CAMOSUN COLLEGE BIOLOGY 144 (2010) LABS
LAB 6: SENSORY PERCEPTION
PRELAB:
1. Read the section on near point determination (p 7). Before coming to class, measure the
near point determination of 4 individuals over the age of 40. Bring these values to class!
2. Read the following journal article. which can be accessed in the course schedule at
http://hunterp.disted.camosun.bc.ca
Peng J-H, Z-Z Toa, Z-W Huang Risk of damage to hearing from personal listening devices in
young adults Journal of Otolaryngology (2007) Vol 36 (3):181-185
3. Answer the questions regarding this journal article at the end of the lab
4. Obtain a “near point of focus” value (in cm) for several individuals over the age of 30 (see p 8
for the procedure). Bring these values to class!
INTRODUCTION
Our perceptions of the environment are based on the reception of external stimuli through various
sensory structures. In this series of exercises, we will explore normal and abnormal sensations
that are determined by sight, hearing, taste and touch. Each test will be introduced separately.
Sensory receptors act as transducers, changing one form of energy (eg. light, vibration) into
another (eg. electrical energy in form of action potentials). Each receptor is sensitive to one form
of energy, though it may respond to another if the stimulus is very strong (eg. photoreceptors
respond to light but you may ‘see stars’ if you are hit on the head).
receptor
detect
sense organ / location
thermoreceptors
baroreceptors
nociceptor
lamellated (Pacinian) corpuscles
hair cells
photoreceptors
proprioceptors
tactile (Meissner’s) corpuscles
chemoreceptors
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CAMOSUN COLLEGE BIOLOGY 144 (2010) LABS
PART I: GENERAL SENSES
Receptor Density
The skin has a variety of sensory receptors that respond to different types of stimuli. Some areas
of the body have relatively few sensory receptors and are quite insensitive. Others have large
numbers of cutaneous receptors and are quite sensitive. This difference can be demonstrated
by the two point discrimination test for touch.
Purpose:
To determine receptor density on the body surface.
Procedure:
•
Ask your subject to close their eyes
•
Using a two-point compass, separate the points by 4 cm
•
Beginning with the palm of your subject, touch the two points simultaneously to the skin.
Record whether the subject feels one point or two points.
•
Decrease the distance between the points by 5 mm and repeat the process
•
Continue decreasing the distance between the points until the subject cannot distinguish
the 2 separate points. Try to determine within one mm what this distance is. This
distance approximates the distance between cutaneous touch receptors on that part of
the body
•
Repeat this procedure with the back of the hand, the back of the neck, the finger tip and
the side of the nose (with the latter 2 you may begin with the compass points at 2 cm
apart), recording the distances in the Table below.
Table 1. Results of the two-point discrimination test
body surface
Discrimination
distance (mm)
Subject 1
Subject 2
palm
back of hand
back of neck
fingertip
Side of nose
QUESTIONS:
1. Name the specific type of cutaneous receptor that detects touch: ___________________
2. Would this type of receptor be classified as an
exteroreceptor or interoreceptor? ___________________________________________
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3. Place the body regions tested in order from most sensitive to least sensitive:
_______________________________________________________________________
4. Does receptor density appear to be greater on the front of the body or the back of the
body? Explain.
_______________________________________________________________________
_______________________________________________________________________
5. Generally, the more sensory input there is from a specific region of the body, the more of
the cerebral cortex that is devoted to that area. Examine the sensory ‘homunculus’
below. The sensory homunculus is a distorted human figure drawn to reflect the relative
space our body parts occupy in the somatosensory cortex. Do your observations
regarding receptor density reflect the relative amount of cortical tissue (as shown in the
homunculus)? Explain
_______________________________________________________________________
_______________________________________________________________________
Figure 1. Sensory Homunculus
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Receptor Adaptation
Receptors respond to a stimulus by producing graded potentials; action potentials result when the
frequency or cumulative strength of these graded potentials is sufficiently high. However, with
continued stimulation receptors may cease to respond. This phenomenon is known as receptor
adaptation. Adaptation preserves the ability of a receptor to respond to a new stimulus.
Adaptation is a characteristic of phasic (‘fast adapting’) receptors which respond strongly at
first, but rapidly decline in activity with continued stimulation. Cutaneous receptors are typically
phasic. The pain receptors in the skin however, are tonic (’slow adapting’) receptors; they
continue to fire with stimulation. Adaptation also occurs in the CNS (central adaptation). For
example awareness of a new smell rapidly disappears with continued exposure.
