Understanding how language is heard, interpreted, and understood is the goal of those who study speech perception. The varying elements of speech perception, such as acoustics, phonemes, syntax and other properties, can help provide a roadmap of how speech is processed and understood. Beyond the auditory processes used in speech perception, visual cues also need to be explored.
Two processes seek to explain the way humans process incoming acoustic signals when it comes to processing and understanding language. When humans use stored language skills and cues to fill in missing phonetic information, it is considered top-down processing. The absence of stored information forces humans to use bottom-up processing. Bottom-up processing can be demonstrated by studying infants and how they listen to and react to language acoustics.
The internal organs of the ear work to transfer the sounds related to speech to the temporal lobe of the brain for comprehension. Vibrations associated with speech acoustics are passed through the eardrum to the auditory ossicles which continue the vibration to the inner ear, cochlea, and hair cells. At this point, the auditory nerve begins to pick up signals from neurons and transmit the information to the areas of the brain responsible for the initial interpretation of speech properties, including pitch and tone.
Sounds related to speech are considered speech acoustics. These sounds are produced by vibrations of the human vocal tract. Each letter and sound produced by the vocal tract requires the vocal tract to change its shape.
Phonemes help distinguish between similar sounds in language. Even smaller than the syllables that make up speech and words, phonemes contribute to speech perception. Phonemes and other speech sounds used to construct language overlap, and are hard to distinguish. The sound of each segment of speech is affected by the sounds that come before and after, leading to this difficulty.
Visual cues, including mouth formations and facial expressions, help identify speech signals and sounds. In some studies, changing the face and visual cues affect the visual cues provided and the sounds perceived. This is known in the field of speech perception as the McGurk effect.
Several additional terms are used in the discussion of language as it pertains to speech perception. Syntax is understood as the combination of words, also known as grammar. Semantics refers to the meaning of the message itself. An understanding of syntax and semantics helps further speech perception understanding and research.