Access to dimensional values can be unselective during early perceptual processing.

On each trial of the primary task for the study, a pair of small circles appeared on a computer screen. Across trials, the circles appeared in an array of positions on the screen. The participant was required on each trial to indicate whether or not the test circles were two or fewer position units apart in terms of the horizontal dimension of this array. The discrimination that the task required was easier to the extent that the vertical distance between the circles was ignored. When the task was performed under a high degree of speed stress, vertical distance and horizontal distance exerted equivalent effects on measures of performance. When the task was performed under a lesser degree of speed stress, horizontal distance exerted a larger effect than vertical distance did. The results supported the early holistic hypothesis over the dimensional similarity hypothesis as an account of the way information from different dimensions is accessed in perceptual processing.