Flexible serial response learning by pigeons (Columba livia) and humans (Homo sapiens)

Experimental tasks designed to involve procedural memory are often rigid and unchanging, despite many reasons to expect that implicit learning processes can be flexible and support considerable variability. A version of the serial response time (SRT) task was developed, in which the locations of targets were probabilistically determined. Targets appeared in locations according to both a structured sequence and a cue validity parameter, and the time to respond to each target was measured. Pigeons (Columba livia) and humans (Homo sapiens) both showed response time facilitation at the highest tested value for cue validity, and the magnitude of that facilitation gradually weakened as cue validity was decreased. Both species showed evidence that response times were largely determined by the local predictabilities of individual cue locations. In addition, humans showed some evidence that explicit knowledge of the sequence affected response times, specifically when cue validity was 100%.     

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

Three experiment 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 perceptionand use of features and contextual information in the discrimination of line information.     

Interpreting the effects of image manipulation on picture perception in pigeons (Columba livia) and humans (Homo sapiens)

The effects of picture manipulations on humans' and pigeons' performance were examined in a go/no-go discrimination of two perceptually similar categories, cat and dog faces. Four types of manipulation were used to modify the images. Mosaicization and scrambling were used to produce degraded versions of the training stimuli, while morphing and cell exchange were used to manipulate the relative contribution of positive and negative training stimuli to test stimuli. Mosaicization mainly removes information at high spatial frequencies, whereas scrambling removes information at low spatial frequencies to a greater degree. Morphing leads to complex transformations of the stimuli that are not concentrated at any particular spatial frequency band. Cell exchange preserves high spatial frequency details, but sometimes moves them into the "wrong" stimulus. The four manipulations also introduce high-frequency noise to differing degrees. Responses to test stimuli indicated that high and low spatial frequency information were both sufficient but not necessary to maintain discrimination performance in both species, but there were also species differences in relative sensitivity to higher and lower spatial frequency information.     

Frequency-range discriminations and absolute pitch in black-capped chickadees (Poecile atricapillus), mountain chickadees (Poecile gambeli), and zebra finches (Taeniopygia guttata)

The acoustic frequency ranges in birdsongs provide important absolute pitch cues for the recognition of conspecifics. Black-capped chickadees (Poecile atricapillus), mountain chickadees (Poecile gambeli), and zebra finches (Taeniopygia guttata) were trained to sort tones contiguous in frequency into 8 ranges on the basis of associations between response to the tones in each range and reward. All 3 species acquired accurate frequency-range discriminations, but zebra finches acquired the discrimination in fewer trials and to a higher standard than black-capped or mountain chickadees, which did not differ appreciably in the discrimination. Chickadees' relatively poorer accuracy was traced to poorer discrimination of tones in the higher frequency ranges. During transfer tests, the discrimination generalized to novel tones when the training tones were included, but not when they were omitted.     

Cross-fostering diminishes song discrimination in zebra finches (Taeniopygia guttata)

Song-production, -discrimination, and -preferences in oscine birds are dually influenced by species identity and the ontogenetic environment. The cross-fostering of a model species for recognition research, the zebra finch (Taeniopygia guttata) into heterospecific nests of the Bengalese finch (Lonchura striata vars. domestica) allows an exploration of the sensory limits of early development and the effects of species-specific acoustic cues upon song discrimination in adulthood. To quantify the song preferences of female and male normal-reared (control) and Bengalese finch fostered zebra finches, we recorded multiple behavioral measures, including spatial proximity, vocalization rates and response latency, during sequential song-playback choice-trials using both tutor species’ songs and the songs of two other ecologically relevant Australian species, the owl finch (Taeniopygia bichenovii) and the star finch (Neochmia ruficauda). Response strength was variable between the different measures, but no differences were detected within the specific behavioral responses towards the song playbacks of the two sexes. Control subjects strongly preferred their own species’ songs while Bengalese-fostered zebra finches exhibited reduced song discrimination between con-, tutor-, and heterospecific songs. Overall behavioral responsiveness was also modulated by social ontogeny. These results indicate a difference in the strength of preference for song that is dependent on the species identity of the rearing environment in oscine birds and illustrate the role of multiple behavioral measures and ecologically relevant stimulus species selection in behavioral research using zebra finches.     

