ASSUMPTION 2: A GIVEN TASK CAN BE DECOMPOSED INTO A SET OF MORE BASIC OR PRIMITIVE TASKS (EVENTS)

THUS, IN PRINCIPLE ONE COULD MEASURE THE TIME TAKEN TO PERFORM EACH MENTAL EVENT TO CALCULATE (PREDICT) HOW LONG IT SHOULD TAKE TO PERFORM THE COMPLETE TASK

e.g., LET US SAY THE TASK IS TO SIT IN FRONT OF A SCREEN WITH FINGERS ON A LEVER, WHEN A CERTAIN SHAPE COMES ON (CIRCLE) ONE PUSHES THE LEVER ON THE RIGHT, FOR ANY OTHER SHAPE USE THE LEVER ON THE LEFT. MEASURE TIME TAKEN TO MAKE A RESPONSE FROM ONSET OF SHAPE TO ONSET OF LEVER PUSH

WHAT ARE THE ELEMENTARY SUB-PROCESSES?
-PERCEIVE OBJECT (El) DECIDE WHAT SHAPE IT IS (E2), DECIDE WHICH LEVER TO PUSH (E3), INITIATE FINGER MOVEMENT (E4)
THUS RT=E1+E2+E3+E4

CAN ONE FIND ANOTHER TASK THAT ELIMINATES ONE OF THESE STAGES; RT=E1+E3+E4

SUBTRACTIVE LOGIC: CAN CALCULATE TIME TO PERFORM PATTERN (SHAPE) PERCEPTION (E2)

NOTE: CRITICISM OF THIS APPROACH BY INTROSPECTIONISTS