Understanding Nonverbal Learning Disorders
Developmental Processes and Dysfunction of the Right Hemisphere:
Implications for Learning and Social Perception
1. The Right Hemisphere and Emotional Information Processing
It is well-known that the left hemisphere of the brain is specialized to process verbal information, and to control the production of speech. It is also relatively well-known that the right hemisphere of the brain is specialized to process visuo-spatial information. The right hemisphere of the brain is also specialized to process a variety of other kinds of information. This fact is less well-known, partly because for many years the left hemisphere was considered the "dominant" hemisphere for all or almost all kinds of information processing. Therefore, not enough research was carried out on right hemisphere functions for us to understand fully its importance in everyday cognitive, social and emotional functions.
One of the most important aspects of right hemisphere function has to do with the ability to understand emotional information. The right hemisphere excels in the recognition, interpretation, and expression of emotion. These functions are interwoven with the visuo-spatial functions that are specialized in the right hemisphere. For example, it requires complex visuo-spatial processing to decipher the meaning of a facial expression or to understand a series of complex gestures.
Most of us take for granted the knowledge that when we notice a person frowning at us, it means something very different from a smile, say, or a wrinkled nose. Sometimes, a frown might mean puzzlement, suggesting a need for clarification or explanation. Often, a frown will signal displeasure or disapproval. It might cue us that something we have said or done has annoyed or disturbed another person. That facial expression then becomes an important piece of information that we can take into account as we engage further in the interaction. We can decide to ignore the frown and continue on our path, knowing we are in danger of a confrontation; or we can decide to avoid the confrontation and steer clear of the disturbing conversation or behavior. Human beings, who coexist with each other in highly complex social structures, depend on such nonverbal signals to communicate effectively.
There are several channels for such nonverbal signals, including facial expression, tone of voice (often referred to as prosody), and gestures. It turns out that when investigators compare the ability of left (LBD) versus right brain damaged (RBD) patients to make sense of emotional information conveyed through any of these channels, they typically conclude that the right hemisphere is specialized for these skills. Patients with right hemisphere lesions in parietal and parietotemporal regions are significantly impaired relative to patients with left hemisphere lesions in comprehending emotional tone of voice. RBD patients also perform more poorly than LBD patients when asked to discriminate between emotional faces and to name emotional scenes, when matching emotional expressions, and when grouping both pictorially presented and written emotional scenes. RBD patients are also impaired in the comprehension and appreciation of humorous or affective aspects of cartoons, films, and stories.
According to Dawn Bowers and her colleagues, who have studied many patients with damage to the right hemisphere, these kinds of tasks rely on a nonverbal affect lexicon, a knowledge base coming under the rubric of "cold cognition", so-called because it involves judgments and knowledge about emotion that are independent of an emotional state or experience. The nonverbal affect lexicon is contrasted with another type of cold cognition, referred to by Bowers and colleagues as emotional semantics, which is the understanding of the link between certain situations and specific emotions. They make a distinction, therefore, between the ability to comprehend the meaning of a facial expression, a gesture, or a tone of voice, and the ability to know that 'fear' is likely to be the response to a hold-up, or 'sadness' the response to a death. Whereas the nonverbal affect lexicon appears to be housed in the right hemisphere, the mechanisms that mediate emotional semantics seem to be distributed widely, and are not hemisphere specific. Bowers and Heilman described an interesting case that suggested that disconnections between different emotional functions can occur from damage to the right hemisphere. They evaluated a 54-year-old man with a large glioma located in the deep white matter of the posterior parietotemporal region in the right hemisphere (Bowers and Heilman, 1981, 1984). Note that the cortex itself was not damaged-- just the fiber pathways that carry information from the posterior parietotemporal areas of the right hemisphere to other parts of the brain. This patient had no difficulty matching different views of facial emotions. However, he was unable to name an emotion depicted on a face, nor could he understand labels for facial emotions. Thus, when the task involved translating the meaning of a facial expression into a verbal label, his performance was impaired. It is important to note that his anomia (inability to name) did not extend to other kinds of stimuli, including the ability to identify familiar faces. Furthermore, his ability to express emotion was not disrupted, nor was his ability to describe his emotional experience.
Reprinted with the permission of MAAP Service, Inc. © 2008 MAAP Service, Inc.