Cerebrum Article

Slow But Sure in an Age of “Make It Quick”

You are in a crowded restaurant, celebrating your grandson’s high school graduation. With the recorded jazz music for accompaniment, you listen to the waiter rattle off a list of the day’s specials. Less than a minute later, you are wondering: Was that salmon? Or swordfish?

No, it’s not simply your memory that’s failing. Brandeis University scientists Patricia A. Tun, Ph.D., and Arthur Wing-field, Ph.D., explore how, as we grow older, changes in our brains affect how we understand and remember what we hear spoken aloud. Some of our capabilities may decrease, but others increase, they argue, and if we modify our high speed technological world to address the strengths of the aging brain, people of all ages will benefit.

Published: April 1, 2000

We live in a fast-paced society, as we never tire of reminding ourselves, with more information, and more complex information, coming at us more rapidly. Laptop computers, cell phones, e-mail, and fax machines keep us in instant touch with the world, but exert tremendous pressure to respond quickly. As many of us are learning from personal experience, growing older can increase these challenges.

Americans are becoming older, on average, and with age our cognitive and sensory systems undergo normal, gradual, but inexorable slowing. The “baby boomers,” some 77 million people born between 1946 and 1964, now comprise one-third of Americans, the biggest generation in our history.1 By the year 2030, some 22 percent of Americans will be over 65.

What are the implications of cognitive slowing for those who are aging and for our society as a whole? If we consider what scientists have learned about changes in our brains as we get older, particularly how we understand and remember what we hear spoken aloud, we may see that while some capabilities decrease, others increase. We need not resist technology but can understand and use it to create situations in which both young brains and old can flourish.

Is Older Always Slower?

What happens to cognitive function as we age? The single problem older people report most often is memory: remembering where you parked your car in a mall parking lot, remembering the names of people at meetings or social gatherings, or walking into a room and trying to remember why you went in there. Age also can increase the frequency with which the name of an acquaintance, a movie star, or the author of a favorite book remains on the tip of your tongue, just out of reach.

Although these difficulties with memory capture our attention, aging is also accompanied by a general slowing of our motor, perceptual, and cognitive speed. This slowing can be found throughout the central nervous system and in all types of human activities as synaptic transmission between the neurons of the brain becomes less efficient. Even the simplest response slows down by milliseconds (thousandths of a second) each year from about age 20 on through adulthood. For example, if we ask a person to press a key on a computer as rapidly as possible every time a light flashes on the screen, this simple response, which takes someone in their 20s an average of .25 seconds, may require .30 seconds for someone in their 70s. Although these differences are small, if there is slowing in each step of a complex operation, these effects will multiply.

Happily, not all cognitive tasks slow equally with age. Researchers at Washington University have shown that an average mental and physical task that does not involve language (for example, keying in a series of numbers) takes about twice as long for a typical 75 year old as for a 20 year old.2 But when a task involves language, such as deciding whether a string of letters is a real English word (“nurse”) or not (“surne”), the older adults only take one and a half times as long as their younger counterparts. This relative preservation of language-related abilities allows people to preserve their skills in communicating with others well into old age.

Expertise in a given activity can also radically affect performance, and thereby compensate for any slowing down in parts of the activity. Well-practiced tasks often show minimal age-related slowing, so that although older typists and piano players may have generally slower reflexes than young adults, their expertise allows them to continue performing at an outstanding level. Similarly, although older expert chess players may have poorer memory for numbers than young chess novices, the old are more proficient at remembering patterns of playing pieces on briefly seen images of chess boards. These are examples of what computer scientists call “expert systems,” which demonstrate a continuously evolving complex pattern of choices. They also illustrate the dynamic interplay between those functions that are lost in aging and those that are preserved.

Understanding Language: Nature’s Expert System

An expert system that occurs naturally is our everyday activity of comprehending spoken language, whether it be casual conversation, listening to a radio broadcast, or trying to follow a fast-talking weather forecaster on TV. Not only is this type of speech fast, but, more often than not, it is heard in the midst of activity going on around us, background noise, or other people talking at the same time. Because we listen like this every day, we tend to take this skill for granted, but it represents an extraordinarily complex task carried out by our brains at a very fast rate.