Imitation of conditional discriminations in pigeons (Columba livia)

In the present experiments, the 2-action method was used to determine whether pigeons could learn to imitate a conditional discrimination. Demonstrator pigeons (Columba livia) stepped on a treadle in the presence of 1 light and pecked at the treadle in the presence of another light. Demonstration did not seem to affect acquisition of the conditional discrimination (Experiment 1) but did facilitate its reversal of the conditional discrimination (Experiments 2 and 3). The results suggest that pigeons are not only able to learn a specific behavior by observing another pigeon, but they can also learn under which circumstances to perform that behavior. The results have implications for proposed mechanisms of imitation in animals.     

Time discrimination in Columba livia and Homo sapiens.

Pigeons' ability to discriminate stimulus duration, focusing on stimuli less than 1 s in duration, was evaluated in 4 experiments. In Experiment 1, the performances of pigeons and humans were compared with a staircase technique, and in Experiment 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 (Getty, 1975). Experiment 3 demonstrated that the birds did not use perceived brightness to mediate the discrimination of brief visual durations. Experiment 4 used a modified staircase procedure that yielded a continuous measure of discrimination from absolute threshold (0 s) to about 1 s. The difference thresholds were constant over a considerable range, similar to findings reported by Kristofferson (1980) for human timing.     

Discrimination of artificial categories structured by family resemblances: a comparative study in people (Homo sapiens) and pigeons (Columba livia)

Adult humans (Homo sapiens) and pigeons (Columba livia) were trained to discriminate artificial categories that the authors created by mimicking 2 properties of natural categories. One was a family resemblance relationship: The highly variable exemplars, including those that did not have features in common, were structured by a similarity network with the features correlating to one another in each category. The other was a polymorphous rule: No single feature was essential for distinguishing the categories, and all the features overlapped between the categories. Pigeons learned the categories with ease and then showed a prototype effect in accord with the degrees of family resemblance for novel stimuli. Some evidence was also observed for interactive effects of learning of individual exemplars and feature frequencies. Humans had difficulty in learning the categories. The participants who learned the categories generally responded to novel stimuli in an all-or-none fashion on the basis of their acquired classification decision rules. The processes that underlie the classification performances of the 2 species are discussed.     

Rapidly learned song-discrimination without behavioral reinforcement in adult male zebra finches (Taeniopygia guttata)

Zebra finches communicate via several distinct vocalizations, of which song is the most studied. Behavioral observations indicate that adults are able to discriminate among the songs of different conspecific individuals. In the wild, zebra finches live in structured but mobile colonies, and encounter new individuals on a frequent basis. Thus it seems plausible that adult finches might have the capacity to recognize and remember new songs they encounter on a single day, but this has never been directly tested. Here we devised a simple observational assay to determine whether adult male zebra finches show recognition of a song they have heard repeatedly from taped playbacks, over a single three hour period the day before. We quantified the rate of production of six discrete behaviors (short calls, contact calls, singing, short hops, long hops, and beak swipes) made by adult male zebra finches as they listened to the playbacks. At the onset of song playback, all birds suspended these behaviors and sat silently-occasionally moving their heads. Then, after a measurable period ("response latency"), the birds resumed these activities. We observed that the response latency was long (approximately 10 min) when birds were hearing a particular song for the first time. The response latency was much shorter (approximately 1-2 min) when the birds had heard the same song the day before. Thus, functional song memories must result from as little as 3 h of passive song-exposure. These results suggest that ongoing song learning may play a natural role in the daily life of adult zebra finches, and provide a behavioral reference point for studies of molecular and physiological plasticity in the adult auditory system.     

