a sensitive neurolinguisticmarker (Cokluk&Butur,2025).

A substantial body of neurolinguistic and neuropsychological research demonstrates that the processing of sentence-level intonation is subject to hemispheric specialisation. While the left hemispherepredominantly supports segmental phonology, lexical access, and syntactic computation, the right hemisphere plays a central role in pitch contour formation, pitch range modulation, and the integration of prosodic information across the utterance (Friederici& Alter, 2004; Geschwind, 1970; Ross, 1981). Damage to right-hemisphere networks is frequently associated with aprosodic speech characterised by reduced pitch variation, inappropriate contour selection, and impaired pragmatic interpretation, whereas bilateral interaction is required for the alignment of linguistic form and prosodic function (Ross &Monnot, 2008).

Acquired language disorder (ALD) and developmental language disorder (DLD) provide contrasting neurolinguistic conditions for examining the role of hemispheric specialisation in sentence-level intonation. In ALD, prosodic impairment reflects the disruption of previously established neural systems due to brain injury, often allowing for partial preservation or reorganisation of hemisphericallyestablised functions. In contrast, DLD is associated with atypical neurodevelopment, in which the formation and lateralisation of prosodic networks may be incomplete or inefficient from early stages. Despite this fundamental distinction, direct neurolinguistic comparisons of sentence-level intonation in ALD and DLD remain scarceparticularly those integrating perceptual and acoustic evidence. Addressing this gap, the present study contrasts intonation tune assignment and F0 realisation in individuals with ALD and DLD.

1.1 Nigerian English Prosody

Nigerian English (NE) is produced in a multilingual environment dominated by indigenous languages that are predominantly tonal(Bamgbose, 1995). In tonal languages such as Yoruba and Igbo, pitch variation functions lexically, distinguishing meaning at the word or morpheme level, whereas in English, pitch is primarily deployed at the sentence level to show grammatical and pragmatic contrasts. This difference has important implications for prosodic representation and processing in second-language English speakers (Udofot, 2022; Ufomata, 2004). Consequently, NE prosody reflects systematic deviations from canonical British English intonation patterns, not as random performance errors but as stable outcomes of language contact and prosodic transfer.

Empirical studies of NE intonation consistently report a predominance of falling contours across sentence types, high pitch realisation on lexical items, limited use of complex nuclear tones such as fall-rise contours (Gut, 2001;Jowitt, 1991, 2000, 2007;Melefa, 2021; Ngor, 2024; Udofot, 2022), deficiency in the employment of attitudinal function of intonation (Akindele&Oladipupo, 2022) and poor performance in assigning intonation tunes to sentences (Ekeruke, 2024). Rising contours in polar and tag questions are attested but occur with lower frequency and reduced pitch excursion relative to Standard British English. These patterns suggest a prosodic system in which pitch is distributed more evenly across syllables rather than being hierarchically organised around a nuclear accent (Essien&Udo, 2023; Udofot, 2022). From a neurolinguistic perspective, this has been interpreted as evidence that pitch in NE is processed with greater lexical prominence, reflecting the influence of tonal first languages on prosodic encoding strategies.

Speakers who acquire English in a tonal linguistic environment may develop prosodic representations in which pitch is less tightly joined with sentence-level grammatical structure. When such speakers experience neurological injury or atypical neurodevelopment, existing prosodic representations may distinctly interact with neural disruption. Incorporating NE prosody as a contextual variable therefore allows for a better interpretation of sentence-level intonation impairment.

2. Literature Review

Previous investigations into language disorders in Nigeria have predominantly examined phonological impairments at the segmental and syllable levels in both acquired and developmental conditions. These studies have documented recurrent phenomena such as consonant cluster reduction, segment deletion, vowel modification, epenthesis, and syllable restructuring in individuals with aphasia, autism spectrum disorder, and related developmental impairments (Abe, 2024; Agbedo, 2008; Esan, 2017, 2019, 2024; Ojo, 2013; Salami, 2005; Salami, 2008; Sunday, 2008, 2010, 2013; Yul-Ifode, 2004). While these findings are often described in phonological terms, they implicitly point to disruptions in underlying speech planning and encoding mechanisms, processes that are typically associated with the left-hemisphere language networks.

