MAKING SENSE OF YOUR SENSESThe relationship between the world “out there” and the brain’s construction of it “in here” has fed centuries of highfalutin debate. In the 17th century, British philosopher John Locke argued that the brain passively processed information it collected about the world through the five senses. The German Immanuel Kant responded by proposing that the brain played a more active role, constructing the reality that humans navigate every day. Although the world has an underlying reality, he said, humans can never know it directly. Instead, all they have is the brain’s constructed stage set of the world, with sights and sounds independent of the things they represented. A third philosopher, a contrary Irish theologian named George Berkeley, took things even further. He said there is no “real” world. To Berkeley, nothing existed without its being perceived by the brain through the senses. That idea seemed a bit much, not only to wags who wondered where the world went when it wasn’t being perceived, but also to the British lexicographer and essayist Samuel Johnson, who kicked a rock and proclaimed, “I refute it thus!”
MAKING SENSE OF YOUR SENSESTheir debate sheds light on the importance of a healthy brain and healthy senses. The nerves that sense light, sound, smell, taste, and touch are nothing but extensions of the brain. Without the optic nerve and light-sensitive retina, as well as the nerves that stretch and contract the muscles that cause the eye to blink, change focus, and shift its gaze, the brain would have no information to process in the visual cortex. So, questions about whether problems such as declining vision or hearing are matters of the eye or ear, or rather of the brain, are moot. The senses and the brain act as an integrated system, mixing perception and reality beyond the ability to separate them.
The aging process changes the way sensory nerves send information to the brain. All senses become less acute at some point, causing the brain to have greater difficulty distinguishing details. This occurs for a variety of reasons, but two are paramount. First, the minimum amount of information required to register on the senses, called a threshold, increases with age. It takes more sound or more light, for example, to cause sensory nerves to fire, sending electrical signals to the brain. Second, changes in the sense organs themselves effect changes in perception. Alterations in organs and nerves associated with vision and hearing typically have the greatest impact, as sight and sound bear the greatest burden of constructing a mental map of the world that’s useful for walking, driving, working, and other important activities. But changes in smell, taste, and touch shouldn’t be dismissed. A world without pleasant scents and delicious food would lose much of the flavor of life; a world without appreciation of a soft breeze or a lover’s caress also would feel diminished.
OUT OF FOCUSMany vision problems have nothing to do with aging. Myopia, or difficulty in seeing things at a distance, has become increasingly prevalent in the last few decades. It typically starts in childhood. In the United States, myopia rates have increased by two-thirds since the 1970s, a period that correlates to the introduction and diffusion of computers in the home and workplace. Theories that blamed computer monitors and other screens for the apparent epidemic emerged and gained popularity. A study of Alaskan Inuit seemed particularly compelling: They had few cases of myopia until television came to their homelands in the extreme north, when the number of cases zoomed.
However, a 1996 myopia study found no smoking gun. It said computers were no more likely than other forms of long-term, close-in work, such as reading, to be associated with myopia. The strongest indicator of a person’s likelihood to develop nearsightedness, according to a 2007 study of California third graders, is heredity. Rates doubled if a child had one myopic parent and quintupled if he or she had two.
A more recent study, conducted by visual disorder expert Kathryn Rose of the University of Sydney, pointed to lack of exposure to sunlight as a possible contributing factor. Sunlight boosts dopamine levels in the brain, she found, in a way that fights the development of nearsightedness. The threshold for seeing benefits from sunlight seems to be 10 to 14 hours of exposure each week, she said. Slavish devotion to computers, television, and books may be linked to myopia merely because it tends to keep people indoors.
However, evidence remains plentiful for the connection between close work and something called “transient myopia,” which is the bleary vision associated with long periods of reading. It results from the eyes’ constant focus on a near plane. The condition won’t cause permanent myopia, but it’s an inconvenience in a world that relies so heavily on reading. The strain of prolonged attention to a computer screen also causes stress. It can cause eyes to go dry (from lack of blinking), and result in headache and muscle pains in the neck and shoulders. Once the symptoms of eyestrain appear, sufferers can try closing their eyes and rubbing their temples to feel better, or to improve reading conditions by increasing text size on a computer screen and adjusting ambient light.
