Wolffsohn J S, Edgar G K, Stone H E, Williams M, McBrien N A
Department of Optometry and Vision Sciences, University of Melbourne, Parkville, Victoria, Australia.
Aviat Space Environ Med. 1999 Jul;70(7):666-73.
Whether over-accommodation is caused by the use of head-up displays is still under debate. Most prior experimentation has involved cognitively demanding tasks, which are known to affect the accommodation response. The simulations have often been unrealistic and involved short working distances.
Over-accommodation is caused not by the presence of a head-up display per se, but rather by the cognitive demand of the task.
The effect of increasing the task cognitive load and the use of forward looking infra-red imagery (FLIR) on the ocular accommodative response and task performance was assessed with a realistic head-up display assisted flying task. FLIR increases cognitive load due to its poor resolution and the need for interpretation of the images.
Over-accommodation was found to be small in magnitude (0.17+/-0.03D; range -0.02-0.45D) occurring only with cognitively demanding tasks and with forward looking infrared imagery. Response times to detect tanks in the outside world scene were slower with increased cognitive load and forward looking infra-red imagery, along with a reduced detection rate, decreased accuracy of tracking tanks in the outside world and poorer control of the head-up display pitch ladder. When discrimination was added to detection in an outside world task, decisions were delayed until they could be accurately made, rather than performance degraded.
The use of a virtual head-up display in a simulated aircraft environment did not adversely affect ocular accommodation. However, increased cognitive demand or FLIR imagery caused significant inward shifts of accommodation.
使用平视显示器是否会导致过度调节仍存在争议。大多数先前的实验都涉及认知要求较高的任务，而这些任务已知会影响调节反应。模拟往往不切实际，且工作距离较短。
过度调节不是由平视显示器本身的存在引起的，而是由任务的认知要求导致的。
通过一项逼真的平视显示器辅助飞行任务，评估增加任务认知负荷以及使用前视红外图像（FLIR）对眼部调节反应和任务表现的影响。由于FLIR分辨率差且需要对图像进行解读，所以会增加认知负荷。
发现过度调节幅度较小（0.17±0.03D；范围为-0.02 - 0.45D），仅在认知要求较高的任务以及使用前视红外图像时出现。随着认知负荷和前视红外图像的增加，在外界场景中检测坦克的反应时间变慢，同时检测率降低，对外界坦克跟踪的准确性下降，平视显示器俯仰阶梯的控制变差。当在外界任务的检测中增加辨别任务时，决策会延迟到能够准确做出，而不是表现下降。
在模拟飞机环境中使用虚拟平视显示器不会对眼部调节产生不利影响。然而，认知需求增加或FLIR图像会导致调节显著向内偏移。
