Those are 0.3 stop, 0.7 stop, and 1.0 stop lower than the base ISO 100. More or less equivalent of ISO 80, 64, and 50. Same effect as lower ISO, but they cannot call them that because of the necessary method to go below the base. Not exactly the same - The dynamic range is also lowered, and there can be a little less contrast. May not be noticeable.