Perception and Balance


Cutting Edge Seminars

Balance and Perception

Welcome back! In this section are going do something a little different than we did this morning. This morning, we talked about the anatomy of the slip and fall, what elements are necessary to establish liability and to prove it, what we need in the way of evidence and what laws are likely to be applicable. Now we are going to discuss one issue that is the most troublesome in slip and fall  and pedestrian fall accidents cases in which  the handicapped and the elderly are the victims. This problem also occurs in most slip and fall cases generally. Often, the defense is “why didn’t they watch where they were going? If they did, they could have avoided the hazard.” This a common argument made for the jury. It certainly has some elements of the truth to it. Should the hazard have  been recognizable? Since few things are invisible, the hazard probably would be recognizable under the right conditions.

We must look at the circumstances and take into consideration both the physiology and the psychology of the victim, as well as physical characteristics of the walkway surface to determine whether the hazard would be readily identifiable to the pedestrian. Consider the phrase: “watch where you’re going.” During a normal stride and while an individual is standing erect, there is a cone a vision that extends about 30° of from each side of their nose and about 30° up and down. So, we have a cone of about 60° that is in front of us with the highest visual acuity.

If you look forward, you can see in an area are in front of you an area about 60° to from each side with the greatest visual acuity. As far as distances are concerned, the distance that you can see with the greatest visual acuity ranges from 5 to 9 feet. This of course is for the average individual with corrected vision and does not consider any visual impairment. As we walk normally, objects that are 9 feet ahead of its first become distinctly visible.

Then as we approach closer and closer, at 4 feet (that’s about two steps or a step and half) it then becomes peripherical and it is no longer in sharp contrast. This is where it where visibility decreases. When cone of vision is extended, it enables to determine both direction and vertical orientation and help us identify the features of the walkway as we approach. For example, picture a mud puddle which we can see about 9 feet away with clarity if there’s sufficient light, contrast and other things. We see the mud puddle and can easily step around it or step across it. We do not step in it because we’ve been able to see, delineate and adapt our walking characteristics to avoid the hazard.

For something to be visible it must be conspicuous, and this is called conspicuity. There are a couple types of conspicuity: perceptual conspicuity when we can perceive the characteristics of the condition and thereby it becomes conspicuous because we were aware of it. We have the consciousness of the knowledge of the of the condition and we can take appropriate steps to avoid it; thereby reducing the risk of injury. The slippery conditions remain; slipping hazard may still remain but we do not fall victim to it because we’ve been able to see it. Thereby lies the argument if we had looked at this condition, we would have seen it becoming aware of it and been on alert or on guard that the hazard exists. On notice we should take appropriate precautions to avoid the hazard.
Perceptual conspicuity is based mainly on contrasts. If there is not sufficient contrast either in color or in texture, the obstruction or edge is difficult to see. In areas where there is reduced lighting and there is less reflected light, the conspicuousness of the condition is less and less.

Of the four basic factors of seeing, these are the ones we must consider: contrast, size, brightness and time. Contrast is a difference between the items on the walkway surface that is between an individual and its background. We will be talking about this and in more detail in just a moment. Without this difference in contrast, an obstruction or slipping hazard may not be readily visible. For example, light yellow type on the yellow screen does not provide enough contrast for us to be able to read it easily. If we change the type to black or blue, the contrast is significant, and the type becomes substantially more visible.

In the case of wheel stops or curbs where the natural color of the concrete structure and the concrete itself is essentially the same, the wheel stop becomes more difficult to see or the edge of the curb becomes more difficult to see. However, if the wheel stop is white against a black or dark background visibility is increased; the obstruction stands out becomes more visible. You can see the difference both in size and the placement or location of the slipping or tripping hazard.
The contrasts also depend on the comparison of the light reflected from the walkway surface and the light reflected from an obstruction or foreign material. For example, if one were walking toward a wet spot on the walkway and the light is shining directly behind it reflecting off the wet spot into your eye, you’ll see a difference in reflection. The wet spot becomes visible. However, if we took the light so it shined 90° or perpendicular to our travel, the wet spot essentially disappears. There is reduced visibility because there is no visual contrast and this, of course, is based on brightness more than color.