From a neurolinguistic perspective, the observed phonological patterns in Nigerian clinical populations have been interpreted as reflecting impairments in the formulation and execution stages of speech production. For instance, consistent reduction of complex onsets and preference for less sonorous segments have been linked to reduced articulatory planning capacity and increased motoric constraint following neurological insult (Sunday &Esan, 2018). Similarly, patterns of substitution and epenthesis in developmental conditions have been associated with atypical phonological representation and delayed maturation of linguistic processing systems (Esan, 2017). These interpretations situate Nigerian phonological disorder research within broader neurolinguistic models of language production, even where explicit neural theorisation has been limited.

Notably, however, the focus of these studies has been on lower-level phonological units, with minimal attention to suprasegmental organisation and virtually no systematic investigation of sentence-level prosody. Where suprasegmental features have been mentioned, they are often treated impressionistically or described as relatively preserved, without acoustic verification or theoretical analysis with hemispheric specialisation (Sunday, 2010). As a result, little is known about how prosodic features,particularly intonation, are affected in Nigerian speakers with language disorders.

This gap is especially significant given that the absence of neurolinguistically grounded studies on intonation in Nigerian clinical populations limits our understanding of how acquired versus developmental disruptions manifest prosodically. By extending the focus beyond segmental phonology to sentence-level intonation, the present study addresses this gap and situates Nigerian language disorder research within contemporary neurolinguistic debates on hemispheric specialisation and prosodic processing.

3. Theoretical Framework

This study draws on Hemispheric Specialisation Theory, often associated with Paul Broca and Roger Sperry, for analysis. Thetheoryproposes that the two cerebral hemispheres, the right and the left, have different involvement in language processing. Each performs distinct linguistic functions. The left hemisphere is associated with segmental phonology, syntactic and lexical processing, while the suprasegmental aspects of speech, comprising intonation, rhythm, stress, pitch and affective prosody are frequently associated with right hemisphere networks(Friederici& Alter, 2004; Geschwind, 1970; Heilman,et al., 1975; Ross, 1981; Ross &Monnot, 2008), although contemporary models recognise substantial bilateral involvement (Patel, et al. 2018).

The impairment to the right hemisphere manifests in monotonic speech, inappropriate pitch variation, and difficulty in interpreting pragmatic intention communicated through intonation. On the other hand, damage to the left-hemisphere is associated with aphasic symptoms which affect grammatical and lexical processing. Intonationencompasses bilateral processing where left-hemisphere relates to rule-based intonation patterns and right-hemisphere relates to pitch modulation and contour shape (Friederici& Alter, 2004).

Thistheory suggests that individual with acquired language disorder experience interruption of previously established neural systems, although with a reduced retention of the knowledge of appropriate intonation patterns depending on the extent and location of damage. In contrast, atypical hemispheric specialization may occur during neurodevelopment in individuals with developmental language disorders. This may result in inefficient formation of prosodic systems even in the absence of brain injury. The theory provides a detailed justification for how intonation is represented, processed, and disrupted in individuals with acquired language disorder (ALD) and developmental language disorder (DLD).

4. Methodology

The study adopted a qualitative-dominant descriptive design with quantitative support, accompanied by acoustic measurements, to examine sentence-level intonation in individuals with acquired language disorder (ALD) and developmental language disorder (DLD). The population of the study includedeighteen participants with acquired language disorder (ALD) and seventeen participants with developmental language disorder (DLD)whose reading abilities were not severely compromised. They were recruited from two tertiary hospitals, one rehabilitation centre, and two government special schools in Ekiti State, Nigeria. Purposive sampling was employed. Ethical approval for the study was obtained from the Ethics and Research Committees of Ekiti State Teaching Hospital, Ado Ekiti, Federal Teaching Hospital, IdoEkiti and Ekiti State Ministry of Education. All the participants, or their guardians, were informed of the purpose of the study and guaranteed confidentiality and anonymity. Participation was voluntary, and all ethical guidelines governing research with clinical populations were strictly observed.

