Understanding Nonverbal Learning Disorders (page 2)
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.
Nonverbal Affect Lexicon and Emotional Semantics
Bowers and Heilman believe that the damage to the fiber pathways in the right hemisphere caused a roadblock between the nonverbal affect lexicon located in the right hemisphere and the language areas in the left hemisphere that are needed for naming. Thus, although the nonverbal affect lexicon was not inherently damaged, the lesion blocked the access route between that knowledge and the generation of a verbal label for it.
How important is it to be able to identify emotional signals? The significance of these right hemisphere skills is highlighted when we examine the impact of their loss on the quality of a person's life. Right brain damaged patients can be extremely difficult to deal with on a daily basis. They often seem to have lost the most basic social skills--simple things such as knowing when to take turns in a conversation (typically cued by facial expression and voice intonation), or how close to get to someone while engaged in a conversation. They tend to be very talkative but the things they say are often described by listeners as shallow and inconsequential. They laugh during inappropriate moments, or display other emotions that don't seem to fit the context. To the dismay of those around them, they seem to have difficulty putting themselves in someone else's shoes and often alienate their family members and friends. It seems likely that the inability to comprehend nonverbal signals is at the root of many of these problems. Thus, in trying to help these patients and their families adjust, one focus of rehabilitation is to modify these behaviors and to help the brain injured patient to become more sensitive to emotional and social cues.
Anosognosia and "Plausibility" Assessment
Even more problematic, they often seem to be unaware of their disabilities, a syndrome called anosognosia. Patients with anosognosia don't realize that they aren't thinking clearly, or that they can't do all the things they used to do. For example, an airplane pilot with a right hemisphere stroke and a left hemiparesis talked about going back to work the very next day, ignoring the fact that he was even in the hospital.
This problem may be related to another important specialization of the right hemisphere. The difficulty that right brain damaged patients have in understanding social situations seems to extend to a difficulty in contextualizing all sorts of information. In an interesting study, Howard Gardner and his colleagues had right and left brain damaged patients listen to a series of narratives. The narratives were designed so that each one included something that didn't make sense in the context of the story. When asked to recall the story, the left brain damaged patients and the non brain damaged control subjects either changed the nonsensical detail to fit the story or simply left it out. In contrast, the right brain damaged patients not only remembered the detail but tried to make the rest of the story fit. This process caused them to sacrifice the essence of the narrative and end up with a highly implausible construction. On the basis of these results, Gardner and his colleagues suggested that the right hemisphere houses a system that assesses the 'plausibility' of events. This system, they suggest, is important to the ability to judge the likelihood or probability that an event could actually take place. This notion fits well with some other data showing that right brain damaged patients violate the contextual reality of objects (drawing things like a 'potato bush', for example). These results might be related to the anecdotes about right brain damaged people who seem to be unaware of the magnitude of their deficits--here, they seem "out of touch with reality" in another way.
The fact that the right hemisphere would be in a special position to judge the 'reality' of something seems to be compatible with its other specializations, such as the ability to judge spatial relationships and the ability to distribute attention across both sides of space. The fact that right brain damaged patients have difficulty getting the gist of a narrative suggests that the right hemisphere is also good at judging relationships between other kinds of concepts as well, a skill that would be needed to put things in an appropriate context i.e. to assess how realistic they might be.
Reprinted with the permission of MAAP Service, Inc. © 2008 MAAP Service, Inc.