Results from work by Steenbekkers [21] show that illumination is an important aspect when designing for the readability of text by older people. When illumination levels are low only relatively large letters are readable, regardless of the contrast. Under high illumination levels contrast levels influence readability.
It is important that design professionals take into consideration visually impaired people (of all ages) when designing everyday items and processes. If a “universal” or “design for all” process is used then this will inevitably benefit people who do not have any visual problems also. For example, if an appropriate font size and colour is used against an appropriate background then a normally sighted person will still be able to read easily, but the difference for visually impaired people maybe crucial.
It is important that the design process accounts for older people with visual impairments in scenarios such as thew domestic environment, shopping, public transport and so on, to enable them to carry on living and caring for themselves independently without suffering any degradation of living quality that poor design may cause. It should also be noted that older people may still have diminished visual acuity even with the use of corrective devices such as spectacles.
Hearing
In much the same way as vision, hearing related problems are among the most commonly occurring changes with ageing. Presbycusis is the term used to describe naturally occurring loss of hearing due to the ageing process. General observations on the changing in auditory functioning are:
- There is a loss of hearing sensitivity at the higher frequencies, with loss generally greater among men that women, and with the difference increasing with age [23].
- Figure 8 illustrates the minimum decibel level that can be heard for a 1000 Hz frequency by a Dutch population.
As can be seen, as a persons age increases the mean minimum decibel level that can be heard at 1000 Hz frequency also increases.
- It would also appear that frequency discrimination declines with age [25,26]; as a person grows older they are less likely to be able to tell the difference between similar sounds.
- Auditory temporal resolution (the time scale over which the sounds are heard by the person), which is essential for speech perception and sound localisation, declines with age. For example, Rastatter et al. [27] found that speech comprehension was more impaired for old people than young when subjected to time compression, that is, when the sounds came closer together. However, Moore et al. [28] have concluded, on the basis of their work, that loss of temporal resolution due to ageing is not inevitable.
- Work on auditory attention has found that older people may have difficulty in shadowing (repeating the stimulus information that they are presented with) if a competing source of information is presented to the other ear.
- This may imply a divided attention deficit, where older people find it difficult to simultaneously focus their attention on more than one stimulus at a time [29,30].
- Wickens et al. [31] found that older people need more time to switch their attention from ear to ear, missing information that maybe heard by younger people.
The general trends in hearing degradation need to be taken into consideration by designers and manufacturers of a wide range of applications. At the one extreme are safety critical systems, such as alarm bells or messages that maybe broadcast in an emergency situation. The potential consequences of not considering the requirements of older adults with hearing difficulties when designing a safety system are all too easy to imagine. On the other hand, there are design issues relating to ensuring high life quality and independence for a person. Issues here include all aspects of voice communication systems (telephone, radio, television etc) which may be important to an older person with hearing difficulties.
It should be noted that it is not advisable to design products and systems and assume that correction devices such as hearing aids will be worn. There is still a greater stigma attached to the wearing of hearing aids compared to spectacles which may mean that some people manage without aids for social reasons (it is also possible that some hearing problems are not correctable even with hearing aids).
Table 2 summarises the general changes that may occur to the vision and hearing of a person as they grow older.
Psychological Changes
Changes in Cognitive Functioning with Age
The area of cognitive psychology is vast and complex. The summary of ageing effects provided below is necessarily simplified. The interactions between different mental processes are myriad and important to how a person functions. This section is intended to serve as a general guide to the effects that ageing may have on certain cognitive processes. More specific information and expertise should be consulted if necessary.
Cognitive Functioning
General Overview
Cognitive functioning refers to the various mental processes that are responsible for how an individual ‘knows’ or understands the world in which they exist, using perception, memory, learning and so on. Certain aspects of these functions may change as a person grows older: a person may become ill, sustain injury or suffer decline due to the ageing effect.
A large scale study has been conducted by Schaie et al. in the Seattle Longitudinal Study, where data on over 5000 people have been gathered over six testing cycles at seven year intervals [32]. The results of this study show that there is no uniform pattern of changes in cognitive ability in adulthood as a result of ageing. However, there are differences in the degree to which different cognitive functions change as the person grows older.