The speech material consisted of short and simplesentences, making them accessible to participants with developmental language disorder. The material targeteddeclarative sentence, wh-question,polar question, and reanalysed interrogative sentence. All utterances were audio-recorded with a digital recorder. Data analysis combined perceptual analysiswith acoustic analysis using Speech Filing System (SFS) version 1.51. Contours were classified as falling, rising, fall-rise, rise-fall, level or indeterminate (here termed ‘obscure’) according to observable F0 direction and perceptible pitch excursion. Frequency counts and percentage distributions were calculated for each tune type across sentence categories and clinical groups.

5. Data Presentation and Analysis

This study examined sentence-level intonation abilities in individuals with ALD and DLD using Hemispheric Specialisation Theory. The data for the study is presented below in Table 1showing thedifferences in the pattern of intonation tune assignment between the two groups.

Table 1 Distribution of intonation tunes across sentence types in ALD and DLD

Tune type	Group	Declarative sentences	Wh-question	Declarative-form statement	Polar Question	Reanalysed interrogative Sentence
Falling	ALD	12 (66.7)	14 (77.8)	12 (66.7)	1 (5.6)	10 (55.5)
	DLD	10 (58.8)	1 (5.9)	12 (70.6)	7 (41.2)	7 (41.2)
Rising	ALD	-	-	-	12 (66.6)	1 (5.6)
	DLD	-	-	-	1 (5.9)	1 (5.9)
Fall-rise	ALD	4 (22.2)	-	-	-	-
	DLD	-	-	-	-	-
Level	ALD	1 (5.6)	1 (5.6)	5 (27.7)	3 (16.6)	5 (27.7)
	DLD	6 (35.3)	-	4 (23.5)	8 (47)	6 (35.3)
Rise-fall	ALD	-	-	-	1 (5.6)	1 (5.6)
	DLD	-	-	-	-	-
Obscure	ALD	1 (5.6)	3 (16.6)	1 (5.6)	1 (5.6)	1 (5.6)
	DLD	1 (5.9)	16 (94.1)	1 (5.9)	1 (5.9)	3 (17.6)

 

5.1. Sentence types with expected falling contours

Conventionally, declarative sentences, and wh-questions attract falling tunes. The patterns of the distribution of the various realisations for these sentence types are hereby discussed.

5.1.1. Declarative sentences

As evident in Table 1, both groups demonstrated a preference for the canonical falling tune for simple statements and declarative-form statements. Appropriate tune assignment was recordedin 66.7% of cases for the ALD group, and 58.8% for the DLD group. However, DLD participants relied heavily on level tune (35.3%) compared with the ALD group. This is captured in Fig. 1 and Fig. 2 below:

Fig. 1. ALD: Spectrogram of declarative sentence with falling tune

Fig. 2DLD: Spectrogram of declarative sentence with falling tune

Acoustically, as shown in Fig. 1, falling tune in declarative sentences is characterised by a downward F0 glide from a relatively high onset to a lower terminal pitch. In both declarative sentence and declarative-form statement, the ALD group demonstrated clearer realisation of this pattern, with F0 glides such as 199Hz to 170Hzand 207Hz to 174Hz, respectively.The contours show sufficient pitch excursion and directional clarity, which characterise acoustically well-formed falling tunes. In contrast, the DLD group, as shown in Fig. 2, displayed lower overall pitch registers and compressed F0 ranges, as evident in glides such as from 125Hz to 102Hz and from 125Hz to 113Hz suggesting that the contours are likely perceived as level or indeterminate rather than clearly falling. This explains the higher frequency of level and obscure tunes in the DLD group, even when the intention was falling tune.

