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27 Cards in this Set

  • Front
  • Back
218. What is the definition of visible light?
The range of electromagnetic radiation observable by the human eye (approximately 400-750 nm).
219. What is the wavelength range of ultraviolet radiation?
10 nm - 400 nm
220. What is the wavelength range of infrared radiation?
750 nm - 1 mm
221. Which physical characteristics of the eye lens are changed during accommodation?
The shape (radius of curvature) and the refractive index of the lens. In the case of humans the former is dominant.
222. Give the definition and unit of diopter.
D (diopter) = 1/f
where f is the focal length of the lens.
Unit: 1/m.
223. What is the resolution of an eye?
The smallest visual angle at which the images of two points can be distinguished.
224. What is the physical and biological limit of the resolution of an eye?
Physical: The separation between the two points to be distinguished should not be less than the wavelength of the illuminating light.
Biological: Images of the two points to be distinguished have to be on different photoreceptors, and there has to be an unstimulated receptor between them.
225. What does it mean that photons are only triggers for photoreceptors?
The energy of photons is used by the receptors for inducing chemical (signal transducing) processes.
226. Which receptor cells of the retina are responsible for color vision and vision under dim conditions?
color vision: cones;
vision under dim conditions: rods.
227. What is monochromatic light?
Light is monochromatic if its spectrum consists of a single wavelength only.
228. What is the principle of Young-Helmholtz theory?
The phsyiological basis of color vision is the existence of 3 different color sensitive receptors (the cones) with different photopigments which are able to make a distinction between red, green and blue colors.
229. What is ERG?
Electrotinogram: it records the potential charges of the retina as a whole during stimulation with light.
230. Give the frequency range of sound waves audible by a normal human ear.
16 Hz - 16000 Hz
231. What is ultrasound?
Sounds whose frequency is between 16000 and 10^10 Hz.
232. What is infrasound?
Sound with a frequency less than 16 Hz.
233. Give the definition and unit of sound intensity.
The energy carried by a sound wave perpendicularly through unit cross-sectional area per unit time. Its unit is Watt/m^2
234. What is the threshold intensity of hearing? Give its value.
Threshold intensity hearing is the minimal intensity of the 1000 Hz sinusoidal sound audible by a normal human ear. Its value is about 10^-12 Watt/m^2
235. How does the intensity of sensation (loudness) change as a function of the intensity of the stimulus?
Sensation is proportional to the logarithm of the relative intensity of the stimulus.
236. What is the advantage of the phon scale compared to the bel and decibel scales?
When using the phon scale the intensities of both the reference and actual sound intensities are converted to the intensities of the corresponding 1000 Hz sound, i.e. the reference is the threshold intensity of the 1000 Hz sound (10^-12 Watt/m^2), the actual intensity is the intensity of the 1000 Hz sound inducing the same sensation of loudness as the sound under investigation. Therefore, the threshold of hearing is 0 phon for every frequency.
237. Give the Weber-Fechner law.
sensation =
(actual stimulus intensity)/reference stimulus intensity
238. A sound with intensity "I" and v=2000 Hz frequency is given by a sound generator. What is the loudness according to the phon scale?
L=(10)(lg)((I1000/Io)) (phon)
where L is the loudness in phons;
I1000 is the intensity of the 1000 Hz sound which causes the same sensation of loudness as the given 2000 Hz sound with intensity "I";
Io is the threshold intensity of hearing for the 1000 Hz sound (10^-12 Watt/m^2).
239. What relations are plotted by isophonic curves?
The sound intensities producing the same sensation of loudness are plotted against the sound frequency.
240. Give the threshold values of hearing according to the phon scale for sounds whose frequences are 1000 Hz and 2000 Hz, respectively.
0 phon, the threshold of hearing is the same (0 phon) for any frequency.
241. What is the basis of the son scale?
Sensation can be more precisely described by the power of the relative stimulus intensity with a fractional exponent.

where Hson is the loudness in son, and I and Iref are the stimulus intensity in question and the reference stimulus intensity, respectively.
242. What is the mechanism of hearing by means of air conduction(also called ossicular conduction)?
The vibration reaches the inner ear through auditory meatuses and the system of the tympanic membrane and auditory ossicles.
243. What is the mechanism of hearing by means of bone conduction?
The vibration reaches the inner ear directly through the cranial bones.
244. What are the physical principles giving rise to an increased pressure on the foot plate of the stapes compared to the pressure of the original sound?
1. the cross-sectional area of the ear drum is much larger than that of the stapes foot plate;
2. lever-like functioning of auditory ossicles.