The extent to which such loss is driven by exposure to noise versus normal aging is a matter of dispute. Losses are linked to noise exposure as well as to factors such as cardiovascular disease, smoking, and dietary factors. There are a number of approaches to remediating hearing loss. In general, hearing aids have not been particularly functional in fully restoring hearing acuity because they boost both signal and noise.

Given that some have estimated that normative hearing loss is at least partially attributed to noise exposure in the workplace (e.g., Corso, 1981), prevention is a potentially useful approach. One important source of noise exposure is aging equipment. Farmers using older tractors can be exposed to noise levels in excess of 100 dB (Pessina and Guerretti, 2000). Also, hearing loss is strongly associated with livestock-related injuries for farmers (Sprince et al., 2003). Noise reduction engineering and promotion of safe practices in inherently noisy environments, such as the use of noise reduction devices (e.g., ear protective equipment such as earplugs), may be important components in preventing problems.

Given that hearing loss may pose a significant problem (particularly for older male workers), redesign can be an important tool in preventing hearing impairments from becoming disabilities. One such design change is to make use of other less-impaired sensory channels, described below, to signal important information (such as warnings).

Use of Redundant Channels and Substitution of Channels

There are many examples of using redundant channels to compensate for hearing loss. It is possible to provide both visual and auditory warnings (flashing lights with sound). Perhaps the best-known example is the use of a warning sound (beep) to indicate when a vehicle is backing up (moving in the unexpected direction). Other examples can be found in catalogs of assistive devices, such as those that supplement normal sound channels with tactual feedback (e.g., a vibrating cell phone). For those with profound hearing loss, substitution of vision for hearing is sometimes possible (flashing lights for a doorbell, closed captioning on television). Vanderheiden (1997) offers specific recommendations on redesigning to accommodate those with disabilities.

Minimizing Background Noise

Several studies show greater comprehension impairment for older adults than younger ones at the same signal-to-noise ratios, compared to the case of detection of pure tones in quiet surroundings. Minimizing background noise should aid older workers differentially for comprehension tasks. Sim-

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