| Perceptual organization is determined partly by the interaction among dimension and features of stimuli entering the perceptual system. Automatization of two dimensions (i.e., the ability to attend to both simultaneously without decrement) requires prolonged practice at conjunctive search. When conjunctively defined stimuli are processed automatically, unitization (perceptual recoding of the underlying dimensions into distinct units) is said to occur. If two separable dimensions were trained to automaticity in a search task, the stimuli composed of these two dimension should be perceptual redefined as nominal dimensions (stimuli without subject-defined dimensions). This hypothesis was tested with dimensions of color and form. Subjects automatically processed the stimuli, but no perceptual redefinition was obtained as measured by performance in a subsequent speeded classification task. Because the speeded classification task is sensitive to dimensional structure, this experiment provided no evidence that unitization occurs. |