Data from this study show that a reliable decrement with age, on average, is found, for all the cognitive functions that were studied, by the age of 67 [32,33]. For most people this decrement is modest in nature until the 8th decade is reached. Schaie [34] identified that such decline is not linear in nature, but occurs in step fashion.
Such decline is attributed to the slowing of processing speed and response speed when faced with a limited time situation ie the cognitive processes involved in the tasks could not cope with the time demands placed upon them as successfully as when the person was younger [32].
However, it should be noted that research has indicated the potential for considerable ‘cognitive plasticity’ of older people, ie it is possible to recover cognitive function lost through degradation to some degree, or even to increase cognitive function [35,36]. Thus, it is not acceptable to assume that all older people will have lesser cognitive abilities than when they were younger.
Specific Cognitive Abilities
In a review of published material on memory systems and ageing effects Schacter and Tulving [37] identified five main systems of human memory. They considered that four of these systems are of particular regard for ergonomics issues in the design of products for older adults. These four areas are considered below, starting with the concept of working memory.
Working Memory
Working (or short term) memory involves the storage of a limited amount of information for a brief time period, usually 15-20 seconds.
Evidence tends to suggest that the storage capacity of working memory per se does not decline with age, but rather that it is the processing efficiency that degrades with time. Salthouse [38] suggests that this decrease in efficiency is due to a decline in the processing speed of older people. The following points illustrate this:
- generally, the age differences that exist for simple retention tasks of small amounts of information for short time periods of time are negligible [39]
- when age differences are apparent, the deficit in digit span recall (the ability to correctly remember and recall a string of numbers after memorising them) is usually less than 10% [40] which means that older adults still fall within the range predicted by Miller [41] for working memory capacity of correct recall of 5-9 digits
- when the individual is required to use working memory as part of a mental process or manipulation of information, such as working out what 10% of a bill is for example, substantial decreases in capacity tend to be found [38,42].
Basically, older people do not have any worse a working memory capacity or efficiency than when they were younger. However, deficits are more likely to occur when required to use working memory in conjunction with other processing mechanisms.
Long Term Memory System
It is generally agreed by cognitive psychologists that long term memory can be divided into 3 divisions. The first two, episodic and semantic memory, are considered to be explicit or declarative memory systems. This means that the memories that are served by this system are reasonably easily described or declared by the person who is remembering them.
The third system, procedural memory, differs from episodic and demantic memory in the sense that is considered to be nondeclarative, or implicit. The memories that are served by this system are not easily described or declared by the person who is remembering. Such a distinction will become more evident when each system is discussed in more detail.
Episodic Memory
Episodic Memory refers to memories that are autobiographical, personal and context sensitive. They are considered to be organised by the time and place of occurrence, and can often be described by the perceptual characteristics that are associated with them (eg taste, smell, touch etc.). Examples of episodic memory are where a person went to school, knowledge of events that a person has experienced, and so on.
The literature that has been produced on episodic memory and ageing reveals that performance declines with age, possibly due in part to the fact that working memory processing is required for episodic memory recall [40,43].
Semantic Memory
Semantic memory refers to the knowledge of particular facts about the world, in contrast to episodic memory. They are considered to be organised hierarchically. Examples of semantic memory include the name of the Prime Minister, the location of the pub in the village, the meaning of words, and so on.
Bowles [44] and Light [45] report that age deficits in semantic memory are rare. In other words, our conceptual and lexical knowledge remains relatively constant or even improves throughout our lifetime. Any decreases in semantic memory that are evident are likely to be due to the slowing down of processing speed that has already been mentioned, rather than due to deficits in memory content or organisation of the information held in it [40].
Procedural Memory
This theory of memory, as described by Squire [46], refers to a range of different abilities, in which early experience affects subsequent performance, taking into account the absence of conscious awareness on the part of the individual. Basically it is the knowledge of how to do something, for example how to make a cup of coffee, change a car tyre, use a computer, and so on.
Some aspects of this type of memory are affected by ageing, others are not. Howard and Howard [40] consider three types of procedural memory: classical conditioning, skill learning and priming.