HOW TO STAY SHARPThe eyes operate through muscle contractions. Exercise strengthens the muscles surrounding the eyes and helps keep their lenses flexible. Computer users in particular should take short breaks throughout the day to exercise their eyes. Exercises have been shown not only to help maintain a current level of vision but also to improve vision among people 65 and older.
Eye exercises include the following, all of which should be accompanied by regular breathing to supply oxygen to the eyes, and blinking to keep the eyeball surface moist:
Palming. This exercise, done without glasses or contact lenses, reduces stress. Sit at a table, lean forward, and put your left hand over your left eye so the heel rests on the cheekbone, the fingers lie flat on the forehead, and the cup of your palm covers but does not touch the eye. Then place your right hand over your right eye in the same manner, with your right-hand fingers on top of your left-hand ones. Keep your eyes open, and blink often. This technique relaxes both mind and eyes.
Tracking figure eights. Visually trace a reclining figure eight, in the shape of the infinity symbol, about ten feet in front of you. Reverse the pattern once in a while.
Switching focal length. Put your finger a few inches in front of your eyes. Focus on the finger, then focus on something in the distance beyond it. Switch back and forth.
Zooming. Hold your thumb at arm’s length. Focus your eyes on it as you bring your thumb close to your face, and move it back again.
Vision relies on neural networks in the brain. Like other neurons, they require stimulation to remain strong. “Use it or lose it” applies to seeing as much as it does to other brain activities. This was demonstrated by a study in 2010, in which test subjects improved their vision with the use of brain-challenging exercises.
A research team at the University of California, Riverside, and Boston University found that a specific set of eye exercises could clarify vision for a test group aged 65 and older. Subjects were shown a series of visual stimuli consisting of a letter embedded amid a field of horizontally oriented lines. The stimulus also included an array of peripherally located lines, in a diagonal orientation, that formed a vertical or horizontal object, and that always appeared in the same quadrant. Immediately after flashing an image, the researchers put up a masking pattern. The test subjects had to identify the central letter and peripheral object. Thus, their task was to perceive and process a confusing image in an instant. Two days of training in one-hour sessions with difficult stimuli prompted older subjects to substantially improve their vision, said chief researcher G. John Anderson. The improvement, related to physical changes in the visual cortex, lasted up to three months.
WHY IS IT ALL BLURRY?Around age 40, most adults start to experience an age-related decline in their ability to see things clearly at short distances, a condition known as presbyopia. It manifests itself gradually, but eventually causes difficulty in reading print. Those with the condition may find themselves “playing trombone,” zooming a handheld page in and out until the eyes can bring it into focus. People who are already nearsighted sometimes find they have better close-in vision when they remove their eyeglasses. Some get two pairs of glasses, for near and distance vision, whereas others choose a single pair of bifocals or multifocals.
Presbyopia occurs as the lens—a transparent, flexible structure behind the iris—grows more rigid. The condition cannot be prevented or cured. It typically gets gradually worse, requiring changes in eyeglass prescriptions every two years or so, until about age 60, when it grows more stable.
Other conditions associated with aging of the visual system include the need for more light—to compensate for nerves’ rising threshold—to read and perform other tasks; blurred vision and changes in the perception of color, especially blues and greens, as the lens becomes cloudy and the cornea grows flatter; reduced production of tears, especially in postmenopausal women; greater incidence of glare, caused by the less-flexible lens scattering light on the retina instead of focusing it sharply; and pupils dilating less in low light.
BRAIN INSIGHT
The Proper Glasses, Always Ready
Ben Franklin’s resourceful answer to presbyopia
Benjamin Franklin wore glasses for much of his life. As he aged, he had trouble not only with a general loss of visual acuity, but also a more pronounced blurriness when he looked at nearby objects.
