Studying the Song Development Process: Rationale and Methods

Current technology makes it possible to measure song development continuously throughout a vocal ontogeny. Here we briefly review some of the problems involved and describe experimental and analytic methods for automatic tracing of vocal changes. These techniques make it possible to characterize the specific methods the bird uses to imitate sounds: an automated song recognition procedure allows continuous song recording, followed by automated sound analysis that partition the song to syllables, extract acoustic features of each syllable, and summarize the entire song development process over time into a single database. The entire song development is then presentable in the form of images or movie clips. These Dynamic Vocal Development (DVD) maps show how each syllable type emerges, and how the bird manipulates syllable features to eventually approximate the model song. Most of the experimental and analytic methods described here have been organized into a software package, which also allows combined neural and sound recording to monitor changes in brain activity as vocal learning occurs. The software is available at http://ofer.sci.ccny.cuny.edu.

Song Development: In Search of the Error-Signal

Song development provides an opportunity to study the mechanisms of vocal learning dynamically at molecular, cellular and systems levels, and across time scales ranging from minutes to months. To exploit these opportunities one needs to identify appropriate units, types and time scales of vocal change in nearly real time. The previous chapter by Tchernikovski et al. in this volume described techniques that make this research strategy feasible by allowing us to observe the song learning process through a "temporal microscope" with variable degrees of resolution. In this chapter we summarize some of the new observations and raise hypotheses about the learning strategy of the bird. We focus on inferences that can be drawn from behavioral observations to the nature and complexity of the instructive signal that guides the vocal change (error-signal). We examine two effects: i) the emergence of syllable types and ii) changes in features within a syllable type. We found that different features of the same syllable change during different and sometimes disjointed developmental windows. We discuss the possibility that song imitation is achieved by correcting partial errors, and that features of those partial errors change adaptively during development, perhaps concurrently with changes in perception and in motor proficiency. Those hypotheses can be best examined by across levels investigation, starting from identifying critical moments in song development and recording of articulatory dynamics and neural patterns when only a few features of specific syllables undergo rapid changes. Such investigation could relate behavioral events to brain mechanisms that guide song learning from moment-to-moment and across extended periods.

Towards quantification of vocal imitation in the zebra finch

The transition from an amorphous subsong into mature song requires a series of vocal changes. By tracing song elements during development, we have shown that the imitation trajectory to the target could not be predicted based on monotonic progression of vocal changes, indicating an internal component that imposes constraints on song development. Here we further examine the nature of constraints on song imitation in the zebra finch. We first present techniques for identifying and tracing distinctive vocal changes, and then we examine how sequences of vocal change are expressed and coordinated. Examples suggest two types of constraints on song imitation, based on the nature of the temporal context. Developmentally diachronic constraints are imposed by sequential dependencies between vocal changes as a function of developmental time, whereas developmentally synchronic constraints are given by the acoustic context of notes within the song. Finally, we show that the tendency of birds to copy certain sounds in the song model before others might be related to such constraints. We suggest that documenting the full range of distinctive vocal changes and the coordination of their expression would be useful for testing mechanisms of vocal imitation.

Dynamics of the vocal imitation process: how a zebra finch learns its song

Song imitation in birds provides good material for studying the basic biology of vocal learning. Techniques were developed for inducing the rapid onset of song imitation in young zebra finches and for tracking trajectories of vocal change over a 7-week period until a match to a model song was achieved. Exposure to a model song induced the prompt generation of repeated structured sounds (prototypes) followed by a slow transition from repetitive to serial delivery of syllables. Tracking this transition revealed two phenomena: (i) Imitations of dissimilar sounds can emerge from successive renditions of the same prototype, and (ii) developmental trajectories for some sounds followed paths of increasing acoustic mismatch until an abrupt correction occurred by period doubling. These dynamics are likely to reflect underlying neural and articulatory constraints on the production and imitation of sounds.