Classical conditioning
Classical conditioning refers to the learning process that occurs when we associate two stimuli which exist in the environment, as first described by Pavlov (1849-1936). In the experiment made famous by Pavlov, a ringing bell came to elicit salivation in a dog after it had been paired with food. Conditioning appears to be degraded with advancing age, although the degradation that has been observed can be reduced by or eliminated through increasing the time between the conditioned and unconditioned stimulus, or in terms of Pavlov’s example, between the bell and the food presentation [47].
Skill learning
Skill learning covers a wide range of areas, from a motor skill such as walking to a cognitive skill such as chess playing. Generally, age degradation is observed, especially when new tasks are being learnt. Work such as that by Charness and Bosman [48] has shown that the older adult is able to learn new skills but requires a longer time period to do so. Kausler [49] reviews the literature, which shows evidence that the learning of cognitive skills takes longer for older adults than for younger adults. However, age differences that occur can be significantly reduced or even eliminated through practice and its effects.
Priming
Priming refers to the furthering of performance which results from an earlier experience with a specific stimulus. For example, if people are shown the same stimulus on two separate occasions then they will usually identify the stimulus faster on the second occasion. Priming appears to decline very little, if at all, with ageing [50,51,52].
Changes in Psychomotor Functioning with Age
Psychomotor functions involve any behaviour that involves a persons ability to take action. The most common type of research conducted on psychomotor functioning is on reaction time. Typically, the person is asked to react to a stimulus as soon as they perceive it by performing a task such as pressing a button.
Salthouse [53] asserted that nearly all psychomotor processes are degraded by approximately the same proportional amount with increasing age. Basically, as a person grows older their ability to perform a certain task degrades accordingly. A review of the available data by Stelmach and Nahom [54] concluded that all of the evidence supports this position. Essentially there is a slowing of behaviour as age increases [55,56].
Typically, men respond faster than women [57,58].
Using the example of reaction time, when there is a simple choice (ie a single option to choose from, so a person is asked to press one button when a single stimulus is presented) reaction time degrades (i.e.increases) by 20% at 60 years of age compared to 20 years of age.
For complex choice tasks (ie multiple choices, all equally possible, so a person must press one of 5 buttons depending on which one of 5 stimuli is presented) reaction time increases as the number of signals does [59]. Older people, when compared to younger people, perform relatively more poorly on complex tasks than simple tasks.
Figure 9 illustrates (for a visual stimulus) the difference in reaction times (with age), for both simple and choice tasks. The results are for men and women combined.
As the figure shows, reaction time is always greater for the choice task than the simple task.
Reaction time may also slow with age dependent on whether the stimuli is visual or auditory. Figure 10 presents reaction times in milliseconds for a simple task where the person was asked to release a button on the presentation of a light (visual) or a sound (auditory) in separate experiments.
The results shown are for men and women combined.
The figure illustrates the increase in reaction time as the person grows older. This also holds true for a choice task, again for both visual and auditory stimuli, as shown in figure 11.
Houtkamp & van Beijsterveldt [60] found that response to a visual stimuli was faster than to an auditory stimuli for a choice task, leading them to conclude that the degree of difficulty between visual and auditory stimuli presentation for choice tasks is different. They found that for the visual stimuli the increase in task time was mainly due to the increase in the time taken to react by the person, while for the auditory stimuli the increase in time was due to an increase in both the reaction time and movement time. The auditory stimulus, however, required the person to memorise the correct response to the given stimuli, while the visual stimuli did not. This means that the person was required to also use attentional and memory processes to complete the auditory stimuli task. As mentioned earlier, it is when cognitive systems are simultaneously used that deficits in working memory become more pronounced, which may explain the difference between the results for the two stimuli.
It is also likely that movement time will degrade with age, this being the act of reacting to a stimulus by performing a specified task. Houtkamp & van Beijsterveldt [60] assessed movement time for simple and choice tasks, and for auditory and visual stimuli. The simple task involved reacting to the lighting of a lamp or the sounding of a tone by releasing one button and then moving to and activating a target button.
