Keen, R., & Machado, A. (1999).
How pigeons discriminate the relative frequency of events.
Journal of the Experimental Analysis of Behavior,
72, 151-175.
This study examined how pigeons discriminate the relative
frequencies of events when the events occur serially. In a
discrete-trials procedure, 6 pigeons were shown one light
nf times and then another nl times. Next, they
received food for choosing the light that had occurred the least
number of times during the sample. At issue were (a) how the
discrimination was related to two variables, the difference
between the frequencies of the two lights, D= nf–
nl, and the total number of lights in the sample, T
= nf+nl; and (b) whether a simple mathematical
model of the discrimination process could account for the data.
In contrast with models that assume that pigeons count the
stimulus lights, engage in mental arithmetic on numerons, or
remember the number of stimuli, the present model assumed only
that the influence of a sample stimulus on choice increases
linearly when the stimulus is presented, but decays exponentially
when the stimulus is absent. The results showed that, overall,
the pigeons discriminated the relative frequencies well. Their
accuracy always increased with the absolute value of the
difference D and, for D>0, it decreased with
T. Performance also showed clear recency, primacy, and
contextual effects. The model accounted well for the major trends
in the data.
Key words: relative frequency discrimination, recency and primacy
effects, context, mathematical model, key peck, pigeon