Perceptual organization of acoustic stimuli by budgerigars (Melopsittacus undulatus): II. Vocal signals.

Operant conditioning and multidimensional scaling procedures were used to study auditory perception of complex sounds in the budgerigar. In a same–different discrimination task, budgerigars learned to discriminate among natural vocal signals. Multidimensional scaling procedures were used to arrange these complex acoustic stimuli in a two-dimensional space reflecting perceptual organization. Results show that budgerigars group vocal stimuli according to functional and acoustical categories. Studies with only contact calls show that birds also make within-category discriminations. The acoustic cues in contact calls most salient to budgerigars appear to be quite complex. There is a suggestion that the sex of the signaler may also be encoded in these calls. The results from budgerigars were compared with the results from humans tested on some of the same sets of complex sounds. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceptual organization of acoustic stimuli by budgerigars (Melopsittacus undulatus): I. Pure tones.

A new combination of operant conditioning and psychophysical scaling procedures was used to study auditory perception in a small bird. In a same–different discrimination task, budgerigars learned to discriminate among pure tones that varied along one or more acoustic dimensions. Response latencies were used to generate a matrix of interstimulus similarities. Multidimensional scaling procedures were used to arrange these acoustic stimuli in a multidimensional space that supposedly reflects the bird's perceptual organization. For tones that varied in intensity, duration and frequency simultaneously, budgerigars were much more sensitive to frequency changes. From a set of tones that varied only in intensity, it was possible to calculate the growth of loudness with intensity for the budgerigar. For tones that varied only in frequency, budgerigars showed evidence of an "acoustic fovea" for frequency change in the spectral region of 2–4 kHz. Budgerigars and humans also differed in their perceptual grouping of tone sequences that rise, fall, or remain constant in pitch. Surprisingly, budgerigars were much less responsive to pitch contour than were humans. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Vocal development in budgerigars (Melopsittacus undulatus): Contact calls.

Budgerigars have a complex vocal repertoire, some of which develops through learning. The authors examined the course of vocal development in budgerigars from hatching to about 4 weeks postfledging (approximately 85 days old). Food-begging calls showed changes in duration, peak frequency, bandwidth, and frequency modulation with age. Within a week of fledging, each bird produced a contact call bearing a strong resemblance to a shortened version of its patterned food-begging call. By 4 weeks postfledging, budgerigar contact call repertoires often contained more than one call type, and there was clear evidence of sharing and imitation among the calls of parents, fledglings, and other social companions. Perceptual testing showed that whereas acoustic variation in the structure of developing calls decreased both within and between nestling birds, the discrimination of these calls was easier for adult birds as young birds matured. These results suggest parallels with certain aspects of language development in humans. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perception of species-specific contact calls by budgerigars (Melopsittacus undulatus).

In Exp I, 3 budgerigars were trained with operant techniques to discriminate examples of species-specific contact calls (5 male and 5 female). In Exp II, Ss were tested on vocalizations from 5 male and 5 female canaries. Ss showed an equivalent ability to discriminate and remember both budgerigar and canary calls. Additional tests (Exps III and IV) showed that both temporal and spectral cues were important in Ss' discrimination of species-specific calls. However, spectral cues occurring in the region of 2.0–4.0 kHz appeared to be critical for the discrimination. Results support the notion of a generalized, but highly sophisticated, perceptual learning system in the budgerigar for the processing of vocal signals. The perceptual and memory skills involved in this learning system are discussed. (38 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Free-field binaural unmasking in budgerigars ( Melopsittacus undulatus ).

The detection of signals in noise is important for understanding both the mechanisms of hearing and how the auditory system functions under more natural conditions. In humans, the auditory system gains some improvement if the signal and noise are separated in space (binaural masking release). Birds with small heads are at a disadvantage in separating noise and signal sources relative to large mammals, because interaural time differences are much smaller. Two binaural phenomena in budgerigars related to the detection of tones in noise were examined. Budgerigars show 8 dB of free-field binaural masking release when signal and noise are presented to their right side and correlated noise is presented to their left side. Budgerigars also show a spatial masking release of 9 dB when a signal and noise are separated in azimuth by 90°. These results are similar to those found in humans and other mammals with much larger heads. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perception of conspecific faces by budgerigars (Melopsittacus undulatus): I. Natural faces.

