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Distinguished Member
Join Date: Apr 2006
Location: In the Superstitions
Posts: 1,378
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part 2
The autonomic nervous system has two major branches; the parasympathetic and sympathetic branches. Generally speaking, the sympathetic nervous system prepares the body for direct action and confrontation by increasing heart pulse rate and bringing blood supply to large muscle groups. Also, eye pupil diameter increases, and the ciliary muscle relaxes, forcing a shooter to focus the eyes at far distances, perhaps to be behaviorally better prepared for a perceived oncoming threat. There is a slight bulging of the eyes associated with sympathetic nervous system dominance.
The parasympathetic nervous system allows you to maintain a more relaxed, balanced state of readiness by slowing an accelerated heart rate, decreasing pupil size, and allowing the eye’s accommodative system to focus at increasingly close distances of up to inches from your eyes. The parasympathetic nervous system aims to bring neural physiology back to a state of balance or relative homeostasis.
When the BAR is activated, along with the neural changes, there are hormonal and other biochemical channels activated concurrently by a part of the brain called the hypothalamus. These chemical mediators are useful in helping maintain the influence of the autonomic nervous system response by either encouraging the body to stay in ‘high alert’ or by reversing this high intensity response to strong stimuli and resume a more normal relaxed controlled state of neural balance. However, during the early stages of the BAR, adrenalin is released in the body to further enhance the excitatory component of the BAR. (see flow chart)
It is important to remember that the sympathetic nervous system can exert its neural messengers either in a focal manner (through secretion of noradrenalin or norepinephrine) at local end organs (as is the case at the ciliary muscle of the eye’s focusing system), or through releasing noradrenalin or norepinephrine directly into the bloodstream to prepare the body for combat.
It is worthwhile to note that during the BAR there are a series of other biochemical and hormonal changes that are activated throughout the body. One example is that the adrenal glands secrete a group of hormones called glucocorticoids. Cortisol is the most prevalent of these hormones. Cortisol increases blood sugar levels to contribute energy for muscle function. Research has also correlated decreased learning and decreased memory function, as well as attention anomalies with increased cortisol levels in the body. These changes in response to cortisol levels increasing during the BAR help explain, in part, why visual memory and visual attention is narrowed during the BAR. These types of physiological changes that accompany the BAR begin to explain the perceptual changes called “tunnel vision” and “perceptual narrowing”. Humans have an innate tendency to narrow attention upon a threat during extreme stress. It can be argued that learning how to expand peripheral awareness of space can minimize the effects of “tunnel vision” during the BAR. Other strategies to overcome the tunneling effects of perceptual narrowing will be outlined in the visual training section of this bulletin.
From a behavioral perspective, Dr. A. M. Skeffington, the father of behavioral optometry, theorized that during stress, the human ability to center on a task and identify and maintain meaningful awareness on a specific target is severely hampered. BAR type of stress causes a decline in your ability to derive meaning from your visual memory image due to a perceptual narrowing that accompanies the breakdown of optimal human performance. His theory postulated in the 1940s has gained strength and understanding during the last half century as much current neurological and psychological research has proven the bulk of his intuitive understanding of human responses to stress.
Other behavioral and performance changes have been reported to be associated with “perceptual narrowing”. The theory of perceptual narrowing suggests that as the level of demand increases on a central, straight ahead target, there will be a corresponding decrease in the visual area surrounding the central area from which peripheral information can be extracted. Increased arousal causes increased narrowing of the attentional focus, with a progressive elimination of input from the more peripheral aspects of the visual field. Another way of viewing “tunnel vision” is that as stress increases, there is a reduction of cues used to regulate performance. When stress levels are further increased, there is a further restriction in the range of visual cues used to sample visual space. Under stress, the useful field of view shrinks, and the amount of processing of visual information is narrowed.
A summary of behavioral changes that are associated with high levels of stress, such as seen during the BAR, include;
1. Narrowing of attention span and range of perceived alternatives,
2. Reduction in problem-solving capabilities,
3. Oversight of long-term consequences,
4. Inefficiency in information search strategies,
5. Difficulties in maintaining attention to fine detail discrimination, and
6. With intense fear, there is also temporary loss of fine visual-motor (e.g. eye-hand) coordination.
With the possibility of some of the above mentioned changes affecting shooter’s during high stress encounters, it follows that a person involved in a combat situation may have difficulty accurately recording and remembering all the details of an encounter. During the active stages of the BAR, it may be quite difficult to recall with high accuracy and detail the events that just occurred during a shooting exchange. However, once the high stress has been relieved and a shooter returns to a state of more controlled relaxation, there may be recall of more visual images related to a specific previous combat situation.
Contemporary visual research describes a parallel, dual processing visual system that is useful to further understand the complex nature of how visual information travels from the retina to the brain. One pathway (M-pathway) is more sensitive to coarse visual forms and images that move quickly. The other pathway (P-pathway) is more sensitive to fine spatial details of forms that are stationary or move at very slow rates.
It appears that the P-pathway processing visual information that is dominated by central, detailed labeling of information, whereas the M-pathway processes information dominated by peripheral vision awareness of movement, orientation and location of visual images. It may be that these pathways work in a synchronous manner to efficiently process visual information. Under high stress there seems to be an imbalance between the P and M pathways such that one pathway overrides the other. “Tunnel vision” appears to be related to P-pathway dominance and M-pathway inhibition during the BAR.
There are certain visual attributes that relate to object visibility that help shooters better understand why certain targets are easier to see that other targets. For example, size of a target is related to visibility because relatively larger image sizes have the potential to stimulate more retinal cells resulting in more information sent to the visual areas of the brain for processing. This increases the chances of a more accurate visual interpretation of the details of the target of interest.
Contrast of a target is a critical variable directly related to ease of visibility. Contrast corresponds to the ability to discriminate a dark visual image from a lighter visual image within a total visual surround. In general terms, contrast is the relationship between the lighting intensity of two adjacent areas. A dark target, approaching black (having no reflected light) is most easily seen next to a white (reflecting all light) background. Shades of gray that have similar light reflective intensities are most difficult to visually discriminate and separate because the contrast values are most similar. Shading differences, reflective light patterns and texture gradients are learned behaviors that improve a shooter’s ability to recognize contrast.
Colors of objects have a direct influence on visibility in daylight (photopic) conditions. In low light (scotopic) conditions, color has no influence on visibility of a target because rod cell physiology operates during scotopic conditions and rod cells do not have color discrimination ability. The colors white and yellow have the highest visibility potential, followed by orange, red, green and blue. Since white reflects all wavelengths of light visible to the human eye, white is highly visible during daylight conditions.
Another visual attribute related to color and contrast is brightness (luminance) of a target. When light falls upon a target, it is absorbed or reflected. The light reflected by a target is what the eye senses if the light is of sufficient intensity to stimulate the cones and rods. Materials that reflect or radiate the highest amount of light are most easily seen by the human visual system. Brightness is a shooter’s subjective appreciation of the intensity of light entering the eye. However, glare, an excessive amount of light that serves no purpose, can be counterproductive to ease of visibility.
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