Prehension in the pigeon. I. Descriptive analysis

Gulper, ripper and scrapper: anatomy of the neck in three species of vultures

The head-neck system of birds is a highly complex structure that performs a variety of demanding and competing tasks. Morphofunctional adaptations to feeding specializations have previously been identified in the head and neck, but performance is also influenced by other factors such as its phylogenetic history. In order to minimize the effects of this factor, we here analyzed the anatomy of three closely related vultures that distinctly differ in feeding strategy. Vultures, as obligate scavengers, have occupied a special ecological niche by exclusively feeding on carrion. However, competition among sympatric vultures led to ecological differences such as preference of certain types of food from a carcass. Via comparative dissections we systematically described the craniocervical anatomy in the Griffon vulture (Gyps fulvus), the Cinereous vulture (Aegypius monachus) and the Hooded vulture (Necrosyrtes monachus) that exploit the same food resources in different ways. Our results revealed differences in the number of cervical vertebrae, in the morphology of the atlas-axis complex as well as in the neck musculature despite overall similarities in the musculoskeletal system. Gulpers, rippers and scrappers adopt specific postures while feeding from a carcass, but the cervical vertebral column is indispensable to position the head during all kinds of behavior. The great range of demands may explain the conservation of the overall muscle topography of the neck across the studied taxa.

Rapid adjustment of pecking trajectory to prism-induced visual shifts in crows as compared with pigeons

Pecking in birds is analogous to reaching and grasping movements in primates. Earlier studies on visuomotor control in birds, which were conducted mostly in pigeons, suggested that avian pecking is controlled feedforwardly, and is out of the control of visual guidance during movement. However, recent studies using crows suggested a role of vision in pecking control during movement. To unveil what visuomotor mechanisms underlie the flexibility of pecking in crows, we examined whether pigeons and crows adjust their pecking to the visual distortion induced by prisms. Because prisms induce visual shifts of object positions, birds were required to adjust their movements. Pecking kinematics were examined before and after attaching prisms in front of the birds' eyes. Analysis of lateral deviation caused by the prisms showed that crows rapidly adjusted their pecking trajectories, but pigeons did so slowly. Angular displacement also increased in pigeons after attachment of the prism, but decreased in crows. These responses to prisms were consistent among individuals in pigeons but varied in crows, though the adjustment of pecking commonly succeeded in crows. These results suggest that pecking in pigeons predominantly involves feedforward control and that the movement is determined depending on the visual information available before the initiation of pecking. In contrast, the results from crows suggest that their pecking trajectories are corrected during the movement, supporting on-line visual control. Our findings provide the first evidence to suggest the on-line visual control of pecking in birds.

Ontogeny has a phylogeny: background to adjunctive behaviors in pigeons and budgerigars

Animals coping with operant conditioning tasks often show behaviors that are not recorded by keys, levers and similar response transducers. Nevertheless, these adjunctive behaviors should not be disposed of by classifying them as incidental. Often they are found to be at least partially influenced by the experimentally programmed contingencies, and under certain conditions they can in turn influence conditioned behaviors. Here we describe the occurrence and characteristics of two such behaviors, stimulus grasping in operantly key-pecking pigeons and intra-delay stereotypies in a delayed matching-to-sample task with budgerigars. It is argued that for a proper account of these behaviors it is necessary to refer to a behavioral systems approach that appeals to longer ranging ontogenetic and phylogenetic histories than is usually considered in the psychological literature. The gaping towards on-key stimuli by pigeons is attributed to the hypothesis that operantly conditioned key-pecks probably relate to a grasp-pecking response that is normally executed towards non-edible items covering food. The intra-delay behaviors shown by the budgerigars are assumed to have originated from stress-induced displacement responses that adventitiously came under the influence of differential reinforcement contingencies. Finally, we discuss what kinds of evidence are needed to put these hypothetical explanations on a more certain footing.

Is it pointing to grasping or grasping pointing?

The Smeets and Brenner view on grasping is simple: grasping is in fact pointing. In our comments we examine the model beyond the reach-to-grasp task, namely, by grasping (without reaching) of moving objects and eating. The model fits the data of both tasks. Although generalization of a model to different tasks usually strengthens its acceptance, in the present case it reveals its shortcomings, namely, both tasks include a clear grasping component that is hard to accept as pointing.

