Hierarchical Frequency Tagging animation

The trial was constructed using one house and one face SWIFT sequence. In order to preserve low level image attributes within a given trial, regardless of the specific images presented in each cycle, we created and merged additional ‘noise’ sequences in the following way. First, we randomly selected one of the scrambled frames from each of the original SWIFT sequences. Then, we created noise sequences by applying the SWIFT method on each of the selected scrambled frames. In this way, each original ‘image’ sequence had a matching ‘noise’ sequence. Finally, each ‘image’ sequence was alpha blended with the ‘noise’ sequences of the other image with equal weights in luminance value at each pixel at any given frame. This way, for example, cycles in which a face image was to appear contained the face image superimposed with a house noise sequence. The overall low level visual attributes were therefore constant across all frames in the trial regardless of the identifiable image in each cycle, ensuring that the frequency tagged signal would not reflect local physical input properties.