Physiology of human perception

Transcription

1 Physiology of human perception Vision Hearing Thermal and tactile sensations Basic introduction and the list and description of the tasks to be carried out

2 Visible light: nm. Vision or sight

3 Anatomy of the eyeball

4 Task 1: blood vessel shadow experiment Subject closes his eyes and presses the sclera lamp to the lower eyelid with the tip turned towards the eye bulb Eyes are turned upwards while the eyelids are closed The lamp is to be moved slowly and gently to the sides while switched on sclera lamp (light) Describe the observed visual sensation and explain it!

5 Opthalmoscopy Normal retina Rods and cones are distributed in the retina in an uneven manner macula lutea: center of the posterior portion of the retina fovea centralis: only cones; highest visual acuity/resolution optic disc (blind spot): exit site of the retinal axons

6 Retinal degeneration age-related macular disease (AMD) degenerative retina in glaucoma

7 Task 2: Opthalmoscopy on an artificial eye model Lean close to the eye model and enlight the inner surface with the small torch Make a draft drawing of the retinal model and determine the characteristic regions of the human retina!

8 Perimetry: determining the field of vision Rods and cones are distributed in the retina in an uneven manner rods: sensing light and movements cones: colour vision optic disc (blind spot): exit site of the retinal axons field of vision: surface area of the retina capable of percepting light and/or colour informatin

9 Task 3: Perimetry A) Determination of the field of view Subject places his/her chin onto the holder of the perimeter so that one eye faces the middle of the perimeter. The other eye is covered. Director places a recording sheet into the back of the perimeter, corresponding to the eye used for the experiment. Director positions the moving dot into the middle of the perimeter and slowly moves it outwards. Subject focuses onto the middle of the perimeter and signals when (s)he loses sight of the outside moving point from his/her field of view - Director marks this position on the recording sheet. The arm of the perimeter is turned by 10, the point is positioned back to the middle and the whole procedure is repeated. Record the complete field of view, using the white dot! Determine the position of the blind spot!

10 Task 3: Perimetry B) Comparing black-and-white and colour vision Change the white dot to red or green and determine the field of colour view (this time the Subject should indicate how long (s)he sees the colour of the moving dot!) Repeat the same procedure as before, using the same recording sheet. Compare the field of view in case of using the white or the coloured dot! Compare the position of the blind spot under the two experiments! Explain your findings!

11 Accommodation and the near point of vision Increase in the curvature of the lens for near vision is called accommodation. Near point of vision is the minimum distance from the eye that an object can be clearly focused. Refraction is the bending of light rays. The cornea and lens refract light rays.

12 Refraction abnormalities and their correction Nearsightedness (myopia)- close objects are seen clearly. Image is focused in front of the retina. Correction: use of concave lens. Farsightedness (hyperopia)- distant objects are seen clearly. Image is focused behind the retina. Correction: use of convex lens.

13 Task 4: Testing visual abilities A) Accomodation and near point of vision Determine the minimum distance from the eye within which a normal text can be read! Compare the results between Subjects with myopia / hypermetropia B) Sharpness of vision Stand 5m distance from the test numbers; determine which numbers you can read correctly using only one eye at one time! Compare the results between Subjects with myopia / hypermetropia and between the left and right eyes of the same Subjects

14 Task 4: Testing visual abilities C) Astigmatism (irregular curvature of the cornea and/or the lense) Director and Subject sit face to face. Director holds the Placido's disc with the concentric rings facing the Subject with the disc lit from the side by a lamp. Director peaks through the middle of the keratoscope, leans close to the Subject and check the mirror image of the keratoscope over the surface of the Subject's cornea. Describe the findings and determine whether the Subject has corneal astigmatism! Placido's disc (keratoscope)

15 Rods and Cones structure of the retina Named after the shapes of their outer segments. Cones: three types: red, green and blue. Outer segment- contains photopigments. Transduction of light energy into receptor potential occurs here. Inner segment- contains the nucleus, Golgi complex and mitochondria. rod cone

16 Photopigments Two parts: opsin (four types, three in the cones and one in the rod) and retinal (light absorbing part). Absorption of light by a photopigment structural changes. Color blindness and night blindness Color blindness- inherited inability to distinguish between certain colors. Result from the absence of one of the three types of cones. Most common type: red-green color blindness. Night blindness or Nyctalopia- vitamin A deficiency.

