Language and arts in education and practice

¶ … home sign systems challenge the idea that language input is necessary for language acquisition?

Home sign systems do not challenge the idea that language input is necessary for language acquisition. Home sign systems are a substitute for verbal language that rely on alternate mechanisms precisely because language input is required for linguistic development. In infancy, human beings possess a so-called "window of opportunity" to develop the cognitive elements of linguistic speech (Gerrig & Zimbardo, 2009). During that time, the infant has the capacity to absorb and learn all of the sounds in all of the languages in human societies. Infants watch their parents, listen to the sounds that they make in communication, and perpetually mimic those sounds. That is part of the cognitive development process in which the neural pathways associated with producing those sounds are formed, reused, and thereby strengthened (Brownlee, 1998; Dennet, 2001).

Initially, the infant can learn all of the different sounds that the human mouth is capable of producing; however, if the infant is not exposed to certain sounds during this critical period, the capacity to produce sounds not heard repeatedly is lost. Thereafter, we may still learn how to speak foreign languages but with greater difficulty and a foreign accent characteristic of our natural language (Brownlee, 1998; Gerrig & Zimbardo, 2009). When infants engage in the behavior we refer to as babbling, the linguistic content of the sounds they make include all of the sounds in all human languages, including those to which the infant will not learn. At that stage, the content of infant babble is identical everywhere in the world (Brownlee, 1998; Gerrig & Zimbardo, 2009).

More importantly, there is also a critical window during which we must be exposed to verbal language after which it may no longer be possible to establish the same neural pathways necessary for verbal speech (Brownlee, 1998; Gerrig & Zimbardo, 2009). Furthermore, this element of cognitive aspect of linguistic development is equally evident in other species with complex languages, such as in many species of birds (Edey & Johanson, 1999; Simonds, 2002). Typically among songbirds, if infant birds are not exposed to the songs of their parents (or other adults of their species), they lose the ability to communicate in that manner even if they are repeatedly exposed to those languages later in life (Simonds, 2002).

Feral children demonstrate precisely the same phenomenon: they lose the ability to mimic any form of human speech because they lack exposure to it in infancy. They may possess normal levels of intelligence and that accounts for their ability to establish alternate forms of communication, such as through sign language based on the logical connection to the physical world and even to some abstract concepts. Even deaf children likely have more opportunity to absorb critical information about human speech during infancy, because they observe the mouth movement patterns of their parents even if they do not hear the sounds they make.