The latter condition, called presbyopia, begins to affect many people around age 40. Unlike astigmatism, nearsightedness, and farsightedness, which arise from environmental and genetic factors reshaping the eyeball, presbyopia stems from the slow thickening and stiffness of the eyes’ lenses with the passing of the years.
The 18th-century solution to Franklin’s problem was to switch between two pair of glasses: one for reading, and one for general vision.
Franklin tried that for a while but thought better of it. “Finding this change troublesome, and not always sufficiently ready, I had the glasses cut and half of each kind associated in the same circle,” he wrote. “By this means, as I wear my spectacles constantly, I have only to move my eyes up or down, as I want to see distinctly far or near, the proper glasses being always ready.”
Although he may not have invented bifocals (historians argue the point), he was among the first to wear them, and he popularized them in the United States.
Compensation strategies allow many people to cope. Some may find it too difficult to drive at night, but will be perfectly comfortable behind the wheel in daytime. Older people may use a red light in a darkened room, instead of a frosted-white or clear-bulb night-light, to reduce glare and may make a room more visible at night. Or they may adjust for the brain’s lowered ability to distinguish blues and greens by decorating with more discernible reds, oranges, and yellows. Bright, warm colors make good accents not only on walls and furniture but also in pillows and afghans, which stimulate vision and sense of touch. These substitutions may help avoid bumps and bruises.
GOOD VIBRATIONSEars transform the vibrations of sound to electrical impulses that the brain can interpret in meaningful ways. The process begins when sounds collected by the outer ear travel to the eardrum, a thin flap of tissue that separates the outer ear from the middle ear, and set it to vibrating. High-pitched sounds make it vibrate more quickly than low ones, while loud sounds move the surface greater distances in and out. Each sound’s distinct vibrations are passed through a succession of three tiny bones—the hammer, anvil, and stirrup—and wind their way to the inner ear. There, they strike tiny hairs growing in the cochlea, a snail-shaped organ that plays perhaps the most crucial role in hearing. The hairs transform the vibrations into electrical impulses, the only form of communication that can be read by the brain, and forward them along the auditory nerve.
The eardrum automatically grows more rigid in the presence of loud, low sound, which offers some protection against neural damage. But it remains vulnerable to sounds that blast too loud or last too long. Such sounds can weaken and even kill the sensitive hair cells in the cochlea. Once those cells are damaged or dead, they cannot be repaired or replaced. Cochlear implants bypass the hair cells by converting sounds into electrical impulses that directly stimulate the auditory nerve, but the implant-induced sensations lack the richness of natural sound. To maintain optimal hearing, it’s best to avoid exposure to loud sounds, or to use protective ear wear if such exposure cannot be helped.
How much noise is too much? It depends on the loudness of the sound as well as duration of exposure. A single, powerful impulse, such as an explosion next to the head of a soldier in combat, can be enough to cause a condition called noise-induced hearing loss. On the other hand, long hours of moderately loud music can have a similar effect. In general, the louder the sound the less time it takes for the sound to cause serious damage.
Sound energy is measured on the decibel scale. A whisper measures about 20 decibels, normal conversation about 60, and a rock concert as many as 120. It’s a logarithmic scale, making 40 decibels about one hundred times as intense as a 20-decibel sound. An instant’s exposure to the 140-decibel whine of a jet engine can damage the hair cells of the cochlea, but so too can two constant hours of exposure to 100 decibels. Hearing may return after such exposure, but it’s often accompanied by a ringing or buzzing known as tinnitus. A lifetime of such ear damage can add up to a permanent decline. Audiologist Scott Bradley of the University of Wisconsin at Whitewater likens cochlear hair cells to a lawn and the sounds that wash over them to people walking on the grass. A single stroll over the lawn won’t hurt it, but frequent travel will cut bare pathways.
Music lovers may not be aware of the potential for damage, despite warnings since the 1980s about portable music players equipped with headphones. More recent technology, which fits earbuds into the exterior opening of the ear canal, has only increased the risk.
“We’re seeing the kind of hearing loss in younger people typically found in aging adults,” said Dean Garstecki, a Northwestern University audiologist. He partly blames in-ear earphones, which can boost sound intensity by six to nine decibels. Garstecki’s advice: To protect your ears, turn down the music.
