Can a casino "let you win"?

Wife and i have been going to different casinos for several years. if you are a gambler, you are familiar with each casino’s “reward cards” you insert into a slot machine. the theory is the more you play, the more reward points you receive. a computer keeps tally with your points and the time and money you spend on slot machines. my question is this: when i insert my plastic rewards card into a slot machine, my play information is sent to a computer, located somewhere within the casino, that records my activity. if this information goes one way to a computer, can the computer also send information back to allow me to win on the slot machine i am playing? sometimes, i can take this card out and i begin to win. i reinsert the card and my winning ceases. am i gambling against the slot machine or am i gambling against the casino’s computer?