One Simple Speech Pattern Could Predict Your Risk Of Cognitive Decline

The human brain is a truly remarkable organ. Whereas most animals have brains that correlate to the size of their bodies, human brains are much larger than they should be given our body sizes. What's more, the human cortex — an area of the brain responsible for planning, reasoning, language and other uniquely human characteristics — is immensely enlarged giving humans a unique ability to think and reason in ways that no other creatures can. In short, then, the human brain is a special product of evolution, but it's not without its issues.

For one, it doesn't last forever. We all get old, and every year seems faster as we age. Along with this disconcerting sense of time speeding up, signs of cognitive decline start to emerge in our later years — for some earlier than others. Often, these signs aren't all that obvious. One study, for example, found that nightmares may predict cognitive decline later in life, but we don't necessarily worry about getting dementia every time we have a bad dream. When we can't remember the word for something, however, we might feel a little pang of concern.

We've all had trouble remembering specific words and giving ourselves a hard time for not being able to recall a term that's on the tip of our tongue. It's not that rare an occurrence but there's still that part of us that wonders if we've lost a few brain cells. Well, it turns out that not being able to recall specific words isn't the thing we should be worried most about when it comes potential cognitive issues down the line. 

There is actually a technical term (that doesn't sound all that technical) for the phenomenon of not being able to recall a specific word: Word-finding difficulty, or WFD. While we've all had experiences whereby we can't recall certain words or phrases, that same experience becomes more common for many as they age. As such, researchers are eager to understand whether WFD and its underlying mechanisms might help with diagnosing neurodegenerative diseases, such as Alzheimer's, early.

In a 2023 study, published in the journal Aging, Neuropsychology, and Cognition, researchers looked at three influential theories about WFD. The processing speed theory suggests that a general slowdown of all cognitive processes is to blame for such a phenomenon, whereby the brain simply gets slower as we age and this results in us taking longer when finding the right words. The inhibitory deficit hypothesis, on the other hand, posits that older people find it harder to dismiss irrelevant information when searching for the right word, and get confused when being confronted with the various pieces of information their brain provides, leading them to pause when trying to find the right word. Another theory, the transmission deficit hypothesis, looks at words in a specific structure, with concept, word form, and sound forming the three layers. As we age, the hypothesis argues, the link between the word form and sound weakens, resulting in older people being able to identify the concept but not necessarily the right sound to express it. In the study, however, researchers found that processing speed was more indicative of cognitive decline overall and a better explanation for WFD.

The study involved 125 adults aged 18 to 85, who took part in executive function tasks as well as providing a naturalistic speech sample. For the latter, participants were asked to describe a scene before recordings of their description were analyzed by artificial intelligence, which identified features of their speech including the speed with which they talked, how long they paused between words, and their range of vocabulary. The participants then took executive function tests that measured concentration, thinking speed, and the ability to plan and carry out tasks. By comparing the results of the tests with the natural speech sample, the researchers were able to identify that age-related decline in the executive functions (concentration, thinking speed, and planning) was closely linked to participant's rate of speech. This suggests that the processing speed theory is a more accurate description of why WFD happens, that is, as a result of a general slowdown in cognitive function.

The researchers also used a picture-word interference task, which involved showing participants pictures while playing audio clips of either a word related to the picture or a word that sounded like the object in the picture. This was designed to separate the steps involved in correctly naming an object: finding the right word and actually saying it. The team found that the natural speech speed of older participants was linked with their speed when naming pictures. This suggests a general slowdown in processing is at the base of wider cognitive and linguistic changes that come with age. As such, slowed speech could be a better indication of cognitive decline than the odd WFD experience, and verbal reaction time could be an important clinical measure.