Perception

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Nominal - User interested in categorizing

In associative perception the viewer ignores variation in one visible dimension in reading the remainder of the display

An associative variable does not affect the visibility of other dimensions (e.g. we can recognize hue regardless of orientation.) A variable is dissociative if visibility is significantly reduced for some values along that dimension (e.g. its hard to determine hue of a very thin line or small dot)

Hue, Orientation, Texture, Shape, Position are associative

Size and Value are dissociative - they dominate perception and disrupt processing of other correlated dimensions

In selective perception viewer attempts to isolate all instances of a given category and perceptually group them into a single image. The task is to ignore everything but the target value on the dimension of interest - to see at a glance where all the targets are within the display

All the variables except shape are selective

Visual Variables:

visual variables for qualitative should reflect only a nominal level of measurement - ie there shouldn't be a sense that one value is 'more' than another, just that they are different.

• orientation - direction/orientation of the marks/symbol
• shape - different shapes are used
• arrangement - different arrangement of marks making up the symbol
• hue - different colors are used but careful choices need to be made here so there is NO sense of 'less' to 'more' in the different hues