Visualization for Machine Learning

Spring 2024

Perception for Design

Brain

“Visual thinking consists of a series of acts of attention, driving eye movements, and tuning our pattern finding circuits”, Colin Aware

The Vision Brain

“Visual thinking consists of a series of acts of attention, driving eye movements, and tuning our pattern finding circuits”, Colin Aware

The Act of Perception

• Botton-Up and Top-Down Processes

The Act of Perception

• Bottom-up: information is sucessively selected and filtered into patterns as it passes a sequence of stages. Ware outlines three stages: 1) optical nerve to V1 Cortex; 2) use texture and colors to aggregate patterns; 3) visual objects are recognized in the visual working memory.

The Act of Perception

• Top-Down: Every stage of bottom-up processing contains a corresponding top-down process. Ware describes the process as “attention”. The dominant principle is that we only get the information that we need, when we need it.

The Implications for Design

• “Just-in-time visual queries” (Ware)

• “One way to look at the brain operates is a set of nested loops. Outer loops deal with generality while inner loops process detail.” (Ware)

Low-Level Feature Analysis

• David Hubel and Torsten Wiesel won Nobel prize for this discovery.

What and Where Pathways

• What: identification of objects in environment.
• Where: location of objects and eye movement.

What Stands Out (Popout)

• Anne Triesman studied how to find patterns and shapes when surrounded by others.

For some configurations the time did not depend on the number of distracters (pre-attentive).

What Stands Out (Popout)

The Gestalt Principles link, see video

• Visualization is a two-way street:
  • We (the vis designer) bring something to the table.
  • The human (end user) brings their prior experience.
• Design should take such prior experience into account!
• What is prior experience? Gestalt laws.

Closure

• We can complete incomplete shapes

• Implications: visualizations can be unintentionally misleading! Conversely: sometimes only necessary to show sparse set of marks to convey trend (dot plot)

Similarity

• Elements with the same visual properties considered to be grouped

Similarity

• Elements with the same visual properties considered to be grouped

Proximity

• Elements that are of close spatial proximity are somehow grouped.

Proximity

• Elements that are of close spatial proximity are somehow grouped.

Enclosure

• Explicit visual encoding of enclosure also depicts grouping.

Enclosure

• Explicit visual encoding of enclosure also depicts grouping.

Bubblesets video link

Connection

• Objects connected together are perceived as a group.

Connection

• Objects connected together are perceived as a group.

Connection

• Objects connected together are perceived as a group.

Connection

• Objects connected together are perceived as a group.

Just Noticeable Difference (JND)

• In psychophysics a just-noticeable difference or JND is the amount something must be changed in order for a difference to be noticeable, detectable at least half the time.

• Stevens’s power law: link

Accuracy

• How accurately a channel can express quantitative information

Graphical Perception

Graphical Perception Experiment

Graphical Perception Results

Accuracy

• Position > Length and Angle > Area

• Prioritize high-rank channels (with reason)

• Do not expect precise judgments from low-rank channels

Effectiveness Effect

Discriminability

• How many distinct values can be distinguished within a channel

• It depends on:

  • Channel properties
  • Spatial arrangement
  • Size (resolution)
  • Cardinality

• Warning: Do not overestimate the number of values viewers can perceive/discriminate

Discriminability

• Many channels, in particular identity channels, can only support a limited number of discriminable levels.
  • Line width is one of the most limited with perhaps 3 levels.
  • Using more than 5 or 6 color hues is not recommended.
  • Similarly, using more than 5 or 6 symbol shapes can create difficulties.
• If the number of levels that can be represented by a channel is smaller than the number of attribute levels then some form of meaningful aggregation is needed.

Popout

• Tasks performed in less than 200 to 250 milliseconds.

• Faster than eyes movement initiation.

• Suggest processing by parallel low-level visual system.

Popout

Some features are not pre-attentive

Tasks requiring the use of multiple channels are (most of the time) not preattentive

Separability

• Amount of interference between channels

Relative vs Absolute