The ability to discriminate changes in the fine structure of complex sounds is well developed in birds. However, the precise limit of this discrimination ability and how it is used in the context of natural communication remains unclear. Here we describe natural variability in acoustic fine structure of male and female zebra finch calls. Results from psychoacoustic experiments demonstrate that zebra finches are able to discriminate extremely small differences in fine structure, which are on the order of the variation in acoustic fine structure that is present in their vocal signals. Results from signal analysis methods also suggest that acoustic fine structure may carry information that distinguishes between biologically relevant categories including sex, call type and individual identity. Combined, our results are consistent with the hypothesis that zebra finches can encode biologically relevant information within the fine structure of their calls. This study provides a foundation for our understanding of how acoustic fine structure may be involved in animal communication.

An individual’s ability to respond to and align with the behavior of others is a fundamental component of social behavior. Zebra finches form lifelong monogamous pair bonds; however, zebra finches are also gregarious and can form strong social bonds with same-sex conspecifics. Here, we quantified behavior during brief 10-min reunions for males and females in five types of social conditions: monogamously bonded opposite-sex partners, familiar same-sex, familiar opposite-sex, novel same-sex, and novel opposite-sex dyads. We analyzed these interactions in three ways. First, we quantified overall activity levels (call and movement rates) for each individual. Second, we measured how coordinated calls and movements were by calculating (a) the percent difference in activity rates as an estimate of how similar calling and movement activity were between individuals within a dyad, and (b) the sliding correlation coefficients for time-stamped calls and movements for each dyad. Finally, we described multimodal behavioral profiles of coordination using principal component analyses. Overall, females were more active than males. For both females and males, activity levels as well as the coordination of calls and movements were significantly affected by social condition. In general, monogamous partners, female familiar same-sex dyads and familiar opposite-sex dyads were the most coordinated. This effect of familiarity shows that moment-to-moment behavioral coordination can be influenced by prior social experiences. Quantifying patterns of coordination or social synchrony may prove valuable for understanding the effects of social experience on brain and behavior.

The warble songs of budgerigars (Melopsittacus undulatus) are composed of a number of complex, variable acoustic elements that are sung by male birds in intimate courtship contexts for periods lasting up to several minutes. If these variable acoustic elements can be assigned to distinct acoustic-perceptual categories, it provides the opportunity to explore whether birds are perceptually sensitive to the proportion or sequential combination of warble elements belonging to different categories. By the inspection of spectrograms and by listening to recordings, humans assigned the acoustic elements in budgerigar warble from several birds to eight broad, overlapping categories. A neural-network program was developed and trained on these warble elements to simulate human categorization. The classification reliability between human raters and between human raters and the neural network classifier was better than 80% both within and across birds. Using operant conditioning and a psychophysical task, budgerigars were tested on large sets of these elements from different acoustic categories and different individuals. The birds consistently showed high discriminability for pairs of warble elements drawn from between acoustic categories and low discriminability for pairs drawn from within acoustic categories. With warble elements reliably assigned to different acoustic categories by humans and birds, it affords the opportunity to ask questions about the ordering of elements in natural warble streams and the perceptual significance of this ordering.

Heart rate and skin resistance responses from thirty-six participants (5 men and 31 women) were recorded to determine if significant differences exist among three different types of inducing anger including the present state of anger (Actual Anger), anger elicited through imagination (Imagined Anger), and anger elicited through recollection (Recollected Anger). An analysis of variance indicated significant differences for heart rate among the three methods, F(2,35) = 8.75, p = .0009, but not for skin resistance, F(2,35) = 1.298, p = .287. However, contrary to the hypotheses forwarded, both Imagined and Recollected Anger generated significantly higher heart rate responses than Actual Anger. Implications of these findings and a theoretical framework for interpretation are both presented.

Participants' heart rate and skin resistance responses to emotional memories (fear, anger, joy, sadness, and embarrassment) were studied to determine if the recollection of emotion is sufficient to produce psychophysiological changes, to determine if such changes differ for the various emotions, and to determine the relationship between imaginal abilities and psychophysiological responses to emotional memories. The Absorption Scale of the Multidimensional Personality Questionnaire was used as the measure of imaginal ability [1]. A repeated measures analysis of variance indicated significant differences for skin resistance but not heart rate among emotional memories, F(5,75) = 4.22, p = .002. Recollection of emotional memories, therefore, can produce psychophysiological changes in skin resistance which resemble emotions in real-life circumstances. A theoretical framework for interpretation of results on emotional memories is presented.