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How do Limitation of Senses, Defect in Sensory Organs and Ageing Affect Human Hearing and Sight? Audio visual which combines the senses of hearing and sight, plays an important role in daily life. Let us investigate SCIENCE INFO how limitation of senses, defect in sensory organs and...

How do Limitation of Senses, Defect in Sensory Organs and Ageing Affect Human Hearing and Sight? Audio visual which combines the senses of hearing and sight, plays an important role in daily life. Let us investigate SCIENCE INFO how limitation of senses, defect in sensory organs and Audio visual refers to the use ageing affect the sensitivity of hearing and sight of humans. of two components, sound component (audio) and graphic component (visual). Limitations of Sight Limitation of sight is the limitation in the ability of the eye to see objects. We cannot see very tiny objects such as microorganisms as well as very distant objects such as planet Jupiter. Limitations of sight include optical illusions and blind spot. Optical Illusions P R X Y Q S (a) Which line is longer? (b) Which spot in the (c) Are the sides of the square centre is larger? straight or curved? Figure 1.20 Optical illusions Look at Figure 1.20 and answer the questions given. Check your Optical illusion Without optical illusion answer using a straight ruler. Is your P R P R answer correct or wrong? Why? Optical illusion occurs when an object that is seen differs from its actual state. Optical illusion occurs because the brain is unable to Q S Q S accurately interpret the object seen by With distractions around Without distractions around the eye due to distractions around the straight lines PQ and RS straight lines PQ and RS object. Look at Figure 1.21. Figure 1.21 Factor causing an optical illusion 24 1.2.4  Chapter 1: Stimuli and Responses Blind Spot Refer to the blind spot shown in Figure 1.8 on page 12. Why are images that fall on the blind spot invisible? We are unaware of the presence of the blind spot in the eye because it is not possible for the image of the same object to fall on the blind spots of both eyes simultaneously. Carry out the following simple activity to investigate the blind spot. Figure 1.22 Investigating the blind spot Instructions 1. Hold this book with your right hand and straighten your arm. 2. Cover your left eye and look at the cat in Figure 1.22 with your right eye. 3. Move this book slowly towards your eyes. Does the bird disappear from your sight at a certain position? Why? Photograph 1.14 shows examples of various devices used to overcome the limitations of sight. Name these devices. Gather information on the use of these devices from the Internet, magazines, books, newspapers and other sources. Discuss the information gathered. Present the findings of your discussions collaboratively using multimedia presentation. Binoculars Light microscope Scanning electron microscope Ultrasound machine X-ray machine Photograph 1.14 Examples of devices to overcome limitations of sight 1.2.4 25  Defects of Sight and Ways to Correct Them Defects of sight include short-sightedness, long-sightedness and astigmatism. How can these defects of sight be corrected? Study Table 1.2. Table 1.2 Defects of sight and ways to correct them Defect of sight How it is corrected Short-sightedness (a) Inability to see distant objects clearly. Short-sightedness can be corrected using (b) Distant objects appear blurry because the concave lens. image is focused in front of the retina. (c) This defect is caused by the eye lens being too thick or the eyeball being too long. Eye lens too thick Distant object Distant object Image formed Concave lens Image formed in front of the retina on the retina Eyeball too long Distant object Distant object Long-sightedness (a) Inability to see near objects clearly. Long-sightedness can be corrected using (b) Near objects appear blurry because the image convex lens. is focused behind the retina. (c) This defect is caused by the eye lens being too thin or the eyeball being too short. Eye lens too thin Near object Near object Image formed Image formed Convex behind the retina on the retina lens Eyeball too short Near object Near object 26 1.2.4  Chapter 1: Stimuli and Responses Defect of sight How it is corrected Astigmatism Astigmatism can be corrected using cylindrical (a) Seeing part of an object clearer than the rest lenses. of the object. (b) This defect is caused by the uneven curvature of the cornea or eye lens.          Cylindrical lens    Figure 1.23 Test your eyes by looking at Figure 1.23. Can you see all the lines clearly? If you cannot, you have astigmatism. Today in history Limitations of Hearing Limitations of hearing are limitations in the ability of the ear to hear sound. We can only hear sounds of frequencies between the range of 20 Hz to 20 000 Hz. The ears are unable to detect sounds which lie outside this frequency range. The frequency range of hearing of every individual is different. When a person gets older, the frequency range The first stethoscope made of of his hearing gets narrower as his eardrum becomes less wood was invented by Rene elastic. Examples of devices invented and used to overcome Laennec at Necker-Enfants the limitations of hearing are shown in Photograph 1.15. Malades Hospital, Paris in 1816. A loudspeaker amplifies sound so that it can be heard from far away. Stethoscope helps us to listen to the heartbeats. Photograph 1.15 Examples of equipment used to overcome limitations of hearing 1.2.4 27  Defects of Hearing and Ways to Correct Them Defects of hearing occur when the sense of hearing of a person does not function well. Defects of hearing are normally caused by damage to the ear due to infection by microorganisms, injury, ageing process or continuous exposure to loud sounds. Damages to the outer ear and middle ear can be corrected easily. For example, the clearing of foreign objects in the ear canal. Punctured eardrum and damaged ossicles can also be corrected using medicine or surgery. Damage to the inner ear is more difficult to correct. A damaged cochlea can be corrected using a cochlear implant but a damaged auditory nerve cannot be corrected using medicine or surgery. Photograph 1.16 shows how innovation and technology are applied to invent smaller and more sophisticated hearing aids. Photograph 1.16 Advancements in hearing aids The Five Senses – a Gift The five senses is a gift from God that we should appreciate. However, unhealthy lifestyles and high risk careers can affect the sensitivity of the sensory organs. Based on Photographs 1.17 and 1.18: name the sensory organ whereby the sensitivity is affected in each situation describe how each situation can affect the sensitivity of the sensory organ h h 1.17 Unhealthy Photograph h l h lifestyle lf l what are the devices or safety measures taken to maintain the safety and health of the sensory organ in each situation? Photograph 1.18 High risk careers 28 1.2.5