Manipulating stimulus’ complexity by tuning the spatiotemporal characteristics of the moving stimuli: The MC stimuli are characterized by the parameters of their spatio-temporal spectral envelope and in these experiments we used a specific set of parameters to progressively modify the complexity of the stimuli. The left panel is a bi-dimensional representation of the spatio-temporal frequency space. Points along the continuous line correspond to simple drifting grating stimuli moving at a given speed but with different spatial frequencies (blue dots). MC stimuli have their spectral energy distributed in an ”ellipse” (Gaussian distribution) distributed around a given speed plane. Interestingly, these can be parameterized with the same mean spatial (\(\text{sf}_{0}\)) frequency and speed (\(V\)) as as the gratings, but with different levels of spatial frequency bandwidths (defined by the parameter \(B_{\text{sf}}\), with \(B_{\text{sf}}=0\) for the grating). The green ellipse represents a narrow bandwidth stimulus and the orange ellipse a broader bandwidth stimulus. The panel on the right shows some realizations of this set of stimuli at different complexity levels. For simplicity, we plot the light intensity along one single row of the image (vertical axis) and for the whole duration of the stimulation (horizontal axis). We show respectively the drifting grating (top panel) which is constituted by a single spatial and temporal frequency (and thus a single speed, seen as the slope in this view), and the MCs (middle and lower panels) which have the same speed and central spatial frequency but with respectively a narrow or wide bandwidth in spatial frequency space. This illustrates the smooth transition using a single parameter (\(B_{\text{sf}}\)) from a ”cristal-like” pattern (the grating) to progressively more complex and naturalistic stimuli.