Auditory Behavior, Speech-Language Development & Effects of Hearing Loss Across the Lifespan
Key Takeaways
Infant auditory behavior develops from startle and arousal at birth to head turns toward sound beginning around 3 to 6 months and localization in most directions by about 2 years; infant behavioral results are minimum response levels, not thresholds.
Canonical babbling normally begins between about 6 and 10 months; infants with severe-to-profound hearing loss start much later, so absent canonical babbling by about 10 months is a red flag.
Prelingual hearing loss begins before spoken language is acquired and threatens language development, whereas postlingual loss mainly limits speech access and gradually changes speech production.
Cortical P1 studies show that children who receive cochlear implants before about 3.5 years usually develop age-appropriate central auditory responses, supporting the EHDI 1-3-6 timeline.
In adults, untreated hearing loss is linked to social isolation, depression, reduced earnings, falls, and dementia risk; the 2024 Lancet Commission attributes about 7% of dementia cases to hearing loss.
Auditory Behavior, Speech-Language Development & the Effects of Hearing Loss Across the Lifespan
The Praxis Audiology test expects you to connect hearing to development and daily life: what a typical infant should do at each age, how hearing loss changes speech and language, why age of onset matters, and how hearing loss affects school-age children and adults. This section covers normal auditory behavior over the lifespan, speech and language milestones, prelingual versus postlingual hearing loss, and age-related changes in hearing and balance.
Normal Auditory Behavior From Birth to School Age
The cochlea is structurally formed by mid-gestation, and the fetus responds to sound during the third trimester. A newborn already prefers the mother's voice and the rhythm of the language heard in the womb. Auditory behavior then develops in a predictable order.
| Approximate Age | Typical Auditory Behavior |
|---|---|
| Birth to 3 months | Startles (Moro reflex), eye widening, stilling, or arousal to loud sounds; calms to a familiar voice |
| 3 to 6 months | Begins turning the eyes and head toward a sound source; responds to changes in voice tone |
| 6 to 12 months | Localizes sound to the side, then downward; responds to own name; understands a few common words |
| 12 to 24 months | Localizes sound in most directions; follows simple directions; points to familiar objects when named |
| 2 to 5 years | Listens to stories, follows multi-step directions, and develops speech-in-noise and binaural skills that keep maturing into adolescence |
Two points are frequently tested:
- Infant responses are not adult thresholds. Young infants respond at higher levels than older children, so behavioral results are reported as minimum response levels. Behavioral observation audiometry describes responsiveness but cannot reliably estimate thresholds, which is why physiologic tests (ABR, OAEs) are used for young infants.
- Auditory skills build in a hierarchy. Erber's model describes four levels: detection (is a sound present?), discrimination (same or different?), identification (what is it?), and comprehension (what does it mean?). Auditory training programs follow the same order.
Some auditory abilities mature slowly. Temporal resolution, frequency selectivity, binaural hearing, and especially speech understanding in noise continue to improve through childhood, which is one reason children need a better signal-to-noise ratio than adults to understand speech in a classroom.
Speech and Language Milestones
| Approximate Age | Speech and Language Milestone |
|---|---|
| 0 to 3 months | Cooing and comfort sounds |
| 4 to 6 months | Vocal play, squeals, and early babbling |
| 6 to 10 months | Canonical babbling (well-formed consonant-vowel syllables such as "baba") |
| About 12 months | First words; uses gestures such as pointing and waving |
| 18 to 24 months | Vocabulary grows rapidly; two-word combinations appear |
| 3 years | Short sentences; familiar listeners understand most speech |
| 4 years | Unfamiliar listeners understand most speech |
Canonical babbling is a key marker. Hearing infants typically begin canonical babbling between about 6 and 10 months. In Oller and Eilers' classic study, infants with severe-to-profound hearing loss started much later (roughly 11 to 25 months), so the absence of canonical babbling by about 10 months is a red flag for hearing loss or another developmental disorder.
Why Age of Onset and Age of Intervention Matter
Prelingual Versus Postlingual Hearing Loss
- Prelingual hearing loss begins before spoken language is acquired (congenital or very early onset). Without early access to sound or to a visual language, the child misses the period when the brain most readily learns language.
- Postlingual hearing loss begins after spoken language is established. The person already has a language system, so the main problems are access to speech and gradual changes in speech production.
Sensitive Periods for Auditory Development
Central auditory pathways need auditory input to develop normally. Cortical auditory evoked potential studies (P1 latency) of children with cochlear implants show the clearest pattern: children implanted before about 3.5 years usually develop age-appropriate P1 latencies, while those implanted after about 7 years often do not. This evidence supports the EHDI 1-3-6 goals (screening by 1 month, diagnosis by 3 months, intervention by 6 months), and children identified and served by 6 months show better language outcomes on average.
