SCIENCE 08 BIOLOGYNotebook Page E

EXPERIMENT # 4

THE EYE AND VISION

PROBLEM:

1.To study the method by which the eye produces an image.

2.To determine the location of your "blind spot".

3.To determine the extent of your "peripheral vision".

4.To study your retention of vision.

5.To determine your "near point".

6.To study "optical illusions".

APPARATUS AND MATERIALS:

Small mirrorPencilBird in cage Blind spot cardOptical illusions sheet

Convex lensCandleScreen

PROCEDURE:

1.Observe your eye in a small mirror. Make a LARGE properly formatted diagram of your eye as seen in the mirror. Identify the following features and add appropriate labels to your diagram:

EyebrowEyelashesSclerotic coatPupilIris (indicate colour)CorneaEyelid

2.Observe the demonstration of the image of a burning candle produced by a convex lens similar to the lens found in your eye. Describe the orientation of the image. Draw a neat sketch diagram showing the burning candle, the convex lens, and the image of the candle on the screen.

3.Find your "blind spot" as follows individually. Obtain a "blind spot card" and hold it at arms length in front of you, stare at the cross but be aware of the dot. Close your left eye but don't squint too severely. Move the card slowly toward you. Continue to stare at the cross but still be aware of the dot. Measure in centimetres how close you are to your eye when the dot seems to disappear. Record this as the blind spot of your right eye in Data Table I.

4.Repeat procedure #3 this time closing the right eye and using the left eye.

5.Test your "peripheral vision" with the help of your partner. Look straight ahead. Have your partner hold a pencil about 15 centimetres directly in front of you and slowly move it horizontally to the right side. Measure in centimetres with the aid of your partner the position of the pencil from its starting point directly in front of you when you lose sight of it as indicated in the diagram. Don't move your eyes ! Record your results in Data Table I.

 

 

 

 

 

 

 

 

 

 

EXPERIMENT #4: EYES AND VISION PAGE 2Notebook Page E

6.Repeat procedure #5 three more times moving the pencil first to the left side, then straight up from centre, and finally straight down from center. Record your results in Data Table I.

7.Check your "retention vision". Hold the "bird in the cage" apparatus between your palms. Slowly rotate the apparatus by rubbing back and forth. Gradually increase your rubbing speed until you first are able to see the bird appear to be inside the cage. Continue rubbing at this speed and count the number of times you rub in a 10 second period. Count each pair of back and forth motions as "one rub". Multiply by 6 to calculate the number of times you had to rub per minute. Record your results in the data table.

8.Using the following procedure to find your "near point", the closest point at which you can focus.

a)Attach a strip of masking tape about 1 metre long parallel to, and approximately 30 cm from, the edge of the table.

b)Position your eyes at the level of the table top. Using your right eye, look straight along the length of the masking tape.

c)Cover your left eye with your left hand but do not squint. Focus your right eye on the blunt end of a pencil your partner has placed at the far end of the tape. Continue to focus on the pencil as your partner slowly moves the pencil towards you along the tape. When the blunt end of the pencil begins to look blurred tell your partner to stop. Measure the distance from your right eye to the pencil to the nearest centimetre. Record this in Data Table I as your "near point".

d)Repeat this procedure with your right eye again two more times and then three times with your left eye while your right eye is covered.

e)Calculate the average distance of your "near point" for each eye to the nearest whole number of centimetres and enter the result in Data Table I.

9.Obtain an "optical illusions" sheet. Do this part entirely individually because any prior discussion with another student may distort your visual perceptions.

a.Answer the question posed beside each diagram based only on your personal visual observations.

b.Using a ruler confirm or prove false your visual perception by either measuring with or aligning the ruler as necessary. Measurements should be in centimetres to one decimal.

c.Record your visual and measured results in Data Table II.

DATA:Record all measurements in the appropriate Data Tables.

OBSERVATIONS:

1.Write the following statement: "Refer to Diagram I. Complete the diagram of your eye properly labelling the parts listed in the Procedure. The diagram should be properly labelled and formatted and titled Diagram I: " External View of My Eye". Colour the iris to match the colour of your iris.

2.Write the following statement: "Refer to Diagram II. Complete the diagram of the burning candle and its image as focused by a convex lens properly labelling the parts listed in the Procedure. The diagram should be properly labelled and formatted and titled Diagram II: " Convex Lens Image of a Burning Candle".

 

 

 

 

 

EXPERIMENT #4: EYES AND VISION PAGE 3Notebook Page E

DISCUSSION:

1.How do your eyelids, eyebrows, and eyelashes all protect your eyes?

2.What is the function of the tough outer sclerotic coat ?

3.Why do you not normally notice the existence of your "blind spot" ?

4.Why is peripheral vision important to humans as well as other animals ?

5.Why does the bird appear to be in the cage ?

6.Movies are made from a series of slightly changed still frames. Why is it possible to watch "movies" without seeing the "blinks" between frames ?

7.What happens to the "near point" distance of people as they age ? Why ?

8.Approximately what fraction of the questions on the "Optical Illusions" sheet did your brain correctly analyze when your visual perception was compared to actual measurements ?

CONCLUSION:

1.Why is the image of objects that fall on the retinas of our eyes always upside down ? Why do we then see it right side up ?

2.Diagram III: "My Field of Vision" is drawn to a scale of about 1:5. That is every real 5 centimetres is represented by only 1 centimetre on the diagram. Therefore all of your data must be divided by 5 before any is measured and marked on the diagram. Complete the following on Diagram III: "My Field of Vision".

a.Measure, mark, and label the "blind spot" distance for each eye on the "top view".

b.Measure, mark, lightly shade in , and label your vertical (up/down) field of peripheral vision on the "side view".

c.Measure, mark, lightly shade in , and label your horizontal (left/right) field of peripheral vision on the "top view".

d.Measure, mark, and label the "near spot" distance for each eye on the "top view".

3.What is an "optical illusion" ?

SOURCES OF ERROR:

1.Instrumental:

List the names and state the uncertainty of any measuring instruments used.

2.Procedural:

List factors that we were unable to control but that might affect the results.

 

EXPERIMENT #4: EYES AND VISIONNotebook Page E

DIAGRAM I: EXTERNAL VIEW OF MY EYE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DIAGRAM II: CONVEX LENS IMAGE OF A BURNING CANDLE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DIAGRAM III: MY FIELD OF VISION

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

EXPERIMENT #4: EYES AND VISIONNotebook Page E

TABLE I: FIELD OF VISION DATA

RIGHT EYELEFT EYE

3 & 4. BLIND SPOT DISTANCE (cm)

5 & 6.PERIPHERALRIGHT

VISION (cm)LEFT

BOTH EYESUP

TOGETHERDOWN

7.RETENTION VISION

(rubs per minute)

8.NEAR POINT (cm)RIGHT EYELEFT EYE

TRIAL 1

TRIAL 2

TRIAL 3

AVERAGE

TABLE II: OPTICAL ILLUSIONS

VISUALACTUAL

PICTUREPERCEPTIONMEASUREMENT

1LINES

2PRONGS

3LINES

4CIRCLES

5STAIRS

6PENCILS

7RECTANGLE

8RECTANGLE

9ARROWS

10CIRCLES

11LINES

12LADDERS

13PRONGS

14CARS

15ARCS

16TRAINS

17TRAINS

 

BLIND SPOT CARD

 

 

 

 

 

 

 

 

 

PERIPHERAL VISION

side viewtop view