Perception of faces by 4 budgerigars, a species of small parrot, was studied with a same–different discrimination task. Reaction times (RTs) were taken as a measure of the similarity between pairs of faces and analyzed with multidimensional scaling to reveal patterns of similarity among the faces. The perception of natural faces was tested to determine which characteristics were perceptually salient. Color, patterns of markings, darkness of the iris, and size of the pupil corresponded to the observed patterns of similarity among the faces. Differences among budgerigar faces were more salient than differences among zebra finch faces, and budgerigar faces were perceptually distinct from the faces of other avian species. The results from these experiments provide a basis for understanding the ways in which these signals function in the coordination of social behaviors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perception of conspecific faces by budgerigars (Melopsittacus undulatus): II. Synthetic models.

Perception of faces by budgerigars was studied with computerized images modeled after natural faces. Individual facial characteristics were varied with all others held constant; then relative importance among several features was determined by varying each within a single experiment. Characteristics with the potential to signal important biological information (e.g., age or sex) were perceptually salient, whereas characteristics that vary among faces but have limited potential to signal important information were not. Model faces were also presented in a normal or an altered configuration. Birds discriminated among faces in a normal configuration more easily than among models with an altered configuration even when the facial features on which the discrimination was based differed in the same way; this suggests that configurational cues play an important role in face perception by budgerigars. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Vocal plasticity in budgerigars (Melopsittacus undulatus): Evidence for social factors in the learning of contact calls.

Recorded distance or contact calls of 6 unrelated adult male budgerigars before and during 8 wks of social contact. The 6 birds were housed in 2 separate groups of 3 each in adjoining cages. Birds in each cage could hear but not see the birds in the neighboring cage. At the beginning of the study, none of the birds shared any contact call types. The first appearance of 1 bird's imitation of a cagemate's contact call type occurred after 1 wk. Call type repertoires continued to change; some call types dropped out of the repertoires, and others were modified over time. Birds in the same cage shared the same dominant call type 8 wks later, and the dominant call types differed between the 2 cages. Thus, budgerigars can learn calls as adults, and call type convergence is achieved through mutual vocal imitation of social companions. In the absence of social but not aural contact, vocal imitation was greatly reduced. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Control of vocal repertoire by reward in budgerigars (Melopsittacus undulatus).

The calls of some bird species may be modified by reward and punishment. However, the operant control of vocal topographies (i.e., the effect of reward or punishment on the physical dimensions of a vocal response) in such species has not been extensively explored. Using a computer-based, real-time system for rewarding vocalizations with food, the authors placed 3 budgerigars under a frequency-dependent reward schedule. During a session, the budgerigars received food for each vocalization that differed from the last N rewarded vocalizations. It was found that each of the budgerigars adapted their vocalizations to this procedure. When the value of N was 1 or 2, the birds "solved" the frequency-dependent schedule by developing N ?+?1 call types and used a simple "win stay, lose switch" sequencing strategy. At N?=?3, 1 of the birds again produced N ?+?1 (i.e., 4) call types, and another solved the criterion by markedly increasing call variability. New calls developed from the elements of old call types and using multidimensional scaling techniques, the authors traced the evolution of each new call type from the previous experimental call repertoire. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hearing and vocalizations of wild-caught Australian budgerigars (Melopsittacus undulatus).

This study examined the hearing and contact calls of wild-caught Australian budgerigars (Melopsittacus undulatus) and compared these data to hearing and vocalizations in the much more extensively studied domesticated budgerigar. The spectral energy in the contact calls of both wild-caught and domesticated budgerigars falls almost exclusively in the frequency of 2–4 kHz. Absolute and masked thresholds were similar in both groups of birds. Similar to the results found in domesticated birds, critical ratio functions for the wild-caught budgerigars decreased at frequencies of 1.0 kHz–2.86 kHz and then increased again dramatically at frequencies above 2.86 kHz. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial unmasking of birdsong in zebra finches (Taeniopygia guttata) and budgerigars (Melopsittacus undulatus).

