designing appliances for older persons-老年人(3)

老年人设计

devices. The attention-action cycles associated with usage are contingent on users reprocessing informa-tion stored in working memory. Response times of users, whether young or old, inflate with increasing task complexity [33]. However, increasing age ac-centuates this effect, due to both cognitive loading during processing and subsequent temporary storage of information for later processing. When systems are complex, users must recall operations performed, recognize current state of information based on op-erations already performed, and further apprehend the subsequent operations to achieve their goal. Suc-cess and efficiency depends not only on working memory, but also on the ability to inhibit irrelevant stimuli that could influence processing or state rec-ognition. These activities become increasingly diffi-cult as cognitive abilities decline.

As executive control in working memory declines with age, so does functional status measured by IADL [24]. Performance of IADL concerns planning, organization and flexibility, which are functions of executive control. Carlson et al. found that attention is critical for completion of many complex everyday activities [3]. Schieber decomposes attention into four modes [25]. Within these modes, selective and divided attention are of particular interest for the de-sign of appliances to support age-related cognitive impairment.

3.3.Search and attention

When using unfamiliar household appliance, users have to find specific controls for particular actions. They must identify these objects from their visual features, formed from primitives, such as shape, col-or and orientation. Identification depends on their perceptual system extracting the graphical primitives followed by integrating features to create meaningful associations [29]. Basak and Verhaeghen found that the response time for the pre-attentive extraction pro-cess does not depend on age [2]. While extraction takes advantage of perceptual automaticity, the inte-gration process relies on selective attention. If target items in visual search have either simple features or features unlike surrounding objects, then searchers can detect the separate features in parallel, without the second serial stage of attention [30]. Older adults can readily identify such targets [20]. For more com-plex items, focal attention is required for detection of targets—defined by a conjunction of separable prop-erties. The reaction time for this more complex serial processing is proportional to the number of items in the search space and is significantly longer for older than younger adults [20].

3.4.Inhibiting distractions to attention

In searching for a specific display element or con-trol, users of an appliance must be able to cope with distractions from task irrelevant information. Inhibi-tory control over interference from well-practiced extraneous, goal irrelevant, actions decreases with age [6,35]. Inhibition depends on the modality of the input and competing limited attentional resources and the processing codes (numeric, textual, spatial). Ver-haeghen and Cerella demonstrated that older people find difficulty inhibiting distractions from stimuli that are irrelevant to the prevailing task [33]. If the imposing stimuli concern other tasks that need ad-dressing, they will switch between tasks.

3.5.Redirecting attention

Success in using one or more appliances depends on users monitoring performance and actuating con-trols in response to cues. To respond to a cue, they disengage their attention from the immediate activity and move it to the cue [21]. For example, a grand-mother cooking a Christmas dinner for her extended family oversees multiple pots on a stovetop and a roast in the oven. She must respond to cues from sight (bubbling, color), sound and smell, and inter-vene when necessary (heat adjustment, removal from stove, beginning another subtask, e.g., plating of meal). The complexity involved may overwhelm someone with MCI or more severe impairments.

4.Appliance use and mental models

Effective use of an appliance depends upon users understanding the purpose of the device and how it operates. That is, they have some mental representa-tion of both the functions it can perform and the means for accessing this functionality. For users to interact successfully with an appliance, they must recognize that the appliance provides the means for achieving their purpose. Effective operation accords with users forging an appropriate mental model of its operation, in which they can relate the activities they wish to pursue to the functionality of the device. Ability of older adults to use an appliance depends on their mental model of operation. This may depend on the transfer of understanding from similar, more

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