BRAIN INSIGHT
Turning It Up to Eleven
The unwanted legacy of rock and roll
“Tommy, can you hear me?” Pete Townshend of the Who wrote those lyrics for his 1969 rock opera, Tommy, about a boy unable to see, hear, or speak.
It’s also a question that hits home for Townshend, who lost much of his hearing after a lifetime of performing and recording loud rock music. Now in his late 60s, Townshend relies on two hearing aids, and according to a bandmate must stand next to the speakers to hear any of the music.
For a while, the Who held the world record for the loudest concert, a 1976 affair in London where the music topped 120 decibels. Other bands have broken that mark, and many other rockers have suffered hearing loss.
But Townshend puts primary blame on wearing earphones for studio work, and not concerts, for his decline. Prolonged exposure to loud music in earphones and their modern iPod cousin, earbuds, can damage hearing. One study at Wichita State University found students experiencing 110 to 120 decibels during normal earbud use. Constant exposure to 100 decibels can cause damage in two hours.
Diets rich in antioxidants appear to strengthen neurons in the brain’s auditory system against noise-induced hearing loss. Antioxidants neutralize free radicals, which damage neurons, including those that sense and process sound. Studies conducted in 2004 on Marines undergoing rifle training in California suggested that boosting the amount of antioxidants in their diet could lessen the effects of later exposure to loud battlefield noises—and possibly even help protect their cochlear hair cells if the antioxidants were ingested immediately after hearing extreme sounds. About 10 percent of Marines typically suffer some hearing loss as a result of rifle training. Now, daily doses of a drink that tastes like herbal tea and contains the supplement N-acetylcysteine, or NAC, may help them maintain their hearing.
COULD YOU REPEAT THAT?Other forms of hearing loss occur naturally with age. The eardrum thickens and becomes more rigid, making it less sensitive to soft and high-frequency sounds. The ability to hear high-frequency sounds weakens more and more with age, with men older than age 70 experiencing hearing loss the most at the highest frequencies. Speech encodes vowel sounds in the lower range and consonant sounds in the higher range. As consonants carry more of the information of speech than vowels, high-frequency sound impairment can interfere with speech comprehension. That, in turn, can lead to social isolation and the mental health issues associated with it, such as loneliness and depression.
Most people experience some degree of presbycusis, or age-related hearing loss, and significant impairment strikes about a third of people older than 65. Loss of sharpness in the sense of hearing begins to be noticeable around age 50. Two common causes are changes in the auditory nerves and the buildup of wax in the ear canal. The latter can easily be remedied by a doctor’s cleaning.
Age-related hearing loss can be slowed by practicing healthy habits. Any exercise that increases blood flow raises the level of life-giving oxygen available to the tissues surrounding the hair cells of the cochlea, likely extending their lives.
As with vision, exercises can help maintain or even increase the ability to detect sounds. One such exercise involves closing the eyes and pinpointing a sound merely by analyzing the slight differences in wave patterns hitting your left and right ears. Stand in an open area, shut your eyes, and have a friend stand at least several yards away from you. Have your friend make a gentle sound, such as clicking a metal cricket. Point to the origin of the sound. Keep pointing as your friend moves around and repeats the sound. In another exercise, try carrying on a conversation as you add distracting noises in the background one at a time—a radio, computer, television, and so on. Although it may be confusing, your brain should sort out the screening noises and let you concentrate on the sounds you want to follow. In addition to exercising the ears themselves, regular workouts of the body’s muscles, heart, and lungs also help keep hearing sharp. Regularly working up a sweat increases blood flow to the ears’ cells and removes damaging waste products.