Song perception during the sensitive period of song learning in zebra finches (Taeniopygia guttata)

The sensitive period is a special time for auditory learning in songbirds. However, little is known about perception and discrimination of song during this period of development. The authors used a go/no-go operant task to compare discrimination of conspecific song from reversed song in juvenile and adult zebra finches (Taeniopygia guttata), and to test for possible developmental changes in perception of syllable structure and syllable syntax. In Experiment 1, there were no age or sex differences in the ability to learn the discrimination, and the birds discriminated the forward from reversed song primarily on the basis of local syllable structure. Similar results were found in Experiment 2 with juvenile birds reared in isolation from song. Experiment 3 found that juvenile zebra finches could discriminate songs on the basis of syllable order alone, although this discrimination was more difficult than one based on syllable structure. The results reveal well-developed song discrimination and song perception in juvenile zebra finches, even in birds with little experience with song.     

Effects of humidity on reproductive behavior in male and female zebra finches (Taeniopygia guttata).

Zebra finches (Taeniopygia guttata) are regarded as opportunistic breeders with reproductive behaviors mediated by short-term proximal environmental conditions. This article provides experimental evidence for the role of humidity in reproductive behaviors. Zebra finches were subjected to experimentally manipulated high levels of relative humidity. Males gathered more nest material and sang more. Females showed no relationship between humidity and gathering nest materials, egg laying, or changes in rates of vocalization.     

Effect of acoustic cue modifications on evoked vocal response to calls in zebra finches (Taeniopygia guttata)

Besides their song, which is usually a functionally well-defined communication signal with an elaborate acoustic structure, songbirds also produce a variety of shorter vocalizations named calls. While a considerable amount of work has focused on information coding in songs, little is known about how calls' acoustic structure supports communication processes. Because male and female zebra finches use calls during most of their interactions and answer to conspecific calls without visual contact, we aimed at identifying which calls' acoustic cues are necessary to elicit a vocal response. Using synthetic zebra finch calls, we examined evoked vocal response of male and female zebra finches to modified versions of the distance calls. Our results show that the vocal response of zebra finches to female calls requires the full harmonic structure of the call, whereas the frequency downsweep of male calls is necessary to evoke a vocal response. It is likely that both female and male calls require matching a similar frequency bandwidth to trigger a response in conspecific individuals.     

Syllable chunking in zebra finch (Taeniopygia guttata) song.

We examined how 61 young zebra finch (Taeniopygia guttata) males copied song from 5 adult tutors. Zebra finch song consists of a string of 5-15 distinct syllables, and these syllables were copied as chunks, or strings of consecutive syllables (modal length = 3). The silent interval between 2 syllables was copied as part of the syllable after the silence. Copied chunks had boundaries that fell at consistent locations within the tutor's song, marked by a relatively long intersyllable silent period, a transition between call-like and noncall-like syllables, and a tendency for the tutor male to stop his song short. Young males also tended to break their songs off at the boundaries of the chunks they had copied. Chunks appear to be an intermediate level of hierarchy in song organization and to have both perceptual (syllables were learned as part of a chunk) and motor (song delivery was broken almost exclusively at chunk boundaries) aspects.     

Timbre control in zebra finch (Taeniopygia guttata) song syllables

Zebra finch (Taeniopygia guttata) song syllables often include harmonically related frequency components. These harmonics may be suppressed, and this differential emphasis varies between the syllables in a song and between individual birds' songs. These patterns of harmonic suppression are timbre. Individual syllables' patterns of harmonic suppression are constant with adult males' songs. Young males that imitate the songs of older males also imitate their patterns of harmonic suppression. Syringeal denervation distorts these patterns, which suggests that they are produced through active control of the vocal organ. The selective suppression and emphasis of some harmonics creates a great number of possible timbre variants for any one syllable. These add signal diversity to the limited array of frequency modulations and range of fundamental frequencies found in zebra finch song. Analyses of bird song that disregard timbre may overlook a feature that is important in vocal communication.     

