Page 12 - Winter 2020
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 When Speech Goes Wrong: Evidence from Aphasia
Sheila E. Blumstein
   The sounds of speech are our primary means of communicating with the surrounding world. Speech sounds are critical for communication because they serve as the necessary link to the words, sentences, and meanings of the language system. And yet, speech sounds in both perception and production are vulnerable to errors. Whether fatigued, distracted, or just getting older, we all have experienced times when we have misperceived what was said, as in “let’s look for the cape” misheard as “let’s look for the cake” (Garnes and Bond, 1980, p. 232), or we have misspoke an intended message, as in “speech production” produced as “preach seduction” (Fromkin, 1980, p. 6). As annoying as these “slips of the ear” and “slips of the tongue” might be, they occur relatively rarely.
Unfortunately, this is not the case for those individuals who have sustained brain injury resulting in aphasia, where deficits in perceiving and producing speech are pervasive. Examining how speech breaks down in aphasia is crucial for understanding the nature of the impairment, and this ultimately informs the aphasia diagnosis and strategies for rehabilitation. Such analyses also afford a unique window into how speech is represented and processed in the brain and how it ultimately connects to language.
Two avenues of research are followed in this article. First is a look at how brain injury affects the production and perception of speech sounds. Then the acoustic properties giving rise to these sounds are examined. Focusing on the acoustics of speech allows for distinguishing “normal” variability in speech, often not perceived by listeners, from “pathological” variability.
A Brief Introduction to Aphasia
Aphasia can occur at any time across the life span. However, the focus is on those individuals who have sustained a brain injury as adults where language, speech, and the cognitive resources underlying their usage is normal and fully developed prior to the injury.
By definition, aphasia is a language disorder affecting speaking and understanding as well as associated language skills such as reading and writing. The National Aphasia Association (see reports that there are over 2,000,000 people who have aphasia in the United States, with about 180,000 new cases occurring annually. Stroke is the most common cause. Despite the fact that the brain has two structurally symmetrical hemispheres, it is the left hemisphere that is typically dominant for language and hence vulnerable to aphasia.
It is important to understand that there is not one aphasia. The type and severity of language impairment varies as a function of the locus and extent of the brain injury. It is beyond the scope of this article to review all of the
  12 Acoustics Today • Winter 2020 | Volume 16, issue 4
©2020 Acoustical Society of America. All rights reserved.
Figure 1. The left cerebral cortex (anterior to the left) showing the four lobes of the human brain: frontal, temporal, parietal, and occipital. The neural areas (inferior frontal gyrus [IFG]; MOTOR; superior temporal gyrus [STG]; middle temporal gyrus [MTG]; AUDITORY; angular [AG] and supramarginal [SMG] gyri; red) are involved in language and speech processing. The red dashed ovals encircle the neural areas that, when damaged, typically result in Broca’s and Wernicke’s aphasia. The insula, an area implicated in Broca’s aphasia, is not shown because it is located under the surface of the cortex.

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