In the movie, Dr. Lull asks Quaid how he likes his women: demure, aggressive, sleazy? Quaid replies sleazy, but wanton is selected before he even says it. Likewise, before he says demure, demure is selected before he says it. Could the machine read Quaid's thoughts, is that that why the choices were highlighted before he even expressed them?
If you follow the sequence of events closely, there appears to be a difference between the various words being highlighted on-screen, and those things actually being confirmed as selections.
The previous list of options Quaid was given were...
... and as Dr. Lull spoke each word in the list, that particular word would be highlighted on-screen a moment later, and the wireframe model of a woman would morph its body type to give a preview of each option.
Quaid verbally selects the 'ATHLETIC' option, and we then see Dr. Lull look down and to her to her right, and appear to input something into a manual interface with her right hand, at which point the highlighted option on the screen moves from 'VOLUPTUOUS' to 'ATHLETIC', and that selection is confirmed with a sound effect, and the wireframe model changing back to the athletic body type and filling in with colour.
So, at this point at least, it would appear that the computer was responding to manual inputs from Dr. Lull, rather than reading Quaid's thoughts.
The next list of options is the one you mentioned...
... and rather than the words being highlighted in sequence as Dr. Lull spoke them, this time 'WANTON' was the first to be highlighted (after she'd spoken all three words, replacing 'wanton' with 'sleazy' for whatever reason), and then 'DEMURE' after that. Nothing appears to have been confirmed at this point though, as we only hear the sound effect and see the position of the on-screen model change after Quaid verbalises his selections.
It's unclear why 'WANTON' was the first word to be highlighted, but since the computer apparently wasn't reading his thoughts before -- and we're never given any clear indication that it's even capable of that -- there's no reason to think it did so at this point either. It seems more likely that it was just a minor goof by the effects crew.
Or if you really need an in-universe explanation, then perhaps Dr. Lull anticipated what Quaid's selections would be -- based on her impression of him, and her experience in the job -- and manually highlighted 'WANTON' and then 'DEMURE' herself, using the same interface she used to highlight and confirm his previous choice of 'ATHLETIC'.
One theory about the film is that Quaid gets exactly what he asked for from Rekall, a daydream about a trip to Mars as a secret agent, where he meets a girl who is, as requested, both wanton and demure. If that is true, then the choices on the machine are being filled out before he provides them, and counter to his actual words in one case, because it's dream logic.