The same thing occurs with color is well recognized that the elderly needs substantially more contrast between objects to have the same level of visual acuity, that is our ability to see, as younger people. The elderly are particularly those suffering from some level of cataracts or some macular degeneration needs brighter and brighter lights progressively in order to see the same thing that has someone much younger would be able to see without difficulty. The contrast can be adjusted by increasing the amount of light or altering the composition of the reflected light or sometimes just the angle of reflection. For example, if you had a dull mat material on a shiny bright surface, the reflected light between the dull mat and the shiny surface would be readily visible. Similarly, if you had a highly reflective area against a relatively dull, dark surface, the object would be more visible than if everything were on an bright and shiny.

For example, water on a highly waxed floor is very difficult to see because both and reflect light very well; better than 80 to 90% of the light is reflected. This reduces the visibility in general. The larger an object or the obstruction appears the easier it is to see. This pretty self-evident. Often if you have something that is change of elevation that measures 1½ inches or less it is more difficult to see than 9-inch curb or 7-inch step.

Brightness which is one of the other issues is a measure of the amount of light reflecting from the surface to our eye in a certain direction. Brightness that is a function of the luminance and that is the amount of light reflecting from an object and the surrounding or background. Both the color and texture the surface can affect the luminance. For example, we just described a mat color contrast on a shiny background. The amount of color on may well affect the amount of luminous or amount of light that reflecting backwards to the eye. Both color and texture are important then as a means of identifying hazards that may present themselves to pedestrians. The obvious examples are glossy services that reflect more light than dull. Mat surfaces and light colors reflect more light than dark ones and the amount of perceived luminance is greater when both the amount of light reaching the eye is increased and the contrast between the surfaces are significant.

Now we need to discuss the last factor; which is probably the most important one: the element of time. This is most often ignored and becomes the most critical when dealing with the elderly pedestrian. The time a person takes to view an object affects vision because it takes time for the eye to assimilate the details. If the object has poor contrast and luminance, it will take more time to bring to process the information. Under poor lighting conditions one may logically assume that the pedestrian will walk at a reduced speed. One of the prominent human factors researchers, Redford, determined that a walking speed of 3.6 feet per second of would not be an unreasonable estimate for pedestrians walking slowly. This essentially is two steps every 1.1 seconds and in an average step and some were brought 18 to 20 inches. Using this  pace; we will use 3.6 FPS [n our example. Average pace would be about 1-1/2 feet per each step of 18 inches. Approaching a wheel stop for example, the wheel stop may be as close as 5 feet. When one steps off the curb the wheel stop is less than 1-1/2 seconds away. Decreasing the amount of available  time for recognition can be the placement the wheel stops or the location of cars in the stall. The tripping hazard may be in view for less  than a second. Because of the mechanics of walking , this is insufficient amount of time for the pedestrian to see,  delineate and evaluate the hazard.

Balance and perception go hand in hand maintaining  balance. There must be orientation of oneself to the physical conditions. We must know which way up is, for example, to see we’re going. For vertical stability we use orientation edges.   As I stand here, I have orientation edges to assist me in keeping my balance; I have the ceiling line; I have the door frame; I have the podium in front of me. All of which gives me a sense of level and/or perspective so that I know both which way up is and which way I would go to leave the room. Where conditions and circumstances interfere with this perception of vertical in a new location or the physical conditions such as a change of elevation loss of equilibrium or balance is likely to occur. If you just are not oriented and balanced, you may not be able to see and delineate the existence or location and degree of slope of a ramp or changes of elevation.  It is like being in the funhouse where it is difficult to see on where you are and how to maintain your balance. The pedestrian needs to evaluate all these relevant conditions accurately to maintain stability and avoid falling victim to the hazards.