1. Ch 6: The Visual System

2. Think about it…
The light from the outside world enters your eye and creates a 2-D upside-down image on your retina…
Yet somehow, your brain is able to translate it into a complex 3-D representation of the world around you!

3. Light With no light, there is no vision.
Light can be quantified as particles called photons
Simultaneously, it is a wave
For humans, the visible light spectrum is nm
Other species can see beyond this range
Wavelength value dictates the color seen
Intensity is related to the brightness of the light

5. Light Entering the Eye
The amount of light entering the eye through the pupil depends on the constriction of the muscles of the iris.
The eye will dilate and contract to accommodate for changes in the ambient illumination; balancing sensitivity & acuity.

6. Light Entering the Eye
Sensitivity: ability to detect dimly lit objects
Acuity: ability to see the details of objects
Must tradeoff between the two
Illumination high:
Sensitivity not important, constrict pupils & get a sharper image and greater depth of focus
Illumination low:
Pupils dilate to let available light in, sacrifice depth of focus and acuity

7. Light Entering the Eye
Behind the pupil is the lens, which focuses the incoming light onto the retina.
Depending on the distance of the object, the ciliary muscles will adjust the shape of the lens
This changes the refraction or bending of the light so it will come into sharp focus on the retina

8. 2 Eyes
We have a pair of eyes because, as vertebrates, we have 2 sides.
The common set up is to have one eye on each side, which allows the animal to see in most directions without moving their heads.
Along with some other animals, we have our eyes positioned front-facing
This allows us to have depth perception

9. 2 Eyes

10. 2 Eyes
The movements of your 2 eyes are coordinated, so that the visual input from each of your eyes comes to the same point on your retina