This is a bit of a logic problem that should be figure-outable from the information At the turn of the last century there was a debate about whether attention increased the perception of something by increasing the clarity of that one thing, or by decreasing the clarity of everything except that one thing. Mach and Stumpf did an "experiment" that I can't find anywhere except my textbook, where they listened to a note (on its own and then) as part of a chord. One of them found that the tone was more intense (louder) as part of the chord and the other found that it wasn't. I put that bit in brackets in myself, it isn't mentioned in the book. .but I think they must mean that. I also think that they must mean that Mach, who said that the tone was more intense (seemed louder) in the chord, was concluding that the tone was made more clear in order to be perceived better.. and Stumpf, who said that the tone wasn't more intense, was concluding that everything else was dimmed in order to allow him to focus on that one note. What it, infuriatingly, doesn't say is whether it was louder than the other notes in the chord or whether it was louder than in the other condition, which I assume there was even though it isn't mentioned: the condition of the tone without a chord. The book is Attention by Addie Johnson and Robert W. Procter. Does my interpretation of this make sense or is there some gaping flaw that I am missing? When I first read it I was completely stumpfed ba dam bam tsh sorry.