Budgerigars and zebra finches were tested, using operant conditioning techniques, on their ability to identify a zebra finch song in the presence of a background masker emitted from either the same or a different location as the signal. Identification thresholds were obtained for three masker types differing in their spectrotemporal characteristics (noise, modulated noise, and a song chorus). Both bird species exhibited similar amounts of spatial unmasking across the three masker types. The amount of unmasking was greater when the masker was played continuously compared to when the target and masker were presented simultaneously. These results suggest that spatial factors are important for birds in the identification of natural signals in noisy environments. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Detection of changes in timbre and harmonicity in complex sounds by zebra finches (Taeniopygia guttata) and budgerigars (Melopsittacus undulatus).

Thresholds for detecting alterations in the timbre and harmonicity of complex harmonic signals were measured in zebra finches, budgerigars, and humans. The stimuli used in this experiment were designed to have particular salience for zebra finches by modeling them after natural zebra finch calls. All 3 species showed similar abilities for detecting an amplitude decrement in a single component of a harmonic complex. However, zebra finches and budgerigars were extraordinarily sensitive to the mistunings of single harmonics and exhibited significantly lower thresholds compared with humans at 2 different fundamental frequencies, 570 Hz and 285 Hz. Randomizing relative phases of components in a harmonic stimulus resulted in a significant increase in threshold for detecting in zebra finches but not in humans. Decreasing the duration of mistuned harmonic stimuli resulted in higher thresholds for both birds and humans. The overall superiority of birds in discriminating inharmonicity suggests that birds and mammals may use different strategies in processing these complex harmonic sounds. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of deafening on the development of nestling and juvenile vocalizations in budgerigars (Melopsittacus undulatus).

The effects of complete and partial cochlear extirpation at ages 9–11 days posthatch were assessed in 5 nestling budgerigars (Melopsittacus undulatus) to determine if auditory feedback is necessary for the production of nestling vocalizations. Although early deafening had no effect on the production of food-begging calls produced during the first 2 weeks posthatch, deafening did disrupt the expected transition from these early calls to the longer and more complex frequency-modulated, patterned food-begging calls normally appearing 3–4 weeks posthatch. All birds sustaining either complete or partial cochlear extirpation failed to develop stereotyped contact calls around the time of fledging at 5 weeks. These results are consistent with previous research showing that deafened nestlings do not develop normal contact calls (R. J. Dooling, B. R Gephart, P. H. Price, C. McHale, & S. E. Brauth; see record 1989-32132-001) and also indicate that a form of sensorimotor learning is involved in the production of mature, patterned food-begging calls in budgerigars. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Budgerigars (Melopsittacus undulatus) Copy Virtual Demonstrators in a Two-Action Test.

Juvenile budgerigars (Melopsittacus undulatus) observed thin film transistor video playback of a virtual conspecific demonstrator using its beak to remove a stopper from a food box, either by pulling the object upward or by pushing it downward. Simultaneously (Experiment 1) or subsequently (Experiment 2), the observers were offered a similar stopper box and rewarded with access to food for each removal response, regardless of its direction. Observers of upward movement made a greater proportion of up responses in total and showed a stronger tendency to increase the proportion of up responses over test trials than observers of downward movement. These findings provide the first demonstration of which the authors are aware that birds are able not only to detect and respond to a moving video image but also to copy its movements. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Frequency selectivity in the parakeet (Melopsittacus undulatus) studied with psychophysical tuning curves.

Seven parakeets were trained to avoid shock during pure-tone stimulation. A modified method of limits was used to measure detection thresholds of the pure tones. The intensity of masker tones, at numerous frequencies, was varied to measure the masked threshold of a probe-tone signal set at a fixed frequency and intensity. Masking curves were obtained for 3 probe tones (.63, 1.6, and 2.5 kHz) at each of 5 sensation levels (10, 20, 30, 40, and 50 db). The masking curves from this procedure, which are frequently referred to as "psychophysical tuning curves," provide an indication of frequency selectivity. Results are compared with analogous data in other species and suggest that frequency analysis in the parakeet ear is somewhat less accurate than in the mammalian ear. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The discrimination of natural movement by budgerigars (Melopsittacus undulates) and pigeons (Columba livia).