The choice task for visual stimulus involved reacting to the lighting of a lamp (or combination of lamps) and then releasing one button and moving to the correct target button. The auditory stimulus choice task involved similar movement but to one of three tones of different pitch, again to the correct target button. Figures 12 and 13 illustrate the simple and choice mean reaction times in milliseconds, again for men and women combined.
Individual Differences
While it is possible to make these statements about various facets of human psychological and psychomotor abilities and age related performance changes, it needs to be borne in mind that we are all individuals, and should be treated as such.
Some people may well suffer vast memory performance degradation with age, others nay continue at the same level as when they were younger or even improve. Take, for example, the area of expertise. It is not unusual to find experts in fields who are of advanced years, for example writers, scientists and so on. Charness [61] reviews this area of research, from which a theme emerges. It would appear that older experts compensate for the ageing deficits that they encounter by employing other cognitive facets. For example, older adult typists may keep their typing speed to a high level by looking further ahead at text as they grow older [62,63].
Cognitive ability and health
The data presented in this Handbook are mainly from studies conducted on healthy volunteers (much as this can be confidently stated). Even within this group of people individual differences can be vast. For example, some older people will be more aerobically fit than others. Bashore and Goddard [64] provide evidence that positive factors of general health in older people can significantly contribute to their cognitive functioning abilities: fitness over the life period has been shown to correlate with mental processing speed in older people.
Mental health has also been shown to play a similar role (for a review of the literature see [65]). For example, older people with depression have been found to complain of memory problems frequently (approximately 5% of the population of the UK over 65 years and 20% aged over 80 years suffer from dementia [66]).
Meyer and Rice [67] have found that a person’s age effect deficits maybe slower for those with higher verbal ability than others. This emphasises the importance that the individuals cognitive capabilities may play in the ageing degradation process.
Design Implications
The following are a selection of products that may involve the use of cognitive, psychomotor or sensory functions:
- warning lights / signals on products
- traffic lights
- telephone /communication devices
- computer interfaces eg Automated Teller Machines (ATM’s)
- automated systems
- domestic electrical products eg televisions, videos, clocks
- cooking equipment
- central heating timers
- security systems eg burglar alarms, medical and emergency alarms
Any products that necessarily involve an interaction between the person and the controls or displays of a product may benefit from consideration of the effects of ageing on cognitive functions. The design of products should allow for tasks that are simple and that can be performed at the pace of the user, over a broad time period.
Table 3 summarises the general changes that generally occur to certain cognitive and psychomotor functions with ageing.
Ageing
Figure ? shows the average heights and weights of the adult civilian populations of Great Britain and the US plotted against age. A steady decline in stature is apparent, whereas weight climbs steadily before subsequently declining at around 50 years in men or 60 years in women. In analysing such a pattern we must consider the combined effects of the ageing process and the secular trend, together with the possibilities of differential mortality (i.e. that people with certain kinds of physique may tend to die younger.) Damon (1973) showed that men of average height and weight had greater longevity than those who deviated strongly in either respect. These interactions require multicohort longitudinal studies for their elucidation. Investigations of this kind include the Welsh study of Miall et al. (1967) and the extensive Boston programme of the Veterans Administration (Damon et al. 1972, Friedlander et al. 1977, Borkan et al. 1983.) Longitudinal studies show that at around 40 years of age we begin to shrink in stature, that the shrinkage accelerates with age, and that women shrink more than men. The shrinkage is generally believed to occur in the intervertebral discs of the spine – resulting in the characteristic round back of the elderly (e.g. Trotter and Gleser 1951) – although Borkan et al. (1983) suggest that some decrease also occurs in the lower limbs. The data show a longitudinal increase in weight for height until 55 years followed by a decline. Friedlander et al. (1977) showed a steady longitudinal increase not only in hip breadth but also in the bi-iliac breadth of the bony pelvis. The mechanism of the latter is obscure but it suggests that ‘middle-age spread’ may not be totally due to the accumulation of fat, but may also involve changes in the bony pelvis.