Close your eyes and have your partner place a small object (e.g. cork) on the skin of the forearm.
Determine how long it takes for the initial sensation of pressure to give way to an indifferent
sensation (phasic receptor response). Repeat twice and then repeat on the back of your hand
and on your partner.
inside of forearm
subject #1
trial 1
subject #2
trial 2
trial 1
back of hand
trial 2
Is adaptation speed similar ? __________________________________________________
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CAMOSUN COLLEGE BIOLOGY 144 (2010) LABS
PART 2. TASTE SENSITIVITY
Taste or ‘gustatory’ receptors are a special type of chemoreceptor distributed over the surface
of the tongue and adjacent portions of the larynx and pharynx. The receptors reside in structures
called taste buds which are located in the epithelium along the sides of the papillae or bumps on
the tongue. Taste sensitivity differs significantly among individuals; individuals vary in the number
of taste receptors they have and in the sensitivity of these receptors to certain chemicals. Taste
sensitivity has a hereditary component.
Ability to taste PTC
You have been provided with several taste testing strips. These strips contain chemicals which
some people cannot taste. Test each strip separately, rinsing your mouth in between. Indicate
whether you and your partner can taste the test chemical in the table below. Record class results
on the board.
Chemical
Subject #1
Subject #2
Class results
# students
%
PTC
(phenylthiocarbamide)
potassium benzoate
In the general population approximately 70% can taste PTC.
Do class results reflect this? If not, why?
_____________________________________________________________________________
_____________________________________________________________________________
Tasting threshold
Receptors respond to a stimulus by producing graded potentials. Action potentials result from
adequate stimuli. Taste receptors vary in their sensitivity to chemicals. Low concentrations of
bitter or sour chemicals can be detected, but higher concentrations of sweet or salty chemicals
are required to exceed the taste threshold.
Purpose:
•
•
determine the threshold for taste by successively tasting sucrose solutions of increasing
concentration.
Learn how to prepare serial dilutions of a solution
You have been provided with a 1.0 M solution of sucrose in water and will prepare several
dilutions by pipetting into disposable paper cups.
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CAMOSUN COLLEGE BIOLOGY 144 (2010) LABS
Serial dilutions are a series of diluted solutions prepared by successively diluting a stock
solution. The stock solution you are using is a 1.0 M sucrose solution. A solution that is 1 part
sucrose solution and 9 parts water will have a sucrose concentration that is 1/10 of the original
solution = 0.1 M in concentration .
THINK! If you take 1 part of the 0.1 M solution and add 9
parts water, what will be the concentration of the new dilution? _______________________
You will prepare 10 mls of 5 different sucrose dilutions from the 1.0 M stock solution
Procedure:
•
Obtain 10 small paper cups, 50-100 ml water and 10 ml of the stock sucrose solution
•
Label 5 paper cups with the following:
0.001 M sucrose 0.005 M sucrose 0.01 M sucrose
0.05 M sucrose 0.1 M sucrose 0.5 M sucrose
•
Determine how you will prepare these dilutions and write this in column 2 in the table
below (the first 2 have been completed for you)
•
Prepare the dilutions in the appropriately labeled disposable cup
•
Beginning with the MOST DILUTE SUCROSE SOLUTION (0.001M), share half of this
solution with your lab partner by pouring approximately 5 ml into one of the empty paper
cups
•
Record whether or not you can taste the sugar; have a mouthful of water (swish it around
before swallowing) then taste the next more concentrated solution
•
Continue tasting progressively more concentrated solutions until you both detect the
sucrose
taste or not
sucrose conc.
contents
subject
#1
0.50 M
0.05 M
subject
#2
5.0 ml of 1.0 M sucrose
5.0 ml water
1.0 ml of 0.5 M sucrose
9.0 ml water
0.005 M
0.10 M
0.01 M
0.001 M
Is the concentration threshold for the sugar chemoreceptors the same for all class participants?
Explain:
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CAMOSUN COLLEGE BIOLOGY 144 (2010) LABS
PART 3: VISUAL TESTS
A. THE BLIND SPOT
Recall the structure of the retina and, in particular, the position of the fovea relative to the optic
disc. Review the functional relevance of these structures.
