Tracking cortical entrainment to stages of optic-flow processing.

In human visual processing, information from the visual field passes through numerous transformations before perceptual attributes such as motion are derived. Determining the sequence of transforms involved in the perception of visual motion has been an active field since the 1940s. One plausible family of models are the spatiotemporal energy models, based on computations of motion energy computed from the spatiotemporal features the visual field. One of the most venerated is that of Heeger (1988), which hypotheses that motion is estimated by matching the predicted spatiotemporal energy in frequency space. In this study, we investigate the plausibility of Heeger's model by testing for evidence of cortical entrainment to its components. Entrainment of cortical activity to these components was estimated using measurements of electro- and magnetoencephalographic (EMEG) activity, recorded while healthy subjects watched videos of dots moving left and right across their visual field. We find entrainment to several components of Heeger's model bilaterally in occipital lobe regions, including representations of motion energy at a latency of 80 ms, overall velocity at 95 ms, and acceleration at 130 ms. We find little evidence of entrainment to displacement. We contrast Heeger's biologically inspired model with alternative baseline models, finding that Heeger's model provides a closer fit to the observed data. These results help shed light on the processes through which perception of motion arises in the visual processing stream.