If we assume that no secular change has occurred in the proportions of the body, then proportional ratios calculated from cross-sectional studies should be comparable with the longitudinal results. Figure ? plotted from the data of Stoudt et al. (1965, 1970) shows that this is indeed the case. The proportional decrease in sitting height is compatible with the spinal shrinkage explanation of stature decline, and the greater change in women matches the longitudinal findings of Miall et al. (1967). Dimensions with a substantial soft-tissue component such as hip breadth and buttock–knee length show a proportional increase (until 75 years) which is more pronounced in women. The proportional decline in the biacromial breadth of men over 60 years old presumably reflects the characteristic rounding of the shoulders of the elderly. It is of interest that for both sitting height and biacromial breadth the ageing process finally abolishes the sex difference altogether.
Cross-sectional studies such as Stoudt et al. (1970) have shown an increase in skinfold thickness followed by a decline at around 40 years in men and 60 years in women. There is evidence, however, that this represents a redistribution rather than a loss of body fat. Durnin and Womersley (1974) showed that the relationship between skinfold thickness and whole body fat, as measured by densitometry, changes with age. It seems there is a transfer of fat from subcutaneous positions to deep ones (e.g. around the abdominal organs). The net quantity as a percentage of body weight continues to increase, and the longitudinal decline in weight that we see late in life is probably due, therefore, to the loss of lean tissue. Borkan and Norris (1977) found that the weight of fat was constant with age in a cross-sectional sample of middle-aged men, but that lean tissue declined markedly. Subcutaneous fat decreased on the trunk but increased on the hips, but this was accompanied by an increase of abdominal (waist) circumference indicative of a sagging of the abdominal contents (due presumably to increased internal fat and decreased muscular resistance.) A similar redistribution presumably occurs in women – but there is little numerical evidence.
The above studies are all based on the populations of the US and Great Britain, where obesity, consequent upon an abundant food supply and a sedentary lifestyle, is prevalent. The situation in other communities will, of course, be different, and in societies where food is scarce, adult increase in body weight does not occur.
The loss of lean body weight is due principally to a wasting away of muscles (although the bones also become less dense in later life) and this leads to a decrease in muscular strength – as shown for example in Figure ?.
According, for example, to Asmussen and Heeboll-Nielsen (1962), the decline is more rapid in women than in men; and more rapid in lower limb muscle groups than in upper limb muscle groups. In other words, women age more rapidly than men and the legs give out first. Both of these conclusions have been challenged, however: the first by Montoye and Lamphier (1977) and the second by Viitisalo et al. (1985).
We live in a ‘greying’ society. Figure ? shows some recent demographic predictions. In 1971 about one person in six in the UK was of retirement age (i.e. 65 for men, 60 for women); by 2031, it is estimated, the figure will be closer to one person in four. The rate of increase is greatest in the oldest age groups – specifically the over-75s who will increase dramatically in numbers by the turn of the century.
Beyond the middle years of life, most of us will tend to suffer from a steady diminution in our functional capacities – due partly to the ageing process as such and partly to the effects of previous disease or injury from which recovery has been incomplete. As a consequence, we experience a steady increase in the number of critical mismatches that we encounter in the performance of the everyday tasks of life. The net effect of these changes are illustrated in Figure ? which shows the percentage of people in different age groups having one or more specific disabilities: that is, one or more functional impairments that lead to significant difficulties in the performance of tasks in everyday life. The figure takes a dramatic upswing beyond the age of 60. As things stand at present therefore, we typically seem to continue working until we reach the age when our bodily framework starts to pack upon us. There is something of an irony in this.
The rate of onset of the decrepitude which comes with old age is highly variable. Part of this is just luck – a matter of the genes we are born with and the misfortunes we encounter along the way. Lifestyle is a major factor, however. In particular, it seems fairly certain that (within limits) regular physical activity can fend off the ageing process. Unfortunately, however, we not uncommonly get trapped in a downward spiral in which diminished functional capacity leads to a reduction of activity; which leads to a further reduction in functional capacity and so on. We encounter difficulties in doing things, so we stop doing them, and in due course are able to do less and less. The problems of the ageing society present a major challenge for ergonomics.
