The Certified Deaf Interpreter role is unfamiliar to many legal and medical clients. Here is the explanation. A CDI is a Deaf or hard-of-hearing person who is certified by the Registry of Interpreters for the Deaf (RID) to work as a professional interpreter. CDIs do not interpret directly from spoken English. They work paired with a hearing interpreter, who interprets between spoken English and signed language. The CDI then interprets between that signed language and the version of signing the Deaf client actually uses.
Why a CDI is sometimes necessary
Many Deaf clients sign standard ASL or standard LSM, and a hearing certified ASL interpreter alone is sufficient. But some Deaf clients sign in ways that differ from the standard register:
- Clients whose first language is a foreign sign language (e.g., a Deaf person from Vietnam who signs Vietnamese Sign Language) and who have not fully acquired ASL.
- Clients who acquired language late in life and have a non-standard signing pattern (sometimes called "home sign" or idiosyncratic signing).
- Clients with limited formal education in sign language, where vocabulary and grammar are less standardized than typical school-trained ASL.
- Deaf clients with disabilities (low vision, cognitive disability) where additional accommodation in the signing is needed.
- Children and young adolescents whose linguistic register differs from adult signers.
In these cases, a hearing-only interpreter may miss meaning, mis-render testimony, or fail to recognize when the client is not following the proceeding. A CDI bridges that gap by working in the client's actual signing pattern and rendering it into standard ASL for the hearing interpreter to convert to spoken English (and vice versa for incoming questions).
How a CDI team works at a deposition or trial
In a deposition with a CDI: the deposing attorney asks a question in English. The hearing interpreter renders the question in ASL. The CDI then re-renders the ASL into the client's actual signing pattern. The client answers. The CDI renders the client's signing into standard ASL. The hearing interpreter renders the standard ASL into spoken English for the record. There are two interpretation steps in each direction, but the result is meaningfully more accurate when the client's signing diverges from standard ASL.
When is a CDI legally required?
There is no single statutory rule. Best practice in U.S. courts holds that when the Deaf client's linguistic profile suggests a hearing-only interpreter may be insufficient, a CDI should be engaged. Many U.S. District Courts and several state courts now routinely engage CDIs in capital and serious felony cases involving Deaf defendants and witnesses. In civil litigation and medical encounters, the decision to engage a CDI is typically made jointly by counsel and the interpreter agency after a pre-assessment.
Cost considerations
A CDI team costs roughly twice what a hearing-only certified interpreter costs (two professionals, both billing for their time). For high-stakes legal proceedings involving a non-standard-signing Deaf client, the cost is justified because the alternative is a transcript that misrepresents what the client actually said. AMS provides CDI teams on request and advises when an assignment likely requires one.