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Visual perception in low-light levels.



Implications for Shooting Incidents

While on evening patrol, officers discovered two men lurking See lurk.

(messaging, jargon) lurking - The activity of one of the "silent majority" in a electronic forum such as Usenet; posting occasionally or not at all but reading the group's postings regularly.
 near a closed gas station in a high-crime area. In the confrontation that followed, the officers fired on the suspects, one of whom appeared to be holding a shotgun. The officers believed that the other man had pulled a chrome-plated handgun from his waistband. Later investigation revealed that the man was, in fact, holding a beer can. He sued the officer who shot him.

During the trial, expert testimony Testimony about a scientific, technical, or professional issue given by a person qualified to testify because of familiarity with the subject or special training in the field.  centered on the nature of human vision, the low level of light at the time of the incident, and the results of a research study that demonstrated the ability of healthy subjects to identify lethal versus nonlethal items under a range of low levels of light, the type of conditions officers often face when working at night.(1) The results of this study can assist investigators when determining what an officer can identify under certain environmental circumstances.

Procedure

This experiment used 12 police cadets as subjects. Prior to admission to the academy, a general physician had prescreened the cadets for corrected 20/20 distance visual acuity visual acuity
n.
Sharpness of vision, especially as tested with a Snellen chart. Normal visual acuity based on the Snellen chart is 20/20.


Visual acuity
The ability to distinguish details and shapes of objects.
. Each cadet was reexamined individually for corrected 20/20 vision and measured for hidden refractive error refractive error Ametropia, myopic shift Ophthalmology The inability of images to focus properly on the retina, often corrected by glasses contact lenses, or refractive surgery. See Astigmatism, Farsightedness, Myopia, Presbyopia.  - the cause of nearsightedness nearsightedness or myopia, defect of vision in which far objects appear blurred but near objects are seen clearly. Because the eyeball is too long or the refractive power of the eye's lens is too strong, the image is focused in front of the , farsightedness farsightedness or hyperopia, condition in which far objects can be seen easily but there is difficulty in near vision. It is caused by a defect of refraction in which the image is focused behind the retina of the eye rather than upon it, either . and astigmatism astigmatism (əstĭg`mətĭz'əm), type of faulty vision caused by a nonuniform curvature in the refractive surfaces—usually the cornea, less frequently the lens—of the eye.  - by observing how parallel beams of light reflect off the retina of the eye. The examination detected no eye disease among the cadets.

The cadets were taken from their classroom. which was at a standard office lighting level, and brought to the research room. A research assistant wore a black jacket, consistent with clothing often worn by crime suspects, and showed each cadet three nonlethal objects and a large-frame handgun under each of four incrementally increasing levels of low light. The black jacket served as a background for the object, and the assistant stood behind an opaque partition that was quickly shifted down for 1 second. The assistant did not point the object in the direction of the cadet but held each object in a clenched clench  
tr.v. clenched, clench·ing, clench·es
1. To close tightly: clench one's teeth; clenched my fists in anger.

2.
 fist close to his body, similar to the physical circumstance of many shooting incidents.

Specifically, the nonlethal objects consisted of a 6-inch piece of green garden hose, an 8-inch piece of black pipe, and a 6-inch chrome-plated screw driver, According to according to
prep.
1. As stated or indicated by; on the authority of: according to historians.

2. In keeping with: according to instructions.

3.
 police documents, officers had misidentified similar objects as lethal during the past 10 years. Academy regulations prescribed only the use of academy-deactivated firearms This is an extensive list of small arms — pistol, machine gun, grenade launcher, anti-tank rifle — that includes variants.

: Top - 0–9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A
  • A-91 (Russia - Compact Assault Rifle - 5.
 in this study; therefore, a blue steel model 59 Smith & Wesson Smith & Wesson

U.S. gun manufacturer. The company has its roots in an 1852 partnership between Horace Smith (1808–93) and Daniel B. Wesson (1825–1906), who designed and marketed a lever-action, repeating magazine handgun that held a self-contained cartridge.
 handgun was chosen as the lethal object because it has a large and distinctive shape.

