Things We Can Measure in the Ear

1. Things We Can Measure in the Ear

2. The bottom line Auditory transduction produces acoustic and electrical signals that can be measured in the ear canal. These measures are used in research and in clinical practice to assess the status of the inner ear.

3. Otoacoustic emissions Otoacoustic emissions are sounds measured in the ear canal that are produced in the inner ear by the outer hair cells.Otoacoustic emissions are sounds measured in the ear canal that are produced in the inner ear by the outer hair cells.

4. Uses of Otoacoustic Emissions In research, a tool for studying how the inner ear works. In the clinic, a useful assessment of inner ear function, because most sensorineural hearing loss involves loss of outer hair cells. Outer hair cells are generally more sensitive to wear and tear and trauma than are inner hair cells.Outer hair cells are generally more sensitive to wear and tear and trauma than are inner hair cells.

5. Types of Otoacoustic Emissions Spontaneous Evoked

6. Spontaneous OAEs Occur in 60-70% of people Do not indicate damage or disease Tend to remain stable in frequency and level Generally are not heard

7. Types of Evoked OAEs Transient Stimulus Frequency Distortion Product EOAEs are becoming very popular as a means for screening for hearing loss, particularly among infants and children. Many states now require that all newborn infants be screened for hearing loss, and EOAEs are the most popular way to do that,EOAEs are becoming very popular as a means for screening for hearing loss, particularly among infants and children. Many states now require that all newborn infants be screened for hearing loss, and EOAEs are the most popular way to do that,

8. Transient EOAEs TEOAEs are elicited by clicks or tone pips. The spectrum of the emission tends to resemble that of the stimulus, but the level of the emission at each frequency is not a good indicator of the degree of hearing loss at those frequencies.TEOAEs are elicited by clicks or tone pips. The spectrum of the emission tends to resemble that of the stimulus, but the level of the emission at each frequency is not a good indicator of the degree of hearing loss at those frequencies.

9. Stimulus Frequency EOAEs SFEOAEs are elicited by a continuous pure tone. Although they are a sensitive indicator of hearing at the test frequency, they are not commonly used, because special processing is required to separate the emission from the stimulus in the ear canal.SFEOAEs are elicited by a continuous pure tone. Although they are a sensitive indicator of hearing at the test frequency, they are not commonly used, because special processing is required to separate the emission from the stimulus in the ear canal.

10. Distortion Product EOAEs DPEOAEs are sensitive indicators of hearing at the f2 frequency. Because the emission is at a different frequency from the stimulating tones, it is relatively easy to measure the response and these emissions are a rather popular assessment tool. (However, it should be mentioned that the processes underlying the production of the DPEOAE are not particularly well understood.)DPEOAEs are sensitive indicators of hearing at the f2 frequency. Because the emission is at a different frequency from the stimulating tones, it is relatively easy to measure the response and these emissions are a rather popular assessment tool. (However, it should be mentioned that the processes underlying the production of the DPEOAE are not particularly well understood.)

11. Electrical �by-products� of Transduction Cochlear Microphonic Summating Potential Compound Action Potential (N1) Electrical potentials from the cochlea are somewhat more difficult to measure than are emissions, so they are not commonly used in the clinic, although they are often used in research.Electrical potentials from the cochlea are somewhat more difficult to measure than are emissions, so they are not commonly used in the clinic, although they are often used in research.

12. Cochlear Microphonic The CM is a receptor potential. That is, it reflects the electrical changes that occur in the receptors, the hair cells, during transduction. The CM is an alternating current, or AC, potential, that follows the time wave form of the stimulus. It can be recorded with electrodes in the ear canal.The CM is a receptor potential. That is, it reflects the electrical changes that occur in the receptors, the hair cells, during transduction. The CM is an alternating current, or AC, potential, that follows the time wave form of the stimulus. It can be recorded with electrodes in the ear canal.

13. Summating Potential The SP is a direct current or DC, potential. In other words, it represents a �step� in the electrical potential measured in the cochlea. The SP is a direct current or DC, potential. In other words, it represents a �step� in the electrical potential measured in the cochlea.

14. CM, SP and frequency At low frequencies, the CM is the dominant response measured, at high frequencies, the SP is the dominant response.At low frequencies, the CM is the dominant response measured, at high frequencies, the SP is the dominant response.

15. Compound Action Potential The CAP represents the synchronous firing of lots of auditory nerve fibers. It can be recorded with ear canal electrodes, or from the scalp, when it is usually referred to as N1.The CAP represents the synchronous firing of lots of auditory nerve fibers. It can be recorded with ear canal electrodes, or from the scalp, when it is usually referred to as N1.

16. Conclusions By-products of auditory transduction, OAEs, CM, SP, and CAP, can be measured outside the cochlea in humans and nonhumans. These measures provide a means for studying and assessing the function of the inner ear.