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)     

Differential effects of visual context on pattern discrimination by pigeons (Columba livia) and humans (Homo sapiens).

Three experiments examined the role of contextual information during line orientation and line position discriminations by pigeons (Columba livia) and humans (Homo sapiens). Experiment 1 tested pigeons' performance with these stimuli in a target localization task using texture displays. Experiments 2 and 3 tested pigeons and humans, respectively, with small and large variations of these stimuli in a same-different task. Humans showed a configural superiority effect when tested with displays constructed from large elements but not when tested with the smaller, more densely packed texture displays. The pigeons, in contrast, exhibited a configural inferiority effect when required to discriminate line orientation, regardless of stimulus size. These contrasting results suggest a species difference in the perception and use of features and contextual information in the discrimination of line information. (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)     

Auditory scene analysis by songbirds: Stream segregation of birdsong by European starlings (Sturnus vulgaris).

Three experiments examined the capacity of European starlings to segregate perceptually 2 superimposed, intermixed auditory stimuli. The stimuli were 10-s song samples from 2 of 4 songbird species: European starling, brown thrasher, mockingbird, and nightingale. The birds first learned a discrimination between the intermixed song pairs. Then, they maintained the discrimination with novel song exemplars in the mixtures and when song stimuli for each species were presented alone. Performance fell, but remained above chance, when song pairs were mixed with the dawn chorus of bird song. The results show that starlings were identifying the songs of individual species within the baseline superimposed song pairs, a process of auditory stream segregation and scene analysis (A. S. Bregman, 1990). (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)     

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)     

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)     

Auditory localization skills in mentally retarded children.

Measured the gross auditory and visual localization skills of 24 6–18 yr old mentally retarded Ss. Half of the Ss were selected randomly from a group of residents who had demonstrated visual discrimination skills and auditory speech discrimination skills. The other Ss were selected randomly from a group of residents who demonstrated visual discrimination skills but not auditory speech discrimination. Findings indicate that all Ss who previously demonstrated auditory speech discrimination passed the auditory localization task, and all Ss who previously failed to demonstrate auditory speech discrimination failed the auditory localization task. It is suggested that auditory localization skills may be used as an approximation to the development of auditory speech discrimination skills. (9 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Letter localization, not discrimination, is constrained by attention

Shaw (1984; Shaw, Mulligan & Stone, 1983) measured the probability of detecting a target letter in displays containing different numbers of items. The set size effect was significantly larger than the effect predicted by unlimited-capacity models of visual processing, and Shaw concluded that attention constrains the discrimination of complex, but not simple, patterns. We re-examined the role of attention in letter discrimination by measuring the effect of set size on the contrast needed to identify a target embedded among distractors. The results of 5 experiments show that set size effects are small for letter discrimination, but large for letter localization. The findings suggest that the large set size effect reported by Shaw (1984) was a result of asking subjects to localize the target. In addition, the results are consistent with the hypothesis that limited processing capacity constrains the perceptual processes involved in letter localization, but not discrimination.     

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)     

Numerical discrimination by rats (Rattus norvegicus) using body and vibrissal touch.

Three experiments were performed to test if tactile stimuli could serve as the basis for a numerical discrimination in rats (Rattus norvegicus). In Experiment 1, touch delivered symmetrically to both sides of the animal's body yielded no evidence of numerical discrimination. In Experiment 2, the restriction of tactile cues to one side of the animal's body resulted in marginally better results, although performance remained below conventional levels of significance. In Experiment 3, tactile contact with the animal's vibrissae yielded statistically significant evidence of numerical processing. Subjects learned to enter one arm of a Y-maze when three vibrissal deflections were presented, and the other arm when either two or four stimuli occurred. The demonstration of a two-three-four discrimination extends the use of this relatively complex intermediate number procedure from a previous demonstration in rats involving auditory stimuli (Davis & Albert, 1986) and indicates for the first time in any species that touch may be used as the basis for numerical behavior. (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)     

