**1. Introduction**

The capability of judging the correct speed of a dynamic scene in a video clip is surprisingly poor. We have recently shown that (i) speeding up a soccer match video by as much as 12% goes completely undetected [1]; (ii) there are systematic biases in judging the correct video speed, often consisting of speed underestimation [2]; and (iii) 6–7-year-old children judge videos to be slower, as compared to older children and adults [3]. Thus, it appears that there is a mechanism in the brain that implicitly codes a subjective "right" speed of events. This mechanism seems to be specific to event speed, as judgments of video clip speed and video clip duration are not correlated [2].

These findings led us to ask how the speed of a complex video scene is coded in the brain. Taking a somewhat different approach as compared to existing work on visual speed processing [4,5], in this exploratory study we addressed the capability of detecting speed manipulations of complex visual stimuli, both a naturalistic video clip and a laboratory stimulus (random dot kinematogram, RDK). We also had a more specific aim: given that observers appear to be unaware of even large video speed changes, and ye<sup>t</sup> are apparently capable of providing systematic, though often biased, judgments about video speed, there must be a processing stage that automatically and covertly codes the expected speed given the available contextual cues. This processing stage may involve sensory mechanisms, decisional mechanisms, or both. Here, we searched for possible neural correlates of the former, namely, subliminal speed processing. As an initial step towards a more comprehensive understanding of complex visual speed tuning, we recorded perceptual as well as cortical responses to a simple manipulation of the visual stimuli, namely, sinusoidal speed modulation.

#### **2. Materials and Methods**
