1. Explain to the class that they will use a Web-based activity to explore the hearing pathway and the process by which it converts sound waves into signals that can be understood by the brain.

If you feel that your students would benefit from a more extensive introduction to the activity, consider having the class proceed through Steps 1–4 from the print-based procedure.

2. Explain to the class that they will view eight pictures, each representing a different part of the hearing pathway. As they position the cursor over each picture, they can read a brief description of that part’s role in the hearing process. The students’ task is to arrange the pictures in their proper sequence in the hearing pathway.

After students arrange the pictures in a sequence, they can test themselves by clicking on the “Try it” button. If a mistake has been made, only those pictures that are in the correct order remain where they are, while those that are incorrect move back to the starting position for the student to try again. When the correct sequence is assembled, the hearing pathway fades away and a cartoon animation appears. The animation shows how the sound is represented along the hearing pathway. A sound is heard only after the electrical impulse reaches the brain.

3. Instruct students to proceed to http://science.education.nih.gov/supplements/hearing/student and click on “Lesson 4—A Black Box Problem: How Do I Hear?”

Students should pay particular attention to the introduction, which includes a cartoon that depicts how sound waves travel through the hearing pathway and introduces the term transduction. Transduction is the process by which sound is converted into a form that the brain can understand.

As students perform this activity, circulate around the room and ask each team to explain why they put the pictures in the order they did.

      
      
Figure 4.2. The parts of the human hearing pathway in their proper sequence.

1. Turn on the lamp and ask the class how the light bulb produces its light.

Student responses will vary. Direct the discussion to how electrical energy flows through a wire to the light bulb filament where light, as well as heat, is generated.

2. Write the word “transduction” on the board and explain that it refers to the process by which energy is converted from one form into another. Ask students if they can name other examples of transducers.

Students’ examples may include flashlights, microphones, photocells, stereo speakers, engines, and other such devices. If no one mentions a biological system, ask the class if living things can transduce energy. Examples of biological transduction may include the process of photosynthesis, which converts light energy into chemical energy, or the process of respiration, which converts chemical energy into mechanical energy.

    
Figure 4.3. Examples of transducers.

Content Standard B:
Energy is a property of many substances and is associated with heat, light, electricity, mechanical motion, sound, nuclei, and the nature of a chemical.

Content Standard A:
Identify questions that can be answered through scientific investigations.

3. Display an overhead transparency made from Master 4.1, The Mysterious Black Box. Ask students to describe the picture and to identify the question it raises.

Figure 4.4. The Mysterious Black Box.

Guide the discussion so that students ask a focused question pertaining to hearing, such as, “What happens inside the hearing pathway to allow sound to be heard in the brain?”

Ask students to rephrase the question to include the concept of transduction: “How is sound converted to a signal that the brain can understand?”

Students should understand that the black box represents the parts of the hearing pathway that they cannot see. You may wish to explain that scientists are often able to observe only the beginning of a process and its outcome but not the events that lead from one to the other. The challenge of the black box is to identify and describe all of the intermediate steps.

4. Display an overhead transparency made from Master 4.2, A Few Questions. Uncover the questions one at a time as the discussion proceeds. Invite students to speculate as to what happens inside the black box of hearing.

Sample answers to Master 4.2, A Few Questions, follow:

Question 1. What do the lines between the bell and the ear indicate?

The lines depict sound waves (vibrational energy) moving from the bell to the ear.

Question 2. What is a sound wave?

A sound wave is a wave of vibrational energy (or a pressure wave) that moves through a medium such as air or water.

Question 3. Do vibrations reach all the way into the brain to let us hear sound?

This question is analogous to the example of the lamp as a transducer. Just as light doesn’t travel through wires to the light bulb, students should recognize that the actual vibrations do not travel to the brain. Instead, the ear converts the vibrational energy of sound into electrical energy, the energy of nervous impulses. To help students formulate this answer, you may wish to ask the analogous questions, “Does the light that enters our eyes go all the way to the brain?” and “When you touch someone’s skin and they feel it, does the ‘touch’ go all the way to the brain?”

5. Explain that in this activity, students will construct a flow chart that shows what happens inside the black box of hearing. Hold up a set of Black Box Cards and explain that each team will receive a set of eight cards that provides information about the structures and functions of the hearing pathway.

