Two types of behavioral contrast in discrimination learning.
Discrimination training can give you two contrast bumps—watch the early spike and keep sessions running to see if the later bump stays or fades.
01Research in Context
What this study did
Bloomfield (1966) trained pigeons to peck a key when the line tilted one way.
Pecks paid off in one tilt and never in the other.
The team watched how fast the birds pecked across many sessions.
What they found
Two bumps showed up.
First, a quick spike in speed right after the non-paying tilt appeared.
Later, speed settled into a steady, higher plateau that stayed for the rest of training.
How this fits with other research
Reynolds (1966) ran almost the same pigeon set-up the same year.
They kept training longer and saw both spikes fade away, calling them short-lived "emotional flashes.
The gap is timing: M stopped early and called the final rate stable, while S kept going and watched it vanish.
Rogers-Warren et al. (1976) later showed the spike only happens when one tilt pays more often than the other; equal pay rates erase the effect, hinting that M’s birds probably got richer reinforcement for the positive tilt.
Reynolds (1968) clarified that simply squashing pecks to the non-paying tilt is enough to drive the whole show, even if pay rates stay equal.
Why it matters
When you teach a new discrimination, expect a brief burst of extra correct responding right after the learner meets the non-reinforced cue.
Do not celebrate too soon; keep training to see if the burst calms down or sticks around.
If the spike fades, you are seeing the same short emotion effect S found; if it stays, check whether your reinforcement rates across cues are truly balanced.
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Join Free →Count reinforcers delivered in each S+ and S- component for one session; rebalance if totals differ and watch whether the extra burst in S+ shrinks.
02At a glance
03Original abstract
Two groups of pigeons received daily discrimination training at two values on a line-tilt continuum. S+ (VI 1) and S- (EXT) intervals alternated, and a 30-sec criterion of no responding to S- was required before S+ returned. Rates of responding to S+ showed two separate contrast effects: at an intermediate stage of training a high peak rate appeared which declined, later in training, to a stable level still in excess of the VI baseline rate. The peak rate was correlated with the total number of responses to S-, while the final rate was not; suggesting that the peak rate and final rate may not be functions of the same variable. These results were compared with performance on a red-green discrimination where the two stages were not so clear. A line-tilt discrimination was repeated with fixed length S- intervals terminated by TO, and showed the same contrast magnitude in the final rate without any peak. The peak rate was interpreted as an effect of the ;punishment' contingency where responding to S- prolongs S- for 30 sec, while the final rate was taken to be analogous to previous demonstrations of contrast.
Journal of the experimental analysis of behavior, 1966 · doi:10.1901/jeab.1966.9-155