ESTIMATION OF RESPONSE TIMES USING A THREE FUNCTION WEIBULL DISTRIBUTION Part 2 #0024

(1) Professor Emeritus, Dept. of Mechanical Engineering Southern Methodist University, Dallas TX 75240

(2) Assistant Professor, Dept. of Counseling and Educational Psychology, University of Nevada, Reno, NV, 89557

This can be defined as the instinctive reaction to a sudden or unexpected stimulus. Individual responses to the same unexpected stimulus can be very different. These responses can be both muscle movement and cognitive or emotional. Some people freeze, others move in unexpected directions. Others become angry or defensive, or can become too focused, all of which increase their total reaction time.

Reaction times tend to slow with aging, and males tend to have faster reaction times than females at all ages. (Clemson U, 2001) This contrasts with the earlier findings of Keele, (1986)

The effect of cellular telephone use on reaction time was reported in an experimental study published on the internet. (http://ojas,ucok.edu/01/papers/crabree01.html,2006). Eighty teenagers and 80 adults were divided into control and experimental groups. A simple reaction time test was developed requiring a foot reaction timer measuring the response to a light stimulus. The experimental group was engaged in conversation on a cell phone during the tests. As would be expected, the reaction time of the non-cell phone users was shorter than the cell phone user group. Teenagers had better reaction times than adults under both conversation and non-conversation conditions. This supported the results of the earlier Clemson study.(Clemson 2001)

The response time situation in driving is one of a single stimulus with multiple responses. The use of cell phones while driving provides several different distractions. Dialing and looking away from the road at the phone are primarily visual and mechanical distractions. The distraction that results from the telephone conversation is largely cognitive and is influenced by the nature of the conversation and the attention taken away from the primary task of driving. Accident report data indicates that drivers using cell phones tend to swerve out of the lane or hit something in front of them rather than step on the brakes. (Spencer, 2000) Many municipalities have passes ordnances prohibiting use of a cell phone while driving unless the unit is hands free. While this may reduce accidents due to visual and mechanical distraction, it would not necessarily reduce accidents due to cognitive distractions.

A study reported on the internet (http;//www.sizes.com/people/ reaction_time.html, 2006) discusses reaction time experiments conduced on men and women ages 20-60. The data is not verified, nor is the experimental validity presented. However, the raw data is presented in Table I below.

COMPARISON OF SIMPLE REACTION TIMES FOR MALE AND FEMALES AS A FUNCTION OF AGE

	FEMALES		MALES
Age (years)	visual	aural	Visual	Aural
20	320	310	240	230
30	260	200	220	190
40	340	300	260	240
50	360	300	270	250
60	440	420	380	370

The tests were simple reaction time experiments conducted in the laboratory. The visual stimulus was a light and the aural stimulus was a buzzer. No information is given as to what was the required response. The information has no author, and cannot be verified.

The data indicates that males have a faster reaction time than females at all ages. It further indicates that both male and females react quicker to an aural (sound) stimulus than to a visual stimulus. This conclusion has been verified by other research. One interesting conclusion is that reaction times are at a minimum for 30 year olds males and females. The text continues that responding with the feet takes about 20% longer than responding with the hands.

Aging does not seem to change the speed of nerve signal transmission. “As we age we see little change in the speed of these impulses. The greatest delays are in the processing of information that is necessary to formulate the messages that tell the muscles what to do.” Dr. L. Z. Stern, M.D. director of the Muscular Dystrophy Association’s Mucio F. Delgado Clinic for Neuromuscular Disorders at the University of Arizona Health Science Center in Tucson, quoted in MotherNature.com (2006)

The gradual increases in reaction time observed are not attributed to physical changes due to aging. The increase is suggested to be due to additional information and experience in memory. This increases the time required to make responses requiring choice or complex cognitive reactions. It is suggested that as we age we lose brain cells that help process newer information. (Mother Nature, 2006)

The increases in reaction time associated with aging of healthy adults are related to increases in the time for cognitive actions. The use of video and computer games has been shown to increase mental and motor skills. “They are often used to help rehab patients develop speed, and even pilot these days practice on video simulators before the climb in the cockpit.” (Dr. Ralph Tarter, Ph.D. professor of psychiatry and neurology at the University of Pittsburgh School of Medicine, quoted in Mother Nature 2006)

Reaction time studies by Deary and Der, (2005) builds upon earlier studies that indicate people with lower IQs tend to die at younger ages than those with higher IQs. The authors believed that a more fundamental measure of mental processing of information might be a better indicator of age at death. They studied 412 males and 486 females in west Scotland aged 54 to 58 over a period of 14 years.

