Why do we see things the way we do? How, exactly do we perceive anything? More specifically, how long does it take to perceive a certain visual stimulus? Perceptual organization involves perceiving structure in the environment based on both bottom-up (stimulus driven) and top-down (experience driven) information. In order to assess the role of bottom-up versus top-down influences in perceptual organization, I examined the temporal constraints on perceptual grouping. I presented 14 naïve subjects with displays that alternated between a horizontal and a vertical organization and asked subjects to indicate if they perceived coherently alternating displays or a random jumble of shapes. Presentation rates were varied between 33 ms and 200 ms per frame. I found that at slower alternation rates, subjects were clearly able to perceive the alternating displays as coherently grouped, while at faster alternation rates (33 and 66 ms) subjects perceived the displays as random jumbles of moving shapes. I assessed the effects of shape using circles, squares, and triangles. I found that subjects could perceive displays composed of squares as being coherently grouped more rapidly than displays composed of circles and triangles. Based on my results, I found 133 ms to be the optimal speed where alternating visual stimuli could be coherently grouped into rows or columns. This specific time gave me an estimate of the time required for the brain to process the information using bottom-up with top down influences. This time could be used to detect the exact number of stages involved in perception.