The Senses
The Senses
The five classical senses attributed to Aristotle (384BC – 322BC)
1.
2.
3.
4.
5.
Sight
Hearing
Taste
Smell
Touch
The Senses
In addition we now know of other senses that include
1.
2.
3.
4.
Temperature
Pain
Balance and Acceleration
Internal Sensors:
1. Stretching
2. Pressure (eg Blood pressure)
3. Chemoreceptors (eg CO2)
4. Osmoreceptors
5. Body awareness
The Eye
Characteristics:
1.
2.
3.
4.
Self-focusing
Adjusts for light intensity (adaptation, night or day)
Auto tracking
Real-time video feed with large scale parallel processing of
100 million pixels, preprocessed down to 1.2 million nerve
fibers.
5. Self cleaning
6. Binocular vison to give depth information
The Eye
Figure 10-27
Cross-section
Figure 10-28a
Figure 10-28b
Figure 10-29b
http://www.morphonix.com/software/education/science/brain/game/specimens/wet_brain.html
Figure 10-29c
Split Brain
Some treatments of epilepsy involve the
cutting of the corpus callosum, a wiring
bridge between the two halves of the brain.
It is known that the language center is
usually on the left side of the brain.
Thalamus
It has been observed in these patients the
following effect.
Observe an object with the left visual
field and the patient will be unable to tell
you what the object is called, but they will
know what it is for.
On the other hand, show an object with the
right visual field and the patient will be
able to name the object but not tell you
what it is for.
http://instruct.uwo.ca/anatomy/530/vistopo.gif
Focusing
About two thirds of focusing occurs in the cornea,
the rest is carried out by the lens for fine tuning.
Figure 10-30 - Overview
Figure 10-30 - Overview
Figure 10-31 - Overview
When the ciliary muscle is relaxed the ligaments are taut, and the lens is
stretched thin enabling it to focus on distant objects. When the ciliary
muscle is contracted the suspensory ligaments become less taut, and the
lens becomes rounder so that it focus on objects that are nearby.
Figure 10-32b
Hyperopia
Hyperopia
Use a convex lens to correct.
Myopia
Myopia
Use a concave lens to correct.
Astigmatism
Astigmatism is caused by either the eye's cornea
(corneal astigmatism) or lens (lenticular astigmatism)
having an irregular shape.
Figure 10-35a
Figure 10-36
Figure 10-35c
Rods: Black/White
Cones: Color
Figure 10-37 - Overview (1 of 6)
Rod and Cone Characteristics
Characteristic
Cones
Rods
Shape
Pointy
Blunt
Number
~ 5 million
~ 100 million
Light Conditions
Well lit
Dimly lit
Acuity (Sharpness)
Excellent
Poor
Sensitivity
Poor
Excellent
Disk Shedding
Evening
Morning
Photopigments
3
1
Figure 10-37 - Overview (1 of 6)
Distribution of Rods and Cones
http://www.webexhibits.org/colorart/i/distribution-of-cones-475.gif
Figure 10-38
Figure 10-35b
Figure 10-35d
Figure 10-35e
Complex Processing
The retina circuitry performs some complex parallel
processing including:
1. Edge detection (contrast enhancement)
2. Sensitivity adaptation
3. Computing rates of change.
See Scientific American, May 2005, p58.
Neuromorphic Microchips
Figure 10-35e
Figure 10-37 (6 of 6)
Figure 10-39 - Overview
Other Animals
Most fish, frogs, turtles and birds have 3 to 5 types of cones (ultraviolet).
Some predators (eg dog, cat) have a visual streak rather than a fovea,
presumably to track fast moving prey (Some prey have a similar feature).
Most non-primates are biased towards green and blue (red is poor).
Many animals have a reflective layer at the back of the retina called the
Tapetum luncidum. The red eye we see in humans is due to blood vessels.
http://cas.bellarmine.edu/tietjen/images/tapetum%20lucidum.htm
Cephalopods
Light
Different photoreceptors and problem color blind
http://io.uwinnipeg.ca/~simmons/16cm05/1116/33-22-CephalopodsCollage.jpg
Assignment: Watch this video
Kwabena Boahen (Stanford):
Making a computer that works like the brain
http://www.youtube.com/watch?v=nyLYQYHGbvI