As a consequence of the aperture problem, when a moving sine-grating is viewed through an aperture, the perceived motion is ambiguous. However, when we superimpose two of these gratings, the resulting pattern usually moves in a coherent way. It has been shown that the orientation, speed, contrast, and spatial frequency of each plaid are parameters that influence the perception of coherence. We have studied the stimulus conditions under which coherence does and does not occur, using human observers who assigned a probability of coherence to each sequence of images. We then tried to find a computational method whose result would correlate with the results from the human observers. The proposed method consists of computing the optical flow field on the image sequence, then using the direction of the optical flow in each point on the image to build a histogram. This histogram can provide information about the probability of coherence of the image sequences. We show that the proposed method provides results very similar to the ones obtained with the human observers in terms of probability of coherence.