Observing responses maintained by compound stimuli in pigeons

Abstract

In order to experimentally analyze the maintenance of observing responses by compound stimuli, four fooddeprived pigeons were exposed to 50-s discreet-trial procedure under response-independent food delivery. A trial always started with the white light on the response key and could end with or without food presentation (p = 0.5). Pecks to the key could change the white color to a different stimulus according to the trial outcome: Red plus vertical line and green plus horizontal line signaled a trial that would end with food presentation; red plus horizontal line and green plus vertical line signaled a trial that would end without food presentation. Three phases were carried out, in which the discriminative properties of the stimuli (line orientation, color, or the combinations of color and line) were manipulated and analyzed with respect to their effects on the frequency of observing responses and stimuli production. The results showed that, when the compound stimuli were used, observing responses initially occurred, but decreased along the sessions. Manipulations on the stimulus control across different phases produced conditions in which observing responses were maintained by the compound stimuli, although for one single subject. This subject was exposed to additional manipulations that aimed to assess possible reinforcing effects of each component of the compound stimuli. Data suggest that observing responses may be maintained by discriminative stimuli established by the combination of two different components, that is, disk color and line orientation. However, it clearly is a complex and fragile repertoire that demands further analyses in order to identify the conditions necessary to establish a more efficient stimulus control.