Discriminative stimulus location as a determinant of positive and negative behavioral contrast in the pigeon.

Schwartz (1975) worked with pigeons on a two-part schedule. Each part had its own light color and its own rate of food payoff.

The twist: sometimes the color sat on the same key the bird had to peck. Other times the color glowed on a second, nearby key.

Positive contrast only showed up when the color cue lived on the response key. Negative contrast happened no matter where the cue sat.

In plain words, location of the signal, not just the payoff change, decided whether the bird worked harder in the rich part.

Green et al. (1975) ran almost the same pigeon set-up and saw the same within-part jump in pecks, giving a direct thumbs-up to the result.

Smith et al. (1975) looks like a clash: they saw no contrast on the main key and said summation of two peck types explains the jump. The gap is method. B et al. counted only pecks on the food key, missing the surge that Schwartz (1975) caught by keeping the cue on that same key.

Scull et al. (1973) add another layer: when the required peck form stayed the same across parts, contrast popped out. When the bird had to peck differently, contrast shrank. So both signal place and response shape gate the effect.

If you run multiple schedules with clients, put the SD right on the manipulandum you want to see grow. Keep the response topography the same across components. These two quick checks make contrast more likely and your teaching loops more powerful.