Oct. 14, 2004 New research suggests that the design of aircraft cockpit displays may benefit from a radical change. The work, to be reported in a forthcoming issue of Phil. Trans. A, a journal of the Royal Society, challenges the previous scientific consensus and indicates that changing displays so they flicker, use one colour and contain more objects will better stimulate visual reactions in pilots than conventional multi-coloured outline displays.
The potential advantages for new types of display arise because our conscious visual perception of the environment is very restricted. The retina in the human eye can register literally thousands of pieces of information simultaneously. But how this information is processed by the brain to isolate a limited number of important features of our environment and allow us to react is a complex process. It has consequences for the design of many critical machine-man interfaces from fighter pilot cockpits to vehicle dashboards and virtual gaming environments.
Saw it – still hit it
"Although the human eye can code many object-images simultaneously, we are only aware of a tiny fraction of this information," explains Dr. Greg Davis of Cambridge University. "Our 'visual' brain has evolved to prioritize relevant features in a scene and ignore irrelevant ones." But this selectivity can lead to problems in information-rich environments, for example driving a car or landing an aircraft, where we need to monitor a large number of items. In some cases vision can fail to cope and accidents result. Examples include 'looked but failed to see' accidents in which sober drivers run into highly visible, stationary police cars in broad daylight.
To reduce the incidence of these events, a large amount of research in psychophysics and ergonomics has examined how display characteristics effect our ability to simultaneously process multiple features in the visual environment.
The majority of experiments have found that the human performance can be optimized by combining several features into one object in a display situation. Combining a number of pieces of information in a single object appeared to improve reaction times and visual memory compared to separating the information in two or more objects. "However our recent experiments have shown that, in many cases, exactly the opposite is true," says Dr. Davis. "The design of previous experiments was flawed, effectively eliminating one important visual processing pathway in the brain."
Dr Davis has found that information sources can be more efficiently processed when they belong to separate objects. "Contrary to conclusions from previous work, reducing the number of objects in a display appears to have no general effect on perceptual performance. Indeed, in many cases, this adversely affects performance," says Dr. Davis. "This has important implications for a diverse range of display technologies including cockpit displays, car dashboards and virtual environment situations."
Two paths to perception
Dr. Davis suggests that there are two separate pathways that process different visual information. "To process 'within-object' relationships between shape, colour and texture features of the same object, one brain pathway, the parvocellular-ventral processing stream, is used. In contrast, our research indicates that 'between-object' information, that relationships between features from separate, neighbouring objects, are processed via a second pathway: the magnocellular-dorsal processing stream," explains Dr. Davis.
Cells in the parvocellular-ventral pathway show long-lived responses to objects in the visual field and play a major role in our recognition of objects. However, the magnocelllular-dorsal process is implicated in the visual guidance of action: the mechanism by which we judge distances between objects and that allows us (usually) to reach out and grab objects.
"All previous experimental approaches of this type, including some of our own, have only fully stimulated the parvocellular-ventral pathway, whilst ignoring or under stimulating the magnocellular-dorsal process," says Dr. Davis. "This has led to results that show improved performance for single object, multi-feature displays. By reassessing our experimental design to equally stimulate the two pathways we find that multi-object displays often result in better performance."
Dr. Davis's results indicate that stimulation of the magnocellular-dorsal process significantly enhances performance for multi-object displays. The magnocellular-dorsal process is most readily activated by flickering displays and is sensitive even to low contrast, monochromatic objects. In contrast many current displays are non-flickering coloured and are constructed from thin outline symbols. These primarily activate the parvocellular-ventral pathway and do not yield the same performance benefits as displays that activate the magnocellular-dorsal pathway.
"Getting the right information to a pilot is critically important," concludes Dr. Davis. "The most stressful time for a naval pilot is not combat but landing his or her plane on the moving deck of an aircraft carrier. The safety of pilot and crew relies on the right information stimulating the correct action. The same general issues also apply to road vehicles."
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