The Nature and Function of Semantic Memory
The area of semantic memory involves stored information regarding the features and characteristics, which determine the processes of retrieving, using, and producing information in various cognitive processes such as thought and language comprehension/production (Martin & Chao, 2001, p. 194).
In the period before the development of mechanisms for studying brain functioning such as brain imaging techniques, most researchers studied the domain of semantic memory using different attributes of patients suffering from brain injury or diseases.
The research findings identified two major brain areas in the left hemisphere, which determine various functions of semantic memory. For instance, some studies document that patients suffering from damages to the brain (particularly the left prefrontal cortex, LPC) demonstrated various difficulties in retrieving words relative to various cues related to different semantic categories (Martin & Chao, 2001, p. 194).
It then follows that the left prefrontal cortex (LPC) plays a major role in semantic memory relative to the process of retrieving semantic information. On the other hand, patients with damaged temporal lobes demonstrated the inability to name objects and various difficulties in retrieving information regarding object-related attributes.
These findings also suggest that the function of storing object-specific information is limited to the temporal lobe. Consistent with these studies, recent brain imaging studies regarding semantic functioning show that the function is limited to certain regions of the brain including the left prefrontal, posterior, and the parietal temporal lobes.
Additional studies demonstrate that semantic representations particularly object concepts are determined by sensory and motor attributes, which come about as a result of experience. For example, in studies involving word-generation, it is documented that object-specific information may be stored in the ventral and lateral regions (posterior temporal cortex).
This suggestion relates to experiments whereby the subjects were asked to generate object-specific information, and in the process, it is reported that these subjects demonstrated increased activity in the posterior region (Left middle gyrus).
Although there are some differences in brain activity within the ventral and lateral regions (posterior temporal cortex) relative to the type of retrieved information, different studies converge on the notion that object-specific information is stored in different neural systems, which show heightened activity during perception (Martin & Chao, 2001).
The Basic Functions of Language
According to a body of research studies, the human ability of reading and writing, which underlie speaking and understanding language, may be a secondary process that partly arises from visual identification of objects (word forms) and the primary language system (Witruk, 2002, p. 9).
Here, language comprehension is based on various aspects of the primary language system including the morphological, semantic, phonological, and syntactic information. Accordingly, the initial stage in comprehending language entails the phonological processing level, which involves assembling of phonological information to aid the development of phonological representations.
The phonological representations act as a window through which lexicons are accessed by matching the representations with lexical entries. Subsequently, the lexical level entails assembling of semantic, morphological, and syntactic information, which form the basis for sentence formation.
At the sentence level, syntactic structures are developed through relating various thematic elements of the sentence to produce sentence representations. Finally, language comprehension is the product of integrating sentence representations into prior knowledge discourses (Witruk, 2002, pp. 9-11).
Accordingly, language comprehension plays a major role in ensuring that different language forms achieve their functions, which include informing, expressing, and directing. Basically, the informative function of language entails the process of communicating information. Therefore, the informative function of language can affirm or deny a proposition put forth in a sentence.
Moreover, this function can be used to describe a world of knowledge or explaining the state of affairs in the real world besides providing the underlying reasons. On the other hand, the expressive function of language involves reporting the feelings and/or attitudes of the speaker or writer. Moreover, this function can evoke feelings and/or emotions in the listener or reader.
Here, literature and poetry provide the best examples in which language discourses are employed to deliver emotions, feelings, and attitudes. Overall, the expressive function of language entails two major aspects of language, which include evoking and expressing feelings. Finally, the directive function of language underlies the process of using language to cause or prevent overt actions.
Therefore, this function is widely used in delivering commands and requests, and in most cases, the function is considered to be neither true nor false (Witruk, 2002, pp. 11-15). For example, if someone says, “Close the windows”, the directive may be taken to be a request or command besides being declarative.
The Stages of Language Production
As indicated earlier, language comprehension follows a series of stages whose end result is the utilization of sentence representations (meanings) in the real world by relating them to the existing body of knowledge. This constructive process may follow a top-down or bottom-up processing approach to arrive at the desired language meaning.
In contrast, language production entails the process of constructing language meanings and expressing those meanings (O’Malley & Chamot, 1990, p. 37). Accordingly, language production can be divided into three major stages, which include construction, transformation, and execution.
In a nutshell, the construction stage involves selection of communication goals before identifying appropriate meanings while the transformation phase involves application of various rules in transforming meanings into messages. Subsequently, the execution stage entails the expression of messages in various forms (audible or observable forms).
Just like in language comprehension, language production is influenced by various mental processes. For example, in the construction stage, the writer or speaker sets communication goals after which, the goals are converted into facts through searching for declarative knowledge and identifying various information sources that reflect the established goals.
Subsequently, the speaker or writer decides on the structure of facts and information selected using discourse knowledge and sociolinguistic rules. On the other hand, the transformation stage involves instances whereby the speaker or writer uses the facts or information selected in the construction stage to come up with meaningful sentences (O’Malley & Chamot, 1990, p. 40).
This process is analogous to the parsing process of language comprehension in that the incoming information is subdivided to different meaningful units. Subsequently, the language production systems will allow an action to be expressed in the presence of certain conditions.
For example, writing can only occur after various plans and intentions have been converted into meaningful mental representations, which may include sentences or sentence fragments. On the other hand, the execution stage is the work of the hand and mouth.
For example, after the plans, ideas, or intentions have been converted into meaningful mental representations, it is up to the speaker or writer to communicate them through writing them down or delivering them in form of a speech (O’Malley & Chamot, 1990, p. 45).
The relationship between Semantic Memory and Language Production
A myriad of studies document that during speech (language) production, information can flow in either the vertical or horizontal direction. In the vertical flow direction, the information is said to follow through various processing stages within a single unit (single word).
On the other hand, in the horizontal flow direction, the information flows from one sentence unit to the other irrespective of the processing stage of the sentence elements (Yang & Yang, 2008, pp. 267-284).
Therefore, studies on the horizontal flow of information are more concerned with the production of phrases or sentences (multiword utterances) as opposed to those dealing with the vertical flow. Here, several eye-tracking studies have tested whether the access of multiple-words occurs in a serial or parallel form.
As a result, some studies document that multiple-word access occurs in a serial manner. For example, in order to produce the phrases, ‘arm and boat’, the studies show that the subject processes the second word (boat) immediately after the completion of the semantic and phonological processing of the first word (arm) (Yang & Yang, 2008, p. 268).
It then follows that the serial processing of information allows room for spreading of the processing load during language production. However, this process is vulnerable to disfluency. Other studies have tested the parallel and interactive view of producing multiple-word phrases.
In these studies, it is documented that the access of one lemma in a sentence may interact with, and therefore, be influenced by the access of others (lemmas) within the same sentence.
Therefore, the interaction of semantic and grammatical information could influence the process of language production relative to various existing conditions. Overall, there is evidence to suggest that semantic interference and phonological facilitation play a major role in information flow, and thus, language production.
References
Martin, A., & Chao, L.L. (2001). Semantic memory and the brain: Structure and processes. Current Opinion in Neurobiology, 11, 194-201.
O’Malley, J.M., & Chamot, A.U. (1990). Learning strategies in second language acquisition. New York: Cambridge University Press.
Witruk, E. (2002). Neuropsychology and cognition: Basic functions of language, reading and reading disability. Norwell, Massachusetts: Kluwer Academic Publishers.
Yang, J., & Yang, Y. (2008). Horizontal flow of semantic and phonological information in Chinese spoken sentence production. Language and Speech, 51(3), 267-284.