Echo suppression and discrimination suppression aspects of the precedence effect

The precedence effect is a phenomenon that may occur when a sound from one direction (the lead) is followed within a few milliseconds by the same or a similar sound from another direction (the lag, or the echo). Typically, the lag sound is not heard as a separate event, and changes in the lag sound's direction cannot be discriminated. The hypothesis is proposed in this study that these two aspects of precedence (echo suppression and discrimination suppression) are at least partially independent phenomena. Two experiments were conducted in which pairs of noise bursts were presented to subjects from two loudspeakers in the horizontal plane to simulate a lead sound and a lag sound (the echo). Echo suppression threshold was measured as the minimum echo delay at which subjects reported hearing two sounds rather than one sound; discrimination suppression threshold was measured as the minimum echo delay at which subjects could reliably discriminate between two positions of the echo. In Experiment 1, it was found that echo suppression threshold was the same as discrimination suppression threshold when measured with a single burst pair (average 5.4 msec). However, when measured after presentation of a train of burst pairs (a condition that may produce "buildup of suppression"), discrimination suppression threshold increased to 10.4 msec, while echo suppression threshold increased to 26.4 msec. The greater buildup of echo suppression than of discrimination suppression indicates that the two phenomena are distinct under buildup conditions and may be the reflection of different underlying mechanisms. Experiment 2 investigated the effect of the directional properties of the lead and lag sounds on discrimination suppression and echo suppression. There was no consistent effect of the spatial separation between lead and lag sources on discrimination suppression or echo suppression, nor was there any consistent difference between the two types of thresholds (overall average threshold was 5.9 msec). The negative result in Experiment 2 may have been due to the measurements being obtained only for single-stimulus conditions and not for buildup conditions that may involve more central processing by the auditory system.     

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)     

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)     

Open-ended categorization of chick-a-dee calls by black-capped chickadees (Poecile atricapilla).

The authors trained black-capped chickadees (Poecile atricapilla) in an operant discrimination with exemplars of black-capped and Carolina chick-a-dee calls, with the goal of determining whether the birds memorized the calls of conspecifics and heterospecifics or classified the calls by species. Black-capped calls served as both rewarded (S+) and unrewarded (S-) stimuli (the within-category discrimination), whereas Carolina chick-a-dee calls served as S-s (the between-category discrimination) in the black-capped chick-a-dee call S+ group. The Carolina call S+ group had Carolina calls as S+s and S-s (within-category) and black-capped calls as S-s (between-category). Both groups discriminated between call categories faster than within a call category. In 2 subsequent experiments, both S+ groups showed transfer to novel calls and propagation back to between-category calls. The results favor the hypothesis that the acoustically similar social calls of the 2 species constitute separate open-ended categories. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Time discrimination in Columba livia and Homo sapiens..

Evaluates pigeons' ability to discriminate stimulus duration, focusing on stimuli less than 1 sec in duration, in 4 experiments. In Exp 1, the performances of pigeons and humans were compared with a staircase technique, and in Exp 2, the method of constant stimuli was used. Both experiments produced similar results: The pigeon and human data were well described by the generalized form of Weber's law (D. J. Getty; see record 1975-30865-001). Exp 3 demonstrated that the birds did not use perceived brightness to mediate the discrimination of brief visual durations. Exp 4 used a modified staircase procedure that yielded a continuous measure of discrimination from absolute threshold (0 sec) to about 1 sec. The difference thresholds were constant over a considerable range, similar to findings reported by A. B. Kristofferson (see record 1981-09423-001) for human timing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Auditory scene analysis in Estrildid finches (Taeniopygia guttata and striata domestica): A species advantage for detection of conspecific song.

Operant-conditioning techniques were used to investigate the ability of zebra finches (Taeniopygia guttata) and Bengalese finches (Lonchura striata domestica) to detect a zebra finch or a Bengalese finch target song intermixed with other birdsongs. Sixteen birds were trained to respond to the presence of a particular target song, either of their own species (n?=?8) or of another species (n?=?8). The birds were able to learn a discrimination between song mixtures that contained a target song and song mixtures that did not, and they were able to maintain their response to the target song when it was mixed with novel songs. Zebra finches, but not Bengalese finches, learned the discrimination with a conspecific target more quickly and were worse at detecting a Bengalese finch in the presence of a conspecific song. The results indicate that selective attention to birdsongs within an auditory scene is related to their biological relevance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Human listeners provide insights into echo features used by dolphins (Tursiops truncatus) to discriminate among objects.

Echolocating bottlenose dolphins (Tursiops truncatus) discriminate between objects on the basis of the echoes reflected by the objects. However, it is not clear which echo features are important for object discrimination. To gain insight into the salient features, the authors had a dolphin perform a match-to-sample task and then presented human listeners with echoes from the same objects used in the dolphin's task. In 2 experiments, human listeners performed as well or better than the dolphin at discriminating objects, and they reported the salient acoustic cues. The error patterns of the humans and the dolphin were compared to determine which acoustic features were likely to have been used by the dolphin. The results indicate that the dolphin did not appear to use overall echo amplitude, but that it attended to the pattern of changes in the echoes across different object orientations. Human listeners can quickly identify salient combinations of echo features that permit object discrimination, which can be used to generate hypotheses that can be tested using dolphins as subjects. (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)