The definition trapezoid in natural language, refers to a 4-sided [quadrilateral] shape with a shorter top, a longer bottom and a centered top. In mathematics it is called an 'isosceles trapezoid'. Key Features: The top and bottom sides are parallel to each other. The left and right slanted sides have the same length. It has a line of symmetry running straight down the middle. The two bottom base angles are equal. The two top angles are equal. In the Spherical Model, a represents a category of stimuli, e.g., colors, facial expressions, emotions. Different individuals tend to distinguish stimuli of any type into 7 + or - 2 categories ( Miller-1956 ).