One of the most important things to know as a student of speech and language therapy is the history of language acquisition theories. These theories form the foundation of common practice and have informed the development of the therapies that we will use as speech and language therapists.
This essay will discuss and present arguments for three theories of acquisition: the behaviourist model, the social interactionist model, and the information processing model. Each theory will also be discussed in terms of its application to clinical practice.
The behaviourist model of language acquisition came about in the 1940-50s when a lot of research was being done on learning theory and B.F. Skinner is probably the most well-known of the behavioural theorists. According to behavioural theory, all human behaviour is learned. When a person does something it is either positively or negatively reinforced; if the behaviour is positively reinforced its frequency will increase and if the behaviour is negatively reinforced its frequency will decrease and eventually stop. For example, if a child wants to put his hand on the hot stove the pain that this causes will be a negatively reinforcement and he will learn not to touch the stove. Behaviourism suggests that more complex behaviours can also be learned in this way. They argue that this can be done by one behaviour triggering the next (chaining) or by, over time reinforcing a behaviour in a way that it moves towards an ultimate target behaviour. According to Skinner (Owens,2008) humans learn everything through this manner of conditioning, including language. Skinner believed that a child sees models of language in adult communication and when the child imitates this communication, this behaviour is positively reinforced by adults. Skinner theorised that during language acquisition, when a child makes an error adults give the child negative reinforcement and when a child produces the correct language the adult gives positive reinforcement thereby conditioning the child to use the correct form. In terms of word learning, behaviourists suggest that when the child realises a word is associated with an object (e.g. ball), the presence of the object becomes the stimulus for that word. Thus, once the child knows the word ‘ball’ – whenever he sees the ball it will activate the word in his mind so he can say it. In terms of learning sentences, behaviourists believe that the child does this in the same manner as words or through the technique of ‘successive approximation.’ For example, a child hears “Please pass the ball” but this is too complex so he way say “pass ball” instead. As the child gets older the adults in his environment gradually shape his utterance into an adult form through the use of modelling, imitation, and reinforcement (Owens,2008) so that eventually he uses the correct form.
As the influence of a child’s environment on language has become clearer, the importance that behaviourists set on the environment has been supported (Owens, 2008). Over the years, the practice of speech and language therapy has been influenced by the behaviourist model. For example, two techniques from this model that are directly applicable to clinical practice are modelling and reinforcement. In therapy, modelling is often used with children with speech difficulties. One way in which it can be used is for the therapist to model the sound and bring the child’s attention to how it is formed so that they can do it themselves. Using reinforcement is also an important aspect of therapy and a therapist can use it by setting up activities in a manner that positively reinforces the correct pronunciation. For example, a minimal pair therapy where the child gets a sweet when he pronounces the phoneme correctly. According to Owens(2008) there is evidence for the importance of modelling and reinforcement in children as young as 9 months old; this is seen in the fact that by 9 months old a child’s inventory of sounds consists mainly of those that have been said in his environment. In other words, although the child is not speaking the same sounds are constantly being modelled and reinforced in his environment and these are the sounds that will be needed for his speech. A third useful technique for therapists that is suggested by the behaviourist model is imitation. An example of a potential use for imitation in therapy would be with a child who needs to become more aware of his speaking volume or rate- the therapist could have him imitate her speaking at different volumes and different paces to increase his awareness. Evidence to support the usefulness of imitation for generalising sentence structure has been found by Whitehurst and Novak (1973)(Bohannon & Bonvillian, 1993).
The behaviourist model of language acquisition has attracted a lot of criticism over the past decades, much of it brought forward by Chomsky (Owens,2008) who then presented a linguistic model of language acquisition. One of the primary criticisms of the behaviourist model is the fact that it is impossible for a child to be taught every sentence that he ever will have to use- and the behaviourist model doesn’t account for an ability to create novel sentences. Another criticism is the fact that parents don’t use reinforcement consistently and in fact sometimes positively reinforce children’s errors (Owens,2008). Additionally, Chomsky (Owens, 2008) noted that adult speech is full of errors and ungrammatical utterances and therefore would not provide a good model for children to learn from.
As one of the earliest models of language acquisition, this model has been very influential in development of treatments. Our task as future clinicians is to draw ideas from its strengths while keeping in mind the criticisms that have been set forward.
