James L. Fozard, Ph.D.
Baltimore Longitudinal Study of aging
National Institute on Aging
Sandra Gordon-Salant, Ph.D.
Associate Professor of Hearing and Speech Sciences
University of Maryland
Frank Schieber, Ph.D.
Assistant Professor of Psychology
James M. Weiffenbach, Ph.D.
National Institute Of Dental Research
This paper summarizes selected information on age-related differences in sensory and perceptual experience with vision, hearing, taste, and smell. In addition, it reviews human factors interventions that are possible for improving sensory functioning where needed. The goals of such interventions include improving the quality of task relevant information, helping a person adapt to or transcend situations in which sensory information is poor, and redesigning tasks by reassigning functions between machine and human components of a task.
No single age signals "old" across sensory systems. Moreover, age changes within a single sensory system are rarely uniformed. Thresholds for pure tones in high frequencies, around 8 kilohertz (kHz), increase regularly throughout adulthood at a rate of about decide per year while those in lower frequencies, around 1 kHz, show a different pattern. They increase at a rate of about 0.3 db annually from the twenties through the sixties and then at an accelerated rate of up to 1.3 db per year thereafter.
Changes in visual acuity for targets at three meters or more from the viewer vary little across age until about age 75, while corrective lenses are almost universally necessary for good acuity at optical distances of less than 0.5 meters from about age 40 on. Taste thresholds for sucrose and the perception of sweetness are both remarkably robust with age. Conversely, both detection of a bitter taste and Bitterness, the reliability of intensity judgment for bitterness to decline significantly with age. Thus, the human factors interventions required for age will vary, depending on the particular requirements of the task.
Human factors practitioners want to know how specific interventions need to be with respect to age. There is no simple answer to this. Better contrast between signal and background as well as suppression of background noise for speech intelligibility will help improve hearing for most adults. But in many situations, a less-than-optimal environment can be better tolerated by younger persons. Visual tasks that require rapid adaptation to dim lighting and perception of detail at changing optical distances would not be well tolerated by older adults who have lost the power of visual accommodation and require greater target illumination for task performance. Thus, designing an adequate environment for older adults may also help younger ones, more than the reverse.
Almost all published research on interventions for sensory and perceptual problems of elderly people concern limitations in receiving information from the environment, not providing it. One useful classification of person-environment relationships is whether the person, the environment, or both are either static or changing. When both are changing simultaneously-for example, when a person is out driving or is walking through an airport, where the level and source of information is continuously changing interventions with the environment or task redesign offer the most promising possibilities.
Environmental interventions would also be relatively powerful where the environment is static. In vision, for example, there are many possibilities for changing the amount and configurations of lighting in office, factory, and home situations. In listening, the effectiveness of personal hearing aids may be greatest when the sources and levels of signal and background noise are relatively stable; when the auditory environment is changing, however, the burden of improving performance falls more heavily on the person to use lip reading and know how to be positioned to get the most information. In the case of taste and smell, the major burden of intervention is with the environment to change or increase the stimuli available to the individual.
Interventions with people independent of changes in the environment are restricted to selecting individuals who are able to perform certain tasks or training persons in how to overcome their sensory limitations. Traditionally, selection of people on the basis of adequate sensory functioning is limited to highly specialized tasks-for example, certain military tasks or ones in which the "screen" is very coarse with respect to age as are the visual and binocular depth perception tests used in vision screening for automobile driver's licenses. In the former case, age is not usually a limiting factor; in the latter, the screen does not identify many of the well-known age-related problems in vision older people have. At present, there is little research or information available on the relationships between individual differences and sensory abilities or aptitudes required in various tasks.
In vision and hearing, various interventions are routinely used to train people to improve their ability to understand visual and spoken information. Many such interventions, however, were developed for persons with more profound limitations than those typically encountered in elderly people and, with the exception of lip reading and auditory training, are not widely used with the elderly. Many interventions do not take into account certain problems that are relatively prominent in older persons for example, slow response time.
Thus, there is a lot more that needs to be done, with respect both to providing appropriate user and environmental interventions and to educating people as to their use. In some situations it is appropriate to provide greater "user adjustable" controls over lighting, sound intensity, noise reduction, etc., than are not available. The degree to which older adults will select the optimal levels of stimulation for task at hand, however, is unknown at present.
