The temperature of the air entering the the air filter and then on to the air flow sensor is not measured. The only temperature that is monitored is the engine and the fuel.
There's no separate, distinct intake air temperature sensor monitored by the ECM (or ECU or how you want to call it). All the info (air quantity) is given by the MAF. That's why is called Mass Air Flow sensor/meter - the data that it gives shows the mass of the air passing through it. And at this stage you don't need anything else to know more about the air in order to tell how much fuel to inject (i mean the computer, not you).
In other words, the info given by the MAF is already temperature corrected, if I may say so.
In fact, the MAF has a hot wire (located in the air flow) and cold wire that is used as a temperature compensator (not in the air flow). This cold wire acts like (in fact is) a thermistor and it's connected in a (little bit more complicated) Wheatstone bridge together with the hot wire to compensate the current through it with the temperature. Simple as that
Basically, alter the Air Temp sensor to fool the ECU that the air is colder (that means is more dense) so it will inject more fuel (because it thinks there is more air in the cylinder) in order to get some tiny little bit more power from the engine.
Plenty info on the net, take you pick from some search results.