The subjects were given an IQ test and a simple reaction time test that measured time to press a button after seeing a number on a screen.

Their research showed that those with higher IQ sores lived longer, consistent with earlier studies. The study showed that faster reaction times was an even better predictor of long life that IQ scores. The data could indicate that slower reaction times reflect degeneration of physical and mental health resulting in earlier mortality. However, another study on the reaction time and IQs of 11-year-old subjects was also found to predict life span length as well.

Alcohol and drugs increase reaction time. Drugs that can cause drowsiness or decreased vision increase reaction times. Alcohol or medications that affect the central nervous system increase reaction time, primarily cognitive time.

Smoking tobacco can increase reaction time in a number of ways. Smoking reduces the amount of oxygen available to the muscles and brain, thus increasing cognitive time and possible muscle movement times.

Fankhauser (2004) lists some of the stages associated with the response time associated with a visual stimuli. The stages include:

The total length of time for these steps is measured by a simple reaction time experiment using visual stimulus and hand movement associated with dropping a ruler. The total response time is given by

As an example, if the distance of the drop was 18 cm. The calculation would be as follows

This is the time it takes for the nerve impulse to travel from the brain to the motor muscles once the decision has been made within the brain to move the major muscles as part of the response. Nerve signals travel about 30,000 cm/sec. This implies that muscle movement response for the leg and foot would be slightly longer than the movement of the arms and hand. This implication has been verified by studies that show simple reaction times for the foot were 20% longer than hand responses. http://ojas,ucok.edu/01/ papers/crabree01.html,2006). The dynamic time is the time it takes the muscles to move as part of the response. This is difficult to measure. Some studies indicate that response times are the shortest if the only muscle response required is moving the eyes, i.e. focusing on a new region. Standing up form a sitting position would require a longer response time than eye movement, 1.6 seconds compared to .5 seconds. The cognitive processing time would be the total reaction time minimum the nerve time minus the dynamic time.

Motor movements in response time studies are usually a purposeful movement and are initiated by a person in response to a stimulus and to achieve a goal. The concept of purposeful movement is related to motor skills. Skill in a motor response is the ability to use the correct muscle movement with the appropriate amount of force to obtain the desired result with proper sequencing and appropriate timing. (Jensen, Schultz and Bangerter, 1983)

An engineer looking for design data regarding operator reaction time would initially look in a design manual such as Morgan, C.T., et al (1963 and other editions) Human Factors Engineering Guide to Equipment Design or other Human factors Handbooks. The Air Force and military Human Factors handbooks are often cited. The engineer is faced with a large array of conflicting information on reaction time ranging from 0.1 seconds for simple responses to response times over 6 seconds for complex responses. There are individual studies on reaction times from a large variety of simple laboratory experiments. Design data is rare and often conflicting. The application of the handbook data to the specific design problem of the engineer is often vague and misleading. It is recognized that the complex reaction times more closely resemble real-world situations. The designer is concerned with the magnitude of complex reaction time and the range of total response times that might be expected in a particular design situation. Certain real-world situations such as driving, highway design and cockpit simulations have been extensively studies. However equipment design, movement requirements, and operating system response time considerations are difficult to quantify. Because this type of information is often lacking, most engineers are willing to accept the single value of 1.5 seconds as an average indicative of reaction time.

Reaction time may be an inherent ability; however response time to particular stimuli can be reduced by training. Athletes can reduce their reaction time by proper coaching and understanding of clues and anticipation of the opponent’s behavior. Practice sessions work on set movements and game situations to improve reaction times.

Coaches can train athletes to anticipate possible movements of their opponent that can be used to reduce the time to respond to a given stimulus. Knowledge of possible moves e.g. a tennis player who anticipates the type of return shot of the opponent. This allows the player to move into position to return the ball earlier and more time to play the shot when the ball does arrive. In a similar manner baseball players study the movements of opposing pitchers to detect relevant clues that indicate possible pitches.

Reduction in reaction times can improve player response in sudden movement sports such as football. One offence objective is for the ball movement and offensive line to move more rapidly than the defensive line. The offense has a shorter response time to the verbal and movement clues because of anticipation and knowledge. This permits the offense to be in motion after the snap and slightly ahead of the defense. The defense tries to anticipate the ball snap, and if the players respond too early they incur a penalty. Football rules do not allow certain movements of the offensive line because they provide false start clues to which the opposing players respond.