The experiment used several lighting levels. These levels ranged from .04 foot-candles to .45 foot-candles. For comparison, a bright, full moon on a clear night exhibits illumination comparable to a .01 foot-candle lighting level. A person standing 30 to 40 feet from the direct beam of a vehicle's headlights at night compares to a .45 foot-candle lighting level.

Each cadet viewed each object individually for 1 second. After the presentation of the object, the cadet's attempt to identify the object was recorded.

Results

Each cadet viewed one lethal and three nonlethal objects at each lighting level. Therefore, 48 responses were recorded at each level.

At .04 foot-candles, cadets correctly identified an object only 4 times; they misidentified or said they could not identify an object 44 times. This represented a 9 percent rate of correct identification. At .10 foot-candles, cadets correctly identified an object only 8 times; they misidentified or said they could not identify an object 40 times. This represented an 18 percent rate of correct identification. At .25 foot-candles, cadets correctly identified an object only 15 times; they misidentified or said they could not identify an object 33 times. This represented a 34 percent rate of correct identification. At .45 foot-candles, cadets correctly identified an object 37 times; they misidentified or said they could not identify an object 11 times. This represented an 84 percent rate of correct identification.

Cadets most frequently identified the handgun correctly. At .25 foot-candles, 10 of the 12 cadets identified the handgun correctly, but 2 cadets still incorrectly identified it or stated they could not identify the object. The gun used in the experiment is one of the largest handguns usually encountered on the street. Had a smaller pocket handgun been used, a higher rate of incorrect identification might have occurred in the low-lighting levels due to the smaller size. Cadets most frequently misidentified the 6-inch piece of green garden hose. Even at the .45-foot-candle level, cadets most frequently identified the hose as a gun. Only one cadet identified the hose as a pipe or cylindrical object.

Findings

This study demonstrated the difficulty officers have distinguishing between lethal and nonlethal objects under low-lighting levels. Most of the cadets voiced uncertainty about their responses, even when they were correct. When asked to make a determination of the object in less than .25 foot-candles of light, cadets most frequently responded "I cannot tell." During an exit interview, 80 percent stated they relied upon the positioning of the assistant's hands to help make their determination of the objects. Yet, the assistant purposely had held the object in a neutral manner.

Practical Applications

Officer-involved shootings rarely occur exactly as constructed in this experiment. The time frame involved from when an officer perceives danger to the time deadly force An amount of force that is likely to cause either serious bodily injury or death to another person.

Police officers may use deadly force in specific circumstances when they are trying to enforce the law.
 is considered necessary is more realistically only a fraction of a second and not the full second allotted al·lot  
tr.v. al·lot·ted, al·lot·ting, al·lots
1. To parcel out; distribute or apportion: allotting land to homesteaders; allot blame.

2.
 in this experiment. Additionally, the suspect or the officer is frequently in motion before and during the shooting. This movement decreases visual ability.
Lethal/Nonlethal Lighting Test

Light Levels            Number of           Number of Objects
(Foot-candles)      Objects Identified        Misidentified

.04                         4                      44
.10                         8                      40
.25                        15                      33
.45                        37                      11


The psychological and physiological effects of fear also decrease the level of visual functioning. The human body instantly undergoes profound physiological changes in response to perceived threatening circumstances. Visual functioning dramatically decreases in response to hormones secreted during acute fear.

Without sufficient lighting, the retina of the eye cannot form an accurate image of the external environment. An ambiguous image Ambiguous images are an optical illusion images which are crafted to exploit graphical similarities and other properties of visual system interpretation between two or more distinct image forms. These are famous for inducing the phenomenon of multistable perception.  is created at the retina and transmitted to the brain. The brain then integrates this ambiguity with cognitive, memory, and emotional elements to form a perception. The officer uses this perception to evaluate the suspect's actions and to react. based on the factors that affect officers' visual perceptions during confrontations in low-light levels, officers need at least 2.5 to 3 foot-candles of light to accurately identify an object. Shining a halogen halogen (hăl`əjĕn) [Gr.,=salt-bearing], any of the chemically active elements found in Group 17 of the periodic table; the name applies especially to fluorine (symbol F), chlorine (Cl), bromine (Br), and iodine (I).  flashlight on an object from a distance of 20 feet would create the level necessary for proper visual functioning.

