Observing responses and serial stimuli: searching for the reinforcing properties of the S-.

Escobar et al. (2009) worked with pigeons in a lab. They set up a mixed schedule where food sometimes came after a green light and never came after a red light.

The red light stayed on for a long stretch. Near the end of that stretch, the red light blinked in a set pattern. The birds could peck a small key just to see which light was on.

The team asked: Do those late, serial red blinks make the birds peek more? If yes, the red blinks act like a tiny reward.

Peeks at the lights rose only when the serial red blinks showed up late in the no-food period.

The red light, once just a signal for no food, turned into a conditioned reinforcer for the observing response.

Odom et al. (1986) saw more observing any time a red light popped up, even when it gave no extra reward. They warned that simple S- presentation can fool you into thinking the signal is reinforcing.

Rogelio’s team took that warning and added a timing twist. By placing the serial S- late in extinction, they showed the same stimulus can switch from neutral to reinforcing.

Bland et al. (2018) extend the idea in the other direction: when S- is given right after a response, it can punish that response. One stimulus, two jobs—reinforcer or punisher—depending on when and how you deliver it.

Your client may keep looking at, asking about, or even approaching items linked with "no" if those cues pop up after a long wait. Try spacing those cues and watch if the behavior grows. If it does, the cue itself may be feeding the behavior. Shift timing, add prompts, or reinforce alternate looks to keep the session on track.