Understanding spoken language challenges our speed, sensory acuity, and memory. Two nearly identical phrases, producing virtually the same physical signal, must be distinguished by finely tuned mental processes.  Fast speech and a noisy environment make this more difficult. © 486403 / Image Bank

To appreciate the complexity involved in speech comprehension, let us look at all the variations in vocal sounds, the speed, pitch, timbre, and articulation that make up what we call the speech signal. The first notable feature is how quickly we normally speak. In thoughtful conversation, we may speak as “slowly” as 90 words per minute (wpm), but average speech ranges between 140 and 180 wpm. Speech rates are limited by how quickly we can organize our thoughts; when a newscaster or radio announcer reads from a prepared script, the speech rate can easily reach 210 or more wpm—more than three words per second.

When we closely examine the speech signal, we also see that normal speech is surprisingly under-articulated, with individual sounds slurred or skipped, and many words run together, without clear breaks between them. This apparently casual approach to clear articulation actually represents an efficient honoring of what we might call a “principle of least effort”: a functional adaptation in which speakers unconsciously articulate clearly the most important or least predictable words in the context, while putting less effort into the words that are more predictable. When words run together in speech—as is almost always the case—it is our brains that “hear” the breaks between words, even when no breaks are physically present.

The illustration above is a visual representation of one person saying either “a nice bucket” or “an ice bucket.” This “speech waveform” is a computer-created display of the spoken words unfolding over time, with the vertical displacements representing the sound energy of the speech.

The largest vertical displacements represent the syllables and words and the flat areas show silent periods. Taking the speech waveform alone, we can see that “a nice bucket” and “an ice bucket” produce virtually the same physical signal. It is a consequence of our finely tuned perceptual-linguistic system that when we hear the words in the context of a particular sentence, as indicated in the illustration, no ambiguity appears in the boundaries between words.

Unlike reading, where one can go back to re-read an unclear passage, speech runs past the ear at the speed of sound, and then vanishes. If we hear something unclear, whatever “looking back” we need to do must be done in our memory. The bottom line is that understanding spoken language challenges our speed, sensory acuity, and memory: three capacities that are in shorter supply in old age than in youth. It may thus seem paradoxical that comprehension and memory for language are, in fact, very well-preserved throughout our lives. Why this is so illustrates the marvelous subtleties of brain-behavior interactions in the aging brain.

Run that Past Me Again?

Although in normal aging we usually well maintain our competence with language, understanding rapid speech presents a special challenge. We have demonstrated this phenomenon by using a computer that deletes imperceptibly small elements of the speech signal to produce speech that sounds normal, but that is completed in less than the original speaking time.3 Both young and older listeners recalled less from materials that were presented at this rapid rate, but the negative effects of fast speech were particularly pronounced for older adults. Next, by using the computer to insert pauses at the ends of clauses and sentences, we restored the same amount of time that we had previously removed. When time to mentally process the speech was restored in this way, we found that the listeners’ ability to recall what they had heard was also substantially restored. These results show how perceptual slowing can affect comprehension and how this, in turn, can affect one’s memory for what has been heard.

Divide and Confuse

In our modern world, it is rare that we have the luxury of doing only one thing at a time—including listening to what is being said to us. It is now commonplace to see someone talking on a cell phone while driving, or, less alarmingly, while reading a menu in a restaurant. Yet difficulties in dividing attention between two or more simultaneous activities are commonly reported by older adults. Many people consider this difficulty in multitasking a virtual hallmark of aging.

Noisy environments, or even background sounds of any sort, effectively create a situation where our attention is divided. Indeed, in addition to minor memory complaints, a commonly reported complaint in adults, from middle age on, is difficulty understanding conversations in a crowded restaurant or social situation. Partly this is due to worsening of our hearing, but it is also a result of an increasing difficulty with dividing our attention and filtering out extraneous background noise.

