We offer a re-evaluation of the tone-monitoring technique inthe study of parsing. Experiment 1 shows that reaction times(RTs) to tones are affected by two factors: a) processing load,resulting in a tendency for RTs to decrease across a sentence,and b) a perceptual effect which adds to this tendency andmoreover plays a role in neutralising differences between sen-tence types. Experiment 2 successfully discriminates thesetwo factors by registering event-related brain potentials dur-ing a monitoring task, establishing that the amplitudes of theN1 and P3 components —the first associated with temporaluncertainty, the second with processing load— correlate withRTs. Experiment 3 then behaviourally segregates the two fac-tors by placing the last tone at the end of sentences, activating awrap-up operation and thereby both disrupting the decreasingtendency and highlighting structural factors.