Typical Speech Characteristics
- Prelingual severe-to-profound loss without early access: reduced intelligibility, omission of high-frequency consonants such as /s/, neutralized vowels, abnormal nasality, slow rate, and atypical pitch, loudness, and prosody.
- Postlingual loss in adults: speech stays intelligible, but over time loudness control, pitch, and the precision of high-frequency sounds such as /s/ and /ʃ/ can deteriorate because auditory feedback is reduced.
These differences also predict cochlear implant outcomes: postlingually deafened adults and children implanted early usually achieve better open-set speech recognition than adolescents or adults with long-standing prelingual deafness who are implanted late.
Effects of Hearing Loss on Children's Learning
Even mild, minimal, or unilateral hearing loss can affect a child's development:
- Vocabulary and grammar: Reduced high-frequency audibility makes soft morphemes hard to hear (plural -s, possessive -'s, past tense -ed), which delays grammatical development.
- Incidental learning: Children with hearing loss miss overheard conversation, which normally supplies much of a child's vocabulary and social knowledge.
- Academics and reading: Delays in language feed into reading and academic achievement. Classic studies found that roughly one-third of children with unilateral or minimal sensorineural hearing loss had repeated a grade or needed educational support.
- Listening effort and fatigue: Children work harder to listen in noisy classrooms and can tire faster, which affects attention and behavior.
- Psychosocial effects: Difficulty following group conversation can lead to isolation, lower self-esteem, and peer problems.
Effects of Hearing Loss in Adults
- Communication and relationships: Difficulty in noise, group conversation, and phone use strains relationships with family and coworkers.
- Social isolation, loneliness, and depression: Untreated hearing loss is associated with withdrawal from social activities and higher rates of depressive symptoms.
- Work: Hearing loss is associated with lower income, underemployment, and greater fatigue at work.
- Cognition: The 2024 Lancet Commission identified midlife hearing loss as one of the largest potentially modifiable risk factors for dementia (about 7% of cases). In the ACHIEVE randomized trial (2023), hearing intervention did not slow 3-year cognitive decline in the overall group, but it slowed decline by about 48% in older adults at higher risk for dementia.
- Safety: Hearing loss is associated with a higher risk of falls and reduced awareness of warning signals.
Age-Related Changes in the Auditory and Vestibular Systems
- Peripheral hearing: Age-related hearing loss (presbycusis) is typically bilateral, symmetric, and high-frequency. Schuknecht's classic types are sensory (hair cell loss), neural (spiral ganglion loss with poor word recognition), strial or metabolic (flat loss with good word recognition), and cochlear conductive (gradually sloping loss).
- Central processing: Older adults often have poorer temporal processing (gap detection, rapid speech), reduced binaural benefit, and more difficulty in noise than the audiogram predicts.
- Vestibular system: Hair cells and vestibular ganglion neurons decline with age, and the vestibulo-ocular reflex can weaken. The Bárány Society's presbyvestibulopathy criteria describe adults aged 60 or older with chronic imbalance, gait disturbance, dizziness, or recurrent falls for at least 3 months and mildly reduced bilateral vestibular function (for example, bilateral video head impulse gain between 0.6 and 0.8).
Parents of a 10-month-old with normal newborn hearing screening results report that their child coos and squeals but has never produced repeated consonant-vowel syllables such as "baba" or "dada." Which response is most appropriate?
Reassure the parents, because canonical babbling usually does not begin until about 18 months of age.
Recommend a diagnostic audiologic evaluation, because absent canonical babbling at 10 months is a red flag despite a passed screen.
Recommend waiting for the 12-month well-child visit, because a passed newborn screen rules out permanent childhood hearing loss.
Refer only to speech-language pathology, because babbling depends on oral-motor skill rather than hearing.
Two adults are evaluated for cochlear implants. Patient 1 lost hearing suddenly at age 45 after decades of normal hearing. Patient 2 has had profound hearing loss since birth, used little amplification, and communicates mainly in sign language. Which statement best predicts their outcomes?
Both will have equivalent open-set speech recognition, because implant outcomes depend only on electrode position.
Patient 2 will likely do better, because the auditory cortex of prelingually deaf adults has been preserved by its long lack of use.
Neither is a candidate, because adults with profound hearing loss are not eligible for cochlear implants.
Patient 1 will likely achieve better open-set speech recognition, because postlingual deafness leaves spoken language intact.
A first-grade teacher asks why a student with a mild high-frequency sensorineural hearing loss makes grammar errors such as omitting plural and past-tense endings. Which explanation is most accurate?
Mild hearing loss affects only loudness, so grammar errors indicate a separate language disorder.
High-frequency loss mainly affects vowels, which carry most grammatical information.
Endings such as plural /s/ and past-tense /t/ are soft, high-frequency sounds, so reduced audibility delays learning them.
Grammar errors appear only when hearing loss exceeds 70 dB HL, the level at which most conversational speech becomes inaudible.
Sections you finish are checked off in the contents.