A procedure for an automated measurement of song similarity

Assessment of vocal imitation requires a widely accepted way of describing and measuring any similarities between the song of a tutor and that of its pupil. Quantifying the similarity between two songs, however, can be difficult and fraught with subjective bias. We present a fully automated procedure that measures parametrically the similarity between songs. We tested its performance on a large database of zebra finch, Taeniopygia guttata, songs. The procedure uses an analytical framework of modern spectral analysis to characterize the acoustic structure of a song. This analysis provides a superior sound spectrogram that is then reduced to a set of simple acoustic features. Based on these features, the procedure detects similar sections between songs automatically. In addition, the procedure can be used to examine: (1) imitation accuracy across acoustic features; (2) song development; (3) the effect of brain lesions on specific song features; and (4) variability across different renditions of a song or a call produced by the same individual, across individuals and across populations. By making the procedure available we hope to promote the adoption of a standard, automated method for measuring similarity between songs or calls. Copyright 2000 The Association for the Study of Animal Behaviour.

Vocal imitation in zebra finches is inversely related to model abundance

A juvenile male zebra finch, Taeniopygia guttata, kept singly with its father develops a fairly complete imitation of the father's song. The imitation is less complete when other male siblings are present, possibly because as imitation commences, model abundance increases. Here we examine the consequences of allowing more or less access to a song model. Young males heard a brief song playback when they pecked at a key, but different males were allowed to hear different numbers of playbacks per day. Using an automated procedure that scored the similarity between model and pupil songs, we discovered that 40 playbacks of the song motif per day, lasting a total of 30 sec, resulted in a fairly complete imitation. More exposure led to less complete imitation. Vocal imitation often may reflect the interaction of diverse influences. Among these, we should now include the possible inhibitory effect of model overabundance, which may foster individual identity and explain the vocal diversity found in zebra finches and other songbirds.

Social inhibition of song imitation among sibling male zebra finches

A male zebra finch, Taeniopygia guttata, kept with its father until adulthood develops an imitation of its father's song motif. We report here that the completeness of this imitation was sensitive to the social or auditory context in which the bird grew up: the greater the number of male siblings in a clutch, the shorter the mean duration of the song motif and the fewer the mean number of song notes imitated from the father; the latter shortfall was not compensated by other, improvised notes. We call this effect fraternal inhibition. Fraternal inhibition was avoided by members of a clutch that developed the song first. To our surprise, this role commonly fell to one of the younger birds in the clutch. Early song learning may influence fitness since individuals that produced the most complete imitations also tended to induce more egg laying.

The dynamics of long-term exploration in the rat. Part II. An analytical model of the kinematic structure of rat exploratory behavior

A simple analytical model is proposed here that captures to a large extent the kinematic structure of rat exploratory behavior. Previous studies have shown that such behavior consists of regular excursions into the environment from a preferred place termed a home base. In the first part of this study, we showed that with time and repeated exposure to the same large environment, there is a gradual increase in the length of excursions. Concurrently, the rat's velocity pattern changes in a complex yet structured way, which is correlated with the exposure (= familiarity) to places. In this part, we show that the complex pattern described there might be explained by an analytic model, in terms of a simple dynamical system, with few assumptions concerning motivation and learning. The model is studied both by analysis and simulation. The theoretical examination of the dynamics of excursion length suggests that excursion length increases as a linear function of two system parameters, one governing the rate of motivation loss, and the other the rate of (location-specific) familiarization. Combining this theoretical finding with the empirical results suggests that the two theoretical parameters are linearly related: the less confident the rat, the slower its familiarization rate, and thus differences in patterns of movement between rats can be explained using one rat-specific parameter. Furthermore, the more complex velocity pattern of the rat can then be easily captured by the same model. The analyzed behavior of the rat suggests that the locale sensory information that the rat collects has a gradient towards the home base, with decreasing information input away from home base. This sensory pattern emerges from the simple set of rules and restrictions on the rat's exploratory behavior. Thus, instead of imposing a set of ad hoc restrictions on a simulated rat so that its spatial learning is similar to that of a real rat, the model suggests a set of simple intrinsic constraints to govern the exploratory behavior.

