User:Sarahjk22/American Sign Language phonology

Phonological processing in the brain
The brain processes language phonologically by first identifying the smallest units in an utterance, then combining them to make meaning. In spoken language, these smallest units are often referred to as phonemes, and they are the smallest sounds we identify in a spoken word. In sign language, the smallest units are often referred to as the parameters of a sign (ie. handshape, location, movement and palm orientation), and we can identify these smallest parts within a produced sign. The cognitive method of phonological processing can be described as segmentation and categorization, where the brain recognizes the individual parts within the sign and combines them to form meaning. (Petitto 2016) This is similar to how spoken language combines sounds to form syllables and then words. Even though the modalities of these languages differ (spoken vs. signed), the brain still processes them similarly through segmentation and categorization.

Measuring brain activity while a person produces or perceives sign language reveals that the brain processes signs differently compared to regular hand movements. This is similar to how the brain differentiates between spoken words and semantically-lacking sounds. More specifically, the brain is able to differentiate actual signs from the transition movements in between signs, similarly to how words in spoken language can be identified separately from sounds or breaths that occur in between words that don't contain linguistic meaning. Multiple studies have revealed enhanced brain activity while processing sign language compared to processing only hand movements. For example, during a brain surgery performed on a deaf patient who was still awake, their neural activity was observed and analyzed while they were shown videos in American Sign Language. The results showed that greater brain activity occurred during the moments when the person was perceiving actual signs as compared to the moments that occurred during transition into the next sign (Leonard 2020). This means the brain is segmenting the units of the sign and identifying which units combine to form actual meaning.

An observed difference in location for phonological processing between spoken language and sign language is the activation of areas of the brain specific to auditory vs. visual stimuli. Because of the modality differences, the cortical regions will be stimulated differently depending on which type of language it is. Spoken language creates sounds, which affects the auditory cortices in the superior temporal lobes. Sign language creates visual stimuli, which affects the occipitotemporal regions. Yet both modes of language still activate many of the same regions that are known for language processing in the brain. (MacSweeney et al 2002)  For example, the left superior temporal gyrus is stimulated by language in both spoken and signed forms, even though it was once assumed it was only affected by auditory stimuli (Pettito 2000). No matter the mode of language being used, whether it be spoken or signed, the brain processes language by segmenting the smallest phonological units and combining them to make meaning.