Approach
The emphasis of this project will be product orientated i.e. mainly concentrating on trying to find design solutions to the problem. Of course the designs will be strongly influenced by ergonomics and knowledge will be required of medical conditions occurring due to aging. An important aspect of ergonomics will be the anthropometric measurements of the body. Standards relating to bathtub manufacture, design, installation and plumbing should be investigated. Although one is designing for the home, there should be flexibility in the designs to allow for NHS and other health care installations. Again, standards relating to these commercial installations should be considered. Designs in other westernised and non-westernised countries should be investigated. Up-to-date current and projected statistics should be obtained on the influence of the aging population on the UK and for other relevant bathroom statistics. Of course dimensions of the ‘standard’ UK bath will have to be found out, if indeed a ‘standard’ bath size exists! As full as possible an investigation of current bathroom manufacturers will have to be made along with relevant existing products. Of particular personal interest are the following manufacturers. Ideal Standard (the bathroom market leader), Premier Bathrooms (the special needs bathroom market leader), Doulton Porcelain who supply B & Q (the leading DIY retailer), Twyford, Armitage-Shanks, Shires and C.P. Hart Bathrooms (the C.P.Hart group may be unknown to some, but it supplies to architects specifying for expensive London apartments, not a manufacturer, main manufacturer is Duravit). There are of course other known companies (e.g. Dolphin (market leader of fitted bathrooms), not a manufacturer) and relevant companies and their products will be investigated. Of course comprehensive literature searches will have to made of relevant books, journals, CD-ROMS, the internet, etc.
There are specialist products on the market already. However, it is felt that performance is often compromised; in terms of enjoyment, ease of use and, most commonly, lack of realism to a ‘standard’ bath – e.g. the ‘walk–in bath’. Existing products are often also very expensive. The elderly user may just want to have a ‘standard’ bathing experience, the realism of a ‘standard’ bath, but he / she has to pay currently the cost of a luxury bath if not more. The feeling of a ‘standard’ bath should not be a luxury. Existing products are certainly not attractive and often have a clinical feeling even though they maybe located in the home. One wants to overcome these problems as much as possible. From initial research, the very specialised integrated baths (i.e. not add-ons to a standard bath) for this market range from about 3000.00 pounds including vat to over 10000.00 pounds. This is a lot of money for just the bath tub. Although only the bath tub is being designed in this project, it is intended that a possible suite including wc and hand basin should not cost any more than about 1500.00 pounds including vat. However the design intended will not be optimal in situations where: 1) a user has a high degree of dependence, or 2) the tub is used to bathe several people who require assistance. In these cases the very specialised existing sophisticated tubs with powered lifts, tilting mechanisms and/or doors are more appropriate and are recommended. 1 The walk-in-bath is smaller in length than a standard bath and allows bathing only in a sitting or partially reclined position as opposed to a reclined or recumbent sitting position in a standard bath. As the body is more reclined (increased rake) the water requirement in a bath is reduced. But the bath needs to get longer as a consequence. Therefore, the depth of water in a walk-in-bath is high. As there is a pivot/bi-fold/sliding door, a technical problem of a water seal is required. 2 Another type of product has a standard bath floor raised to sitting height with the bath panel door retracting/rising vertically. It retracts below sitting height. It again requires a water seal when the door is raised and is very expensive. 3 Another product is a standard bath with a pivot door for entry and an optional bath bench. Certainly these products aid access, number 2 being the best because it is felt to give the best bathing experience with improved ingress and egress IF it is reliable. However cost is prohibitive and ‘assistive device’ appearance doesn’t help. 4 There are other products such as costly electric seats or belts to help ingress and egress. However electronics increases the costs and again there are problems of assistive device appearance or space limitations. I am not going to design for shower cubicles. There is less difficulty in the usage of shower cubicles as opposed to baths for the elderly with adjustable shower heads and seats, etc. Very specialist products already exist in this area. Showers are recommended for those who have serious mobility problems and for example, require a wheelchair.