Purpose:
1. To determine the position of the optic disc.
2. To calculate the angle formed between the fovea, lens and the optic disk ie. the angle of
deviation.
3. To calculate using triangulation, the distance between the fovea and the optic disc.
Materials:
chalk, large protractors, meter stick, 4” x 6” cards
Procedure:
•
Draw a chalk line across the lab bench close to one end.
•
Have your partner take one of the cards on which is drawn a “+” at one end and a “0”
at the other and hold it vertically at right angles to the chalk line.
•
Your partner should position the card so that the “+” is on the line and the “0” is to
your left. (subject’s right)
•
Now the subject gets down on their knees so that they are looking down the line
toward the “+” with their right eye. Cover the left eye.
•
The partner moves the card slowly along the line toward the subject.
•
The subject should concentrate on the “+” with their right eye only; tell your partner
when the “0” disappears!
Questions:
1. Explain why the “O” disappears
_____________________________________________________________________________
_____________________________________________________________________________
2. Is this ‘blind spot’ on your retina medial or lateral to the fovea? Explain
_____________________________________________________________________________
_____________________________________________________________________________
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CAMOSUN COLLEGE BIOLOGY 144 (2010) LABS
B. NEAR POINT DETERMINATION
As one ages, the elasticity of the lens decreases as a result of protein denaturation in the lens.
This condition is called presbyopia. This is the reason why most people over the age of 45-50
require reading glasses. A measure of elasticity can be made by determining the closest
distance you can focus on a printed letter with each eye.
Purpose:
To determine your near point of focus and to determine the relation between near point and
age.
Materials:
meter stick, printed page (e.g., news print)
Procedure:
1.
Cover one eye.
2.
Have your partner hold up a sheet of newsprint about 1 meter from the other eye.
3.
Focus on one small letter (e.g, the letter “e”)
4.
Partner; move the paper toward the subject until he/she tells you the letter is going
out of focus. Measure the distance between the paper and your eye at this point.
B. Near Point Determination.
Your near point of focus is:
Right eye_________ Left Eye__________
Average near point = __________
Your age is _______________
Each group of 2 students is also responsible for obtaining one additional near point value
from an individual in an older age cohort (instructors and Camosun staff are usually
willing volunteers). You only need to obtain a value for one eye from these individuals).
Remember to get the volunteer’s age!
Record the near point values and ages on the board. This class data will be analyzed.
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Class data.
Organize the class data (and any additional data acquired) into age
cohorts and calculate the average nearpoint value for each cohort. Plot
these data as a bar graph.
Age Cohort
1.
Avg Near Point (cm)
Construct a bar graph below to show the relationship, if any, between age
and near point of focus using the data collected above.
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CAMOSUN COLLEGE BIOLOGY 144 (2010) LABS
2.
Describe the relationship shown in the graph.
___________________________________________________________________
3.
In order to focus on objects closer than 20 ft (the far point of vision) the lens must
accommodate
a) What is meant by accommodation of the eye?
__________________________________________________________________
__________________________________________________________________
b)
What muscles in the eye change the shape of the lens? ___________________
b) Why is the presbyopic eye unable to focus on near objects?
________________________________________________________________
d) What is the focal point of the eye?
________________________________________________________________
5. The lens of the eye refracts (bends) light, to project an image on to the retina.
Where on the retina are images seen with the greatest clarity?
_______________________________________________________________________
4.
What is a cataract (another age and disease related visual defect)?
______________________________________________________________________
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5. Explain what each of the following terms mean with respect to the eye. Draw rays of light
and their refraction as they pass through the lens to indicate the focal point relative to the
retina with each of the following . Label the lens, retina, cornea, and optic nerve on one of
the eyes.
emmetropia
hypermetropia
myopia
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CAMOSUN COLLEGE BIOLOGY 144 (2010) LABS
C. VISUAL ACUITY
The Snellen eye chart has been developed to assess visual acuity. A normal human eye can
differentiate, at a distance of 10 meters, 2 points that are only 1 mm apart. Points closer than 1
mm will be perceived as a single point. The size and proximity of cones in the fovea determine
the degree of visual acuity.
Purpose:
1. To determine your visual acuity as measured by the Snellen Eye Chart
2. To understand the meaning of Snellen values such as 20/20, 20/10, 20/100 etc.
Materials:
Snellen Eye Chart, meter stick
Procedure:
•
Locate the Snellen Eye Chart on the wall or door of the room.