The second theory of language acquisition chosen for this essay was social interaction theory. This model was developed in response to the behavioural and linguistic theories of language acquisition and incorporates aspects of both of these. The social interaction theory suggests that language develops because of its social-communicative function. According to this theory, not only do we have an innate predisposition to language but many environmental factors also affect the course of language development (Bohannon & Bonvillian,1993); the predisposition to language is seen as innate but the structure of language is not. In this model, the relationship between children and their linguistic environment is seen as a dynamic one in which both are dependent on each other for efficient social communication and development of language skills (Bohannon & Bonvillian, 1993). According to this model, social interaction is what conventionalises a child’s language structure. Social interactionists believe that the child uses techniques to develop his or her language such as imitation or rote learning and the environment also adjusts itself to facilitate language learning by the child; as the child shows an increased ability to understand more complex language, the linguistic environment also increases in complexity (Bohannon & Bonvillian,1993). The type of language that parents often use with children is referred to by social interactionists as Child Directed Speech (CDS). Child directed speech includes communication techniques such as motherese, imitation, and scaffolding. This model suggests that children cue their parents to supply CDS and that the function of CDS is to activate the linguistic tendencies of the child (Bohannon & Bonvillian,1993). According to this model, these techniques are used by adults to slowly build the child’s language while enabling adults and children to communicate more effectively (Bohannon & Bonvillian,1993).
A strength of the social interactionist model is that because it drawn on the behariourist and linguistic models it incorporates strengths from both. Much of the evidence for the social interactionist model comes from studies that look at how caregiver-child interactions and CDS assist in language development. One of the big strengths of this model is the fact that it can account for the pragmatic aspects of language. According to Berko Gleason and Weintraub (1976), imitation and rote learning are used by children to learn things like social conventions (e.g. “Thank-you”) and Ninio and Snow(1999) (Bohannon & Bonvillian, 1993) have shown that this model also accounts for the aspects of language that need to be learned socially. E.g. turn-taking, context, cultural conventions.
Further evidence has been found for the effect of social interaction on a child’s developing vocabulary in a study by Tomasello and Farrar (1986)(Bohannon & Bonvillian, 1993)who found that if a mother talks about the objects a child is looking at the child tends to develop a larger and earlier initial vocabulary. Snow (1972, 1977, 1999)(Bohannon & Bonvillian, 1993) has also found evidence for the fact that parents adjust their communication and use different communication techniques to help them communicate more effectively with their child.
The social interactionist model has also attracted criticisms since it’s development. One of the most important things to take into account when looking at this model is the fact that because it is quite young many aspects of it have not been tested. Also related to this is the criticism that social interactionists are seeing causation where there is only correlation (Bohannon & Bonvillian,1993)- that it is impossible to tell from the studies being done whether a language delay is due to the parents lack of CDS or if the lack of CDS was a response of the parent to the language delay already present in the child (Bohannon & Bonvillian,1993). A number of studies have also been carried out related to child directed speech and have found that CDS may not be as simplified as we believe it to be (Bohannon & Bonvillian, 1993). In addition to this, Shatz (1982)(Bohannon & Bonvillian, 1993) argued that there is no mechanism specified for how CDS actually works to improve child language. These criticisms are important to take into account and place further emphasis on the importance of having a evidence-based practice.
The social interactionist model can both inform how an SLT approaches therapy and provide ides for practical application in clinical practice.
This model suggests that children learn through the process of scaffolding. As a therapist this would sugest that therapy be approached by starting a child off with easier tasks and then gradually raising the difficulty level as he improves. The principle of scaffolding could also be applied to choosing target sounds for phonological therapy. For example, starting with sounds that are developmentally earlier and easier to say. An example of a therapy that uses scaffolding and that is frequently used by therapists is minimal pair therapy (Williams et al., 2010). Another way to apply the social interactionist model in clinical practice would be to help the parents strengthen their use of child directed speech and show them how to incorporate effective language learning into their daily routines with the child. An example of a program that uses this type of technique is the Hanen approach. This is a therapy technique that emphasises the importance of parental involvement in a child’s language development. The program places importance on both the treatment of children and the training of parents to help them incorporate language learning more effectively into their everyday lives. (The Hanen Centre, 2011)
The final model of language acquisition used for this essay was the information processing model. The information processing model is a cognitive view of language development which arose along with other interactionist approaches in the 1960s and 70s as a lot of research into the field of cognition was being carried out. As other aspects of human cognition such as memory and perception were coming to be seen as similar to the workings of a computer, some theorists began exploring whether language development could be explained in a similar manner (Bohannon & Bonvillian,1993). This model theorises that language is acquired in the same way as many other behaviours; the brain receives stimuli, interprets it, stores it, and then can generate the proper output by retrieving the stored information (Bohannon & Bonvillian,1993).
According to the information-processing model, humans have an innate ability to learn language due to the presence of a mechanism called the Parallel Distributed Processor (PDP) (Bohannon & Bonvillian,1993) however, like other interactionist models this theory also suggests that the environment plays an active role in language acquisition.
