Relative Frequency Discrimination in Pigeons Richard Keen and Armando Machado Indiana University, USA This study 1) examined how pigeons discriminate the relative frequencies of events when the events occur serially and 2) tested a simple mathematical model of the discrimination process (Keen and Machado, 1999). Ten pigeons were shown two different colored lights. The first color was shown nf times, while the second was shown nl times. The pigeons then were reinforced for choosing the color that was shown the least number of times during the sample. Two variables were manipulated; 1) the total number of lights in a sample (T = nl + nf) and 2) the difference between the frequencies of the two lights (D = nf - nl). The results showed that the pigeons’ accuracy increased with the absolute value of the difference D, and for D > 0, it increased with T. Performance also showed clear recency, primacy, and contextual effects. The recency and primacy effects were found to be a function of T. The model accounted well for the major trends in the data. Keywords: number discrimination, mathematical models, pigeons.

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