Investigations of the precedence effect in budgerigars: effects of stimulus type, intensity, duration, and location.

Auditory experiments on the localization of sounds in the presence of reflections, or echoes, that arrive later and from different directions are important to understanding hearing in natural environments. The perceived location of the auditory image can change with the time delay between the presentations of a leading and lagging sound. These changes in perceived location, encompassing the precedence effect, have been examined behaviorally or physiologically in humans and a number of animals. Here, these results are extended to include budgerigars. Behavioral methods were used to measure the discrimination performance between a stimulus presented at + and - 90 degrees azimuth with a delay (left-right), from the same two stimuli presented with the opposite delay (right-left). At short delays, where humans experience summing localization, budgerigars have difficulty discriminating between the two presentation types. With increasing delays, where humans experience localization dominance, budgerigars show improved discrimination performance. At even longer delays, where echo thresholds are found in humans, discrimination performance worsens again. The shapes of the discrimination functions are affected by the intensity, locations, and durations of the stimuli, and are subject to a buildup effect. These results show that budgerigars exhibit the phases of the precedence effect similar to humans and other animals.