3.  sensory transduction ◦ - conversion of physical energy from the environment into changes in electrical potential  sensory coding- ◦ Making sense of that input

4.  vision - light waves -  taste – chemicals in fluid –  hearing – sound waves-  touch- pressure, temperature changes,  smell- chemical in air

5.  vision-  taste - -  hearing - -  touch-  smell-

6.  Receptors show adaptation ◦ most sensitive to changes rather than constant stimulation ◦ why is this important?

7.  General pathway for most sensory information: ◦ sensory neurons – sensory nerves  spinal tracts –  thalamus –  primary cortex –  higher association cortex

8. Certain sensory neurons have a spontaneous firing rate. For these cells any change in their firing rate will convey important info (i.e. color vision) Different rhythms of firing also can convey different information

9. * most highly developed sense in humans optic nerve for one eye - 1,000,000 axons auditory nerve contains about 30,000 axons adaptability and plasticity of visual system - make sense out of nonsense

10.  iris ◦ largely a muscle that expands and contracts pupil in response to light ◦ phenotypically unique –  iris scan  sclera ◦ tough opaque tissue  pupil ◦ often used to determine neurological function

11.  light waves along the visual spectrum

14. 1. inverted image on retina 2. region important for transduction is at very back of the eye

15. retina - structure of eye important for transduction - retina contains neurons, glial cells and two types of photoreceptors

16.  responsible for transduction  numerous differences between rods and cones

17.  rods  shaped like a rod  cones  shaped like a cone

19.  a low ratio of synaptic connections between neurons ensures higher definition and sharpness compared to a higher ratio

20. less sharp focused visual input

21.  rods  shaped like a rod  insensitive to color  work well under low illumination  20,000,000/eye  location: found around the periphery of the retina  requires extended time until optimal function  cones  shaped like a cone  sensitive to color  work best in bright light  5,000,000/eye  location – found around the fovea of the retina  responsible for sharp images and vision  works optimally very quickly

22.  there are at least two levels of communication within the neural cells of the eye ◦ rods and cones – bipolar cells – ganglion cells (axons make up the optic nerve) to CNS

24.  there are at least two levels of communication within the neural cells of the eye ◦ rods and cones – bipolar cells – ganglion cells (axons make up the optic nerve) to CNS ◦ across a single layer (rods and cones communicate with each other; bipolar cells communicate with each other; etc)

26. optic nerve (ganglion cell axons) – make a blind spot on each eye!

28. 8 inches

29.  component (trichromatic ) or Young- Helmholz ◦ occurs at level of cones  3 different cones more sensitive to different wavelengths (ie colors)

31.  trichromatic or Young-Helmholz ◦ occurs at level of cones  explains major type of color blindness ◦ deficits in certain types of cones can explain major type of color blindness 

32.  At level of cones- GREAT! ◦ there are different cones that produce greater changes in electrical potentials depending on the color (wave) ◦ abnormalities in cones can explain red/green color blindness

33.  Very rare to see complete color blindness - only usually seen with brain injury  ~ 7% of US males (10,000,000) compared to 0.4% women - red/green  X-linked phenomenon

35. 35  What happens in hereditary color deficiency?  Red or green cone peak sensitivity is shifted.  Red or green cones absent.

36. 36 BRG 437 nm564 nm 533 nm

37. 37 BR G 437 nm564 nm (green shifted toward red) 5% of Males

38.  At level of cones- GREAT!

39.  negative afterimage – ◦ phenomenon that occurs as a result of overactivity or inhibition of neurons (due to color stimulation)

40.  opponent process theory ◦ occurs at level of bipolar cells and higher  black/white, red/green; yellow/blue; one color excites bipolar cell; other color inhibits it

43.  says nothing about complexity as information reaches occipital lobe –  prestriate – primary occipital cortex; multiple layers of higher association cortex

47. Copyright © 2006 by Allyn and Bacon