Effect of anomalous pulse timing on call discrimination by females of the gray treefrog (Hyla versicolor): behavioral correlates of neurobiology.

Research has demonstrated that certain midbrain neurons of anurans 'count' interpulse intervals (IPIs). Some neurons fire after exposure to fewer intervals than do others. Counting can be reset to zero if an IPI falls outside the cell's tolerance range. We tested female gray treefrogs for behavioral correlates of these neural response patterns using phonotaxis tests in order to gain a better understanding of the mechanistic bases of female responses to calls. For example, previous work demonstrated females often prefer longer to shorter pulsed advertisement calls, even when the former occur at lower rates. Call attractiveness can also be reduced when pulse duration and timing have been manipulated experimentally or disrupted by acoustic interference. In this study, female responses were consistent with neural data, emphasizing the importance of IPIs. Females discriminated in favor of calls with normal interpulse timing relative to those in which a single IPI was too long or too short. Our data suggest that neural resetting of interval counting by inappropriate intervals may more strongly influence females than reduced firing in response to such intervals on an individual basis. Data also suggest a transition point between 125 ms and 175 ms at which an interval between pulse strings is treated as an interval between calls.