Some people (including me) generate visual markers without actual visualization. The symptomatic of subliminal reading is very interesting. By following reading speed, eye motion, association creation, reading progress and some other criteria both Anna and me can tell that the student uses visual processing of the text. The student reads fast and retains very well. However, the student has no recall of making any visualization, and complains on failing in visualization exercises and that visualization does not work.
Now, sometimes it is good to have visualization capabilities as a stand-alone skill. However, as long as reading is concerned, you can read everything very fast and remember everything you read without getting concious access to your visualizations. In fact, some of the most prolific speedreaders do not get any access whatsoever to their visual markers, yet they can recreate the text they read and the visual shape (!) of the text in great details.
We are not proponents of subliminal reading or photoreading methodologies due to limited control over reading process and low retention characteristic to these schools. However, we do suggest to play with similar methods when prereading books and retention is not an issue. What is more important, the perceived failure in visualization SHOULD NOT stop you from trying to speedread. If you can remember 20 objects in 1 min, you are ready to speedread, whether you visualize your markers actively or subliminally.
Do not strive for subliminal reading or photoreading: it is notoriously unreliable and you could get any result. However if you follow keytostudy methodology, get the expected results, and cannot remember your visualizations – probably this means you created the markers subliminally and should be happy with that.