Three experiments examined the ability of birds to discriminate between the actions of walking forwards and backwards as demonstrated by video clips of a human walking a dog. Experiment 1 revealed that budgerigars (Melopsittacus undulates) could discriminate between these actions when the demonstrators moved consistently from left to right. Test trials then revealed that the discrimination transferred, without additional training, to clips of the demonstrators moving from right to left. Experiment 2 replicated the findings from Experiment 1 except that the demonstrators walked as if on a treadmill in the center of the display screen. The results from the first 2 experiments were replicated with pigeons in Experiment 3. The results cannot be explained if it is assumed that animals rely on static cues, such as those derived from individual postures, in order to discriminate between the actions of another animal. Instead, this type of discrimination appears to be controlled by dynamic cues derived from changes in the posture of the demonstrators. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Nonsimultaneous auditory masking in the budgerigar (Melopsittacus undulatus).

Compared the frequency resolving power of 3 male budgerigar birds and 3 humans on several nonsimultaneous masking procedures in which one pure tone was used to mask another. Similar patterns of frequency selectivity were found for all 3 masking procedures (forward, backward, and combined forward/backward) for both species. Budgerigars showed considerably greater frequency resolving power on all 3 procedures than humans. Budgerigars also showed differences in frequency resolving power across masking conditions, but human Ss did not. Results indicate that the budgerigar auditory system may be even more highly tuned than was previously thought and suggest fundamental differences between the mechanisms of frequency selectivity of birds and humans. (19 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The direction and range of ambient temperature change influences yawning in budgerigars (melopsittacus undulatus).

Comparative research suggests that yawning is a thermoregulatory behavior in homeotherms. Our previous experiments revealed that yawning increased in budgerigars (Melopsittacus undulatus) as ambient temperature was raised toward body temperature (22→34 °C). In this study, we identify the range of temperatures that triggers yawning to rule out the possible effect of changing temperature in any range. To corroborate its thermoregulatory function, we also related the incidence of yawning to other avian thermoregulatory behaviors in budgerigars (e.g., panting, wing venting). In a repeated measures design, 16 budgerigars were exposed to 4 separate 10-min periods of changing temperatures: (a) low-increasing (23→27 °C), (b) high-increasing (27→33 °C), (c) high-decreasing (34→28 °C), and (d) low-decreasing (28→24 °C). Birds yawned significantly more during the high-increasing temperature range, and yawning was positively correlated with ambient temperature across trials. Yawning was also positively correlated with other thermoregulatory behaviors. This research clarifies the previously demonstrated relationship between yawning rate and temperature by providing evidence that the physiological trigger for yawning is related to increasing body temperatures rather than the detection of changing external temperatures. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acoustic classification of alarm calls by vervet monkeys (Cercopithecus aethiops) and humans (Homo sapiens): I. Natural calls.

A 2-choice, operant-conditioning-based classification procedure was developed in which vervet monkeys (Cercopithecus aethiops) categorized species-typical snake and eagle alarm calls recorded from individually identified free-ranging animals. After preliminary training with a pair of calls from a single animal, 2 vervets were tested with novel exemplars produced by a variety of callers. Experiment 1 combined testing with continued training in routine classification of 14 new calls. In Experiment 2, the Ss were tested with 48 novel calls in rapid succession. Human (Homo sapiens) control Ss participated in the 1st study without extended preliminary training. Monkey and human Ss both showed immediate transfer to classification of unfamiliar alarm calls, despite variations both in voice characteristics and reproduction quality. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acoustic classification of alarm calls by vervet monkeys (Cercopithecus aethiops) and humans (Homo sapiens): II. Synthetic calls.

In 2 experiments classification of synthetic versions of species-typical snake and eagle alarm calls by vervet monkeys (Cercopithecus aethiops) and human (Homo sapiens) control Ss was investigated. In a 2-choice, operant-conditioning-based procedure, this work followed up acoustic analyses that had used various digitally based algorithms (M. J. Owren and R. H. Bernacki; see record 1989-10972-001). All Ss were first tested with alarm-call replicas that were based on analysis data. These models were classified in the same manner as natural stimuli, which verified the appropriateness of the acoustic charcterizations. Synthetic stimuli were then presented to test the importance of specific acoustic cues. Spectral patterning was found to be the most salient cue for classification by the monkeys, whereas results from the human Ss were mixed. Implications for the study of nonhuman primate vocalizations and P. Lieberman's (1984) theory of speech evolution are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)