Recently, 400 participants of the National Institute on Aging's Baltimore Longitudinal Study of Al were surveyed regarding the impact of visual problems upon daily tasks of living and specific driving behaviors.' For tasks of daily living, self-perceived declines occurred in the speed with which visual information could be processed, the ability to read moving targets, near vision, and overall quality of vision under low light conditions. For driving, older respondents reported difficulty with speed judgments, instrument panels that were too dim, other vehicles that moved too quickly, the act of merging with traffic, and the sudden and unexpected appearance of vehicles in the peripheral field of vision. They also reported many more responses that appeared compensatory in nature, such as avoiding 6 4 rush hour" traffic and not driving at night. This suggests, at least to some extent, that older adults modify their behavior in a manner appropriate to their changing abilities. This notion of "appropriate self-regulation" of driving behavior among elderly people has significant implications for licensing agencies and merits additional research consideration.
Laboratory researchers report declines in functions that are consistent with the visual difficulties reported by older adults in the field. Deficits of varying magnitude have been found for adaptation to darkness, visual acuity, contrast sensitivity, color discrimination, detection and recognition of moving, objects, visual search, night vision, and glare sensitivity. These declines in visual function with age reflect losses in the quantity and quality of light reaching the retina, lost ability of the lens to bring near objects into, focus (accommodation), changes in the nervous system structures serving the eye, and the increased prevalence of ocular disease in old age.
Interventions That Benefit the Individual
Despite the age-related declines outlined above, much can be done to improve visual function. Such interventions may involve manipulating the individual or optimizing the visual characteristic of the environment. Figure I reveals the potential benefits of diagnosing and correcting the refractive error that occurs as a function of age. The figure shows that although visual acuity declines remarkably with advancing age, much of this loss is eliminated when individuals avail themselves of appropriate cost effective eyewear.
In fact, according to the Framingham Eye Study, approximately 92 percent of persons aged 65-74 possess visual activities of 20/25 or better when fitted with their best refractive corrections. However, the ability to compensate for visual losses with eyeglasses or contact lenses becomes increasingly limited as age advances since only 69 percent of those aged 75-85 can be corrected to 20/25 or better.
In addition to modifying the individual through the use of refractive aids, recent evidence suggests that age-related declines in higher-order perceptual processes may be ameliorated by visual training protocols.' Relatedly, more frequent and extensive screening aimed at early detection and diagnosis of visual pathologies common among elderly people (e.g., cataracts, glaucoma, retinal disease) could do much to improve visual status as the deleterious effects of many visual disorders can be minimized through constantly improving treatment regimens.
Interventions That Manipulate the Environment
Improvements in both the performance and visual comfort of elderly people may also be realized through the manipulation of the environment. The "real world" is very different from the ideal conditions observed in the eye examiner's office or the vision researcher's laboratory. The visual stimuli that serve as the basic inputs for guidance in everyday tasks tend to be marginally illuminated and low in contrast. Attempts to improve these suboptimal viewing conditions have generally been more beneficial for elderly observers than for their younger counterparts. The major environmental interventions that have been shown to enhance visual function in elderly individuals include increased levels and better distribution of illumination, control of glare, increased stimulus contrast, and reductions in visual "clutter."
Increasing Illumination and Control of Glare
The improved visibility that accompanies increased illumination is dramatic, relatively greater for older adults, and nonlinear; in other words, improvements in performance and comfort are proportional to the square root of the changes in the amount of available light. The application of these facts to the design of environments must be qualified by other factors, however, such as the ratio of the task area to overall illumination, task speed versus accuracy tradeoffs, reflectance of proximal surfaces, and the need to minimize sources of glare. The Illuminating Engineering Society has translated the need for higher levels of illumination by older adults into specific design guidelines, which appear in the most recent edition of the IES Handbook. After determining the class to which a given situation belongs by virtue of its architectural and functional constraints, a designer chooses from among three recommended levels of illumination, based on a system of weights that depends upon the age of the observer. In most cases, recommended light levels are lower for observers under the age of 40 and higher for those over age 55.
