A Greek translation of this short article I wrote was published in Entropia Issue 9: Languages And Education, Fall 2016.

The colloquial use of the term ‘language‘ usually excludes sign languages, reflecting the belief that sign languages are not real languages, but rather finite communication systems. Nevertheless, there’s a strong case to be made that sign languages emerge and behave like (spoken) natural languages do.

There is evidence that there is a critical period for the acquisition of signed languages, roughly from birth to the onset of puberty, after which the mastery of the signed language requires non-trivial effort (Fromkin, et al., 2014¹), and signers learning it outside that period are measurably less fluent (Newport, 1990²). Moreover, stages of acquisition appear to be parallel between speakers and signers: for example children start with babbling and reach the telegraphic stage at approximately 2 years of age, whether they sign or speak (Fromkin, et al., 2014).

Similarly to spoken languages, very little input is required for typically-developing children to acquire a signed language. Far from requiring explicit instruction, ‘home signs’ arise with little or no input (Fromkin, et al., 2014). In Deaf communities such ad hoc signs can develop into full-fledged sign languages and gain native speakers (cf creole genesis). One such case is the Nicaraguan Sign Language, which emerged among children without any prior knowledge of a language and which increased in complexity in the hands of younger children (Boeckx, 2010³).

Brain imaging also points towards sign languages being processed similar to spoken languages. Despite their visual modality, sign languages are processed in the left hemisphere like spoken languages, and signers with brain damage in the left hemisphere will face linguistic difficulties just like speakers would, while damage right hemisphere (where visual processing tasks take place) wouldn’t impact their signing (Poizner, et al., 1987⁴).

Those observations point towards sign languages and spoken languages being fundamentally the same and therefore equally ‘real’.