Introduction
The analysis of parts of the brain has been an object of investigation for many centuries. Modern neuroscientists continue to investigate the various functions of the brain, awareness, and the sensory system (Tatham and Morton 242). They examine the links within these areas to find out how they can impact one another in the formation of various processes in people’s organisms. For instance, our speech production process is a result of neural interaction and involves two components: the ways of producing speech in terms of mental tasks and the related relevant brain tasks, which together form speech behavior (Tatham and Morton 242).
Speech production necessitates a combination of various types of information, such as motor, auditory, and somatosensory. These information forms are reflected in the frontal, temporal, and parietal lobes of the cerebral cortex (Guenther and Vladusich 408). In the integration with subcortical systems such as the brain stem, basal ganglia, and cerebellum, the cortical areas, along with their operative links, establish the motor control system (Guenther and Vladusich 408-409). The current literature review is dedicated to the mechanisms for speech production and their implications in the field of neuroscience.
Speech Production Mechanisms: Present State and Future Implications
In their research, Guenther, and Vladusich investigate DIVA — a “computational model” that creates a quantitative framework, which makes it possible to analyze the functions of different brain areas that take part in the production and acquisition of speech (408). The article pays special attention to the speech sound map of DIVA (409). According to Guenther and Vladusich, this map is engaged at the initial stage of sound production (409). When the neurons of the speech sound map are initiated, the “motor commands” appear in the primary motor cortex (Guenther and Vladusich 409). These commands are enacted through two control subsystems: feedforward and feedback (Guenther and Vladusich 409). The authors note that the speech sound map performs three crucial functions: promoting the discrete sounds obtainment, delineating the probable signals of sensory feedback, and helping to extract the motor programs necessary for the formation of speech sounds (Guenther and Vladusich 418).
Simonyan et al. dedicate their article to progressive experiments in the sphere of speech motor regulation (11440). Simonyan et al. analyze the cohesion of the motor cortex in their study (11440). The authors emphasize scholars’ rising interest in motor control (11440), remarking that electrocorticography (ECoG) studies are a productive way to enhance scholars’ comprehension of the specific organization of the ventral sensorimotor cortex (vSMC) for the speech motor government (11444). In addition, Simonyan et al. note that modern functional magnetic resonance imaging studies (fMRI) and diffusion-weighted tractography are productive in establishing the extensive design of neural network pertaining to the speech sensorimotor command (11444). The authors discuss the following innovative technologies in “invasive human brain mapping” as a changeable cortical perturbation, concurrent field mapping, and the discovery of the electrical stimulation tract (11442). Simonyan et al. remark that these advances in research make it possible to investigate the arrangement of vSMC and the neural mechanisms taking part in speech production control (11442).
Various Types of Feedback from Speech Movements (Somatosensory and Auditory)
Lametti et al. investigate somatosensory (SF) and auditory (AF) feedback occurring in the course of speech production (9351). The authors note that these two types of feedback are closely related (9351). Lametti et al. consider SF the core method of controlling the precision of speech production by the cortical speech areas (9351). To perform the experiment, Lametti et al. resorted to auditory and somatosensory perturbations, kinematic and acoustical analysis, and quantifying adaptation (9352-9353). The scholars conclude that SF and AF can change individually or in combination when a person repeats an uncomplicated speech utterance (9356). Lametti et al. also draw attention to the negative interaction in the compensation measurement for the two perturbations (9356). The negative correlation, according to Lametti et al., appears as an outcome of a favored reliance expressed by the participants for either SF or AF in the course of speech production (9356).
In his research, Perkell also analyzes auditory feedback as a means of acquisition and maintenance of auditory objectives in the progress of feedforward and feedback control processes (382). The author argues that speakers who have sharper sensory discrimination acquire more definite goal areas and, as a result, generate the sound of speech in more divergent ways (382). Perkell pays special attention to the role that phonemic goals play in speech production (385). According to the author, the phonemic goal areas are delineated by the general characteristics of a person’s perception and production structures (385). Perkell emphasizes the importance of cooperation between the somatosensory and auditory spheres (386). He notes that auditory objectives prevail at the early learning stage, where they form the feedforward commands (386). The somatosensory goals, according to Perkell, become an element of the control mechanism when the feedforward motor commands are achieved (386).
Speech Disorders and Ways of Managing Them
Apart from analyzing the investigation into new ways the brain functions, researchers pay attention to speech difficulties that may occur due to brain damage. In her article, Adank summarizes the results of two activation likelihood estimation (ALE) studies aimed at finding out the reasons for difficulties in speech production and comprehension (42). The author notes the spheres most frequently activated when there are complications in intelligible speech: the bilateral anterior insulae, the right and the left posterior middle temporal gyrus (MTG), and anterior supplementary motor area (pre-SMA) (49).
The article by Basilakos et al. is dedicated to two language disorders: acquired apraxia of speech (AOS) and aphasia (1561). The authors aim to investigate whether the errors in the production of speech in the two disorders are connected with particular types of brain damage (1561). Basilakis et al.’s research allowed the authors to establish the sectors in somatosensory and cortical motor spheres that are capable of predicting the AOS failures (1564). The authors conclude that the employment of structural neuroimaging may enhance the differential diagnosis of the failures in speech production caused by AOS and aphasia respectively (1565).
Conclusion
Neuroscience is making critical achievements in the investigation of speech production mechanisms in the human brain. A variety of scholarly articles and experiments have been dedicated to the analysis of the functions of different parts of the brain in the speech process. Researchers have been studying various models of speech regulation and acquisition. Another research trend is devoted to feedforward and feedback types of speech movements. Also, a considerable amount of scholarly work is dedicated to the analysis of speech disorders and ways of dealing with them.
Because of comprehensive research regarding the role of the brain in the production of speech, present and future scholars may focus on the particular areas and identify the gaps in the studies to put forward new research aims.
Works Cited
Adank, Patti. “The Neural Bases of Difficult Speech Comprehension and Speech Production: Two Activation Likelihood Estimation (ALE) Meta-Analyses.” Brain and Language, vol. 122, no. 1, 2012, pp. 42-54.
Basilakos, Alexandra, et al. “Patterns of Poststroke Brain Damage That Predict Speech Production Errors in Apraxia of Speech and Aphasia Dissociate.” Stroke, vol. 46, no. 6, 2015, pp. 1561-1566.
Guenther, Frank H., and Tony Vladusich. “A Neural Theory of Speech Acquisition and Production.” Journal of Neurolinguistics, vol. 25, no. 5, 2012, pp. 408-422.
Lametti, Daniel R., et al. “Sensory Preference in Speech Production Revealed by Simultaneous Alteration of Auditory and Somatosensory Feedback.” The Journal of Neuroscience, vol. 32, no. 27, 2012, pp. 9351-9358.
Perkell, Joseph S. “Movement Goals and Feedback and Feedforward Control Mechanisms in Speech Production.” Journal of Neurolinguistics, vol. 25, no. 5, 2012, pp. 382-407.
Simonyan, Kristina, et al. “New Developments in Understanding the Complexity of Human Speech Production.” The Journal of Neuroscience, vol. 36, no. 45, 2016, pp. 11440-11448.
Tatham. Mark, and Katherine Morton. Speech Production and Perception. Palgrave MacMillan, 2006.