Timbre discrimination in zebra finch (Taeniopygia guttata) song syllables

Zebra finch (Taeniopygia guttata) songs include syllables of a fundamental frequency and harmonics. Individual harmonics in 1 syllable can be more or less emphasized. The functional role of this variability is unknown. These experiments provide evidence of how the phenomenon is perceived. We trained 12 male and female zebra finches on a go-no-go operant procedure to discriminate between 2 song syllables that varied only in the absence of the 2nd or 5th harmonic. Training involved many thousands of trials. Both sexes used the presence or absence of the 2nd harmonic as the sole discriminative cue. Females had more difficulty learning to perform the task when the presence of the 2nd harmonic was the go stimulus, which indicates that their use of the information was biased by stimulus-response contingencies. The results are discussed in terms of a broad strategy to understand how animals perceive sounds used in communication.     

Representation of serial order in pigeons (Columba livia)

In Experiment 1, 2 groups of pigeons were trained to respond to either a 4-item (A→B→C→D) or 5-item (A→B→C→D→E) list. After learning their respective list, half of the subjects were trained on a positive pair with reinforcement provided when pairs were responded to in the order true to that of the original sequence (4-item: B→C; 5-item: B→D). The remaining subjects were trained on a negative pair with reinforcement provided for responding to the pairs in the order opposite to that learned in the original sequence (4-item: C→B; 5-item: D→B). Subjects in the positive pair condition learned their respective pair faster than did subjects in the negative pair condition. In Experiment 2, after reaching criterion on a 4-item list, subjects received 16 BC probe trials spread across 4 sessions of training. Subjects performed significantly above chance on the probe trials. The performance of our subjects in Experiments 1 and 2 demonstrates that, similar to monkeys, pigeons form a representation of the lists that they learn.     

Imitation and affordance learning by pigeons (Columba livia)

The bidirectional control procedure was used to determine whether pigeons (Columba livia) would imitate a demonstrator that pushed a sliding screen for food. One group of observers saw a trained demonstrator push a sliding screen door with its beak (imitation group), whereas 2 other groups watched the screen move independently (possibly learning how the environment works) with a conspecific either present (affordance learning with social facilitation) or absent (affordance learning alone). A 4th group could not see the screen being pushed (sound and odor control). Imitation was evidenced by the finding that pigeons that saw a demonstrator push the screen made a higher proportion of matching screen pushes than observers in 2 appropriate control conditions. Further, observers that watched a screen move without a demonstrator present made a significantly higher proportion of matching screen pushes than would be expected by chance. Thus, these pigeons were capable of affordance learning.     

Breeding cycle aggression in domesticated zebra finches (Poephila guttata)

Patterns of breeding cycle aggressive behavior were examined in colonies of domesticated zebra finches (Poephila guttata). Aggressive behaviors of zebra finch pairs were low during non-nesting periods but were maintained at high levels during the three nesting periods: the incubating, hatching, and nestling periods. Defense of the nest site was the prominent functional category of aggression, followed by defense of individual distance. Defense of mate, defense of young, and defense of nesting material rarely occurred. Male and female members of pair bonds shared the duties of defense of the nest site and parental care. During observation times males exhibited greater frequencies of aggressive actions throughout the breeding cycle and females spent a greater amount of time in the nest during the three nesting periods. The pattern and functional categories of aggressive behavior in the zebra finch colonies correspond most closely to the nest site defense hypothesis for the evolution of breeding season aggression.     

Information processing by pigeons (Columba livia): incentive as information

Experiment 1 showed that the Hick-Hyman law (W. E. Hick, 1952; R. Hyman, 1953) described the effects of anticipated reinforcement, a form of incentive, on pigeons' (Columba livia) reaction time to respond to a target spatial location. Reaction time was an approximately linear function of amount of information interpreted as probability of reinforcement, implying that pigeons processed incentive at a constant rate. Experiment 2 showed that the Hick-Hyman law described effects of incentive even when it varied from moment to moment in a serial reaction time task similar to that of M. J. Nissen and P. Bullemer (1987), and processing information about target spatial location modulated absolute reaction time and not rate of processing incentive. The results support mental continuity and provide comparative support for the idea of the economics of information in economic theory about the incentive value of information.     

Choice biases in no-sample and delay testing in pigeons (Columba livia)

Animal Cognition - In experimental tasks that involve stimuli that vary along a quantitative continuum, some choice biases are commonly found. Take, for instance, a matching-to-sample task where...