4.6 Examples from TSL
5.1.1 Sign languages are real languages: neurolinguistics evidence
Traditionally, neurobiological studies have always been applied to spoken languages.
This spurred some researchers to inquire on whether these mechanisms are only valid for spoken languages, or as should be the case for universal neurobiological mechanisms, for all languages, irrespective of the modality.
The problem with traditional research is that up until not long ago researchers did not view signed languages as languages the way linguists intended them to be.
Therefore, extending these neurobiological studies to signed languages had the double effect of proving the fact that signed languages are indeed languages at all effects; the only difference being their transmission channel, and on the other hand of asserting the universal nature of the neurolinguistic mechanisms scientists and researchers had come to discover.
The two research purposes only differ in terms of perspective. In other words, for all those people who did not believe sign languages to be at the same level of oral languages in terms of linguistic dignity, these studies pioneered by Ursula Bellugi, definitely, or desirably so28, proved them wrong; for all those linguists and scholars who had no doubt on the fact that signed languages are indeed real languages, it was a way to measure the extendibility of the neurobiological bases which had been discovered for oral languages.
Bellugi has studied the neurological bases of sign language extensively, and her work has led to the discovery that the left hemisphere of the human brain becomes specialized for language, whether spoken or signed, a striking demonstration of
28 Unfortunately, there are some people nowadays who are still convinced of the inferiority of sign languages, in terms of linguistic completeness, compared to oral languages. This is the attitude which is at the basis of the discriminating policies regulating Taiwan sign language interpreters.
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neuronal plasticity (Bellugi and Studdert-Kennedy 1980; Klima and Bellugi 1988;
Poizner and Klima 1987).
According to MacSweeney et al. (2008), lesion and neuroimaging studies indicate that the neural systems supporting signed and spoken language are very similar: both involve a predominantly left-lateralised perisylvian network. In other words, some underlying neurobiological mechanisms are modality-independent.
Sign language research has shown that language processing engages left perisylvian regions, regardless of language modality. This has been demonstrated from the level of phonology (Petitto et al. 2000; MacSweeney et al. 2008b) to discourse (Braun et al. 2001; MacSweeney 2008).
Another important discovery is that sign languages and gesture do not share identical neural networks (MacSweeny 2008). However, in this neurolinguistic perspective, gesture is not perceived as something rudimental and primitive, but rather as something important for the development of sign language because the
‘linguisticization of gesture’ (also termed grammaticalization’) seems to be at the genesis of most signs in sign languages (Janzen and Shaffer 2002).
Spoken languages and signed languages are conveyed through two different modalities, this is a fact which cannot be denied. Spoken languages use the audio-oral-articulatory channel, whilst signed languages recur to the spatial-visual one.
The articulators in sign language, for example, like the hands, the upper torso and so on, are visible whereas the vocal articulators are not. As far as the perception is concerned, sign languages need a high spatial resolution and a low temporal resolution, whereas it is exactly the opposite for spoken languages.
These differences are also reflected in everyday linguistic behaviors, which noticeably vary between the two different modalities. For instance, it is common for deaf speakers to be signing happily all at the same time at a table, because the
conversation of two parties will not affect a third party, who in turn will be focused on his interlocutor. This would be perceived as a very loud and noisy behavior in spoken languages because of the different articulators, or again it is possible to sign to a person who is at the opposite side of a room, while it would be considered rude and inappropriate to shout at someone who is far from us. At the same time, though, whispering is deontologically impossible29 in signed languages, because of their articulatory nature, insofar as the objects of perception are visual events and not acoustic events. In other words, it means that signing, no matter how intentionally
“whispered” can always be seen at a conspicuous distance.
These differences have brought about in deaf people a grammaticalization of spatial elements. The use of space characterizes all sign languages and serves important grammatical functions. Space can be used in a ‘topographic’ manner to map the position and orientation of objects or people in real world space or in a non-topographic, grammatical, manner in sign languages like in the sentence “Mary phoned John”, where in practically all sign languages the agent and the patient are assigned imaginary spots in the visual-spatial field in front of the signer.