Although the increased glare sensitivity of elderly adults is also noted, no specific guidelines for ameliorating this problem are proposed in either the IES Handbook or other widely available sources. And while qualitative solutions for meeting the special illumination needs of older persons have been offered by several researchers, these design "rules of thumb" have yet to be cataloged in a single reference source. Such a volume would list such guidelines as "divide and conquer" (use multiple sources of light to achieve one's needs, rather than a single bright luminare) and "incorporate variable intensity controls at personal workplaces or reading stations" (allow for the wide individual differences that exist in the level of lighting needed to optimize comfort and performance).
It should be noted, however, that such recommendations are based on the insights and field experience of designers and have little basis in terms of a systematic program of research, which is much needed. Recent announcements by the National Institute on Aging regarding a call for proposals in the area of "human factors" appear to reflect a recognition of this lack of a scientific database.
The need for improved illumination with advancing age is undeniable. New consumer products, such as 170-watt incandescent lamps with ultra-high diffusion coatings (which "soften" the light to minimize glare), are beginning to address some of these needs within the residential environment. However, the most significant decrement in the everyday functioning of elderly people as a result of inadequate lighting may be found beyond the confines of the home.
Nighttime driving represents a visual challenge that is often so severe that, as noted above, many older persons are compelled to limit their driving to daylight hours. This self-imposed limitation has an economic and social impact, which has yet to be systematically evaluated. One way in which the mobility and safety of the driving public could be increased would be to implement a planned system of improved roadway lighting throughout our major urban and suburban areas. Such illuminated corridors or "brightrays" could be indicated upon regional maps and used by drivers of all ages to negotiate the challenging nighttime environment more effectively.
The cost-effectiveness of urban-suburban brightways needs to be evaluated before policymakers can consider such an approach, but leadership for such an endeavor should be offered by the U.S. Department of Transportation (USDOT), which is currently reassessing its mission in light of the expected completion of the Interstate Highway System later this year. Although USDOT agencies such as the Federal Highway Administration appear to be focusing upon "electronic" and "information based" management of urban traffic flow as the major priority for the 1990s and beyond, the National Highway Traffic Safety Administration has recently launched several initiatives that indicate that the needs of older drivers are beginning to be considered by federal planners. Unfortunately, these recent initiatives have not resulted in the allocation of funds for research and development efforts aimed at meeting these needs.
Increasing Stimulus Contrast
Research indicates that visual performance and comfort among the aged population can be improved significantly by enhancing the luminance contrast of environmental stimuli. The gains achieved by contrast enhancement are especially noteworthy in situations where optimal illumination cannot be maintained. Blackwell and Blackwell have developed an empirical model of "visibility" that clearly reveals how stimulus contrast must be increased with observer age in order to achieve equivalent levels of visual sensitivity for large and small objects alike.' This model entails a series of contrast multipliers that persons of different ages require to attach the visibility level of a standard observer-the healthy 20-year-old. Figure 2 demonstrates the degree of contrast enhancement required to compensate for the loss of visual sensitivity as a function of increasing adult age. Although the Blackwells do not present sample data beyond age 65, recent studies indicate that the need for contrast enhancement becomes even greater beyond age 70.
In addition to the need for increasing the luminance contrast of important objects in the visual environment, J. C. Archea has described how poor "figural contrast" in environmental design can contribute to functional problems among elderly people. For example, the use of certain patterns and textures in carpeting, tile, and other architectural and building materials can greatly diminish depth perception at stairs and landings and contribute to the increased rate of fall-related accidents among older adults. Figure 3 offers some examples of such a "problem" textures that should be avoided in the design of living and working spaces.
There is some evidence for a need to be concerned with color contrast in the design of environments for older adults. The well-known age-related changes in the ability to discriminate color resolution the perception of a world of "washed out" blues and greens and diminished color saturation. In addition to creating aesthetic problems for the designer, age related changes in the color sense can have critical consequences for older adults as well. For example, many older adults depend on multiple medications, many of which are color-coded capsules that must be self-administered at varied schedules. Often such medications are taken under conditions of poor lighting (e.g., in restaurants, waiting areas, etc.). Hence, color-coding combinations that minimize the probability of discrimination errors by older observers should be used. Critical tasks involving color perception by older observers should especially avoid discriminations within the blue-green range as well as among colors within the same hue. Empirical data are currently available to guide such color design processes.
