The most efficient form of Pavlovian conditioning is delayed conditioning, in which the US turns on with a "short" delay after the CS turns on. What short is depends on the response. For eye blink conditioning a 0.25 to 0.5-second delay between turning on CS and US produces the optimal (best) conditioning; the maximum delay that produces successful conditioning is less than about 1 second. For salivary conditioning, the optimal delay between CS onset and US onset is a few seconds. For fear conditioning (CS predicts some kind of unpleasant or feared stimulus or event), very efficient conditioning occurs at delays of 10 to 20 seconds between CS and US onset.

Other forms of Pavlovian conditioning include:

Other forms of Pavlovian conditioning include:

• Long delay conditioning, in which the CS onset precedes US onset by more than the optimal interval, but continues to overlap US in time.
• Trace conditioning, in which the CS ends before the US comes on, so that only a "trace" of the CS is available for the interval between CS turning off and US turning on.
• Simultaneous conditioning, in which the CS and US turn on at the same time.
• Backwards conditioning, in which the CS onset comes after the US onset.

Trace conditioning is produced by ending the CS before turning on the US. Under ordinary conditions, it is much harder to establish. It is called trace conditioning because the conditioning that occurs must be based on associating a trace left by CS with the US. Figure 10 below illustrates a trace conditioned response.

Two other kinds of pairings are; simultaneous conditioning, in which the neutral stimulus and US turn on together, and backwards conditioning, in which the neutral stimulus is turned on only after the US has been turned on. Under ordinary test conditions, these two types of pairing show little or no evidence of a CR, and the neutral stimulus paired with the US does not become a CS. asgn3a