To investigate this, we created a laboratory analog to this everyday problem.4 Younger and older volunteers listened to recordings of ordinary English sentences and stories, then immediately tried to recall what they had just heard. When these materials were presented in a quiet environment, we found no difference in memory for the speech. When we superimposed the din of 20 chattering voices over the target passages, however, the older adults’ ability to process the speech dropped off more rapidly than that of their younger counterparts.

Using a similar procedure, we were also able to show that older adults were measurably distracted by even one speaker talking in the background at a normal conversational level, a condition that did not affect young adults’ memory for what they had heard.5 We later observed that the meaning of the distracting speech also has a significant effect on older adults, but not on their younger counterparts. For example, older adults (but not younger adults) will be more distracted by background speech that is in meaningful English than by background speech in a language they do not know, such as Dutch.

Aging is often accompanied by “presbycusis,” a decline in hearing sensitivity, especially for the higher-frequency sounds, as well more subtle difficulties, such as changes in temporal resolution6 or how well our brains distinguish between very brief, similar sounds. The older adults tested in these studies all had particularly good hearing for their age, however, so their difficulties with distraction cannot be attributed simply to hearing losses. They are more likely the result of age-related changes in the brain’s processing of the information.

Fast Noisy Speech

We can see how normal aging thus produces difficulty with fast speech and with noisy or distracting environments. Even more troublesome for older adults is what we have dubbed “fast-noisy speech”: the double-whammy of rapid speech rates and a noisy background. We created in the laboratory a listening environment that effectively simulated the challenge presented to the older listener in many real-life situations, such as a noisy hospital waiting area, with a harried nurse firing off important verbal instructions to a patient. When we combined rapid speech rates with a background of many voices talking at once, we found that older adults’ speech comprehension lagged even further behind that of their younger peers. This provided additional evidence of the difficulties that older adults may have with rapid-fire advertisements and warp-speed news anchors.

As in our previous study, these difficulties were not simply due to differences in hearing sensitivity because of age. In both studies, we focused on young and older adults who had clinically normal hearing. In fact, in this experiment there were virtually no age-related differences in memory for the content of speech when it was presented at a moderate rate and in a quiet background. What caused the noisy conditions to produce the marked age differences in memory? We discovered that the independent measure we had obtained for mental processing speed was the best single predictor of a person’s memory for what had been heard in a noisy environment. This suggests that individuals with faster central processing rates are more efficient at utilizing every available bit of incoming speech that they can detect through the noise.

Remember that these experiments highlight the conditions under which older adults encounter their greatest difficulty. These are constraints on performance but not on older adults’ accumulated knowledge of language and language structure. We may think of older adults as expert listeners, who have spent a lifetime accumulating their skills in decoding and using spoken language. For example, older adults may have problems quickly retrieving a particular word at any given moment, a difficulty that can begin in middle-age, as many of us are aware. Nevertheless, that same person’s vocabulary is likely to remain stable, or even improve, across the life span, particularly if the person remains intellectually active. The special resistance of linguistic knowledge to negative effects from aging, as well as a lifetime of decoding and using spoken language, can combine to offset any constraints that do occur.

Compensation: Depth, Not Breadth

As we look at the aging adult, we find certain generalities, such as a mental slowing that transcends particular tasks and senses. In studies focusing on sight, rather than on hearing, older adults who are asked to find a specific letter out of a changing array are slowed more than younger adults as the number of irrelevant items increases. We can see here many practical implications for everyday tasks, such as following complex computer menus or surfing the Internet, which require rapid scanning of large amounts of information.

