Sign language is the natural human language used to convey meaning and communicate information using visual and physical gestures. Compared to spoken languages and based on the oral comparison, signed languages function as complex language structures with fully developed grammatical elements, including phonology, morphology, grammar, and semanticizing (Hickok, 1996). Many experiments on language processing have been carried out historically in audio-oral languages, and work in signed languages will serve to enlighten the brain’s neuronal structure, regardless of the language itself.
To understand the processes of the brain signed language, we need a fair brain road map— its overall structure, and the possible roles of various regions. Research on Brain injury (lesions) has developed a well-established technique for asserting structure and role relationships within the brain. The effect of brain injury depends on the affected part of the brain. Any individual with trauma to the front of the left side of the brain, for instance, might not be able to speak. Moreover, someone else may be able to produce organized language utterances with damage to the back of the right side of the brain, but may have lost specific spatial skills and may not be able to see more than one thing at a time.
These anomalies seem to be very common in several individual patients. One clear conclusion is that the front of the left side of the brain is needed in most cases for language development. In contrast, the rear of the right half of the brain is necessary for visuospatial communication. This means that these two activities are “centralized,” and other areas cannot conveniently perform them. Since the mid-19th century, analyses of these structural trends of specific brain disorders have shown the possible associations between particular brain areas and their functions. This study gave a subsequent basic brain map based on studies reviews. Since the mid-19th century, analyses of these structural trends of individual brain disorders have shown the possible associations between particular brain areas and their functions.
A LITTLE REVIEW OF THE BRAIN
The human brain comprises, like in every vertebrate, two nearly identical hemispheres that reflect one another. The grey cortex consists of nerve cells densely and a minute at a depth of 0.5–1 cm. There are many close, white fibres on the cable band separating the two hemispheres. Such fibres can as well be seen under the cortex and continue off to the spine. These are a bunch of different nerve axons that contain nerve cell information. Large axon fibres, such as cables carrying electricity, TV, and telecommunications information on urban roads, are arranged into bundles.
The bright, white protective sheath of myelin insulates the nervous axon, allowing quick and reliable nerve impulse transmission. A simple summary of the human brain, therefore, shows that it consists of two hemispheres comprised of two neural forms: fascicular white matter, and grey cortex matter. The brain can sense electric currents through the exposure of the brain surface and the laying of an electrode (deep electrode mapping) directly on it. If done, stress shifts are detected as movement extends from one part into its neighbours and from one side of the cortex to different parts of the brain along with the disconnected white “cables.” Such complex electro-chemical variations can be seen as registering brain activity with mental activities and processes.
THE CEREBRAL ACTIVITIES IN SIGN LANGUAGE
Recent neurobiological sign language research focused on the recognition of the area of cerebral activation in producing and understanding sign language. Neuro-imaging and brain injury studies have shown differences in language expression, including lateralization and increased movement in a particular language processing centres for activities, both text speeches, and signed language. Moreover, in several studies, brain regions unique to sign language therapy were also detected.
Early brain lesion studies have shown that injury to the frontal lobe in the left hemisphere results in sign production damage similar to Broca Aphasia. In contrast, damage in the left cortex leads to language deficiencies. On the other hand, there are no aphasic signs of right hemisphere lesions (Hickok, 1996; Marshall, 2004).
For recent neuro-imaging studies like PET and fMRI, left lateralization in the understanding of sign language has also improved the activation of the right hemisphere associated with spoken words. Neville contrasted brain activity with the use of fMRI in a vital article when signers showed phrases in the Sign Language of America and written sentences to the speaker (1999). The perisylvian language regions of the left hemisphere were heavily recruited; however, the specific areas of the right hemisphere have only been triggered in the sign language (Neville, 1999).
Capek advocated that semantic and syntactic processing involves different neural methods in both spoken and signed language to address the divergence between the lesion and neuroimaging studies (2009). Based on an ERP report, he found that the semantic processing in both language modalities is alike in place and timing of activation. It suggests the possibility for neuronal networks to be interested in the development of core ordinary language and to be modal.
DIFFERENCE BETWEEN SPOKEN AND SIGNED LANGUAGE
In the left lower temporal gyro and the back of the upper temporal gyro, cerebral activity is common among spoken and signed languages. The left lower temporal gyrus engages in the production of both signed and spoken languages and the high temporal gyrus is important to understand, including the area of Wernicke (MacSweeney, 2002). Therefore, these areas, regardless of the language form, are deemed to involve basic language processing.
CRITICAL PERIOD AND DEVELOPMENT
Many researchers are thinking that the critical time for developing some biological and behavioural processes is linked to plasticity in the brain (Mayberry, 2003). Language learning is known to be limited by a particular time during which language experience is needed for linguistic education. Debate on this hypothesis is reinforced by observations of late-life sign language abilities of deaf kids born to normal parents, as seen in these cases, people are often without full verbal information during early infancy. Research shows that the performance of these deaf people with no early childhood experience in grammatical activities was slightly lower compared to adults with exposure. This indicates the presence of a crucial period of development involving neocortical specialization and growth compared to other biological processes, including binocular vision development.
The effects of the inferior frontal gyrus on neural structures due to a lack of early language awareness in individuals are seen. In this area, signers who are not exposed early are more active compared to indigenous signatories when phonological tasks are demanded.