The dynamics of long-term exploration in the rat. Part I. A phase-plane analysis of the relationship between location and velocity

Rat exploratory behavior consists of regular excursions into the environment from a preferred place termed a home base. A phase plane representation of excursions reveals a geometrical pattern that changes during exploration in both shape and size. We first show that with time and repeated exposures to the same large environment there is a gradual increase in the length of excursions; each rat has its own characteristic length of excursions; but all rats share a similar rate of excursion growth. As in our experimental setup the rats perform increasingly longer paths from one location, while locomoting back and forth along the walls of the arena, exposure is more extensive at the proximal part of the route, and less at the distal part. We consequently show that the rat's velocity pattern changes concurrently with the increase in excursion length, and in correlation with the level of exposure (familiarity) to places. The primitive velocity pattern consists of slow progression while moving away from base and fast progression while returning to it. During exposure the asymmetry in velocity is inverted. The inversion spreads across successive excursions from the home base outwards. The rate of spread of this inversion is higher than the rate of increase in excursion length, and is similar across rats. Because it spreads more rapidly than the increase in excursion length, the global shape of the excursion trajectory changes. The dynamics of excursion shape share similar properties with the dynamics of excursion length. Both might reflect the same intrinsic constraints on the amount of novelty that a rat can handle per excursion.

Context determines the sex appeal of male zebra finch song

We explored the conditions under which playbacks of male zebra finch, Taeniopygia guttata, song induced reproduction in females. In a laboratory study, a rise in faecal oestrogen levels predicted egg laying. Song playbacks by themselves induced a decrease in oestrogen levels. There was an increase in oestrogen levels, followed by egg laying, when the song was broadcast from inside a male model positioned away from the nest. However, this effect occurred only when a second, silent male model was perched on the rim of the nest. If song was broadcast from inside the model perched on the nest, there was no increase in oestrogen levels. We conclude that tests of song efficacy in female songbirds must respect some contextual rules, which are likely to vary between species. Only then does it become possible to ascertain which sounds are most effective in inducing physiological changes leading to reproduction. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

Keeping the Body Straight in the Unconstrained Locomotion of Normal and Dopamine-Stimulant-Treated Rats

During unconstrained locomotor behavior, rats move in and out of a straight posture of the body (including the head). In the present study, the stability of maintaining a straight body was examined in untreated rats and in rats treated with saline (SAL) or with 1 of 3 dopamine stimulants (n = 4 rats per group). The stability of maintaining a straight body can range from very high (with 0.5 mg/kg quinpirole [QUIN]), to high (first half-session with 5 mg/kg (+)-amphetamine [AMPH]), to very low (second half-session with 5 mg/kg AMPH), or can be maintained at a level similar to that observed in untreated rats (with 1.25mg/kg apomorphine [APO]). Stability was assessed by videotaping the rats and, then, by using frame-by-frame analysis, scoring the cumulative proportion of time spent in a straight posture, the frequency of transitions from one hemisphere to the other without being trapped in the midline plane, and the degree of lateral bending during turning and during walking on a curved path. The present study is one in a series identifying key variables that constrain as many degrees of freedom as possible in rat locomotor behavior. The uncovering of such variables is an indispensible step that precedes dynamic systems stability analysis and provides candidates for key variables for the modeling of motor coordination.

A phase plane representation of rat exploratory behavior

Rat spontaneous spatial behavior is considered to be stochastic and is therefore commonly analyzed in terms of cumulative measures. Here, we suggest a method which generates a moment-to-moment representation of this behavior. It has been proposed earlier that rat spatial behavior can be partitioned into natural units termed excursions (round trips) performed from a reference place termed the rat's home base. We offer a phase plane representation of excursions (plotting the rat's momentary location against its momentary velocity). The results reveal a geometrical pattern, typical of young age and early exposure. It consists of low velocity and intermittent progression while moving away from the home base (upstream segment), and high velocity while moving back to it (downstream segment). The asymmetry between the two segments defines a field of significance in the rat's operational world. This field undergoes regular transformations, revealing thereby the rat's strategy of occupancy of the environment. The presented dynamics could provide a framework for the interpretation of concurrent neural events associated with navigation and spatial memory.