Furthermore, lighting conditions that officers face prior to an incident may significantly affect their ability to discern shapes and details in a darker environment. During the 20 minutes prior to the incident, if an officer is exposed to lighting higher than when the incident occurs, a transient disability affects the officer's vision. The retina experiences chemical and neurological neurological, neurologic

pertaining to or emanating from the nervous system or from neurology.


neurological assessment
evaluation of the health status of a patient with a nervous system disorder or dysfunction.
 changes as lighting levels change. After 40 minutes, a person's eyes adapt to low-level lighting conditions. If that lighting condition changes to a higher level of light for even a fraction of a second, the dark adaptation dark adaptation
n.
The adjustment of the eye under reduced illumination, in which sensitivity to light is greatly increased. Also called scotopic adaptation.
 is lost. For example, if an officer seated in a darkened dark·en  
v. dark·ened, dark·en·ing, dark·ens

v.tr.
1.
a. To make dark or darker.

b. To give a darker hue to.

2. To fill with sadness; make gloomy.

3.
 patrol car uses the car's interior light to check an address, the lighting level immediately changes and the officer loses the dark adaptation. An overwhelming majority of officer-involved shooting incidents have demonstrated this often-overlooked disability. A thorough history of the officer's activities prior to the incident will aid a complete understanding of the visual environment under which the incident occurred.

Recommendations

This research study demonstrates that police officers have difficulty differentiating between lethal and nonlethal objects illuminated by less than .50 foot-candles of light, the level frequently encountered during routine police working conditions at night. Officers should recognize this disadvantage and adapt their procedures accordingly, by increasing lighting levels using their car's headlights and flashlights
This article is about the rock album. For the light device, see Flashlight.


Flashlights is the third record by the Atlanta-based independent rock band Y-O-U.
 with halogen bulbs. A weapon-mounted lighting device, attached to the muzzle muzzle

1. the part of the face supported by the maxillae and nasal bones; the part of a dog's head anterior to the stop and cheeks, containing the nasal passages and bearing the nosepad. Longer in dolichocephalics and practically nonexistent in brachycephalics.
 of an officer's weapon, can increase visual ability in low-level lighting conditions. This device is designed for short-barrel defensive shotguns, uses a small halogen bulb, and has an on/off switch. In addition, officers should train in low-level lighting conditions. Finally, during the investigation of an officer-involved shooting, police administrators should document the lighting level at the time of the incident with an illuminometer and consult a vision expert with experience in this area.

Conclusion

The investigation of an officer-involved shooting is never an easy undertaking. A number of variables complicate the process, including the officer's visual perceptions prior to and during the incident. Prior shooting incidents and this research study indicate that officers have difficulty differentiating between lethal and nonlethal objects in low levels of light. By understanding the nature of human vision and the implications of this research, administrators and officers alike can prepare for the inevitable encounter with the suspect in the dark alley. Perhaps more important, by properly documenting shooting incidents, conducting thorough investigations, and preparing expert testimony on the nature of these encounters, law enforcement agencies A law enforcement agency (LEA) is a term used to describe any agency which enforces the law. This may be a local or state police, federal agencies such as the Federal Bureau of Investigation (FBI) or the Drug Enforcement Administration (DEA).  can avoid legal liability while reminding the public of the dangers associated with protecting the community.

Endnote See footnote.

The author of this article conducted the study and testified in court.

Dr. Michel, a board-certified therapeutic optometrist optometrist /op·tom·e·trist/ (op-tom´e-trist) a specialist in optometry.
Optometrist
A medical professional who examines and tests the eyes for disease and treats visual disorders by prescribing corrective
, serves as a specialist reserve police officer for the Los Angeles Los Angeles (lôs ăn`jələs, lŏs, ăn`jəlēz'), city (1990 pop. 3,485,398), seat of Los Angeles co., S Calif.; inc. 1850. , California, Police Department's officer-involved shooting investigations unit.
COPYRIGHT 1998 Federal Bureau of Investigation
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1998, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Article Details
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Author:Michel, Paul
Publication:The FBI Law Enforcement Bulletin
Date:May 1, 1998
Words:1573
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