Despite the large number of bath tubs and assistive devices available to make bathing easier there is still room for innovation. Some innovation has been radical and entails new visions of the bathroom. However it has been elected to design a new bath tub for the home UK market that would be safer and easier for elderly people to use while still being conventional in appearance and affordable. The design should give an enjoyable realistic bathing experience and be attractive. Doors and electronics will be avoided in the design for affordability and attractiveness. The bath tub should give suitable support for the body and impairments such as arthritis of old age should be considered. Ideas may be obtained from shower related products. Initial thoughts on the design suggest that a fully integrated design will be difficult, particularly with the need of grab rails, but one will try to make the designs as attractive as possible. One will try to improve the design of standard baths and use the knowledge obtained to find design solutions to the problem stipulated. The design will try to be in between the extremes of a standard bath and the very specialised expensive baths. It is wanted that the image of the design is as a luxury bath with luxury benefits which help able-bodied and elderly users alike. Incorporationof a jacuzzi/whirlpool/spa must be considered. Compromises will of course have to be made between attractiveness, safety, ideal ergonomics, space constraints and manufacturing /economic constraints. The design of the tub should be conventional in size without any doors or other unfamiliar mechanisms. It should follow the principles of universal design with features that are helpful for most people. The fact that the product should be distributed through regular retailers, rather than health care product distributors, should further avoid any tendency for labelling or stigmatization. If the product was manufactured, it should be well-known i.e. made by a well-known large manufacturer and easily accessible for purchase e.g. a local large DIY store. Its low cost and standard installation should increase acceptance. I want to ideally have designs which fit in the space of a standard straight bath tub. There is no such thing as a standard bath tub. There is now immense variation in size, shape style and budget! However one can think of it in terms of the commonest size. This can be ascertained from the bathroom manufacturer market leader(Ideal Standard)’s ‘Studio’ bathroom suite and the sizes of bath tubs in leading DIY stores. This is about 1700 mm overall in length by 700 mm width. Ideally I want to avoid problems with access, such that a bathroom need not be altered in size, particularly when new house builders are building smaller and smaller properties with consequentially smaller and smaller bathrooms. Consideration may have to be made as to the usage of other assistive devices such as wheelchairs and space and access for carers. Although there is probably a direct correlation that older people have more disabilities, I am designing for the elderly and not for the disabled. Of course in designing for the elderly, I will be designing to some extent for the disabled, but there are so many disabilities. I cannot possibly cover all of them. I want designs which can be used by everybody, not just by the elderly. However, this should not compromise the performance usage by elderly people. Products to be designed in this project include the bath tub, front
/side panel, taps(faucets), shower and waste. A straight bath was chosen over a corner bath for the following reasons. A straight bath is more common. It takes up less space. A corner bath is often wider than a standard straight bath, but it is often shorter in bathing length. A corner bath is more costly to manufacture and the manufacturer must produce left and right hand versions. In the design proposed in this project, the bath tub should only be available in one version. Producing more than one version in this somewhat niche market is economically foolhardy. The design of the bath tub should involve consultation with many individuals. Manufacturing and marketing issues should be identified through discussions with the manufacturer and with other suppliers and retailers of bath tubs. These discussions should result in a definition of the basic design constraints to the design and some preliminary concepts for the form of the tub. Examination of commercial literature and attendance at major trade shows should hopefully confirm the lack of availability of a comparable product. A survey of the current understanding of problems related to bathing and current solutions should be augmented by an extensive series of interactions with elderly people, people with disabilities, and clinicians. Various concepts could be explored in the form of sketches and models. A simple wooden prototype could demonstrate its mechanical function and photo-realistic computer renderings could be generated to show the appearance in typical bathroom settings. These materials could be shown to individual consumers to gain reactions. The design of the product could then be completed in collaboration with the manufacturer. Designs should involve an extensive and iterative consultation process with potential users, purchasers, and health and design professionals. Time is very limited in this project. Access to people for questionnaires, focus groups, evaluation, fitting trials, etc. has been difficult and time unfortunately means that the design cannot