Constant velocity that are designed to follow moving targets
Eye Movement
Eye Movement 
  • Eyes are a performance measure of the mind
  • We look for things that are attractive to us
Types of Movement
  • Necessary to be able to search visual field
Not pursuing objects; abrupt discrete movements from one location to the next
  • Described by Initiation latency, movement time, and destination (dwell)
  • Can't move saccadically more than 4 times in a second due to the time it takes for the Dwell and Inititation and the actual eye movement.
Dwell Initiation
> 200 milliseconds
Actual Movement
30-50 milliseconds
Visual Search
When looking for things in the visual field
Serial search
  • Ex. looking at a list, ordered
  • Average time T = (NxI)/2
    - where I = average inspection time for each item
    - N is the total number of items in the search field
    - T = average time to find the target
  • If everything is equal it will take an average time to fin what you are looking for
Parallel Search
  • "I'm looking for either ____ or _____ at the same time
  • Looking for attributes of object (ex. someone who is large or red)
Random Search
  • Randomly looking around the room to find your friend.
Target Properties Inducing Parallel Search
Discriminability from Background
  • Color
  • Size
  • Brightness
  • Motion
  • One dimension or multiple?
  • The fewer dimensions, the easier it is to find what you are looking for. 
A target that is highly familiar
Probability of Finding What you are Searching For:
goes up with more time, but then tapers off as time goes on. The more time you spend the more likely you are to find it. The graph is steeper when t is smaller and then slopes off toward a probability of 1 as you take longer and longer time. 
Influencing Factors
  • Conspicutiy - bottom up influence that describes how much the item pops out of the rest of the visual field
  • Expectancies - top down influence of where the searcher thinks the target may be in the field. 
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