The nervous system controls & coordinates our reactions to
thousands of stimuli each day. Some of
these reactions are reflexes, but many are voluntary
reactions, responses that are consciously initiated. Reaction
time is the time interval from the instant of stimulation to the instant of
a voluntary response. All responses
result from the formation of impulses by stimulation & the transmission of
these impulses along neurons to effectors that bring about the response.
In reflexes, impulses flow over predetermined
"automated" neural pathways involving very few neurons, & they do
not require processing by the cerebral cortex.
In contrast, voluntary reactions involve a greater number of neurons
& synapses, & require processing of impulses by the cerebral
cortex. Therefore, reflexes have much
shorter response time than voluntary reactions.
The reaction time for a voluntary response is the sum of the times
required for:
- a receptor to form impulses in a response to a stimulus
- transmission of impulses to an integration center of the
cerebral cortex
- processing the impulses in the integration center
- transmission of impulses to effectors
- response by effectors
Do you think people differ in their reaction times to the same
stimulus? In this experiment, you will
test the null hypothesis that there is no difference in the reaction times of
different persons in responding to the same stimulus with the same
predetermined response.
MEASURING REACTION TIMES
You will measure reaction time using a ruler (there are special
rulers - called reaction time rulers- for this purpose, but they are
unavailable to us)
1. The subject sits on a
chair with the experimenter standing facing the subject.
2. The experimenter holds
the top of the ruler between thumb and forefinger at about eye level or higher
(of experimenter) - we may need to make adjustments to this depending on size
of rulers.
3. The subject places the
thumb and forefinger of dominant hand about an inch apart and on each side of
the bottom of the ruler. The subject's
attention is focused on the ruler at thumb level.
4. When the subject
indicates s/he is ready, the experimenter, within 10sec, releases the
ruler. The subject, seeing the falling
ruler, catches it between the thumb and forefinger as quickly as possible.
5. The reaction time is
recorded- as closely as possible - use increments on ruler. (i.e. if drop and
catches on 6 first time and on 4 second time - then has been quicker)
6. The test is repeated 5
times and the reaction is averaged. If
any reaction is grossly different, discard it and repeat the test to obtain 5
results that are fairly consistent.
RESULTS
- record the 5 results
- calculate your average reaction distance
- Do you think practice and learning will decrease your reaction
distance? Repeat the reaction - test 20
times without recording the reaction distance. Then repeat the test 5 times and
record your reaction distances.
- calculate your average reaction after practicing the test 20
times.
SKIN
SENSATIONS
WORKING
WITH A PARTNER, PERFORM THE FOLLOWING EXPERIMENTS AND ANSWER THE ASSOCIATED
QUESTIONS.
1. TWO - POINT DISCRIMINATION TEST
- THE DISTRIBUTION OF TACTILE (TOUCH) RECEPTORS VARIES OVER DIFFERENT AREAS OF THE
BODY. WITH 2 CLEAN TOOTHPICK POINTS,
TOUCH THE SKIN ON THE FOLLOWING SUGGESTED AREAS OF THE BODY. START WITH THE POINTS VERY CLOSE TOGETHER
AND INCREASE THE DISTANCE BETWEEN THE POINTS UNTIL THE PERSON IS ABLE TO
DISCERN TWO DISTINCT POINTS. BE SURE TO
LIFT THE POINTS OFF THE SKIN WHEN INCREASING THE DISTANCE BETWEEN POINTS. RECORD THIS DISTANCE IN MILLIMETERS FOR EACH
OF THE AREAS TESTED.
CHEEK______________ BACK OF NECK
________________ LOWER LEG
____________
PALM OF HAND ____________ BACK OF HAND _______________ BACK
______________
WHAT CAN YOU CONCLUDE FROM THE ABOVE DATA?
2. ADAPTATION OF TOUCH RECEPTORS
- NOTE THE TIME ON A WATCH WITH A SECOND HAND, AND
PLACE A COIN, SUCH AS A PENNY OR A DIME, UPON THE SKIN OF THE INSIDE OF THE
FOREARM. HOW LONG DOES THE SENSATION
LAST?
- THIS DISAPPEARANCE OF SENSATION IS DUE TO THE
FACT THAT THE RECEPTORS ‘ADAPT’ TO THE PARTICULAR STIMULUS AND THEREFORE,
INITIATE NO MORE NERVE IMPULSES UNTIL A CHANGE TAKES PLACE IN THE
STIMULUS. REPEAT THE EXPERIMENT ON A
NEW SPOT ON THE SKIN, BUT AFTER THE SENSATION DISAPPEARS, ADD TWO MORE COINS OF
THE SAME DENOMINATION ON TOP OF THE COIN, DID THE SENSATION RETURN?
HOW LONG DID THE SENSATION LAST WHEN 3 COINS WERE
USED?