These visual search studies, in which individuals must focus their search while ignoring potential distractions, are the counterpart of our studies of listening to speech in noisy backgrounds, where we have demonstrated that older adults have more difficulty than the young in concentrating on one voice while ignoring others. Indeed, some scientists have proposed that an inability to filter out extraneous information, beginning at the neural level, may underlie many of the age-related declines in cognitive function.7

Reflecting on all of this research, we see a mixed message, but with a positive note: mental decline and our ability to compensate exist in a dynamic interplay as we age. Certain responses may become slower with age, but people also gain expertise and are able to assemble and coordinate larger sequences of behavior, in the same way that typing or playing a musical instrument becomes nearly automatic with years of practice. As “bottom-up” sensory processes, such as hearing and sight, become less acute, older adults can compensate by using “top-down” contextual information. As memory for detail and verbatim information declines, older adults focus more on the gist of what they see and hear, and often demonstrate greater wisdom in evaluating and coping with situations that are presented to them. When it becomes more difficult to do many things at once, an older person may adapt by focusing on one thing at a time; for some individuals this can also lead to a greater awareness of the present moment and an appreciation for what is important and what is not. Depth of experience may replace breadth of activities.

The Case for Plasticity

With Alzheimer’s disease, in addition to other neural changes, tissue in certain areas of the brain becomes lost as the disease progresses. In normal aging, however, the problem is not so much an actual loss of brain cells but, rather, changes in the connections and metabolic efficiency of the cells. These changes, in turn, have a negative effect on the efficiency with which a nerve impulse can travel, both from cell to cell across the brain and into the brain from outside, such as from the eye or ear.

Recent research has now brought into question the long-standing belief that, unlike other cells of the body, lost brain cells cannot be regenerated, that is, that brain cells cannot divide to form new cells. We know now that nerve cells are constantly forming new connections, even in old age. When damage occurs to neurons or to their connections, healthy neurons can increase the density of existing connections and form new ones. Indeed, the aging brain should be viewed less as multiple sets of static connections than as a still-dynamic neural system marked by continual growth and reduction of synaptic connections among cells.

A recent collaborative study by investigators from Brandeis and the University of Toronto used the technique of positron emission tomography (PET) to demonstrate that when healthy older adults equaled the performance of young adults in a visual memory task, they did so by recruiting networks in additional brain areas beyond those used by the young adults. In this way, additional activity in certain areas of the brain compensated for declining efficiency in other areas, producing a satisfactory end result.8 We have yet to establish how much neural plasticity is operating in the aging brain and accommodating for decreases in neural efficacy, but this is certainly a fertile area for research, along with the question of how to keep the brain tissues healthy.

This neural plasticity has its behavioral counterpart in the dynamic interplay between abilities that remain strong and those that have weakened with age, for example, linguistic knowledge that can accommodate for losses in auditory sensitivity and processing speed. We expect to see considerable research on the full nature of this dynamic interplay in the coming decade.

Preventive Maintenance

Scientists have also focused on practical measures that older adults can take to minimize age-related declines in the functions of their brains and even to enhance their cognitive performance. Notable among these have been studies providing evidence for the benefits of activity—physical, intellectual, and social—that lend scientific credence to the old maxim, “Use it or lose it.”

For example, research such as a recent study reported in Nature is most encouraging about the potential benefits of aerobic exercise in maintaining good cognitive performance.9 Even an exercise program of simple walking, well within the capacity of most adults, has been shown to have significant effects on older adults’ “executive function,” your ability to divide your attention and organize your responses. Other research has shown the benefits of intellectual, as well as physical, activity. A large-scale study carried out at universities and medical schools, including Brandeis, Duke, Harvard, Mt. Sinai, and Yale, found that some of the best predictors of successful cognitive aging included not only strenuous activity and good pulmonary capacity, but also your years of education.10 This is consistent with studies that have shown that both education and verbal ability (which are highly correlated) attenuate age-related cognitive decline, as does continuing to have an active, engaged lifestyle, including intellectually challenging activities such as employment or a stimulating hobby.

Those activities that maintain our overall health can also help specifically to maintain our cognitive abilities. As more and more research focuses on how age-related declines can be minimized or ameliorated, the advantages become ever clearer of a lifestyle that promotes health on all levels—physical, intellectual, emotional, and social. Our understanding of how these different parts of our experience interact has received a substantial boost as researchers in neuroscience, psychology, and the biological sciences pool their findings. For example, we are beginning to learn about the effects of good nutrition on our memory. Although at this point it might not be possible literally to turn back the clock in terms of behavioral slowing with age, we already know some ways to improve our cognitive performance and others are rapidly being discovered.

