Environmental deprivation, deafness, and neurological disruption such as stroke or brain injury will absolutely influence language acquisition, production, and/or comprehension.
As Kuhl (2010) notes, an infant’s brain is extremely malleable and is constantly changing as it absorbs information from its surroundings. The brain uses auditory and visual cues to gather knowledge about language, so any deprivation of this during the time of language acquisition is going to hinder learning language, and in turn, producing it (Kuhl, 2010).
Stroke or injury to the brain in later life can also affect language. As the neuroscience of language becomes better understood, it has been learned that damage to areas of the brain that are known to focus on speech, such as Broca or Wernicke’s area, does not necessarily reflect in symptoms of speech impairment (Poeppel & Hickok, 2004). Further brain mapping using fMRI, PET, EEG, and MEG will allow researchers more insight into brain language research, such as distinguishing areas of function (Poeppel & Hickok, 2004).
An example that comes to mind comes from a book I read some time ago called The Boy Who Was Raised as a Dog by Dr. Bruce Perry and Maia Szalavitz. In this book Dr. Perry references a child who was, in fact, raised as a dog (Perry & Szalavitz, 2008). The boy lost his caregiver at 11 months old and was raised by an older man who was a dog breeder (Perry & Szalavitz, 2008). With little understanding of how to raise a child, he raised him the way he raised his dogs, even keeping him in a dog cage (Perry & Szalavitz, 2008). He fed and changed the boy but did not interact with him outside of that (Perry & Szalavitz, 2008). The boy lived in that cage for five years, without human environmental stimulation (Perry & Szalavitz, 2008). When he did attend medical appointments, it was found that he had atrophy of the cerebral cortex, and his brain resembled that of a patient with Alzheimer’s disease (Perry & Szalavitz, 2008). By age five, he had little to no language capabilities, among other deficits (Perry & Szalavitz, 2008).
The lack of human connection, severe environmental deprivation resulted in neurological disruption in this case. These combined issues meant that the boy had no chance to learn, use or comprehend language at any time during the first five years of his life. However, once he was removed from that situation, brought to a hospital and the care of Dr. Perry, as well as speech and language therapists (among others), he began to speak (Perry & Szalavitz, 2008). This example shows just how imperative all aspects of learning can be to be able to develop language, as well as how malleable the brain can be in the face of severe deprivation or neurological damage or disruption.
Kuhl, P. K. (2010). Brain mechanisms in early language acquisition. Neuron, 67(5), 713–727.
Poeppel, D., & Hickok, G. (2004). Towards a new functional anatomy of language. Cognition, 92(1–2), 1–12.
Perry, B. D., & Szalavitz, M. (2008). The boy who was raised as a dog: And other stories from a child psychiatrist’s notebook: what traumatized children can teach us about loss, love, and healing. New York: Basic Books.