•
Stand at a point 20 ft from the chart
•
Cover your left eye and read out the lines on the chart from the top down. Continue until
you can no longer distinguish the letters as determined by your partner.
•
Note this line. Repeat with your other eye and note the line where you faltered.
•
Determine exactly what readings of 20/20, 20/10, 20/100 mean.
Answer the following questions:
1. What is your Snellen Reading?
Your partner's?
Right eye________ Left eye________
Right eye________ Left eye________
2. A Snellen reading compares an individual’s vision to normal vision. Eg. If vision were 20/50,
the individual being tested could read letters at a distance of 20 feet that an individual with
normal vision could read at 50 feet
3. Descibe below exactly what a Snellen reading of 20/10, 20/20, 20/100 means, and indicate
the name of the visual defect (if there is one).
20/10_______________________________________________________
20/20_______________________________________________________
20/100______________________________________________________
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D. ASTIGMATISM
Astigmatism is a visual defect caused by irregularities in the shape of the cornea or lens. The
image below is used to test for astigmatism.
Procedure
1. Hold this page about 50 cm (20”) from your face with the image directly in front of your
right eye.
2. Close your left eye and look directly at the white circle in the center of this image.
3. If all of the radiating lines appear equally sharp, there is no astigmatism. If some of the
lines are blurred or less dark, some astigmatism is present.
Questions
1.
Light waves are refracted (bent) by both the cornea and the lens as they pass through
the eye. Most of this refraction is caused by the lens because it is thick and convex.
Images formed by convex lenses are inverted. On the diagram below, draw the letter ‘e’
as it would appear on the retina.
e
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CAMOSUN COLLEGE BIOLOGY 144 (2010) LABS
E. COLOUR BLINDNESS:
The perception of colour is a sensation achieved partly by the retina and partly by the brain. The
receptors of the retina that are sensitive to colour are the cones. According to the YoungHelmholtz theory of color perception, there are three different types of cones, each of which
responds maximally, to a different colour. The three colours that trigger maximum stimulation of
these cones are red, blue, and green. The degree of stimulation that each type of cone gets
from a particular wavelength of light determines what color is perceived by the brain.
For example, when the retina is exposed to red monochromatic light (wavelength of 610
nanometers), the red cones are stimulated at 75%, the green cones at 13%, and the blue cones,
not at all. The ratio of stimulation for red is thus 75:13:0. When the brain receives this ratio of
stimulation from the three types of cones, the interpretation is for red colour. When exposed to
white light, which is a mixture of all colors of the spectrum, the three types of cones are
stimulated equally.
Colour blindness is a sex-linked hereditary condition which affects 8% of the male population
and 0.5% of females. The most common type is red-green colour blindness, in which either the
red or green cones are lacking. If red cones are lacking, a condition called protanopia exists.
Individuals that have this condition see blue-greens and purplish-tinted reds as gray. A lack of
green cones is designated as deuteranopia. Although both protanopes and deuteranopes have
difficulty differentiating reds and greens, their visual spectrums differ enough so that they can be
diagnosed with colour test charts.
Purpose:
To determine whether you or your partners have some degree of protanopia or deuteranopia.
Materials:
Ishihara’s book of plates (Ishihara’s Tests for Colour Blindness, Concise Edition)
Procedure:
•
Have your partner hold the test plates about 1 meter from you. Start with plate #1
and proceed consecutively through plates 1 - 17.
•
You should respond within 3 seconds as to what you see on each plate.
•
Record your responses.
•
After all plates have been observed and recorded, compare your responses with the
correct answers on the separate documents associated with each set of plates.
•
Determine your colour vision status.
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CAMOSUN COLLEGE BIOLOGY 144 (2010) LABS
Questions
1. What is your colour vision status according to the Ishihara Test?
normal or colourblind _________________________________________________________
2. Distinguish between protanopia and deuteranopia
protanopia______________________________________________________________
deuteranopia ___________________________________________________________
F. DIPLOPLIA AND DOMINANCE
Humans have binocular vision. Each eye sees a different view, although there is a large area of
overlap. The cerebral cortex uses these discrepancies to produce stereopsis, or 3 dimensional
vision, an orientation of the object in space that allows us to perceive it’s distance from us (depth
perception). Even though there are differences in the views from each eye, we see a single
image because the cerebral cortex integrates the images. If this integration does not occur,
diploplia or double vision results. We do not however perceive an ‘average’ of right and left
views, rather the view from one eye is dominant.
