Tag Archives: Discriminability

An End to “Death by PowerPoint”: Neuroimaging Studies Improve Visual Display Design

Stephen Kosslyn

Stephen Kosslyn

Harvard’s Stephen Kosslyn‘s fMRI studies of perceptual processes and mental imagery point to  best practices in improving visual display design, such as PowerPoint presentations, so they can be rapidly comprehended.

Alexandra Russell

Alexandra Russell

His imaging studies determined that the left half of the brain excels at encoding categories and generating mental images based on categories.
In contrast he reported that the right half of the brain skillfully encodes specific examples and generating associated images.

While at Stanford, he identified eight psychological principles often violated in PowerPoint® slideshows, in collaboration with Alexandra G. Russell, Harvard colleague Jennifer M. Shephard and Rogier A. Kievit of University of Amsterdam.

Once the viewer has seen a PowerPoint slide, the information must be converted into a storable and retrievable construct for later use.

Rogier Kievit

Rogier Kievit

They noted that perception and comprehension of visual displays require:

  • Encoding based on Discriminability, Perceptual Organization, Salience
  • Working Memory, influenced by Limited Capacity and Informative Changes
  • Accessing Long-Term Memory, enhanced by Appropriate Knowledge, Compatibility, Relevance

 Encodable content must be distinguishable from the background and context.
This requires a “Just Noticeable Difference” (JND) between size, shape, color and other attributes to enable discrimination.

Russell De Valois

Russell De Valois

PowerPoint elements achieve Discriminability with:

  • Sufficiently large typeface with differentiated text (mix of upper case, lower case, bold, italics)
  • Text and graphic color contrast with background color
  • Spatial frequency channel” ratio variance, such as points that are twice as thick as the lines that connect them
    Karen De Valois

    Karen De Valois

    Texture patterns elements, like stripes, should vary by at ratio of least 2:1 to avoid “visual beats,” according to University of California’s Russell DeValois and Karen De Valois

  • Varied line orientation (by at least 30°), to enable processing by different “orientation channels
  • Text or other fine lines in colors other than deep blues, and boundaries in colors other than red.

After encoding, figure/ground segregation processes perceptually organize adjacent (“Law of Proximity”) and similar (“Law of Similarity”) elements into groups of objects, words, and graphics.
Grouping also can be imposed by lines, such as in complex data tables, and this grouping typically increases readability and comprehension.

Additional practices to enhance visual “consumability” by Perceptual Organization include:

  • Applying labels to refer to the nearest graphic element
  • Using a common color to organize parts of a display into a group, even separated
  • Adopting consistent ordering conventions across different parts of displays, such as bar chart legends and pie chart legends
  • Explicitly grouping separated-but-related elements, such as by using inner grid lines to group the tops of bars in a bar graph with locations along the Y axis at the left of the graph
  • Eliminating inadvertently-formed groupings, such as when a banner at the top of a slide groups with nearby, similar but unrelated objects

 Attention is drawn to large perceptible differences, and these elements are processed in detail.  The brain’s superior colliculus draws visual attention to large differences among stimuli.
Salience can be enhanced with:

  • Animation because movement captures and directs attention
  • Text with a distinct format, such as color, size, or typeface
  • Visual incongruities, such as a wedge “exploding” from a pie chart
  • Summary elements like title, keywords, topic sentence, infographic
  • Warm” colors (with longer wavelengths, such as red) for emphasis or in the foreground in contrast to “cool” colors (with short wavelengths, like blue), which recede.
    Avoid using warmer colors for lines that pass beneath other lines to avoid the illusion of background oscillation

After visual patterns are encoded, they must be integrated in Working Memory for later retrieval and application, and are influenced by Limited Capacity and Informative Changes.
People have limited capacity to process and retain information, and presentations can mitigate these constraints by:

  • Limiting perceptual groups to about four units with up to four sub-units for easier processing and retrieval
  • Labeling items in a display rather than using a key or legend to reduce processing load
  • Allowing the audience time to process and assimilate information during a slide presentation
  • Avoiding slow fade-in or fade-out slides, which may lead to incorrect information processing and losing track of the organizational hierarchy.Audience members expect Informative Changes in words and graphics to convey information.
    Similarly, they also expect that each expect unit of information is associated with a perceptible change.
    Capitalize on these expectations by:
  • Avoiding random or arbitrary changes in appearance, transitions, or terminology
  • Clearly indicating section beginnings and ends to enable audience to track progress through the presentation

Retrieving information from Long-Term Memory enables viewers to compare with previously stored information to determine the new information’s relevance and applicability.

Effective presenters ensure that viewers have a common knowledge base of novel concepts, jargon, conventions, formats, terminology or symbols so they understand the presentation’s context.
Presenters ensure Appropriate Knowledge by including an explicit introduction, and explanation and review of these terms and ideas before building reasoning and conclusions.

Kosslyn-Stroop EffectA message is most intelligible and memorable when its form is Compatible with its meaning.
The Stroop effect demonstrates the difficulty people have in processing information when asked to name the color of the ink used to a color name (“red”) a different color from the ink (blue).

Similarly, people are better able to comprehend when audio and visual contents coordinate with text and the overall message.

  • Indicate quantitative difference by color saturation and intensity (or brightness)
    These “prothetic” variables are arranged quantitatively.
    In contrast, hue is ineffective as a measure of quantitative differences because it is a “metathetic” variable that is arranged qualitatively
  • Ensure that animation movements align with the object’s natural movement patterns, such as an automobile entering from the side of the slide rather than the top
  • Select sounds, typefaces, and backgrounds consistent and compatible with the content. such as sans serif typeface for high tech products
  • Use icons that depict the typical examples of represented items, such as a duck to represent “fowl” or “wild bird” but not “pet bird”
  • Include line graphs (rather than bar or mixed graphs) to illustrate trends and interactions:  The continuous variation in the height of a line in a graph directly indicates the continuous variations of a measurement
  • Apply bar graphs to illustrate specific values instead of trends because the discrete heights of the bars directly indicate specific measurements
  • Add maps to illustrate complex information about geographic territories or show alternate routes to a destination
  • Consider charts to portray organizational structure, sequential steps, or processes as in “flow charts.”

Presentations must offer most applicable, meaningful content for the topic in sufficient but not excessive detail.
Enhance Relevance by:

  • Curating content
  • Enabling viewers to organize the information into a narrative by presenting a roadmap of the topic in an outline or overview
  • Providing graphic elements including photos, drawings, graphs, diagrams, and video as well as audio to illustrate concepts clearly and label ambiguous imagery.
Don McMillan

Don McMillan

If presenters adopt Kosslyn’s recommendations, to enhance Discriminability, Perceptual Organization, Salience, Limited Capacity, Informative Changes, Appropriate Knowledge, Compatibility, and Relevance, PowerPoint comedians Don MacMillan and biologist Tim Lee may need to revert to their previous occupations. 

Tim Lee

Tim Lee

-*How do you ensure that your Business Storytelling with PowerPoint keeps your audience engaged?

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