Perception and cognition lec 2
o Light: a wave, stream of photons, tiny particles that each consist of one quantum of
o We are sensitive to 400-700 nanometers in wavelengths
Absorbed: energy is taken up by a medium and transformed to another form of
Transmitted: convey light from one place to another through a transparent
Reflected: energy that is redirected when it strikes a surface
Purkinje reflections, eye movements
o When shining light on an eye, you typically see 4 reflections of
light on that eye. (front/back of schlera, front/back of lense)
o Eye tracking uses this
Diffracted: Bent or having waves that are spread out, (e.g., waves of sound or
light as they encounter an obstacle, e.g. pass through a narrow apature)
Refracted: Energy is altered in its path as it passes into another medium, (eg:
light passing through air, and then water)
Light gets bent, therefore a pencil in water looks bent
Works with lenses too
o Most important sense
Advantage over touch in detection from a distance.
o Evolution of the eye
Photosensitive pigments with which you can sense light, information is
passed to brain.
Depression in photoreceptors can help indicate where light is coming
from, but work better with a smaller aperture.
o “pinhole” eye allows finer directional sensitivity and limited
Light sensitive protein: opsin
Development of membrane to cover cavity. Transparent humor develops inside.
Lens develops to more accurately refract light
Iris and separate cornea develop
Cornea in humans has stronger refraction rate than lens
o Learn all components of the eyeball on slides
o Refraction is necessary to focus light rays. This is done by the four optical components.
The ciliary muscles change the shape of the lens, and thus alters its refractive
The closer an object, the more the ciliary muscles contracts to bend the light
onto the same point on the retina This is called accommodation
o Myopia is caused by the eyeball being too long for the lens
Refractory power of the lens is stronger than it has to be, light points diverge on
o All blood vessels converge on the optic disk
o Light must pass through many structures in retina before hitting the photoreceptors
It is a bit illogical because it is not processed until it hits photoreceptors.
Information is then passed on to horizontal/bipolar cells, then ganglion cells.
o Photoreceptors: cells in the retina that initially transducer light energy into neural
energy. Duplex retinas:
Rods: Photoreceptors that are specialized for night = scotopic vision (90 million)
Cones: Photoreceptors that are specialized for daylight = photopic vision, fine
visual acuity and color (4-5 million)
Some animals have mostly rod retinas
3 photoreceptor for circadian rhythm
o Fovea is not sensitive enough for night vision
o Visual pigments are molecules with two parts
Chromosphore (captures photons)