Scholars and linguists have tried to extend neurobiological experiments to see if beyond these differences, the neural basis of the two modally-different languages actually shared some similarities, which might reflect the neural underpinnings of core language functions (MacSweeney 2008).
Lesion studies are an important branch of neurolinguistics aimed at mapping linguistic-related brain areas. These studies have traditionally been carried out on hearers, the result being that left hemisphere damage would affect language ability.
This led to the discovery that the left hemisphere is the one more directly linked
29 Although signers can sign with smaller movements which might be similar to whispering in spoken languages.
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with language functions. Some neurolinguists conducted the same lesion studies on native signers and found out that left hemisphere damage leads to severely impaired language processing (aphasia) even in signers, whereas right hemisphere damage, which would be involved if signing was a mere gestural activity, does not (Atkinson et al. 2005; Corina 1998; Hickok et al. 1996, 1998; Marshall et al. 2004, Poizner et al.
1987).
In other words, neuroimaging studies also indicate a crucial role for the left hemisphere in signed language processing (MacSweeney 2008) as well as in spoken languages. More specifically, both covert and overt sign production rely on the left inferior frontal gyrus (Braun et al. 2001; Corina et al. 2003; Emmorey et al. 2003;
MacSweeney 2008; McGuire et al. 1997; Petitto et al. 2000; San Jose-Robertson et al.
2004 ), which is exactly what happens for spoken languages as well (Kassubek et al.
2004; Emmorey et al. 2007, MacSweeney 2008).
Some researchers (Capek et al. 2008; Corina et al. 2007; MacSweeney 2002, 2002b, 2004, 2006; Meyer et al. 2007; Neville et al. 1998; Newman et al. 2002; Sakai 2005; Waters et al. 2007) have shown that in addition to the left inferior frontal gyrus, comprehension of sign language in native signers also activates the left superior temporal gyrus and sulcus as can be seen in Fig 4, taken by MacSweeney (2008).
Figure 4
(MacSweeney 2008)
From figure 4, it seems that the neural systems supporting sign language and spoken language are indeed very similar.
As we can see from figure 5, taken from MacSweeney (2008b), these similarities also extend to phonological similarities judgments in response to pictures.
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Figure 5
MacSweeney (2008)
Neuroimaging studies also prove the fact that signed languages are natural languages and not a pantomime or a gestural way to express primitive ideas.
As previously mentioned, gesture is not perceived as something rudimental and primitive, but rather as something which is at the basis of the further development of sign languages, insofar as the ‘linguisticization of gesture’ (also termed grammaticalization’) seems to be at the genesis of most signs in sign languages (Janzen and Shaffer 2002).
According to Hickok (1996), there is no direct neurobiological link between aphasia and apraxia. There are some patients who are unable to understand pantomimes and gestures like yawning, stretching, or brushing one’s teeth, while their comprehension of the sign for “brushing one’s teeth” is untamed, as iconic as it may be.
This is confirmed by Corina et al. (2007), whose research group found greater activation in left perisylvian regions for ASL signs than for the observation of grooming gestures (e.g. scratching) and transitive gestures (e.g. eating an apple).
Figure 6
Composite image illustrating activation in native Deaf signers (n = 10) for American Sign Language (red) and non-linguistic actions (green). The red shading reflects the contrast of ASL activation minus non-linguistic gestures. The green shading reflects the contrast of
107 non-linguistic gesture minus ASL. ASL stimuli were single ASL signs. Non-linguistics gestures were comprised of intransitive actions e.g., “self grooming” and transitive object oriented actions “biting an apple”. The figures shown represent the rendering of the SPM output at p < .005 threshold and display cluster sizes of 20 voxels or greater.
Data reproduced from Corina et al. (2007).
Furthermore, we can see a plastic hemispheric reorganization in Deaf signers, insofar as the processing of emotional facial expressions, typically right hemisphere dominant in hearing non-signers, can be processed bilaterally or predominantly in the left hemisphere in deaf signers. This is likely to reflect reorganization because of the wide range of functions the face, along with its expressions, can serve in signed languages (MacSweeney 2008; McCullough et al. 2005).
