CONTROL OF VOCAL INTENSITY IN BUDGERIGARS (MELOPSITTACUS-UNDULATUS) -DIFFERENTIAL REINFORCEMENT OF VOCAL INTENSITY AND THE LOMBARD EFFECT

Call production in budgerigars was studied using operant conditioning. In several experiments, budgerigars were reinforced with food for pro ducing calls that were above or below a criterion level of intensity. This differential reinforcement procedure was successful in controllin g vocal intensity in both directions showing that the intensity with w hich budgerigars produce vocalizations is under voluntary control. In additional experiments, call intensity maintained by food reinforcemen t was measured both in the quiet and in the presence of various levels of broadband noise. Call intensity in budgerigars increased significa ntly in noise, paralleling the well-known Lombard effect in humans whi ch is the reflexive increase in speech intensity during communication in noise. Call intensity was measured in broadband noise and in a notc hed noise (no energy between 1.5 and 4.5 kHz) with the same overall le vel. Results show that noise in the spectral region of contact calls i s most effective in causing an increase in vocal intensity. In aggrega te, these experiments show that pa budgerigars have voluntary control over the intensive aspect of their vocalizations, that they normally m onitor their vocal output though external auditory feedback, and, like humans, they exhibit the Lombard effect. (C) 1998 Acoustical Society of America. [S0001-4966(98)04402-6].