Purpose:
1. To understand the importance of binocular vision in depth perception
2. To determine which of your eyes is dominant.
Procedure:
Place a book on end at arm length. Open both eyes. Put your left hand at your side and then
touch the nearest corner of the book with the index finger of your right hand. Repeat this
process with the left eye closed and then again with the right eye closed?
a) Was your attempt to touch the corner more accurate with one eye or both eyes? Explain.
________________________________________________________________
________________________________________________________________
Stab a pencil through a piece of paper and remove the scrap. Hold the paper at arms length.
With both eyes open, focus on a small discrete object which just fills the hole. Without
moving the paper, close the left eye and note whether the object is still there; repeat with
the right eye closed.
b) Which of your eyes is dominant? ______________________________________
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CAMOSUN COLLEGE BIOLOGY 144 (2010) LABS
PART 4: HEARING TEST
Although deafness may have many different origins, there are essentially two principal kinds of
deafness: nerve and conduction deafness. If the cochlea or cochlear nerve is damaged, the
condition is referred to as sensorineural deafness. Damage to the eardrum or ossicles, on the
other hand, will result in conduction deafness. While conduction deafness can usually be
remedied with surgery or hearing aids, neural deafness cannot generally be corrected.
The distinction between nerve and conduction deafness can be readily made with the Weber’s
Test using a tuning fork.
Purpose:
1. To evaluate hearing acuity in both ears
2. To distinguish between and understand the difference between nerve and
conduction deafness by performing two clinical tests,
Materials
tuning fork, ticking stop watch
Procedure:
1. Auditory acuity test
Ask your partner to close their eyes. Using cotton, plug one ear. Hold a ticking stop watch close
to the other ear. Move the clock away about 10 cm at a time. Note the distance at which the
person can no longer hear the ticking. Repeat with the left ear.
Record the average of the 2 values on the board, and calculate a class average.
a) distance (right ear)
_________ cm
b) distance (left ear)
_________ cm
c) your average
_________ cm
d) class average
_________ cm
e) How does your hearing compare to the class average? _______________________
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2. Rinne test
The Rhinne test can be used to differentiate sensorineural deafness from conduction deafness.
Strike the tuning fork. Hold it near the ear for a moment, then place the handle against the
mastoid process. Determine which is loudest. Individuals with normal hearing will report the
sound is louder in air (air conduction is greater than bone conduction). If conduction hearing loss
is present, the sound will be louder when transmitted through the mastoid (bone conduction is
greater than air conduction).
Where is the sound louder when you test yourself? _________________________________
What does this indicate? _____________________________________________________
It is possible to simulate conductive hearing loss in yourself by plugging one ear. Repeat the
Rinne test after plugging one ear with cotton
Describe your results _________________________________________________________
Explain the difference between sensorineural and conduction deafness.
sensorineural deafness
____________
________________________________________________________________
conduction deafness
____________
________________________________________________________________
3. Journal Article
Peng J-H, Z-Z Toa, Z-W Huang Risk of damage to hearing from personal listening
devices in young adults Journal of Otolaryngology (2007) Vol 36 (3):181-185
Read this journal article. It can be accessed under links at http://hunterp.disted.camosun.bc.ca)
Answer the following questions:
1. What is NIHL? ______________________________________________________________
2. How many subjects were tested in the personal listening device group? _________________
3. What was the age range of this group? ____________
4. What units are used to measure noise levels? ___________
4. What was the average noise exposure level at the preferred volume setting on the PLD
(in dB)? ___________
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5. At a sound frequency of 6 kHz, how loud did a sound have to be for each of the following to
hear it?
the control group _________
the group with 5 yr or more of PLD exposure to noise? _________
6. Was this difference (above) statistically significant? ________
7. What percentage of PLD users ears were shown to have hearing loss? _________
8. What percentage of control group ears were shown to have hearing loss? ____________
(care to comment on this one?) ______________________________________________
9. Do you think the hearing loss associated with PLD use would be classified as sensorineural or
conduction? ___________________
Explain: ____________________________________________________________________
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