Perception

This is classified as the act of identifying, organizing and interpreting information about our environment we receive through the senses, typically to guide action. Occurs outside out conscious awareness and is virtually impossible to influence.

• Bottom-up processing: combining information from individual sensory cells into more complex representations of objects
• Top-down processing: previous knowledge, memory, expectations and attention

Let's talk about the human eye for a bit. The image is generally inverted, and corrected later.
Humans have two types of photosensitive cells:

• Cones
  • Center of the image (fovea)
  • High resolution of detail
  • Perceives color
• Rods
  • Around the fovea
  • Luminance and contrast
  • Peripheral vision
  • Motion

We have two to provide stereoscopic vision, which combines input into one coherent whole and lets us estimate distance, as well as for redundancy.

This comes into play when it comes to color. The eye has receptors for (vaguely) three different colors: red, green, and blue (RGB). Blue being the least well perceived (only 4% of cones are blue receptors). Thus, humans can be afflicted by color blindness, which affects 9% of the population, preventing them from distinguishing certain colors.

To design for color blindness:

• Avoid salient red-green distinctions
• Use blue/yellow spectrum
• Use gray-scale

Gestalt Principles of Perception

Objects are perceived in their entirety, not as collections of features (lines, shapes).
Several Gestalt principles of grouping (objects are likelier to be perceived as part of a whole):

• Proximity
• Similarity (size, shape)
• Closure
• Common fate
• Good form
• Connectedness
• Common area
• Adaptation and Contrast

Perception has one higher purpose, which is to distinguish what is important/salient/about to eat you from what is not. To do so, our senses will adapt to ambient levels and perceive them as normal, while still being sensitive to changes. This can be seen in the "cocktail party effect," wherein you can tune out a multitude of conversations you are not a part of.

Implications

• Text and visual elements should be legible and clearly contrast from the background
• Avoid over-reliance on color, especially when lighting conditions are sparse or unknown
• Avoid putting salient information far away from the foveal focus OR make it appropriately large
• Bordering, spacing and color are effective ways of grouping visual elements
• Sound cues should be audible and distinguishable