Why psychologists should know about stripes

1
Why psychologists should know about stripes

• Objectives
• Understand the terms spatial frequency,contrast,
  phase, and orientation in relation to spatial
  scale.
• Understand how spatial scale is represented in
  humans and other species
• Describe evidence supporting such representation
• Understand basic measurement of sensitivity to
  spatial scale
• Be able to argue why spatial scale is relevant to
  psychologists drawing on examples

2
What is spatial scale?

• No colour, no motion, no depth
• how light varies in intensity across the visual
  field is spatial information
• different degrees of detail found in spatial
  information
• can be emphasised at different degrees of blur
• examples
• face features v face texture
• tree branches v leaves

3
Grey level image
4
Edges at two spatial scales
5
How do we represent it?

• By sinusoidal stripes with the following
  properties
• contrast
• orientation
• spatial frequency
• phase
• Evidence
• Campbell Robson (1968)
• observing contrast thresholds
• visibility of components outside our ability

6
Properties of Components
7
Making Circles from stripes




8
Measuring Spatial Scale

• Contrast sensitivity measurements (CSF)
• Examples of contrast sensitivitiy
• humans
• infants
• other species

9
Why should we study it?

• Presenting stimuli that observers can see
• To avoid drawing conclusions from ignorance
  examples
• stupid babies v clever babies
• dyslexia revisited
• Applications
• Distinguishing tanks and teddy bears
• object recognition
• Understanding brain damge
• diagnostics

10
References

• Goldstein , E. Bruce (1989) 3rd Ed. Sensation
  and Perception Wadsworth Publishing Co. Belmont,
  California. Chp. 5. p. 154 - 166, Appendix D.
• Sekuler, R. Blake, R Perception (1994) 3rd Ed.
  Perception. McGraw-Hill, Inc. Chp. 5.
• only for the enthusiast
• Campbell, F.W., Robson, J.G. (1968).
  Application of Fourier analysis to the visibility
  of gratings. Journal of Physiology, 197,
  551-566. (163).
• DeValois, R.L. DeValois, K.K. (1988) Spatial
  Vision.
• Watt R. (1988) Visual processing.