Hearing-impaired (also referred to as deaf) people think in terms of their “inner voice”. Some of them think in ASL (American Sign Language), while others think in the vocal language they learned, with their brains coming up with how the vocal language sounds. Additionally, their thinking process is a little different from hearing people. When they think, they’re seeing themselves signing from first person point of view or third person point of view. When they imagine a hearing person speaking, they imagine him/her actually signing instead of speaking because they can understand him/her that way. Because there aren’t signs for every word in ASL, sometimes when deaf people want to think of a word that doesn’t have a sign, they finger-spell it. It’s like imagining letters in hand shapes. Finger-spelling occurs more frequently if a deaf person is reading words instead of signing them.
Of course, there is always room for variability. And, according to the article “How Deaf People Think” by Today I Found Out, “…our brains treat sign language exactly as it treats spoken language, even using the exact same part of the brain to process it. This is counterintuitive as you’d think the brain would use some part of the right hemisphere with sign language being visual. It turns out though that it uses the same portion of the left hemisphere to process sign language as it does for vocal language in the hearing.”