Reducing Visual Clutter
An often ignored property of the visual environment that has been shown to affect performance is "visual clutter": the presentation of superfluous stimuli within the field of view. A survey of the profusion of signs along our primary roadways as well as in busy shopping places and office buildings clearly reveals that visual information in our environment tends to be presented in a confusing and unpredictable fashion. It is often very difficult to "see the trees because of the forest," and the ability to extract needed information from an array of distracting and often conflicting visual displays declines as one grows older. Thus, it is important to present visual information using predictable and simply structured formats. Unfortunately, explicit guidelines for reducing visual clutter are not available, and the designer must, at least for the present, rely upon common sense and experience.
Several factors have been explored for optimizing environmental designs to meet the special visual needs of an aging population. A search of the human engineering database, however, reveals that little information is available in specific quantitative design recommendations that reflect a consideration of these emerging needs. Therefore, any major design effort should be sure to include a panel of our best available experts on aging and the environment-namely, older persons themselves. Even a rapid, inexpensive review of design concepts using the "design eye" of a panel of older adults can do much to avoid future problems and increase the comfort and functionality of our living and working spaces.
Surveys of the self-reported impact of hearing loss on functioning indicate a positive but modest relationship between self-perceived handicap and measured hearing loss. Typically, a moderate hearing loss in the better ear is associated with self-reported hearing handicaps. Results indicate, however, that the handicapping effect of a hearing impairment cannot be predicted accurately just from clinical measures of degree of hearing loss or of suprathreshold speech recognition but also require a self-report of the communication handicap.
By age 60, detection of pure tones is within normal limits in the low to mid frequencies and is within the mid-to-moderate hearing loss range in the higher frequencies. Additional increases in thresholds occur through age 90, resulting in a mild hearing loss in the low frequencies and a moderately severe hearing loss in the higher frequencies. On average, men have poorer auditory thresholds than women. The hearing losses are partly acquired through environmental exposure or disease.
Enhancing Speech Intelligibility
Speech recognition declines with age and is partly related to threshold changes. On standard tests, older adults appear to have relatively greater difficulty understanding speech until they are equated on sensitivity to younger peers. When so equated, however, older adults again experience greater difficulty than younger ones in identifying words if the words are presented in noise and if the context provided by the carrier sentence for the word is poor.
Additionally, reverberation-the prolongation of sound in a room-has a more detrimental effect on the intelligibility of speech for older persons in noisy environments, even after equating for age-associated hearing loss.
Speech understanding can be improved by signal amplification and enhancement, environmental control, and training. Amplification of speech by hearing aids is the most common intervention, but it may be of limited value because such aids amplify environmental noise along with the target signal. However, a new generation of "automatic signal processing" hearing aids attempts to amplify the speech signal while simultaneously reducing the noise level. Some of these devices do improve speech understanding in noise for elderly listeners. In addition to personal hearing aids, other devices that may be useful for improving communication in the home include telephone amplifiers, visual alerting devices, and television listening systems. For people with minimal usable hearing even with amplification, telephone devices for the deaf (TDDs) and television decoders for closed-captioned programs are excellent substitutes that provide communication in visual form. Amplification of the target signal by assistive listening devices that are not hearing aids can be especially useful because they improve the effective signal-to-noise ratio and decrease the effects of reverberation. Such devices include FM transmission systems and infrared systems (as seen in theaters).
Reducing Environmental Noise and Reverberation
Environmental control in both new and existing facilities is designed to reduce noise and reverberation. In new facilities, this can be achieved by locating the facility far from obvious noise sources (e.g., highways and airports), selecting quiet equipment for air conditioning and heating, and using sound absorptive materials within rooms. The same principles apply to existing facilities: reduce sound production and transmission by a sound source; reduce radiation of vibrations from a noise source into the building; and reduce the amount of sound reaching the receiver from the air. According to some studies, the goals of these interventions should be to achieve public rooms with reverberations of about a quarter of a second and an effective signal-to-noise ratio of about + 15 dB.
