(Found) Everyone's memory gets cleared each night in order to see how the population reacts to advertising

[NickDK]

Perhaps written by Frederick Pohl, around 40 pages long novel, where one night the protagonist goes down to the cellar for some repairs and his mind is not reset that night. (Whereas everybody else seems to relive the previous day). He realizes that spending the night in the cellar is somehow key to staying safe (so he keeps staying there in the following nights) and decides to get to the bottom of the mistery. Turns out that there are tunnels under the city and indeed there is some experiment going on to find out how people react to forms of advertising. In the end we learn that the entire population of the city suffered some serious harm as the nearby chemical plant blew up. Some evil mastermind decided that these people would make an ideal raw material for his experiments.

 

[Toby Frost]

It is by Pohl, and is called "The Tunnel Under The World". I used to have it in a compilation called Robots, presented by Isaac Asimov.

 

[NickDK]

Thank you so much. Spent years in vain trying to identify this by myself. So relieved...

 

[Toby Frost]

Happy to help!