One way to categorize hearing loss is based on when it occurs. This classification divides hearing loss into prelingual (before acquiring speech and language) and postlingual (after acquiring speech and language) types. This classification, together with the degree of hearing loss, helps determine a person's preferred mode of communication and how best to interact and communicate with them.

The population of deaf and hard of hearing individuals is extremely diverse. It includes those who use sign language as their primary means of communication, those who primarily use spoken language, and those who lost their hearing later in life (postlingual deaf individuals). Consequently, deaf and hard of hearing people use different methods of communication. The choice of communication method depends on various factors: the degree of hearing loss, when it occurred, when it was diagnosed, the timing and intensity of rehabilitation, the hearing status of the parents, and the support from family and the environment. The chosen communication method is their primary or preferred mode of communication. There are two main language modalities that existing communication systems rely on: sign language and spoken language.

Sign Language

Sign languages emerge spontaneously within deaf communities, and as these communities dissolve, so does the sign language. These are natural and native languages of national deaf communities. They develop independently of spoken languages and other sign languages. Significant linguistic differences exist among national sign languages, to the point where deaf individuals from different sign language communities might not understand each other.

The structure of sign language differs from that of spoken languages. This difference is evident in both grammatical rules and production. In sign languages, signs are produced through simultaneous movements of the hands, arms, face, head, and body within a visual-spatial communication channel. In contrast, spoken languages use an oral-auditory channel for word production.

Throughout history, sign language has faced many prejudices from the hearing community, often rooted in misconceptions that it is ungrammatical, universal, primitive, or overly pictorial. Today, many sign languages are recognized as legitimate languages, and since the 1960s, linguistic research on them has been growing.

Simultaneous communication (SimCom or sign supported speech)

Simultaneous communication is defined as a manual communication system that lacks the characteristics of a true linguistic system, as it simultaneously uses two languages—sign language and spoken language. This system provides a visual representation of spoken language, supplemented by signs borrowed from sign language and fingerspelling. In this communication method, sentences are spoken according to the grammar of the spoken language, while each spoken word is simultaneously conveyed through signs from sign language. Consequently, only the vocabulary (signs) from sign language is used, but it follows the grammatical structure of the spoken language. The grammar of sign language is entirely omitted, along with the non-manual markers that typically convey crucial grammatical information in sign language. In simultaneous communication, facial expressions are used to express emotions or to enhance the clarity of the spoken words.

Fingerspelling

Fingerspelling represents the spoken language in written form. Each handshape corresponds to a specific letter of the alphabet in a given language. With fingerspelling, you can spell out any word or sentence, even entire texts, regardless of their length or complexity. However, this method of communication is extremely slow, with fingerspelling allowing for about 60 words per minute, compared to spoken language, which can convey up to approximately 180 words per minute. Due to its slow pace, fingerspelling is not very efficient for regular communication, so it is mainly used as an auxiliary tool for spelling out new terms, technical and specialized vocabulary, personal names, and so on.

Lip-reading (sometimes called speechreading)

Deaf and hard of hearing individuals who use lip-reading rely on visually observing and interpreting speech by following the movements of the mouth, tongue, jaw, and facial expressions. This method is not entirely reliable since only about 30% of sounds are visible on the face and lips. It can also be challenging and depends on several factors: the quality of lighting, the speaker's position relative to the individual, and the speaker's manner of communication (e.g., speaking too quickly, mumbling, covering their mouth, or turning their head while speaking).

Captioning or Transcription

Captioning or transcription involves converting spoken language into written text using specialized devices. Additionally, various mobile apps and computer programs can capture speech from nearby sources and display it as text on a screen.

Universal Rules for Interacting with Deaf and Hard of Hearing Individuals

Get their attention by gently tapping their shoulder or waving your hand.

Approach from the front and maintain eye contact.

Face a light source so your face and mouth are clearly visible.

Do not cover your mouth while speaking.

Speak slowly and clearly.

Use short, straightforward sentences with simple vocabulary.

Confirm that they have understood your instructions.

If an interpreter is present, address the deaf or hard of hearing person directly, not the interpreter.