A Statistical Analysis of Reaction time and its Correlation with Dominant & Non-Dominant Hands
This experiment seeks to determine reaction times in two groups of matched subjects; dominant and non-dominant hands, using the ruler drop test.
Reaction time experiments are performed to measure the alertness of the mind and will give an indication of the speed of the reflexes that different groups of varied individuals have. The experiment tests how long it takes the brain to translate visual information into the voluntary motor commands, actions which lead to a ruler being grabbed. The shorter the length at which the ruler is grabbed, the shorter time and therefore the faster the person’s reaction. The controls of these processes within the human body are the responsibility of the nervous system which is the seat of voluntary and involuntary movements along with language, emotion and memory. (1)
The experiment begins with an environmental stimulus via light reflected from a moving ruler being dropped from a height above the subject’s hand. (1) This transmits into a sensory nervous impulse within the optic nerve. Beginning in the retina of the eye, information is detected by photoreceptors (rods and cones) they relay the visual signals on to bipolar cells which transmit on to ganglion cells. (2) The axons of all ganglion cells in the retina of each eye join to form the optic nerve. The information (an electrical transmission) is then passed through to the mid brain and the thalamus. (1) The information going to the midbrain does not reach conscious levels but rather produces pupillary reflexes (which are controlled by the autonomic nervous system) and eye movements. (1) In the thalamus, ganglion cell axons transmit signals to the primary visual cortex in the occipital lobe of the cerebrum, this visual association region recognizes the meaning of the visual impulses and the cortical cells then send messages to other "higher" cortical areas, associative centres of the brain, where the information is questioned and transformed into a response. (2) The transmission is then sent to the precentral gyrus, the primary motor complex and a transmission of a motor impulse is carried down to the spinal cord to motor neurons and finally to the muscles of the hand effecting the movement through the contraction of muscles. (2)
This journey of information from receptor to effector in the human body is very complex due to the various neurons and synapses involved. Due to this complexity the human brain and nervous systems ability to process information and relay a response may be hindered or facilitated by many different internal or external factors.
Fatigue influences human performance and affects individuals to varying degrees, ranging from slight to catastrophic. (3) Increasingly, fatigue has been claimed as the primary cause of many major accidents, for example, the incidents of Exxon Valdez oil spill (7) (1989) list fatigue as a root cause, along with many vehicle and work place accidents worldwide. (4) Studies have shown that fatigue causes the reverse of the learning process; moving the decision making from skill based cognition to knowledge based causing people to rely more on their working memory rather than on their long term memory for task completion, and in turn people work harder with lower performance. (5) (6) In extreme cases fatigue may cause a person to disengage briefly in a so-called 'micro-sleep', if this happens at a critical time, accidents may result. (4) A similar factor to fatigue is alcohol, a substance which society believes to be the biggest factor influencing accidents. A recent reaction time study in Stanford University (8) has shown that subjects deprived of sleep had longer average reaction times than that of the intoxicated subjects, this research sheds worrying light upon many occupations in society today that allow employees to work between 12 hours to 24 hours a day, for example, doctors or pilots. Increasing the quantity of alcohol consumed causes the reaction time to become highly impaired (9) (varies between individuals), this is due to the sedative and hypnotic effects as it depresses the central nervous system. (10) It directly interferes with the binding of certain neurotransmitters, especially acetylcholine. (11) However, it is most likely acetaldehyde/ethanal (a primary metabolite of ethanol) which causes differences in brain function. (10) Acetaldehyde is known to react with dopamine (yielding salsolinol) and also to react with tryptamine (producing tetrahydroharman), both by-products have psychotropic activity. (12)
Disability or illnesses, such as schizophrenia have shown to affect performance due to the cognitive defects in the brain caused by a dysfunction of the dopamine system. Studies show that patients with persistent illness perform poorly when given a reaction time task. (13) Lesser illnesses such as the influenza may also cause poor performance; this is due to the intense feeling of fatigue and nausea inflected upon the sufferer. (14) Distractions or lack of concentration and old age are other major factors involved in slowing the reaction time of subjects.
The most widely used psycho-stimulant substance in the world is caffeine which can be used to promote the nervous system and its responses. It works via modulating neurotransmission in the nerve cells by attaching to adenosine receptors, adenosine in the brain binds to receptors which causes drowsiness and eventually sleep by slowing down nerve cell activity. (15) The false attachment of caffeine prevents adenosine from binding and doing its job thus increasing nerve activity and promoting the neurons firing in the brain. (18) The pituitary gland notices this activity and reacts by releasing hormones that tell the adrenal glands to produce adrenaline (epinephrine). The adrenaline then gives the body a boost by activating the sympathetic division of the autonomic nervous system. (15) Further research into the effects of caffeine shows its levels of addiction and impacts, as caffeine works similarly to drugs like cocaine (though on a much smaller level) it blocks adenosine reception so making a person feel alert, (15) injects adrenaline into the system and gives a person a boost while manipulating dopamine production to make a person feel good. Long term this can mean many things to a person’s brain and their reaction time. For instance, a cup of coffee can take between 3 to 12 hours for the body to eliminate one half of a caffeine dose; this is called the half-life of caffeine. Drinking caffeine in the morning and again in the evening will lead to it staying in the blood every hour of the day. The effect of caffeine in the body will be active 24/7. Several factors can shorten or lengthen the half life of caffeine, such as smoking, medications and diseases. (15) People addicted may drink ten or more caffeinated beverages a day, especially if under stress or work early/long hours. A study (16) on the effects of caffeine withdrawal on reaction time and its impact on general well being proved to affect alertness, hand steadiness and reaction time, particularly plummeting on day two of the study and slowly restoring itself by days six and seven. The subject’s performance at the end of the trial, after a full withdrawal, was as good as it was before which shows the caffeine only had an effect insomuch as the subject’s body was craving it. (16)