Additive and suppressive response summation with a chain schedule.

The team used a two-link chain schedule with rats. Each link had its own light or tone cue.

They then paired two cues together in either the first or second link. The question: would responses add up or drop?

When the pair sat in the second link, rats pressed more — an additive boost.

When the same pair sat in the first link, pressing fell — a suppressive dip.

Same rats, same cues, different place — opposite effects.

Cherek et al. (1970) and Schwarz et al. (1970) saw only additive jumps when cues were combined. Their cues were tied to simple suppression or fixed-interval schedules, not chained links.

Davis et al. (1972) also found pure addition under an avoidance schedule. None of these earlier papers tested the chain position, so they missed the flip side.

Gibbon (1967) used two schedules in tandem and saw response rates average out, not add. That result looked like a contradiction, but the key difference is schedule type: VI-DRL mixing versus chained links. Position within the chain, not schedule mixing, drives the add-or-drop rule found here.

If you run chained teaching programs, think twice before stacking cues. A compound picture card at the start of a chain might slow the learner down, while the same pair near the end could speed things up. Test both spots and watch the data; stimulus placement can turn a helper cue into a hurdle.