I think this may be the proof.
Start by assuming that the predictor is a decider P for a computational model of a human M in a situation encoded by w. We can then construct a Turing Machine S that decides A_TM.
S <M, w> {
1. Run P on w.
2. If P halts, run M on w; if M accepts, accept, if it rejects reject.
}
Since S decides A_TM we must have made a mistake somewhere in our proof, our only mistake could be that the predictor P is a decider. Therefore the Predictor is not a decider.
S <M, w> {
1. Run P on w.
2. If P halts, run M on w; if M accepts, accept, if it rejects reject.
}
Since S decides A_TM we must have made a mistake somewhere in our proof, our only mistake could be that the predictor P is a decider. Therefore the Predictor is not a decider.