[MUSIC] From birth onward, children acquire a spoken language seamlessly when surrounded by talking caregivers. Although parents might worry about their baby's health, or paying for child care, private school, or even college, they won't usually be concerned with their child's language development. Most children follow a reasonable trajectory in their language acquisition. Even so, there are large individual differences in the number of words that are understood and produced during a child's first few years of life. No satisfying explanation has been given for these individual differences. We will discuss however the multiple influences that contribute to the acquisition of a child's vocabulary. Does language manifest itself only in spoken language? Perhaps not. Tadoma is another method of communication used by some individuals who are both deaf and blind. It was named after the first two children to whom it was taught, Tad and Oma. The Tadoma users place their hands on various parts of the speakers lips and jaw to track her articulatory movements. Helen Keller used this method to communicate as can be seen in her visit with President Eisenhower. I don't know that anyone has learned tadoma from birth onward without direct instruction however. One might argue, in addition, that tadoma is simply tracking the vocal channel, using a kinesthetic rather than an auditory channel. As many of you have probably anticipated, sign language offers a stronger example to show that language is not inevitably tied to speech. Sign language is a visual-gestural language. It has been rapidly growing in popularity and is also responsible for baby signs being used by parents to facilitate dialogue with their babies. Linguists have shown that sign languages are as rich and complex as any spoken language. And they do not necessarily have a visual correspondence through their referent. That is they are not simply a pictorial language. Most importantly for our purposes, there are strong evidence that sign languages are naturally learn from birth without any formal instruction. Spoken language and sign language can be acquired naturally from birth onward. On the other hand, it is commonly believed that learning to read must be delayed and usually requires formal instruction. Why would such a dramatic difference exist? It cannot be the modality of discourse. Yes, it is true that spoken language is auditory and reading is visual. When born to signing parents however, deaf children acquire sign language at more or less the same rate and with the same competence as speech. Evolutionary theories might rationalize the difference in speech and reading acquisition because speech has an older history than writing. The age of speech cannot be estimated exactly, but it is at least 50,000 years old or more. Whereas writing arrived later, around only 5,000 or 6,000 years ago. So perhaps ontogeny, development, does recapitulate phylogeny, its evolutionary history. But we can counter with drawing a distinction between proximal and distal causes. Influences that support current speech and reading acquisition might not resemble those that led to their original occurrence. Although it is true that writing, at least in alphabetic orthographies, is a surrogate of spoken language, it does not imply that reading must be formally taught as a system derived from spoken language. Evidence for acquiring reading independently of speech would exist if some children, for example the deaf, would learn to read without learning speech or if there were synergy in learning speech and reading simultaneously. Somewhat related, there are impressive observational results of preschool children who talk late but are able to communicate via augmentative and alternative communication devices, which often depend on orthographic indices. We will emphasize another potential important difference between speech perception and reading, which can be described by time-on-task. This variable is a major influence of learning across all domains that have been studied. To date, children have been immersed in spoken from even before birth and certainly after. This type of immersion does not currently occur for written language. Thus time-on-task, a significant determinant of learning, might be responsible for the discrepancy we now have between speech and reading acquisition. If time-on-task is the culprit, how do we implement the necessary time for written language immersion? [MUSIC]