17 Stilling-Ishihara plates

18 Stilling-Ishihara plates

19 Task 5: Testing normal colour vision Determine the correctness of the Subject's colour vision by the Ishihara tables. Compare the results between different Subjects.

20 The visual pathway Receptor potential in rods and cones graded potentials in bipolar neurons and horizontal cells nerve impulses in ganglion cells optic nerve optic chiasm optic tract thalamus primary visual area of cerebral cortex in occipital lobe.

21 Partially overlapping fields of view

22 Task 6: Determining the dominant eye Look for a small object at ~5-10m distance with both eyes opened. Point to the object with your forefinger. While the hand remains in position, close first the left and then the right eye. Describe the observed findings and explain them!

23 Anatomy of the ear

24 Events in the stimulation of auditory receptors Malleus Incus Stapes vibrating in oval window Helicotrema Cochlea Sound waves Perilymph External auditory canal Tympanic membrane Secondary tympanic membrane vibrating in round window Middle ear 8 Scala 7 tympani Scala vestibuli 6 Basilar membrane Spiral organ (organ of Corti) Tectorial membrane Vestibular membrane Cochlear duct (contains endolymph) Auditory tube

25 The auditory pathway

26 Task 7: Rinne's test: comparison of air vs bone conductance Place the vibrating soundfork first close to your ears and measue how long the tone is heard (air conductance). Once you can not hear the tone any longer, press the still vibrating sound fork 1) to the top of your skull or 2) to your teeth (bone conductance), and determine whether and how long the tone is heard. Repeat the above experiment in the opposite order! Determine the time period during which the tone can be recognized in case of the air or bone conductance! Which type of conductance provides longer lasting effects? Explain your results!

27 entire audible range: 20 to Hz; most precisely heard range is 500 to 5000 Hz frequency of sound waves determines the pitch of the sound (the higher the frequency of vibration, the higher the pitch is) intensity of the sound waves determines the loudness of the sound (measured in decibel; db) Audiometry hearing threshold: the minimum sound intensity needed at a given frequency to be percepted lowest hearing threshold exists normally for the most precisely heard range (500 to 5000 Hz)

28 Task 8: Audiometry With the aid of the automated audiometry software, determine hearing threshold values for one ear, using test tones with 500, 800, 1000, 2000, 3000 and 5000 Hz frequencies! Describe the observed findings and explain them!

29 The human skin

30 Sensory receptors in the skin - tactile sensations Include touch, pressure, vibration, itch and tickle. Tactile receptors in the skin are Meissner corpuscles, hair root plexuses, Merkel discs, Ruffini corpuscles, pacinian corpuscles, and free nerve endings.

31 Task 9: Tactile sensitivity Director should determine the smallest distance what the Subject can discriminate on his/her 1) face, 2) forehand, 3) palm, 4) finger, 5) lower arm, 6) upper arm, 7) at the back, 8) lower leg without looking at the touches. List the observed findings and measurements and explain them!

32 Sensory receptors in the skin - thermal sensations free nerve endings 1 mm below the skin surface cold receptors: react between 10ºC to 40ºC hot receptors: react between 32ºC to 48ºC fast adaptation

33 Task 10: Thermal sensitivity Prepare 3 beakers with water: 1) left: cold water 2) middle: room temperature water 3) right: warm water Place the left hand into the left, the right hand into the right beaker, and wait until the hands accustome to the different temperatures. Following this, immerse both hands into the same, middle beaker containing the room temperature water! Describe the observed findings and explain them!