Module 18: Vision

Module 18: Vision

Sensory and Perceptual Processing

Open Ended

Consider your eyes. What exactly do they do? How do your eyes interpret images that you see?

Light Energy and Eye Structures

• our eyes receive light energy and transduce (transform it into neural messages)

• when looking at a red thing, your eyes are interpreting the color red from pulses of electromagentic energy that your visual system perceives it as red

Review: Light Energy

• Humans can only see a small fraction of waves

• Other animals such as bees can see more waves than us but not the colors

Light Waves

• light travels in waves

• shape of those waves influences what we see

• wavelength is the distance between one wave peak to the other

• Wavelength determines hue (color we see)

• Light wave's amplitude (height) determines its intensity - amount of energy the wave contains

• Intensity influences brightness

The Eye

• light enters the eye through the cornea

• Cornea bends light to provide focus

• Light then passes through the pupil (a small adjustable opening)

• The pupil is surrounded by the iris (colored muscle that dilates or constricts in response to light intensity)

• Each iris is so distinctive that an iris-scanning machine can confirm your identity

The Eye

• Iris responds to your cognitive and emotional states

• Ex. Your eyes dilate in a dark room

• Ex. Iris constricts when you answer no or feel disgust

• Ex. Your eyes can also reflect your feelings of love.

Eye

• After light passes through your pupil, light hits the transparent lens in your eye.

• Lens focuses the light rays into an image on your retina.

• Retina is a multilayered tissue on the eye

Eye

• to focus the rays, the lens changes its curvature and thickness - process called accommodation

• if the lens focuses the image on a point in front of the retina, you can see near objects clearly but not distant objects. - nearsightedness (myopia)

• Remedied by glasses, contact lenses, surgery

Poll

How does the eye receive images?

• Upright

• Downright

Open Ended

What is the difference between being nearsighted and farsighted?

Images and the Eye

• Da Vinci believed that the eye's fluid bent light rays

• Johannes Kepler in 1604 disproved this idea by proving the eye did receive images upside down but could not explain how it worked

The Eye Today

• Retina does not "see" a whole image

• Millions of receptor cells convert particles of light energy into neural impulses and send those to the brain which resembles them into an image we see as upright

• visual information percolates through progressively more abstract levels

• Happens very quickly!

The Eye To Brain Pathway

• AP Note on pg. 178

• back of retina - receptor cells

• Rods and Cones

• Light energy triggers chemical changes

• Sparks Bipolar cells

• then activate ganglion cells

Open Ended

What does the optic nerve do?