Another factor which demonstrates unequivocally the fact that signed languages are languages at all effects is related to language learning. Mayberry’s studies (Mayberry et al. 2002; Mayberry and Lock 2003; Mayberry 2007) and an initial neuroimaging study (MacSweeny et al. 2008b) indicate that exposure to a language early in life, be it signed or spoken, is required to establish the neural infrastructure to support not only that language but also any language learned later in life. This clearly states the equal linguistic nature of spoken and signed languages. As Sacks (1989: 88) duly points out “if Deaf children are not exposed, early, to good language or communication [speech or sign does not matter], there may be a delay (even an arrest) of cerebral maturation, with a continuing predominance of right hemisphere processes and a lag in hemispheric ‘shift’”
At the same time, findings from studies contrasting signed language and spoken language processing in hearing people with Deaf signing parents support the
conclusions from between group studies, that signed languages and spoken languages engage very similar neural systems (Braun et al. 2001; Emmorey et al. 2005;
Soederfelt et al. 1997).
As previously mentioned, a key figure in the neurolinguistics analysis of sign language has been, and still is, Bellugi. Her most important finding was to discover that the left hemisphere of the brain is indispensable for sign languages, as much so as it is for spoken languages. She also found out that signers use some of the same neural pathways that are needed in the processing of grammatical speech (Bellugi 1980).
The fact that sign languages are mainly processed in the left hemisphere was also proven by Neville (1978; 1988; 1989). She demonstrated that sign languages are processed more efficiently and accurately if presented in the right visual field, which means it is processed in the left hemisphere because information from each side of the visual field is always processed in the opposite hemisphere. Also, as previously mentioned aphasic signers are not impaired in non-linguistic visual-spatial abilities or, again, signers with right hemisphere strokes may have spatial disorganization, but retain perfect signing ability despite their several visual-spatial deficits (Sacks 1989).
In short, signers show exactly the same cerebral lateralization as oral speakers, irrespective of the modality through which is conveyed their language and even though their articulators are visuo-spatial in nature.
Therefore, according to neurolinguistic studies sign language is a language at all levels and at all effects as proven by the neurobiological mechanisms underlying its processing, even though it is visual rather than auditory and spatially rather than sequentially organized; and as Sacks (1989:76) points out “as a language, it is processed by the left hemisphere of the brain which is biologically specialized for just this function”.
This is also a proof of the plasticity of the human brain, because it is as if the left
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hemisphere in signers modified the visual-spatial characteristics into a whole new analytical concept, making it a language of its own, with its own rules and developing the potentials intrinsically present in the neurobiological mechanisms of the human brain.
As far as plasticity is concerned, there is also another interesting study worth mentioning. Penhune et al. (2003) have studied congenitally deaf individuals. This research group’s study provides a unique opportunity to understand the organization and potential for reorganization of human auditory cortex. They used magnetic resonance imaging (MRI) to examine the structural organization of two auditory cortical regions, Heschl’s gyrus (HG) and the planum temporale (PT), in deaf and hearing subjects.
Figure 7
Heschl’s gyrus (HG) and the planum temporale (PT)
The results show preservation of cortical volume in HG and PT of deaf subjects deprived of auditory input since birth. Measurements of grey and white matter, as well as the location and extent of these regions in the deaf showed complete overlap both with matched controls and with previous samples of hearing subjects. The results of the manual volume measures were supported by findings from voxel-based morphometry analyses that showed increased grey-matter density in the left motor hand area of the deaf, but no differences between the groups in any auditory cortical region. This increased cortical density in motor cortex may be related to more active use of the dominant hand in signed languages. Most importantly, expected interhemispheric asymmetries in HG and PT thought to be related to auditory language processing were preserved in these deaf subjects. These findings suggest a strong genetic component in the development and maintenance of auditory cortical
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asymmetries that does not depend on auditory language experience. Preservation of cortical volume in the deaf suggests plasticity in the input and output of auditory cortex that could include language-specific or more general-purpose information from other sensory modalities.