5.1.2 Wh-questions

Wh-questions usually attract falling tune. The ALD group largely adhered to this pattern by correctly assigning the falling tunes in 77.8% instances of production, while the DLD group achieved this in only 5.9% with 94.1% of their productions classified as obscure.

Fig. 3.ALD: Spectrogram of wh-questionwith falling tune

Fig.4.DLD: Spectrogram of wh-question with falling tune

As shown in Fig. 3, the ALD group produced acoustically robust falling contours with a glide from an F₀ of 123H_Z to 61H_Zrepresenting a large pitch drop that enhances contour perceptibility. By contrast, as shown in Fig. 4, the DLD group showed a markedly shallow descent in wh-questions from an F₀ of 118H_Z to 110H_Z. Acoustically, such minimal pitch movement is not sufficient to signal a reliable falling contour, resulting in contours perceived as obscure or indeterminate. This explains the overwhelming dominance of obscure tune classifications in the DLD group for wh-questions.

5.2 Sentence types with expected rising contours

Polar questions and reanalysed interrogative sentence are expected to be assigned rising intonation. The realisation or otherwise of this tune is examined in this section.

5.2.1 Polar questions

Polar questions usually have the rising tune, a contour that involves controlled pitch elevation towards utterance-final position. This tune was appropriately assigned in 66.6% of casesby ALD participants, clearly outperforming DLD participants who did so in only 5.9%. As shown in Table 1, the number of respondents with inappropriate tune assignment is inconsequential compared to the number of those who gave appropriate tune assignment.DLD productions were dominated by level (47%) and falling (41.2%) contours. The ALD group demonstrated a high frequency of appropriate rising tunes. The spectrograms representing the assignment of rising tune on polar question are given below in Fig.5 andFig. 6:

Fig. 5.ALD: Spectrogram of polar question with rising tune

 

Fig. 6.DLD: Spectrogram of polar questionwith rising tune

Acoustically, rising intonation in polar questions is defined by a progressive upward F₀ movement toward utterance-final position. In the ALD group, appropriate rising tunes were realised with moderate pitch elevation from an F₀ of 120Hz to 168Hz as shown in Fig. 5. For DLD participants, although the F0 range for appropriate rising placements was larger from 120Hz to 198Hzas shown in Fig. 6, correct rising tunes were rare.

5.2.2 Reanalysed interrogative sentence

The reanalysed interrogative sentence,which uses a question mark to signal interrogative force, place greater demands on prosodic reanalysis, as intonation must override declarative syntactic structure to convey interrogative meaning. Both groups performed poorly on this sentence type, especially with low rates of appropriate rising tunes. As shown in Table 1, ALD participants produced reduced but patterned performance, with falling tunes accounting for 55.5%, rising tunes for 5.6%, level tunes for 27.7% and obscure for 5.6%. DLD participants distributed productions across falling (41.2%), level (35.3%), rising (5.9%), and obscure (17.6%) tunes.

Fig. 7.ALD: Spectrogram of reanalysedinterrogative sentence with rising tune

Fig. 8.DLD: Spectrogram of reanalysed interrogative sentencewith rising tune

In the ALD group, rising contours from an F₀ of 172Hz to 203Hzas presented in Fig. 7were present but infrequent, while many productions retained falling or level contours. In the DLD group, the acoustic data of rising contour from 121Hz to 251Hz as shown in Fig. 8. revealed extreme pitch elevation in appropriate placements. This exaggerated F0 rise did not translate into higher perceptual accuracy of rising intonation.This pattern indicates that greater pitch height does not guarantee correct intonation.

