Modulation-filter shapes in the budgerigar inferred from behavioral reverse correlation

Much information in speech is carried by amplitude modulation (AM). AM perception is adversely impacted by competing AM fluctuations present in the noise background, called modulation masking. Modulation masking in humans increases for masker AM frequencies closer to the target, suggesting a bandpass modulation filterbank analysis. The modulation filterbank model is widely adopted in hearing science, but animal models are relatively undeveloped. Using narrowband modulation maskers, we recently found that budgerigars, a parakeet species, show bandpass behavioral modulation masking patterns consistent with the modulation filterbank model. Here, we used wideband modulation maskers and a behavioral reverse correlation approach to characterize modulation shapes. Masker seeds were stored for stimulus reconstruction on a trial-by-trial basis. Animals were trained to perform a single-interval, two-alternative, forced-choice, AM detection task with operant conditioning. The reverse correlation approach estimated modulation filter shapes related to the difference in average stimulus statistics (e.g., envelope spectrum) between response categories (e.g., false alarms versus correct rejections). Most animals showed clear differences in stimulus statistics between response categories which were in some cases explainable by bandpass modulation filtering. Behavioral reverse correlation results are compared to modulation masking patterns with narrowband modulation maskers. [Work supported by R01-DC021953.]