Mitosis Anaphase Motor Proteins??? [OCR AS | PLEASE HELP]

The book from pearson states that in anaphase, motor proteins walk along the tubulin thread to pull the chromatids to opposite poles of the cell.

Other books state however that the spindle fibres at the centrioles are shortened by contraction of the fibres caused by the centrioles, so the centromeres of the chromosomes divide, and move to opposite poles of the cell.

Which one is right?