A new study finds that deaf people fluent in both American Sign Language and written English show different memory strengths depending on which language is used for testing, with surprising asymmetries between learning and forgetting that have implications for neuropsychological assessment and clinical practice.

When neuropsychologists test memory, they typically use a single language. This makes practical sense: use the patient's dominant language, measure memory once, done. But what if someone is genuinely bilingual, fluent in two languages in different modalities? For deaf people, that reality is common. Many are fluent in American Sign Language (ASL) at home and in the deaf community, and in written English for school, work, and formal settings. When assessing their memory, which language should clinicians use? A new study suggests the answer is both.

The findings reveal an unexpected pattern: deaf bilinguals' memory strengths depend less on language dominance than on how a particular language interacts with learning, retention, and forgetting. Testing in only one language misses half the picture and could underestimate or overestimate a person's true cognitive ability.

Background: Why the Researchers Looked at This

Neuropsychological testing relies heavily on standardized assessments administered in a single language. Most people have a dominant language where they acquired literacy and formal education. For deaf people, however, the picture is more complex. ASL is often the primary language for early social development and emotional expression, while written English is the language of school, work, and formal systems. Both are equally "real" languages, but they differ fundamentally: one is signed and accessible from birth; the other is written and requires learning alphabetic literacy.

When deaf individuals undergo neuropyschological evaluation, clinicians face a choice. Test them in ASL (using sign-language stimuli), or in written English (using text). The assumption is usually that testing in the person's self-reported dominant language is sufficient. But this study asked a different question: do deaf bilinguals show equal memory performance in both languages, or does language choice affect how much we learn about their true cognitive ability?

How the Study Was Done

Researchers recruited 32 younger deaf adults (ages 20-45) and 32 older deaf adults (ages 64-84), all fluent in both ASL and written English. Participants completed a standardized word-list memory task, like tests used clinically to detect memory impairment. But here is the key: each person took the test twice, once in each language. In one session, they viewed videos of 10 ASL signs presented one at a time and had to recall them. In another session, they saw 10 written English words on a screen and recalled those. They did three learning trials followed by a delayed recall trial.

The order of testing languages was counterbalanced so that half the participants did ASL first and half did English first. This allowed the researchers to measure not only performance in each language, but also how fatigue or practice effects from one language affected performance in the other.

What the Researchers Found

Younger deaf adults showed no significant difference in recall between the two languages. They learned and retained lists equally well whether items were presented in ASL or written English. This suggests that for younger, cognitively healthy deaf people, language choice does not much matter. However, older adults showed a different pattern. When tested in written English, older deaf adults showed better learning (they recalled more items on successive trials) compared to when tested in ASL. Yet when it came to retention, the opposite was true: they forgot more items between the final learning trial and the delayed recall when tested in English, but retained items better when tested in ASL. This is a striking dissociation: English maximized what they could learn initially, but ASL minimized what they forgot later.

p style="font-family:Arial,sans-serif;font-size:16px;line-height:1.7;color:#2c2e2f;margin:0 0 16px">Interestingly, neither language related to self-reported dominance. Most deaf participants reported being more proficient in ASL, yey nearly half recalled more English items than ASL items, and an equal number recalled more ASL items than English. This suggests that subjective sense of language dominance and actual memory performance for list-learned items are somewhat independent. Both younger and older participants forgot more items in whichever language was tested second, implying that fatigue or reduced attention affects encoding of the second list.

The findings highlight an important neuropyschological principle: a complete picture of memory requires testing in both languages for deaf bilinguals. Using English alone would overestimate learning ability but underestimate retention; using ASL alone would show the opposite pattern. Clinicians relying on single-language testing could miss cognitive changes or misinterpret results in older deaf patients.

What It Means for People With Hearing Loss

These findings have immediate clinical relevance. Deaf adults who seek neuropyschological evaluation for cognitive concerns, age-related decline, or suspected dementia deserve assessment that reflects their full linguistic competence. If a clinician tests only in English and concludes that an older deaf person has memory problems based on poor delayed recall, they might not realize the person would perform better if the same test were given in ASL. Conversely, testing only in ASL might not capture encoding or learning strength. The research affirms that deaf people are not "monolingual in sign"—they are genuinely bilingual, and their bilingualism shapes cognition in subtle but measurable ways.

The age effect is also notable. Younger deaf adults showed robust memory in both languages, suggesting cognitive reserve is strong before age 65. Older deaf adults showed more language-specific variability, suggesting that aging may differentially affect processing in the signed versus written modality. This has implications for healthcare planning: as the deaf population ages, standard neuropsychological protocols may need revision to include bilingual assessment, particularly for high-stakes decisions like dementia diagnosis.

Supporting Deaf Adults Through Language-Specific Assessment

This study's findings align with a broader shift in healthcare toward recognizing and supporting the linguistic needs of deaf communities. Clinics and diagnostic services that serve deaf adults are increasingly using interpreters and ASL-fluent clinicians to conduct assessments in sign, recognizing that accurate evaluation requires testing in a language the patient truly understands. The dual-language finding strengthens the case for comprehensive bilingual assessment protocols.

For deaf individuals themselves, the research confirms what many already know: there is no single "dominant" language in a bilingual brain. Both ASL and English are part of their cognitive identity. When seeking evaluation or diagnosis, requesting that clinicians test in both languages, or at least use ASL alongside written English, ensures that results reflect true memory and cognitive function rather than the limitations of testing in just one modality. Hearing aids and hearing-aid-like solutions are not relevant here, but access to qualified ASL interpreters and clinicians is essential for appropriate diagnosis and care.

Limitations of This Research

The study used a single memory task (free recall of word and sign lists), which is a narrow slice of memory function. Real-world memory involves different processes, like cued recall, recognition, and contextual memory, and language effects might differ for those tasks. Additionally, all participants were deaf from early childhood or birth; the findings may not generalize to late-deafened adults who acquired ASL as a second or third language. The study was also conducted in a controlled laboratory setting with matched lists of 10 items; effects of list length, presentation speed, or semantic relationships between items were not examined.

Participants reported their own language proficiency; standardized measures of ASL and English proficiency were not administered. This means language dominance was based on self-perception rather than objective assessment, which could have influenced group comparisons.

Where This Leaves Us

This research offers a clear message to neuropsychologists, gerontologists, and healthcare systems: testing deaf bilinguals in a single language, regardless of which language, is incomplete. A comprehensive picture of memory and cognition in deaf adults requires assessment in both ASL and written English. For younger deaf adults, both languages appear equally accessible. For older deaf adults, the dual-language difference becomes more apparent, making bilingual assessment critical for distinguishing normal aging from pathological cognitive decline. Healthcare systems that serve deaf populations should incorporate this principle into their assessment protocols to ensure fair, accurate, and linguistically appropriate evaluation.

Camilliere S, Emmorey K, Hauser PC, et al. Influence of Testing Language and Aging on Verbal List Memory in Deaf American Sign Language-English Bilinguals. Neuropsychology. 2026. Retrieved from PubMed. DOI: 10.1037/neu0001065

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