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Introduction to Semantic Cognition

Semantic cognition is the process of identifying and understanding the environment around us, whilst simultaneously applying the appropriate verbal and non-verbal behaviours to particular situations (Jefferies, 2013). This could be as simple as identifying a tree by its leaves and branches, or as complex as behaving more professionally in the workplace setting to conform to societal norms. We are able to access this semantic knowledge throughout our entire lives, as we are constantly manipulating and generalising the information we learn everyday (Martin, 2015). It is believed that the older we get, the more information we retain and process (Dieciuc & Folstein, 2019). This is excluding individuals with pre-existing neurological conditions. Without the ability to understand and interpret semantic knowledge, it would be impossible to observe our surroundings and recognise what it is we are seeing. It would also make it very difficult to appropriately respond to a situation if we are unaware of what it is we are seeing (Martin. 2015). In scientific terms, semantic cognition is the ability to learn from our previous experiences by applying meaning to what we have learnt (Luria, 1976). Semantic cognition shapes our understanding of the world around us through the explanation of words and knowledge of various objects, whilst also shaping our appropriate responses (Maria, 2015). This semantic knowledge is acquired throughout our lives to enable us to perform everyday tasks such as brushing our hair or making a cup of tea (Rodger & McClelland, 2004). Although there is little literature on semantic cognition and what happens to it over time, it is assumed that it is preserved way into the later stages of life. Researchers hypothesized that this preservation of information was due to older individuals having large quantities of knowledge that was obtained over a long period of time (Warrington & Cipolotti, 1996). The Controlled Semantic Framework

For semantic cognition to be effective, it relies on two principal subsystems that help us in acquiring the knowledge we need to help us interpret and recall information at any given time (Patterson et al, 2007). The two interacting principal subsystems are made up of semantic representation (also known as semantic memory) and semantic control. Cooperatively, these subsystems are referred to as the controlled semantic cognition framework (CSCF) (Rogers et al,. 2004; Snowdon et al., 1989). This broad theory has been used to explain a wide variety of brain deficits, ranging from brain damage to aphrasic strokes. Researchers claimed that memories and experiences acquired throughout childhood can be lost or difficult to recall when a person’s semantic system becomes impaired (Mayberry et al 2011). The subsystem referred to as semantic representation in the controlled semantic framework, is where our knowledge of objects (living and nonliving) is stored. In the subsystems we are able to differentiate between objects that are living and non-living as well as being able to interpret what features make them distinguishable. Without this subsystem we would be unable to generate associative relationships between different objects. For example, when we encounter a cow we understand that they usually like living in open fields and eating vegetation such as grass and leaves. Applying the knowledge we learn is impossible if we cannot apply our experiences to new situations (Meteyard et al, 2012). The other subsystem of the controlled semantic framework, is responsible for the executive processes that control knowledge in order to perform the required behaviours for a particular task (Humpphreys et al, 2015). A real world example of this would be reading instructions for how to put up a wardrobe, then applying what you have read to the task. Localisation of the principal subsystems The two subsystems of the controlled semantic framework are dependent on particular regions of the brain that interact with one another. The representative semantic subsystem is thought to be located in the anterior temporal cortices, as this region is responsible for the storing of conceptual information that is obtained through interactions with modality-specific regions (Noonan et al, 2010). Research on the effects of semantic dementia shows that individuals suffering with this neurological condition have significant loss of semantic knowledge as their anterior temporal cortex has been impaired (Pobric et al, 2007). Thus, it is said that the region of the brain known as the temporal anterior cortex is where the representative subsystem is thought to be located. In addition, the control semantic system is said to be linked with an array of networks that is activated in the posterior middle temporal gyrus, the intraparietal sulcus and the inferior prefrontal cortex. Studies on left hemisphere strokes show that damage to this area of the brain, will cause the patient to inhibit irrelevant semantic knowledge. Meaning they lack the semantic control needed to retrieve appropriate words or phrases, and they are unable to create strong semantic connections to understand ambiguous words with competing meanings (Dieciuc & Folstein,  (2019). Semantic errors

Evidence suggests that the two principal subsystems are sustained by an array of neutral networks that can be impaired as a result of injuries to the brain (Jefferies & Lambon, 2006). Many researchers were able to identify the localisation of the two semantic controlled subsystems by investigating damaged regions of the brain that were responsible for control and representation of information (Jefferies & Lambon Ralph, 2006; Patterson et al., 1992). In their findings, they also discovered the presence of semantic errors (Lambon et al., 2017). Semantic errors which are also known as coordinate semantic errors, occur when an individual’s lexical representations and control of semantics is disrupted.. This could be as simple as mistaking a horse for a dog or calling a plate a bowl. These errors are commonly found in patients suffering with semantic dementia and some forms of stroke aphasia. The semantic errors found in these individuals with degenerative diseases offer researchers insight into the processing of semantics and production of speech. It is hypothesized that we are able to locate the origins of  these semantic errors by evaluating the comprehension of words that invoke semantic errors in picture naming tasks (Hodges et al., 1992). A recent study on the coordinate semantic errors exhibited in normal speech production, discovered that healthy participants with no cognitive impairments or damage to their anterior temporal cortex experienced similar speech errors to patients with cognitive impairments when performing simple picture naming tasks. The results showed that the semantic errors exhibited by the normal participants were due to poor semantic control as opposed to the disruption of semantic representation (Hodgson & Ralph, 2008). Although there is little literature on the investigation of semantic error, most indicate that speech impairments arise from damage to distinct cognitive structures (Cloutman et al,. 2009).

References

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