Human Factors

Brien Roche

Human factors is a field that applies knowledge of perception, cognition and response to product design and human behavior. Perception, cognition and response are in large measure governed by our ability to see. Therefore it is important to understand the human eye. All of this may be needed in premises liability and product liability cases.

Human Factors and The Human Eye

The outermost portion of the eye is the cornea. The pupil is the dark center through which the light enters. The iris is the colored portion of the eye that controls the entry of light. It controls the size of the pupil.The light that enters through the pupil passes through the lens and is reflected on the retina at the back of the eye.The lens focuses the light on an area of the retina called the fovea. There are structures within the retina called rods and cones. The rods are throughout the retina but not in the fovea. The job of the rods is to look for light and direct it to the fovea.

The cones are mostly in the fovea and they provide color vision. However the cones need light to function. That light is directed to them by the rods. Most visual perception begins on the periphery. That is the eye moves to the periphery in order to bring things within the range of the fovea.

Foveal Range

An object becomes identifiable when it comes within the foveal range of vision. The cones give the object color. This allows the object to be seen. The rods sense things in the periphery but are not able to produce color vision. Finally when the object is brought within the foveal range of vision it can be seen in color. All of this explains why your best vision at night is peripheral vision. The rods are searching for light to direct to the cones. With that light the cones can apply color to objects which is what allows us to see one object from another. The color provides the borders that divide one object from another. Call, or contact us for a free consult.

Furthermore a person’s ability to see and perceive is a function of :

• age-older people tend to have more difficulty perceiving and reacting to dangers.
• gender-females tend to perform worse on perception-reaction tests than males.
• expectation-you are inclined to see what you expect to see.
• prior routine or habit-the body and mind revert to what it knows.
• fatigue
• stress-high stress tends to adversely effect perception-reaction time.
• impairment
• distractions-visual clutter (such as headlight glare) can effect perception-reaction time
• background-lack of contrasts between objects can effect perception.
• speed

Not Seeing What Is Obvious

So how do you explain that an intelligent adult does not see what appears to be obvious? It may be a function of the mechanics of the eye. In other words did the sign ever get within the foveal range of vision? Or it may be explained by the fact that the person, based on prior behavior, had no reason to expect the sign to be present. In addition it may be that due to the stress or distractions from the event the person simply did not have the ability to digest the threat.

Designing For The Human

So with this in mind product designers and property owners need to realize that the mere possibility that a user may see their warning is not enough. They must move that possibility up into the probability range. Product designers and property owners are well placed to predict user conduct with a high degree of accuracy. Even more where there may be certain expectations of the user or habits of the user.

In other words safe design of products and premises must take people for what they are. It must note their habits, expectations and abilities. It must note where they are at the time of use. The designer cannot wish people to be something they are not. Therefore design must be based on probable human conduct. It should not be based on possible or idealistic human conduct. As a result the mere fact that a user could have prevented an accident does not make the user liable.

Call, or contact us for a free consult. For more information on human factors go to Wikipedia. Also see the page on this site dealing with eye witness identification.