In Poizner et al. (1987), there is an interesting anecdote concerning the grammatical relocalization of the topographic space. The patient analyzed, Brenda I., had a huge right hemisphere lesion and as a consequence she neglected the left side of space. When she described the room by signing she left the left side of the topographic space completely void, however in her right topographic space she signed correctly, including spatial loci and objects in the left side of the right topographic side. In other words, her topographic space, controlled and processed by the right hemisphere, was not functioning properly because of her lesion; however, her syntactic-linguistic space functioned faultlessly.
What we have come to see so far is that linguistically speaking, sign languages are as rich and complex as any oral language, despite the common misconception that they are not "real languages". Professional linguists have studied many different sign languages and found that they exhibit the fundamental properties that exist in all oral languages (Klima and Bellugi 1989; Sandler and Lillo-Martin 2006).
In other words, sign languages are not a form of pantomime; they are conventional, often arbitrary (as are oral languages) and do not necessarily have a visual relationship to their referent, much as most oral language is not onomatopoeic.
Due to the channel of transmission, iconicity seems to be more systematic and widespread in sign languages than it is in spoken ones; however, according to linguists this difference is not categorical (Johnston 1989). The visual-spatial modality allows the human preference for close connections between form and meaning, which is the cause of a slightly higher percentage of iconicity, present but
suppressed in oral languages, to be more full-fledged and more fully expressed (Taub 2001).
However, one should be careful with linguistic definitions because this does not mean that sign languages are a visual rendition or a spatial representation of an oral language. They have complex grammars and syntactic rules of their own, and can be used to discuss any topic, from the simple and concrete to the lofty and abstract, from politics and economics, to religion and philosophy.
Just like any other oral language, sign languages have a hierarchical organization.
They organize elementary, meaningless units (phonemes, which in the past were called cheremes in the case of sign languages) into meaningful semantic units. Just as it happens in oral languages, these meaningless units are represented as (combinations of) features, although often also crude distinctions are made in terms of handshape (or handform), orientation, location (or place of articulation), movement, and non-manual expression.
A linguistic feature which is found in many different sign languages is the occurrence of classifiers, a high degree of inflection, and topic-comment syntax. The existence of classifiers is a trait that sign languages share with most East Asian languages.30 Classifiers are not used in English (for instance, "people" is a countable noun, and to say "three people" no extra word needs to be added), but are, indeed, common in East Asian languages (where the equivalent of "three people" is often "three classifier people").
More than oral languages, sign languages can convey meaning by simultaneous means, e.g. by the use of space, two manual articulators, and the signer's face and body. Though there is still much discussion on the topic of iconicity in sign
30 Although there is a difference because in signed languages classifiers occur with verbs, whilst in Asian languages they occur with nouns (Chang, Su and Tai 2005).
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languages, classifiers are generally perceived to be highly iconic, as these complex constructions function as predicates that may express any or all of the following:
motion, position, stative-descriptive, or handling information (Emmorey 2002).
Actually, iconicity has played an important debate in the history of sign languages. In the past people thought that that ‘real languages’ must consist of an arbitrary relationship between form and meaning, therefore the less iconic forms a language had, the higher linguistic dignity, so to speak, it had, scholars thought. At the same time, if a sign language consisted of signs that had iconic form-meaning relationship, it could not be considered a real language. Consequently, iconicity as a whole was largely neglected in research of sign languages by the pioneers of sign language linguistics.
According to Taub (2001), in a cognitive linguistics perspective, iconicity is not merely defined as a relationship between linguistic form and a concrete, real-world referent; it is more properly defined as a set of selected correspondences between the form and meaning of a sign.
Therefore, as confirmed by Wilcox (2004), iconicity is grounded in a language user’s mental representation (which is technically called “construal” in Cognitive Grammar). It is defined as a fully grammatical and central aspect of a sign language rather than periphery phenomena.
In this perspective, signs have more flexibility because they can be either fully iconic or partly iconic (Wilcox 2000). This serves to say that irrespective of what the pioneers of sign linguistics believed, iconicity does not make a language less so, it is just a way for the language to express itself, and the visual modality certainly helps to make things more iconic.