Reading passage
For most of recorded history, the sign languages used by deaf communities were dismissed as little more than elaborate pantomime, a collection of improvised gestures lacking the structure of true language. Educators generally assumed that signing was a crude substitute for speech, suitable only for those who could not learn to talk. This view began to collapse in 1960, when an American linguist named William Stokoe published a detailed analysis of American Sign Language and demonstrated that it possessed a genuine grammar.
Stokoe showed that signs, like spoken words, are built from a limited set of meaningless components that combine according to strict rules. Where spoken languages assemble sounds, sign languages assemble handshapes, movements, locations and orientations. Later researchers discovered that sign languages also display the deeper hallmarks of language: they can express abstract ideas, discuss events distant in time and place, and generate an infinite number of new sentences. Far from being universal, moreover, each national sign language differs from its neighbours; British and American signers, for example, cannot understand one another without training.
Neuroscience has supplied further evidence of their linguistic status. Brain imaging studies reveal that signing activates the same regions of the left hemisphere that process speech, including areas named after Broca and Wernicke. Deaf patients who suffer damage to these regions lose their ability to sign fluently, yet retain the capacity for everyday gesture, which suggests that the brain treats signing as language rather than as mere movement. In one famous case, a signer who had suffered a stroke produced grammatically broken signs while her gestures for reaching and grasping remained intact.
Children acquire sign language on much the same timetable as spoken language. Deaf infants of deaf parents begin to babble with their hands at around six months, produce their first recognisable signs near their first birthday, and combine signs into simple sentences before the age of two. Studies tracking vocabulary growth have found that signing children occasionally pass milestones slightly earlier than speaking children, perhaps because the muscles of the hand mature before those of the vocal tract, but the overall sequence of development is strikingly similar.
The recognition of sign languages has transformed deaf education. For over a century after an influential conference in Milan in 1880, many schools banned signing altogether and forced pupils to lip-read and speak, a method known as oralism. Followers of oralism believed that signing would prevent deaf children from integrating into hearing society. The results were often disastrous: pupils struggled to follow lessons and fell far behind their hearing peers. Research published in the 1970s showed that deaf children of deaf parents, who signed from birth, consistently outperformed orally educated children on tests of reading and general knowledge.
Today most specialists advocate bilingual education, in which the national sign language is taught as a first language and the surrounding spoken language is taught in its written form. Sweden and Finland were among the earliest countries to adopt this model, and their deaf students now achieve literacy rates comparable to those of hearing students. A signed foundation, it appears, gives children a complete language through which they can later master a second one.
Sign languages continue to evolve. New signs appear constantly, especially for scientific and digital vocabulary, and some communities hold committees that vote on proposed additions. At the same time, many small sign languages used in remote villages are endangered, as younger generations migrate to cities and switch to national sign languages. Linguists estimate that more than 140 distinct sign languages exist worldwide, yet only a minority have been fully described.
The lesson of this research is that language is not bound to the voice. Humans appear to possess a flexible capacity for grammar that will use whatever channel is available, whether sound, gesture or, in some experiments, touch. Sign languages, once punished in classrooms, are now taught in universities and recognised in the laws of several countries, including New Zealand, which made its sign language an official language in 2006.