According to this model, the parallel distributed processor works by enabling children to learn language through example and reinforcement. The PDP is a network of nodes and pathways modelled on the neural pathways in the brain. The ‘nodes’ are connected by many levels and layers of pathways. The information processing model is sometimes called the ‘connectionist model’ for this reason. The nodes receive input from pathways coming from many other nodes and if enough pathways stimulate a node the node will activate and a certain output will be generated.
One of the most well-known aspects of the information processing theory is the Competition Model (Bohannon & Bonvillian, 1993) which attempts to explain how exactly these pathways and nodes generate linguistic output. According to this, a child has multiple possible forms of a word in their head (e.g. past tense of
For example, a child learning to say the past tense of
Over the years this model has accumulated evidence both in favour of it and against it. A strength of this model is that it accounts for many aspects of language learning such as how children learn frequently used forms more quickly than other less frequently used forms (Bohannon & Bonvillian, 1993). It also accounts for both the appearance of overregularisation errors and their disappearance. Additionally, in a study by Meyer and Schwaneveldt (1971) (Bohannon & Bonvillian, 1993), it was found that when a word is used it ‘primes’ (subconsciously makes us think of) other related words – therefore there must be some spreading activation in the language processor. This provides evidence for the existence of interconnected pathways. Much of the other supporting evidence comes from the experimental computerised model of the PDP. In 1987, Rummelhart and McClelland (Bohannon & Bonvillian, 1993) ran simulations on this model and found that in the case of simulating past-tense learning and production they got very similar learning patterns to those found in children. Additionally, when part of the language network of the PDP was shut down to simulate brain damage, the resulting performance was very similar to the deficits found in brain-damaged human patients (Bohannon & Bonvillian, 1993). Studies by Elman (1993)(Bohannon & Bonvillian, 1993) using the same computerised model have shown that the learning ability of the system extends beyond words and can also account for the development of the syntactic system if enough examples of adult language are given.
While this model has many strengths, there are also significant weaknesses. First of all, while it can account for the formation of language, it does not account for the acquisition of semantics. Additionally, as admitted by Rohde and Plaut (1999)(Bohannon & Bonvillian, 1993), it doesn’t take into account the social aspect of conversation, in other words, how we decipher language in relation to the social situation and how that affects what we say. Another criticism of the model of the PDP mechanism is that while it does well with information that is presented all at once (e.g. a picture), it has trouble with serial processing (Bohannon & Bonvillian, 1993). This poses a problem since language is serial by nature. Another common criticism of this theory is that information processing theorists make too much of the superficial similarities between the brain and the proposed PDP when there are actually many differences (Bohannon & Bonvillian, 1993).
A strength of this model is the fact that it may give insight into how to approach the treatment of problems relating to the grammatical structures of language. For example, the PDP system showed it could learn proper grammar through bombardment. Therefore, according to this model, bombardment will allow the child to internalise the desired structure because the input pathways will be provided with enough adult-level examples to form the correct pathway. As an application in therapy then, this suggests that the SLT could choose exercises in which the child hears the correct structure over and over again. The PDP model also suggests that each structure must be worked on separately in treatment because they all use different pathways. For example, if past tense is the problem then regular past tense must be worked on and once that structure overgeneralises then the exceptions should be targeted. As an application in clinical practice then, if the child is trying to acquire regular and irregular past tense, the SLT should start with treatment of the regular past tense, wait for that pattern to overgeneralise and then work on individual irregular past tense verbs.
Both imitation and repetition are also implied as practical applications of this model in clinical practice. By having the child imitate the proper form it is suggested that both the proper input and output pathways will be activated, therefore helping the child to solidify the correct one more quickly. Similarly, by eliciting the child to repeat the proper form this model implies that the correct language pathway to solidify more quickly. In a study by Whitehurst and Novak (1973) imitation was shown to be effective in helping children solidify specific rules in their own speech and the techniques of bombardment and repetition were used as part of the treatment in a study by Seeff-Gabriel et al.(2012) which had success in a child learning to generalise the regular past tense.
It is important to note that while these treatments may be effective in some cases, as previously mentioned, there is criticism for the information- processing model. It is our duty as future clinicians to look further into the research and study the effectiveness of these approaches before spending long periods of time on them with patients.
All of the theories discussed here have strengths and weaknesses and all of them have implications for clinical practice. Depending on which theory an SLT is influenced by, the therapeutic approach will be different. One of the keys to being a good speech and language therapist is the ability to look at these different models and see how their strengths can be applied to create effective therapy for the client. In addition to this however, it should be kept in mind that these are only theories of language acquisition and that while we should be very aware of the theoretical underpinnings that influence the therapy and techniques we use, our aim should not be to create a practice based solely on theories. Our aim needs to be to create an evidence-based practice guided by the continuing advances in theories and current research.
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