Positive relationship between upcoming but not previous ratio requirement and PRP.

A) Individual mean and between-bird SEs of PRP by upcoming ratio requirement (pecks required to complete a trial). B) As A) but by previous ratio requirement. Note: for clarity we present PRP as residual PRP for panels A) and B). This is because both previous and upcoming ratio requirement may act together to influence PRP, making interpretation of the raw data difficult. Thus, residual PRP was calculated for panel A) by extracting residuals from a regression of logged PRP against previous ratio requirement. Residual PRP was calculated for panel B) by extracting residuals from a regression of logged PRP against upcoming ratio requirement. C) Individual mean PRP plus between-bird SEs by upcoming ratio requirement (pecks required to complete a trial). Data were split by whether the ratio requirement came in ascending (up direction, represented by black filled bars) or descending (down direction, represented by grey filled bars) part of the cyclical sequence. The plots represent raw data from 30 birds; note CRG data are shown only to ensure direct comparability with the Ettinger and Staddon study [2] with rats.