Human Vision - Limestone District School Board



4572000-228600Human Vision 541020115570Objective:Do you know if your vision is 20/20 or better? In this activity, you will test you visual acuity and observe some other aspects of human vision. Do all numbered parts. Write your actual observations at bulleted sections on another piece of paper. Answer analysis questions on that same piece of paper and hand it in at the end of class.Materials:Snellen Eye ChartRulerPencilProcedure:Part 1: Visual AcuityYou ability to distinguish detail or visual acuity can be determined by the Snellen eye chart. Have you ever heard someone say he or she has 20/20 vision? This means that the person is able to read the “20” line on an eye chart from a distance of 20ft. (Charts that have been converted to metric measurements show normal vision to be 6/6. This indicates that the line marked “6” can be read from a distance of 6m.) A person with 20/100 can only read line “100” from 20ft., which is very poor vision. A person with 20/15 vision has better than 20/20 vision.Stand 20 ft. from the eye chart. (Stand 6m away if a metric chart is available). Cover your right eye and begin reading letters from each line while a partner observes.Record the visual acuity of your left eye.Repeat the procedure covering your left eye.Record the visual acuity of your right eye.Part 2: Dominant EyeFace the corner of the room and view the upper corner. Holding a pencil in either your right or left hand, extend that arm, bringing the top of the pencil into the middle of your field of view. Align the pencil with the line where the two walls meet.Close your right eye and note the location of the pencil.Describe what, if anything, happened to the position of the pencil.Close your left eye and note the location of the pencil.Describe what, if anything, happened to the position of the pencil.Which is the dominant eye?Part 3: Stereoscopic Vision and Wrod OdrerMsot of waht you see wtih yuor rihgt eye is aslo seen wtih the lfet eye. Viasul fedils oervalp. Ecah eye sees the iamge from a sliglhty dffieenrt alnge. The iamge is certaed in ecah rnteia and soertd on the opipsnog cerrebal heeipmhsres. Iornfmation is raelyed bteeewn the two hemhspirees and the two imgaes are seupmriespod on each oethr, caeitrng a trhee dmeiosnnail iagme. By wronikg tgoheetr, the eeys proidve shligtly deifernft aglnes of view taht pirmet the brian to emtsatie dsctniae.If you are able to read the above passage it is based on the idea that researchers at Cambridge University have concluded that it doesn't matter what order the letters of a word are in; as long as the first and last letters are in the proper place, you can scramble the rest of the word however you like, and it's still readable. If you can not read the passage above, it is in a smaller font on the bottom of this page.Stare directly at a distant object with your hands up, arms outstretched and fingers touching obstructing your field of view of that distant object. Touch your fingertips of your right and left hands, but spread your fingers enough to allow light to pass between them. Extend your arms and slowly bring the fingertips in front of your face, but continue looking at the distant object through your fingers.What do you see?AnalysisIn Part 2 of the lab, you discovered that the pencil moved when you viewed it with one of your eyes. Offer an explanation for this observation.Horses and cows have eyes on the sides of their heads, which means their visual fields overlap very little. What advantage would this kind of vision have over human vision?Like humans, squirrels have eyes on the front of their head. The visual field of the squirrel’s right eye overlaps with the visual field of its left eye. Why does a squirrel need this type of vision?If students place a large piece of cardboard between their eyes while attempting to read two different books at the same time, will they be able to read two books at once? Provide an explanation.Most of what you see with your right eye is also seen with the left eye. Visual fields overlap. Each eye sees the image from a slightly different angle. The image is created in each retina and stored on the opposing cerebral hemispheres. Information is relayed between the two hemispheres and the two images are superimposed on each other, creating a three dimensional image. By working together, the eyes provide slightly different angles of view that permit the brain to estimate distance.Part 4: Optical IllusionsFollow the instructions. What do you see happening? ___________________________________________________________________________________________________Count the black dots. How many do you see?__________________________________________________________________________________________________________________________________________________________________3. Are the horizontal lines straight or bent? ___________________________________________________________________________________________________4. Are the horizontal lines straight or bent? __________________________________________________________________________________________________________________________________________________________________5. Stare at the middle dot. What do you see happening? ___________________________________________________________________________________________________6. Which middle dot is larger? Measure them to make sure.__________________________________________________________________________________________________________________________________________________________________7. What do you see in this picture? Happy pots?___________________________________________________________________________________________________8. Is the one side of the balance lower than the other? __________________________________________________________________________________________________________________________________________________________________9. What do you see? ___________________________________________________________________________________________________10. What do you see? Can you find all 7 faces?__________________________________________________________________________________________________________________________________________________________________ ................
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