Taste and Smell
Older persons have more taste complaints than do younger individuals and may be less well served by their sense of taste in a variety of ways. For example, they may have difficulty telling lightly salted butter from sweet butter, or they may require more sugar to bring their coffee to its accustomed level of sweetness. In laboratory studies, stronger stimuli may be required to elicit tastes from older persons or equally strong stimuli may be judged less intense by them. The most important message from these studies is, however, that taste sensitivity is remarkably robust with age and that age-related declines, when they do occur, are not uniform. While salt solutions must be stronger for older persons to taste them (Figure 4), the same is not true for sugar solutions (Figure 5). Age-related changes in threshold sensitivity are thus specific to the taste quality of the test solution. This implies that interventions should be targeted to particular qualities for which sensitivity is reduced.
Age changes may also be specific to individuals. Even though the average concentration required to detect salt increases with age, an examination of figure 4 shows that some older individuals detect this substance at as low a concentration as the average young person.
Interventions, thus, might be indicated for some, but not all, older individuals.
In large measure, the usefulness of one's sense of taste depends upon its capacity to respond to increases in the strength of taste stimuli with coordinated increases in subjective intensity. This relationship, or psychophysical function, can be measured in the laboratory and has been shown to vary with increasing age. Some studies of age-related change indicate an overall decrease in intensity while others have documented changes in the shape of the function. Still others have shown age stability for the function but age-related declines in the reliability of the underlying judgments. These differences between studies likely reflect differences inherent in the populations from which study subjects were drawn and reinforce the notion that intervention, at the present time, must be individual.
Both threshold sensitivity and intensity judgments for odors decline with age. Since sensitivity to airborne chemicals cooperates with the sense of taste in food perception, older persons may experience reduced enjoyment of eating. Moreover, reduced sensitivity to airborne chemicals may place older persons at risk for exposure to tainted food and escaping propane gas. Age-related threshold declines for olfaction are more marked and may begin at an earlier age than corresponding changes affecting the sense of taste. When taste and smell assessments are made in the same individuals, intensity judgments of odor are more markedly impaired than those for taste. Judgments of airborne stimuli that evoke pungency or tingle decline with age independently of odor judgments.
The findings for taste suggest that interventions should be specific to the person for example, enhancing the options for seasoning available at the table. Subtle changes in the form of an intervention may be important. Adding salt during food preparation might increase food enjoyment of taste impaired older persons but expose them to a health risk. Experience gained from interventions designed to limit the sodium intake of hypertensive patients suggest that seasoning should be added at the table. When hypertensive patients were presented salt-free food along with the opportunity to salt to taste, they added less salt than had been eliminated during initial food preparation. Other interventions at the individual level include improvement of oral hygiene, repair of dentures, resolution of gum disease or other oral problems, treatment of nasal sinus disease, attention to systemic health problems, as well as other medical interventions including trials of alternative medications.
One environmental intervention is suggested by the dependence of food appreciation on odor perception in combination with age-related declines in olfaction. Providing additional food aromas might enhance the pleasure older persons get from eating. This intervention to compensate for age-related declines in sensitivity to odor is currently being researched . Moreover, presenting food in a visually appealing form and providing for social dining are interventions that are known to be effective in insti- tutional settings and are clearly applicable to home care for elderly people.
The currently available research indicates that no single aging problem exists either within or across the sensory and perceptual systems discussed. Three of the recommended environmental interventions for vision and hearing are based on the same principles: increasing signal intensity, enhancing contrast between signal and background by a variety of means, and decreasing visual (glare) or auditory (background) noise. Enhanced visual contrast includes improving brightness, color, and figural aspects as well as temporal contrasting elements. Enhanced auditory contrast includes improving the signal independently of the background. To a lesser extent, these interventions also apply to smell and taste.
The principle of increasing the user's ability to adjust to light, sound, and taste sources needs evaluation. Interventions with people in this regard include prosthetic devices, training, and counseling,
Unfortunately, the major limitation of the existing research is the lack of specific quantitative guidelines. In vision, only the engineering guidelines for illumination and contrast include age, and age was considered in some of the qualitative guidelines for glare. In hearing, there are several recommendations based on research but little in "handbook" form. In taste and smell, there are no applicable standards. Whether the sensory problems of the elderly are uniquely age specific or simply extensions of those for young adults, it is clear that engineering guidelines need to pay more attention to age.