Shaping a Culture that Works for Everyone

As we as a society consider how best to design our culture in the future, we must keep in mind that, just as we shape technology, technology shapes our perceptions, including our attitudes toward aging. In the same way that advertisements and other media influences have convinced many women in the United States that the appropriate female form is that of a waif-thin teenager, we might come to accept uncritically an increasingly rapid and noisy influx of information from our surroundings. In so doing, however, we would be setting the bar unnaturally high for much of our adult population.

Already we have become accustomed to advertising and media messages crammed into every available niche and moment in our surroundings. We are captive audiences of this flood of messages that saturates our daily lives, from recorded commercial messages as we are on telephone hold for banks, airlines and corporations, to printed ads that appear everywhere, from digital readout messages on the local gasoline pump to ads that cover the entire outsides of city buses.

Radio programming, too, has not escaped pressures on advertisers to fit more information into each available minute. Time-compressing speech to require less playing time (the technique we used to study the effects of speech rates on older adults) has long been used to adjust advertisements to fit into precious allotments of air time. We have all become used to these rapid-fire commercials, many of which include warp-speed “auditory fine-print.” More recently, radio stations have begun to still further increase their commercial profits by using a digital compression system that reduces the air time of the live programming itself in order to squeeze more paid commercials into each hour.11

The attitude here and elsewhere seems to be one of pushing the limits on the listener as far as “the market will bear” in terms of degrading the auditory signal and increasing the presentation rate of the spoken programming. This, albeit unintentionally, plays to the potential weaknesses of older citizens and not to their strengths. Moreover, when people cannot understanding this rapid compressed speech, both they and people around them may falsely attribute failure to diminished cognitive function. We know that such poor self-perceptions of one’s ability to understand and remember can become a self-fulfilling prophesy, with further unfortunate consequences.

Taking into account the changing abilities of the elderly is not condescending, but instead, is in the best interests of people of all ages. Young adults may be able to keep up—if just barely—with a rapid barrage of stimuli, but such a pace may not be optimal for anyone, young or old. Similarly, although distracting stimuli are especially troublesome for older adults, younger people as well can benefit from paring away irrelevant material. For example, some studies have shown that television viewers’ memory for information from weather programs was actually poorer from shows with many colored charts and moving graphics, than for simpler versions with fewer extraneous stimuli. The clutter, noise, and constant barrage of information that surround us daily contribute to the hectic pace of our modern lives, in which it is often difficult simply to remain mindful in the moment.

Ironically, promoting efficient information processing is probably cost effective, as well as important for our quality of life. It would be both futile and unwise to resist all technological change, but rather than being slaves to each new development, we should insist that new technology for widespread public use must serve the best interests of all of our population. Ultimately, we believe that creating technological environments that are sensitive to the capacities of adults of all ages will benefit everyone.

Indeed, each of the factors that we have discussed as having a particularly bad effect on older adults’ cognitive performance (rapid speech rates, divided attention, and background noise) also has a negative impact on the performance of young people as well. Chronically noisy environments, for example, not only cause problems for older listeners, but can be equally damaging to the learning environment of school children.

What helps older adults can be used to benefit everyone. For example, the trains still found in some major airports deliver instructions in a robotic monotone voice and some automated phone directory systems use artificial spoken messages, both of which are difficult for everyone to understand. Considerable research already exists showing that both young adults and, especially, older adults benefit from the natural variations in rhythm, pitch, and intonation of normal spoken messages. Listeners of all ages can benefit from adding these variations to recorded messages.

Most of what we understand today about cognitive aging suggests that those operations that may cause difficulty for young adults will impose even larger burdens for the elderly, and the converse is also true for presenting information in a way that facilitates good memory. In short, more and faster may not necessarily be better, when it comes to incoming information. There are indeed limits to the human information processing system, as well as age-related changes in its rate and capacity, but attending to the needs and the cognitive strengths of the aging population will ultimately serve the larger population as well.


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