6. Discussion of Findings

The findings of the study showed variation in the intonation abilities of the two groups. This supports the assumptions of Hemispheric Specialisation Theory as regards the role of the right hemisphere in prosodic processing. Generally, ALD participants had stronger control of canonical intonation patterns than the DLD participants. This pattern is consistent with accounts that attribute pitch contour processing to right-hemisphere networks. This is possibly supported by established lateralisation prior to neurological injury. The increased manifestation of level, fall-rise and obscure contours in both groups is a reflection of disturbance in the neural systems accounting for encoding terminal pitch movement. In ALD, these deviations are consistent with damage to the right hemisphere or impaired interhemispheric harmonisation affecting prosody. In contrast, the comparatively lesser frequency of appropriate falling tunes reflects atypical or incomplete hemispheric specialisation for prosody, significantly resulting in reduced regularity in plotting sentence type to intonation contour. The acoustic analysis renders strong support to this interpretation. Clearer pitch direction and wider pitch excursion were observed in ALD participants. However, compressed F0 ranges weakening the perception of falling tunes were observed in DLD participants.

In wh-questions, the contrast was markedly stronger.Neurolinguistically, the findings suggest that the observed pattern is consistent with stronger functional control of pitch modulation in the ALD group than in the DLD group. This is evident in the acoustic data. In DLD, the near absence of appropriate falling tunes in wh-questions may be compatible with accounts proposing delayed or atypical lateralisation of prosodic functions. This results in difficulty in assigning linguistic intonation patterns. Within Hemispheric Specialisation Theory, such patterns could be interpreted as reflecting incomplete or inefficient development of lateralised prosodic systems.

For polar questions, the ALD group demonstrated a high frequency of appropriate rising tunes. This pattern is compatible with partial preservation of pitch-rising mechanisms often associated with right-hemisphere processing. The occasional production of falling or level contours suggests residual impairment in prosodic control rather than a complete loss of lateralised function. However, the DLD group employed level and falling tunes. This pattern is consistent with underdeveloped or inefficient right-hemisphere systems for encoding interrogative prosody. There was a noticeable dissociation between pitch height and tune appropriateness. This suggests that while DLD speakers are capable of producing large pitch increases, the increases are not consistently aligned with sentence-level intonation structure.

The findings for reanalysed interrogative sentences showed an imposition of increased pragmatic and prosodic demands on both groups.Although it was difficult for the participants to reinterpret the sentences as questions, the difficulty was prominent in the DLD group who mainly employed the falling and level tunes.Thesefindingsshow either the disruption of right-hemisphere networks in ALD or their underdevelopment in DLD.

From the foregoing, the findings show both overlap and dissociation between Nigerian English intonation patterns and the patterns observed in the performance of the participants. However, the relationship is not equal between the two groups. While the ALD group showed greater preservation of Nigerian English prosodic norms, the DLD deviated from it. Patterns such as predominance of falling tune across sentence types, reduction in the use of rising tunes in polar questions,limited use of complex nuclear tunes and instability in tune assignmentobserved in ALD correlate with the established descriptions of NE intonation (Akindele&Oladipupo, 2022; Ekeruke, 2024; Gut, 2001; Jowitt, 1991, 2000, 2007;Melefa, 2021; Ngor, 2024; Udofot, 2022).In contrast, the patterns observed in the DLD group such as the predominance of obscure tunes in wh-questions, the exaggeration of inappropriate pitch ranges and the poor assignment of canonical tunes stretched beyond NE variation. These patterns suggest impairment beyond NE influence.

7. Conclusion

This study investigated sentence-level intonation in individuals with acquired and developmental language disorders using Hemispheric Specialisation Theory. Both groups exhibited difficulty in the assignment of proper intonation tunes, with severity in the DLD group. Although some of the observed patterns are consistent with NE intonation patterns, the predominance of obscure tunes and inconsistent tune assignment were the additional abnormalities observed in the DLD group. The study establishes that prosodic processing is differently affected in the groups. It recommends that future studies should employ typical Nigerian English speakers as control groups and spontaneous speech data in order to differentiate between the features of language disorders and normal NE prosodic features.

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