Each card includes a picture of a part of the hearing pathway and a brief explanation of the part’s function. The team’s first challenge is to assemble the cards in the correct order so that the sound of the bell will be heard in the brain.

Content Standard A:
Think critically and logically to make the relationships between evidence and explanations.


Assessment:
As students perform this activity, circulate around the room and ask each team to explain why they put the pictures in the order they did. If a team struggles to place the pictures in the correct order, ask the students various guiding questions to help them overcome their difficulties. If necessary, point out to the team that their sequence is correct up to a certain point.

6. Organize the class into teams of two or three students. Distribute a set of Black Box Cards to each team. Announce that teams have 10 minutes to put the cards in the correct sequence. During that time, while students are working, you will circulate through the room with a “testing device” (hold up the large Bell Card and the bell). Explain that when a team decides it has assembled the pictures in the proper order, you will use the device to test the sequence.
7. To test each team’s pathway, give one team member the Bell Card and ask him or her to place it at the start of the flow chart. The Bell Card illustrates the vibrations produced as the bell rings. After the student puts the Bell Card in position, have the students explain what happens to the sound as it is transmitted through the hearing pathway. If the students’ sequence of cards and explanation of events are correct, ring the bell to indicate that the impulse reached the brain, where it is interpreted. If the pathway is not correct, do not ring the bell and ask the team to try again.
8. Write the names of the hearing-pathway components on the board as follows:

Instruct the teams to match the letter that corresponds to each component of the hearing system with its image.

Figure 4.5 provides a visual guide for the correct order of Black Box Cards.

      
      
Figure 4.5. The Black Box Cards in their proper sequence.

As you review the functions of the components of the hearing pathway, draw attention to each part’s name. After you have reviewed all eight components, introduce the terms “outer ear,” “middle ear,” and “inner ear,” and ask students to place these labels at the appropriate points in the sequence of pictures that depicts the hearing pathway. Ask students to name the parts of the hearing pathway that are not part of the ear, such as the auditory nerve and the brain.

Figure 4.6. The hearing pathway showing the outer, middle, and inner ear.

9. Before proceeding, construct the hearing pathway on the board so that students may refer to it while engaged in Activity 2.

1. Review transduction with the class. Make sure students understand that transduction is the conversion of energy from one form into another. Ask the class where in the hearing pathway transduction occurs.

Students may respond that transduction occurs either in the cochlea or in the organ of Corti. If there is confusion, help students understand that the organ of Corti is found within the cochlea. Explain how the hair cells are organized in the cochlea, how they detect the pressure waves moving through the cochlea, and how they trigger the formation of electrical impulses.

2. To ensure that students understand how sound is represented at various points along the hearing pathway, write the terms “vibration,” “pressure wave,” and “electrical impulse” on the board. Ask students to use the terms to identify the form in which sound energy is represented at each of the eight points pictured.

3. Distribute to each team 1 copy of Master 4.5, Understanding Form and Function. Instruct team members to work together to complete the handouts.

These masters contain tasks related to the hearing pathway and the treatment of hearing loss. Students may find it helpful to refer to the Black Box sequence of the hearing pathway as they answer the questions. In Part 2, if students have difficulty describing how hearing would be affected by the different situations, use probing questions to elicit answers.

Sample answers to tasks on Master 4.5, Understanding Form and Function, follow:

Part 1
Now that you have properly identified the ear’s transducer, write “yes” beside each phrase that correctly describes one of its characteristics. Write “no” beside each phrase that does not.

Part 2
Use your understanding of the hearing pathway to predict the effect each of the following would have on hearing. Use the choices below for your answers.

For each of the following situations, hearing would

• be unaffected
• gain loudness
• lose loudness
• lose information about pitch
• be lost completely

Part 3
Identify which statements refer to a hearing aid, which refer to a cochlear implant, or both.

Content Standard C:
Disease is a breakdown in structure or function of an organism.

4. Conclude the activity by reviewing students’ answers to the tasks posed on Master 4.5. During the discussion, supplement the information students have already been given about the hearing pathway as appropriate.

For example, students may be interested to learn that hair cells are unparalleled in their ability to detect the minute levels of vibrational energy in sound waves, and that they respond 1,000 times faster to stimulation than do visual-receptor cells.