15.5: The Right Hemisphere's Contribution to Language

Learning Objectives

1. Describe the cause and symptoms of hemineglect (unilateral neglect)
2. Describe the primary contributions of the right hemisphere to human language expression and comprehension
3. Identify and describe language pragmatics and its disorders
4. Describe theory of mind and how it is related to autism

Overview

Hemineglect, also known as unilateral neglect, following damage in the right parietal cortex is characterized by inability to attend to sensory inputs on the left side of the body leading to lack of awareness and emotional indifference to these inputs. Because of the disorder, such patients can "lose track" of the left side of their body and limbs because of the lack of attention to inputs from the left side of space including the left side of their own bodies. Some of these patients may fail to understand that the left side of their bodies belong to them. Right hemisphere damage can disrupt the emotional and contextual aspects of language use, suggesting that the right hemisphere is more emotional than the left and that normally the right hemisphere contributes the emotional aspects of human speech.

The Role of the Right Hemisphere in Language

To follow a conversation, a written document, or an exchange of witticisms, you must be able not only to understand the syntax of sentences and the meanings of words, but also to interrelate multiple elements and interpret them with respect to a given context. While various types of damage to the left hemisphere produce the many documented forms of aphasia, right hemisphere damage (RHD) causes a variety of communication deficits involving the interpretation of context. These deficits can be divided into two main categories.

The first category of RHD-induced deficits affect communication indirectly, by disrupting people’s ability to interact effectively with their environment. One example of a deficit that can be caused by RHD is hemineglect (unilateral neglect), in which an individual pays no attention to stimuli presented to the various sensory modalities on the left side of the body. The individual may also suffer from anosognosia: unawareness of such deficits. For instance, some people who have damage just posterior to the central sulcus in their parietal lobe in their right hemispheres cannot even recognize certain parts of their own bodies as being their own. Thus this type of RHD produces a kind of indifference that is the opposite of the minimum emotional investment required to establish harmonious communication.

The other major family of RHD-induced deficits affect communication and cognition directly. These deficits can be grouped under the heading of pragmatic communication disorders, pragmatics being the discipline that studies the relationships between language and the way that people use it in context. Pragmatic disorders can be subdivided into disorders in prosody, discourse organization, and understanding of non-literal language.

Prosody refers to the intonation and stress with which the phonemes of a language are pronounced. People with aprosodia—RHD that impairs their use of prosody—cannot use intonation and stress to effectively express the emotions they actually feel. As a result, they speak and behave in a way that seems flat and emotionless.

The second category of pragmatic communication disorders that can be caused by RHD affect the organization of discourse according to the rules that govern its construction. In some individuals, these disorders take the form of a reduced ability to interpret the signs that establish the context for a communication, or the nuances conveyed by certain words, or the speaker’s intentions or body language, or the applicable social conventions. With regard to social conventions, for example, people generally do not address their boss the same way they would their brother, but people with certain kinds of RHD have difficulty in making this distinction.

Last but not least among the types of pragmatic communication disorders caused by RHD are disorders in the understanding of non-literal language. It is estimated that fewer than half of the sentences that we speak express our meaning literally, or at least they do not do so entirely. For instance, whenever we use irony, or metaphors, or other forms of indirect language, people’s ability to understand our actual meaning depends on their ability to interpret our intentions.

To understand irony, for example, people must apply two levels of awareness, just as they must do to understand jokes. First, they must understand the speaker’s state of mind, and second, they must understand the speaker’s intentions as to how his or her words should be construed. Someone who is telling a joke wants these words not to be taken seriously, while someone who is speaking ironically wants the listener to perceive their actual meaning as the opposite of their literal one.

Metaphors too express an intention that belies a literal interpretation of the words concerned. If a student turns to a classmate and says “This prof is a real sleeping pill”, the classmate will understand the implicit analogy between the pill and the prof and realize that the other student finds this prof boring. But someone with RHD that affects their understanding of non-literal language might not get this message.

Lastly, the various indirect ways that we commonly use language in everyday life can cause problems for people with RHD. In such cases, the speaker’s actual intention underlies their oral statement as such. For example, someone who says “I wonder what the time is now ” is indirectly asking for someone to tell them the time, but a person with RHD may not understand that.

Figure \(\PageIndex{1}\): The oversimplification of lateralization in pop psychology. This belief was widely held even in the scientific community for some years.　The left brain controls functions that have to do with logic and reason, while the right brain controls functions involving creativity and emotion. This simplified view of brain lateralization is no longer considered accurate by neuroscientists. Instead, new research using brain imaging shows that the two halves of the brain work together much more than earlier research had implied. (Image and first two sentences of caption from Wikimedia Commons, remainer of caption by Kenneth A. Koenigshofer, Ph.D.; File:Brain Lateralization.svg; https://commons.wikimedia.org/wiki/F...ralization.svg; by Chickensaresocute; licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license).

Though the left hemisphere is still regarded as the dominant hemisphere for language, the role of the right hemisphere in understanding the context in which language is used is now well established. We know that in the absence of the left hemisphere (for example, when Wada’s test is performed which temporarily inactivates targeted brain tissue), the right hemisphere can produce some rudimentary language. But lesion studies have shown that the right hemisphere’s role in language appears to be far wider—so much so that it is now more accurate to think of the two hemispheres’ language specializations not as separate functions, but rather as a variety of abilities that operate in parallel and whose interaction makes human language in all its complexity possible.

Many theories have been offered to explain people’s ability to adapt their use of language to the interpersonal context. One of these is the theory of mind. According to Premack and Woodruff (1978), the theory of mind is the ability that lets people ascribe mental processes to other people, to reason on the basis of these ascribed processes, and to understand the behaviors that arise from them. Premack and Woodruff were the first authors to use the term “theory of mind”. They did so in a study on the ability of chimpanzees to ascribe beliefs and intentions to human beings. Since the time of this study, the theory of mind has been applied mainly in studies comparing the cognitive development of normal children and autistic children, because the latter represent a population that is known to display deficits in social reasoning from the very earliest age. In normal children, theory of mind (ToM) develops between 3 and 4 years of age and is fully developed by 5 years of age (Roth & Dicke, 2012).

When experimental subjects are asked to identify the emotional content of recorded sentences that are played back into only one of their ears, they perform better if these sentences are played into their left ear (which sends them to the right hemisphere) than into their right (which sends them to the left hemisphere). These results confirm that the right hemisphere has a role in processing the emotional content of speech.

Summary

Hemineglect, also known as unilateral neglect, caused by damage to the right parietal lobe, is a disorder of attention to sensory inputs from the left side of space including the left side of one's own body. Language in patients with this disorder, reflects indifference to sensory inputs from the left half of space. The right hemisphere is involved in understanding the speaker's intentions and the emotional components of language. Language pragmatics including prosody and indirect language appear to be at least in part dependent upon processing by the right hemisphere. Some researchers suggest that damage to the right hemisphere may interfere with theory of mind, the ability to understand that others have minds, beliefs and intentions, and that persons with autism may have impairments in theory of mind.

References

Premack, D., & Woodruff, G. (1978). Does the chimpanzee have a theory of mind?. Behavioral and brain sciences, 1(4), 515-526.

Roth, G., & Dicke, U. (2012). Evolution of the brain and intelligence in primates. Progress in brain research, 195, 413-430.

Attributions

"The Right Hemisphere's Contribution to Language," adapted from Broca's Area, Wernicke's Area, and other Language-Processing Areas in the Brain by Bruno Dubuc, in The Brain from Top to Bottom, under a Copyleft license.