Modern law enforcement training also discusses and trains officers to reduce reaction time to potential threats. Training in response to stimulus and perception of threat and subsequent muscle movement reaction time can have a major impact on the behavior of the officer in critical situations. This type of training can provide the officer with the ability to make rapid correct tactical decisions in potentially violent situations.

The use of simulators for pilots and other military equipment is used for training and to reduce reaction time to combat situations and emergencies. In early aircraft simulators the concept was to provide pre-flight training to free the aircraft cockpit for flying hours. As simulators improved, they permitted instructor pilots to introduce computer/mechanical malfunctions into the flight profile to train the pilot to react quickly and correctly to in-flight emergencies. This helps build a memory log of responses to complex stimuli that reduce multiple choice reaction times. Modern flight simulators have been used in aircraft accident reconstruction to determine if the pilot responded correctly in time to the known mechanical emergency.

Human factors engineering design of products often requires the proper response at the proper time by the responsible authority. The human factors designer can shorten the user’s response time by matching the needed response to the proper function of the equipment. The handles in an aircraft for throttles, flaps and landing gear are located in a central console. To minimize response time and to minimize mistakes caused by moving the wrong levers, these handles have different shapes. This allows the pilot to determine the proper control by feel rather than looking at the handles. It has been suggested that the catastrophic failures that occurred in Chernobyl and Three Mile Island Power plants were due in part to the complexity of the control system and visual complexity of the instrumentation. When the initial problems arose, there was a loud warning, and the operators were confused as to which of the hundreds of valves was a fault. (Saunders 1998) Because the response time was so long, what should have been a minor incident rapidly became catastrophic. A similar catastrophic incident occurred in India where a Chemical plant exhaust spilled toxic fumes over a local city.

A recent article in the New York Times (2006) summarized a study authored by Beverly A. Shipley of the University of Edinburgh and published in Psychosomatic Medicine. In the article the researchers said they found a strong link between slower reaction times and a higher mortality rate in a given period. Earlier studies had presented similar conclusions. The reported study looked at 7000 people over 19 years and found that poor reaction times seemed to increase mortality rates even among younger subjects. Experts had previously considered poor reaction rates test scores and mortality as a reflection of the deterioration of the aging body. But that would not explain the higher mortality rates for younger people. The researchers wrote, “Perhaps reaction time is picking up some aspects in the brains of even initially healthy individuals that may be associated with survival.”

Rapid response time was a definite survival trait in primitive and prehistoric societies. The recognition of danger and a rapid response time initiates reflexive increased heart rates and massive blood shifts to major muscles in preparation for immediate flight. Modern humans instinctively respond to similar stimuli and experience panic attacks or anxiety that mimics the reflexive behavior flight response. Laboratory measurements using a simple response time experiment is measuring the response to stimuli and cognition and muscle movement time.

Lord and Fitzpatrick (2001) compared elderly subjects with a history of falls to elderly non-fallers subjects of similar ages ranging from 62 to 95 years old. The authors developed a choice response time test which measured the time required by the subjects to step onto one of four panels that were illuminated in random order. The test was called Choice Stepping Reaction Time (CSRP). Impaired CSRP was a significant independent predictor of falls along with complimentary perception of visual and kinetic reaction time stimulus (reduced visual contrast sensitivity and lower limb proprioception.) Subjects with increased reaction time 1322+- 331 milliseconds had a history of falls compared to subjects with more rapid reaction times of 1168+-203 milliseconds.

Elderly individuals who are prone to falls appear to have increased reaction time. These increased CSRP reaction times are associated with other factors (decreased contrast sensitivity and lower limb kinetics) that appear to prevent the occurrences of falls in subjects with shorter reaction times.

1. The the instinctive reaction to a sudden or unexpected stimulus is called the ____.

3. Reaction times tend to ____ with aging, and males tend to have ____ reaction times than females at all ages.

4. Cell phone use while driving provides which of the following types of distractions.

5. ______ is the time it takes for the nerve impulse to travel from the brain to the motor muscles once the decision has been made within the brain to move the major muscles as part of the response.

8. An article in Psychosomatic Medicine indicated a strong link between ____ reaction times and a ____ mortality rate in a given period.

9. Accident report data indicates that drivers using cell phones tend to ____ or hit something in front of them rather than step on the brakes.

10. Elderly individuals who are prone to falls appear to have ___ reaction time.