From stimulus to sensation

2025-02-11

Rick Gilmore

Prelude

JimmyCliffVEVO (2014)

Overview

In the news…

“Fossil-fuel subsidies per capita, 2021” (n.d.)

https://www.reddit.com/r/dataisugly/comments/1imj4cq/where_to_begin_with_this_one/#lightbox

Announcements

Last time…

  • More figure types

Bar/column

Stacked vs. Lollipop

Pie/ring

1D summaries of continuous data

2D scatterplots

Your Ex-03 Surveys

  • Excerpts from figures generated by Google Forms

Today

  • What is vision for?
  • Information in light
  • Detecting information in light

What is vision for?

Information at a distance

James Webb space telescope deep field “Webb’s first deep field (NIRCam image)” (n.d.)

Nature’s speed demon/speed limit

  • Light (+ radiowaves) circumnavigate the Earth in ~133 ms

https://w3tm.org

  • Earth ~8.3 light-minutes from the Sun

Where is it/am I?

  • Azimuth (left/right)
  • Elevation (up/down)
  • Distance (near/far)
  • Orientation

What is it?

  • Edges \(\rightarrow\)
  • Surfaces \(\rightarrow\)
  • Objects or entities

Regarding data figures…

  • What are the figure components
    • Data points, text, bars/segments/rings/boxes
  • Where are different components relative to one another, axes, etc.
  • How do figure components convey information about data?

Information in light

Cairo (2013) Figure 5.12

Electromagnetic spectrum

EM spectrum from Wikipedia

Surfaces reflect/absorb or emit

Source: https://www.cns.nyu.edu/~david/courses/perception/lecturenotes/color/color-slides/Slide14.jpg

Different surfaces == Different reflection/absorption

  • Perceived color differences correspond to different patterns of light reflection.

Randeberg (2005)

Artificial sources

Spatial patterns on retina

  • depend on object geometry and orientation

Source: https://thebrain.mcgill.ca

Source: https://thebrain.mcgill.ca

Detecting information in light

What information?

  • Position
  • Length
  • Area
  • Color
  • Texture
  • (Motion)

The eye

is like an auto-focus, auto-exposure camera…

part of a self-stabilizing system…

Bucalo (2015)

Eye + head + body system

Note

  • Eye + head + body movements align and point the eyes
  • Eye + head + body movements stabilize the eyes
    • When the observer moves
    • When objects move

Demo

  • May I have a volunteer?

Image formation

  • Eye’s optical components
    • Cornea (fixed refraction)
    • Iris/pupil (modifiable aperture)
    • Lens (modifiable refraction)
  • Create projection (image) on retina

The retina…

  • samples spatial patterns of light intensity & wavelength patterns

‘Wavelength-tuned’ photoreceptors

Source: Wikipedia

Retinal rods (green) & cones (blue)

…arranged in mosaics

Normal color vision vs. protanopic (color blind) vision; Source: https://en.wikipedia.org/wiki/Retinal_mosaic

with different concentrations in different parts of the retina

Wikipedia

Consequences

  • Must move eyes to position highest resolution part of retina over target
  • Keep track of sequence of eye movements and positions over time
  • Integrate sequence of samples over time

Cairo (2013) Figure 5.6

Information processing

  • Separate channels for short, medium, long wavelengths (cones): chromatic (color)
  • Black/gray/white or overall illumination (rods): achromatic (dark/light)
  • ~120 M rods + ~ 5 M cones (125 M) vs. professional cameras with 100 M pixels
  • Point by point, topographic (map-like) 2D image of 3D world
  • Non-uniform resolution (center >> periphery)
  • yields focused image except…

…when eye misshapen for cornea +lens

Acuity

  • Detail/pattern vision
  • Grating acuity
  • Vernier
  • Symbol/letter (optotype) acuity

Contrast sensitivity

  • Light/dark ratio (contast)
  • vs. spatial frequency (level of detail)
  • Contrast -> edges; edges -> shape/form
  • e.g., driving in fog

Contrast sensitivity function

Pelli-Robson Contrast Sensitivity Chart

Color perception

  • Perceived color a function of activity in “R”, “G”, and “B” photoreceptors

Source: Wikipedia

Wavelengths are continuous, but are perceived colors?

https://rmit.pressbooks.pub/colourtheory1/part/2-colour-theory-the-visible-spectrum/

Perceived colors seem ordinal, but…

  • Color is a neuropsychological construct

Color vision anomalies

  • Absence of or anomalies in photoreceptors

Wong (2011) Figure 1

Types

  • Protanopia (impaired R/long wavelength)
  • Deuteranopia (impaired G/medium wavelength)
  • Tritanopia (impaired B/short wavelength)

https://www.color-blindness.com/protanopia-red-green-color-blindness/

Color palettes

Wong (2011) Figure 2

Some consequences for data figures

  • Size of visual elements (symbols, including text)
  • Contrast (light/dark or color)
  • Textures of visual patterns
  • Some colors more visible than others
  • How much visual scanning (# of eye movements)?

Your turn

Evaluating figures

Main points

  • Visual perception a reconstruction of reality
  • Continuous pattern of light \(\rightarrow\) intensity detected by 4 photoreceptor types
  • Retina has non-uniform sensivity to light, so some information more easily detected

Next time

From cognition to understanding

Resources

References

Bucalo, P. (2015, October). Falcon belly dance. Youtube. Retrieved from https://www.youtube.com/watch?v=JGArTWOJtXs
Cairo, A. (2013). The functional art: An introduction to information graphics and visualization. Upper Saddle River, N: New Riders Publishing.
Fossil-fuel subsidies per capita, 2021. (n.d.). Retrieved February 10, 2025, from https://ourworldindata.org/grapher/fossil-fuel-subsidies-per-capita
JimmyCliffVEVO. (2014). Jimmy cliff - I can see clearly now (video version). Youtube. Retrieved from https://www.youtube.com/watch?v=MrHxhQPOO2c
Randeberg, L. (2005). Diagnostic applications of diffuse reflectance spectroscopy. Retrieved from https://www.semanticscholar.org/paper/ec9450b79923e2e2152b54ab9241b60bc5374944
Webb’s first deep field (NIRCam image). (n.d.). Retrieved January 11, 2024, from https://webbtelescope.org/contents/media/images/2022/035/01G7DCWB7137MYJ05CSH1Q5Z1Z
Wong, B. (2011). Color blindness. Nature Methods, 8, 441. https://doi.org/10.1038/nmeth.1618