Carefully Arranged Sand and Lightning

Presentation Deck


We see by detecting electromagnetic radiation that reaches our eyes. The information we gather by sight is only a small amount of the information present in the EM field.

We can only see the EM radiation with wavelengths from around 390nm to 700nm that happens enter our pupils. We have limited ability to discern frequencies even in the visible range, and we can’t* detect light polarization.

Even with these constraints, we are able to glean a highly detailed understanding of our surroundings. Vision is perhaps our most powerful sense. We are especially good at building a spacial understanding of our environment based based on light.


Emissive Color

Reflective/Absorptive Color

Visible EM Range

EM Radiation

Cone Response

Our Eyes

Color Sensitivity
Able to perceive electromagnetic waves from 390 to 700nm, and can differentiate hues as close as 1-10 nm.
Trichromatic sensors for red, green, blue.
Contrast Sensitivity
Have a contrast range something like 1:1000000 (20+ stops). Film cameras are 9-10, high end digital camera are a little better. A typical screen might have a true contrast ratio of 1:1000.
Angular resolution
Our eyes focus light through a lens, providing directional information at a resolution of about 1 arcminute or .02°. Thats about 250 dpi at one foot away, 3 pixels/mm at 1 meter, or something 6 inches wide about a mile away. We can see things much smaller than this, when they are bright, we just can’t understand their shape. For example a bright led would be easily visible a mile away in a dark environment.
Field of View
~ 160° x 175° But resolution is very center biased. Foviated rendering
Frame Rate
Our eyes don’t have a frame rate like a camera in which all the photo-sensors refresh in unison at a set rate. We can generally differentiate a solid light from a flickering one, up to 60+ hz.

Vision Impairment

Our Visual Cortex

Our Visual Cortex processes the data collected by our eyes to provide information about our environment.


Our understanding of color and color theory—primary colors and color wheels—is informed from the anatomy of our eye and the way our mind processes vision.

We consider a color as a single value: dark blue, pink, vivid green. We don’t think about the color of something as a little bit green, a little bit blue, and a lot red. We definitely don’t think of color as the sum of the many in-between wavelengths.


Sound is an audible wave of pressure that propagates through the air. Sound begins when something in contact with the air vibrates. As that thing pushes forward, it pushes the particles of air in front of it forward into the the particles of air in front of them. Making an area of higher pressure. This high pressure area pushes out in all directions, and a wave of pressure begins to propagate though the air.

This pressure wave can push on other things like microphones and our ears. Our ears are able to detect very rapid and subtle changes in this pressure. And we are then able to understand the amplitude, frequency, and even “shape” of these changes. Because we have two ears, spaced a few inches apart, we can compare what each ear hears to gain spacial information as well.


How Hearing Works

Our Ears

Pitch Sensitivity
We can hear pitches from 20hz to 20,000hz, and can differentiate frequencies as close as 5 cents (.15hz at Middle C). Pitches are detected by 16,000-20,000 hairs in a curled up tube, the cochlea. The hairs in the cochlea are each “tuned” to different frequencies. For reference, an 88 Key Piano ranges from A0 (27.5 hz) to C8 (4186.01 hz).
Loudness Sensitivity
We can detect pressure changes < 1 billionth of the atmospheric pressure. We can hear sounds 10 trillion times louder than that, at which point they start hurting.
We have the ability to detect “quality” of a tone based on overtones and other information.
Hearing Impairment
About 15% of Americans have some hearing loss. About 8% would benefit from using hearing aids.

Sensitivity of Human Ear

Our Auditory Cortex

Our Auditory Cortex processes the data collected by our ears to provide information about our environment.

Wikipedia: Sound

Auditory Illusions

Vision vs. Hearing

Our visual and auditory sensory systems prioritize different types of information.

Vision Hearing
Two Eyes Two Ears
EM Air Pressure
120 million sensors each ~18k sensors each
1 + 3 frequency responses thousands of frequency responses
Lens + spatially arranged No Lens + not spatially arranged
160° FOV 360° FOV
Contrast 1:1,000,000 Contrast 1:10,000,000,000
great at spatial understanding great at spectral understanding

We see a single color at a very specific point. We hear chords from a general direction.

Vision + Hearing

Our visual and auditory sensory systems support one another.

McGurk Effect

Key Takeaways