FLAVOR OF THE WEEKThe perceptions of taste, smell, and touch also change with time. The brain senses flavor through nerves embedded in taste buds that cover the tongue, as well as through specialized receptors in the nose. The senses of taste and smell grow weaker with age, as thresholds change. After age 60 or so, the ability to taste begins to wane for most, but not all, people, and the sense of smell declines as well. Salty and sweet tastes usually go first, followed by bitter and sour. The loss is gradual. In general, it takes a greater concentration of sweetness to taste something sweet, and a less intense sourness to taste something sour. Why this happens remains a bit of a mystery, but speculation centers on the fact that the mouth grows drier as saliva production decreases with age; environmental factors, too, add up over a lifetime. The number of taste buds also decreases with age, starting at about age 40 in women and age 50 in men. The remaining taste buds lose some of their mass, further reducing the surface area of the mouth sensitive to flavor. Other causes of diminished taste include tooth decay, mouth sores, certain medicines, and poor nutrition.
The sense of touch also dulls a bit with age, typically lifting the threshold of sensation for pain, heat, cold, pressure, and vibration. Lowered sensitivity to heat and cold can be life-threatening, so it is recommended that the elderly cap their water heaters’ maximum temperature at a safe level, and be careful to dress appropriately when they leave the house during periods of high heat and cold.
The origin of changes in skin receptors may be a reduction in blood flow, typically resulting from a more sedentary lifestyle and greater use of medications. Or it could be the aging process itself or health disorders that elderly people more commonly experience. One compensation occurs around age 70: As the skin grows thinner, it often becomes more sensitive to a light touch, such as the caress of a hand.
NEW SENSATIONSChallenging the senses in novel ways helps the brain keep existing neural pathways open and create new ones, allowing the brain to maintain and even expand its processing of information from the five senses. Leonard Katz, a neurobiologist, promotes the concept of exercising the brain by making multisensory associations. He says this can be done in two ways: by combining two or more senses in unexpected ways, or by using one of the five senses in a new context. The former might be appreciating a particular bit of music while smelling a pleasant aroma. Vivaldi’s Four Seasons, seasoned with vanilla, for example. The latter technique might involve reliance on sound, touch, or sight to carry out a task that normally relies on the use of one sense. So, for example, your family might prepare and eat dinner in silence, using only visual cues to get everything set up, and then pass and use things on the table as needed.
You might also pretend to have lost your sense of sight for a short time. After you park the car in the garage, close your eyes, open the car door, and try to get into the house and hang up your coat. This might involve paying extra attention to the contours of your keys in order to pick out the right one for the door from the garage to the living room. Once you’ve found it and turned the lock, you would rely on touch and sound—the softness of the carpet under your feet after the tile of the entryway, the ticking of the mantel clock as an aural anchor to orient you as you make your way across the living room—to complete your task. If you try this, go slowly, and try to re-create your house visually in your mind’s eye. You’ll find landmarks by touch and sound. Just don’t storm ahead and bark a shin on the coffee table, or you’ll get an unwanted sensory stimulation: pain.
Katz also recommends giving your senses a break from their routines. This can be as simple as taking a new route to work or rearranging the furniture in your living room.
BRAIN INSIGHT
Seeing With Your Tongue?
An experimental device can train other body parts to take the place of the eye
A scientist rolls a ball toward a woman in a chair. She reaches out her hand and stops it.
Nothing remarkable there, except the woman is blind. And she “saw” the ball with her tongue.
The blind woman’s tongue was wired to a device called a BrainPort, itself wired to a video camera capturing the movements of the scientist and ball. BrainPort, originally developed by the late Paul Bach-y-Rita of Wicab Inc., works by substituting electrical impulses for other sensory stimuli. In this case, it trades the visual system’s processing of light for encoded bursts of electricity sent to the brain through the surface of the tongue. (The tongue’s sensitivity makes it ideal for maximum data communication.) The brain teaches itself how to interpret tongue-borne electrical bursts as if they had been delivered through the eyes. Similar research is under way to substitute or augment sensory information lost in the skin and ears, as well as compensate for a loss of balance. The vision centers of BrainPort users become active when processing electrical impulses from the skin.
Blind BrainPort operators, once trained, perceive size, shape, depth, and other visual qualities. Letters of the alphabet become clear.
Wicab is working toward release of a commercial version of the product.