be developed beyond sketch level. Adjustments will more than likely have to be made with real suitable evaluation by all parties. Three broad categories of users have been identified who need a new tub design: 1. people who have difficulty stepping safely in and out of the shower and are at risk of falling; 2. people who would like to soak in a tub but have difficulty with ingress and egress, and rising from the bottom of the tub; 3. wheelchair users and others with more severe mobility restrictions who need a safe bath seat. The shape of the new tub should make ingress and egress easier both for people stepping into the shower and for those planning to soak in the tub. The bathroom should combine hedonistic luxury with functional efficiency. It is an environment in which to relax and unwind, soaking in a hot tub, but also a configuration of workstations for the practical activity of washing, grooming and excretion (assuming a special room is not set aside for the latter). The bathtub presents interesting problems of dimensional optimization. It must be large enough for comfortable use by one person (or perhaps two) but should not have needless volume, requiring filling with expensively heated water. It is also a notoriously hazardous environment for the frail and infirm. Two principal postures are adopted in the bath: a reclined sitting position and a recumbent position (possibly with the knees flexed) in which the body is submerged to neck level. For comfort in the sitting position the horizontal bottom of the tub must be sufficient to accommodate the buttock–heel length (it is recommended that the 95th %ile man is 1160 mm by Pheasant) and the end of the bath should provide a suitable backrest. Kira (1976) recommends a rake of 50–65° from the vertical and contouring to conform to the shape of the back. This seems excessive to me. A standard bath has a rake of about 30°. A suitable radius where the base meets the end should be quite adequate. One is not particularly looking for postural support since the buoyancy of the water will both unload the spine and lift it away from the backrest. The more one increases the length of the horizontal base the greater the possibility for total submersion. One may shorten recumbent bodies by around 100 mm by flexing the knees according to Pheasant, given that one wishes to keep the head above water, and that as the 95th %ile male shoulder height is 1535 mm according to Pheasant there seems little point in lengthening the horizontal part beyond around 1400 mm according to Pheasant. The width of the bath must at least accommodate the maximum body breadth of a single bather (the 95th %ile man is 580 mm according to Pheasant). I am not designing a two person bath because space is limited in length. However, it is interesting to discuss it. For couples wishing to sit side-by-side the necessary clearance is given by their combined shoulder breadth (920 mm for a 95th %ile couple of the opposite sex according to Pheasant). For couples sitting at opposite ends (probably the more common arrangement) the clearance is given by the combined breadth of the hips of one person and the feet of the other. This is greatest when the hips are female and the feet are male, in which case the 95th %ile combination is 625 mm according to Pheasant. This arrangement does, however, demand that the taps should be in the centre to avoid arguments. Consider a 95th %ile man (sitting shoulder height of 645 mm according to Pheasant) reclining against the end of the bath. His shoulders will be 645 cos 30 = 558 mm above the base of the bath. He could not reasonably require more than 400 mm of water. If the backrest was raked further, say to 45°, then 300 mm of water would suffice. (These figures are mere speculation; it would be very interesting to perform a fitting trial to find out what depth of water people really do want.) Assuming a 30° rake, a bath depth of 500 mm would be required for an adequate quantity of water without too much danger of it splashing over the edge. In fact, a typical tub depth at the present is about 380 mm (15 in.), although older models are often deeper. The outside height of the rim (above the floor) is, of course, generally greater than the tub depth (often by as much as 100 mm). A deep bath or a high rim is generally deemed to make entering and leaving more difficult and hazardous and one is also of this feeling. Kira (1976) casts some doubt on this, arguing that the manoeuvres people use to enter and leave baths have been insufficiently analysed. Grandjean (1973) cites evidence that a height of 500mm is acceptable to most elderly or frail people. Grab rails are usually advocated as an aid to stability. These could reasonably be a little above knuckle height at the point where you climb in (e.g. 800 mm above the bath base according to Pheasant), around shoulder height (e.g. 575 mm according to Pheasant) at the sitting end and about 40 mm in diameter according to Pheasant. Vertical grab rails may well be better for the infirm. Additional holds along the side of the bath are also desirable and for the frail, a non-slip mat inside the bath is essential.
Risks
As far as I can see there are no risks as far as I am concerned with this project as it involves designing and researching in a non-indutrial environment except for the use of computers. I am epileptic and I reduce any risk if I have any choice with computer interaction to work a maximum of 40 minutes and then have a minimum of 10 minutes break before any further computer interaction.