Trigeminal deafferentation and conditioned pecking in pigeons

To clarify the contribution of peripheral trigeminal input to the control of pecking behavior we examined head and jaw movement kinematics and peck localization in pigeons with surgical section of trigeminal nerves providing somatosensory input to the beak. Conditioning procedures were used to bring the pecking/grasping components of pecking under the control of a visual target. Conditioned head and jaw movements were monitored 'on-line' using movement transducers and terminal peck location was recorded using 'touch-screen' technology. The periodic delivery of a food reinforcer provided repeated opportunities to monitor the kinematics of ingestive pecks. Deafferentation produced deficits in mandibulation during ingestive pecking and in the coordination of head and jaw movements during conditioned pecking. These results are attributed to disruptions in trigeminal feedback and feedforward mechanisms, respectively. In contrast with previous studies, deafferentation did not impair the precision of peck localization. Possible reasons for the absence of localization deficits are presented. The results are discussed in relation to the role of peripheral inputs in the control of prehensile movements.

Optoelectronic monitoring of individual whisker movements in rats

We describe two systems for the real-time recording and display of individual vibrissa movements in head-fixed rats. Both systems utilize high-speed, linear image sensors, each composed of an array of light sensitive elements (CCDs). Uniform illumination of the array generates a constant baseline voltage in each element. The shadow produced by the movement of a whisker interposed between the light source and the sensors produces a voltage shift in a subset of elements. The successive position of the shift is linearly related to the momentary whisker position. Associated software/hardware scans the array at regular intervals to identify the successive positions of voltages above a preset threshold and outputs the data to a microprocessor for computation of the whisker movement trajectory. In both systems, movements of a single whisker may be monitored 'on-line' with high spatial and temporal resolution; in one case with, in the other without the presence of neighboring whiskers. Optoelectronic monitoring facilitates rapid and efficient (computer-assisted) acquisition and analysis of data on rodent whisking behavior.

Conditioned 'prehension' in the pigeon: kinematics, coordination and stimulus control of the pecking response

Like human prehensile behavior, the pigeon's ingestive pecking response is elicited by visual stimuli conveying information about the location and size of the target. This information is used to generate localized ingestive pecks whose gapes are amplitude-scaled to seed size, prior to contact. We employed high-resolution, 'real-time' monitoring of head acceleration, jaw movements and terminal peck location to examine the kinematics, coordination and stimulus control of conditioned pecking. Conditioning procedures were used to bring pecking under the control of visual targets whose stimulus properties (size, location) were independently varied, while simultaneously monitoring pecking response parameters. Stimulus control of the transport component (peck localization) is extremely precise, even in the absence of a specific localization-dependent reinforcement contingency. Subjects also showed amplitude-scaling of gape size to the size of a visual target, but over a more restricted range than shown to food pellets of comparable sizes. Comparison of the kinematic profiles of conditioned and ingestive pecks suggests that conditioned pecking is functionally analogous to human 'pointing' rather than 'grasping' behavior.

Feed pecking in young chickens: new techniques of evaluation

Three techniques were compared: automated recording (A) of 2 h of feeding activities conveyed to a computer by constantly connected electronic balances, videotaping (V) of a closeup of the head of a chick during a feed-pecking session analyzed by focal sampling at reduced speed (16 times slower), strength of pecking (S) at feed particles recorded from a feeder-weight signal conveyed to a computer by a customized electronic balance at rapid speed (24 times/s). These techniques were applied to 16-18-day-old chicks fed either a complete feed or a split diet (whole grain wheat + a complementary feed). The two feeds had similar pellet forms. The complementary feed particles were eaten at a slower rate than the complete feed particles (A and V techniques). Wheat grains were pecked with a weaker measured strength than the pellets (technique S). Two pecks of three did not result in prehension of a feed particle and were categorized as "exploratory" pecks. For 75% of the time during a continuous pecking session the head of the chick was in a static position, suggesting a long period of observation of the feed between 2 consecutive pecks. Videotaping with slow-motion focal sampling (V) offers potential development for the study of food intake behavior of chickens.

Effects of food-pellet size on rate, latency, and topography of autoshaped key pecks and gapes in pigeons

Four pigeons responded under autoshaping contingencies in which different conditional stimuli (red or green keylights) were associated with unconditional stimuli of different magnitudes (large or small food pellets) over successive trials within a session. Both topography (beak opening or gape) and strength (rates and latencies of key pecks and gapes) of responding during the conditional stimuli depended on the magnitude of the correlated unconditional stimulus. Key-peck and gape rates were higher and latencies were shorter in large-pellet trials than in small-pellet trials. Gape amplitudes varied directly with pellet size, although conditional and unconditional gapes were larger than either pellet. These findings were replicated when the key colors were presented either on one or two keys and after reversals of the color-size correlations. Because the unconditional stimulus was varied through pellet size, magnitude was not confounded with food-access duration or quality. These results demonstrate the effects of the magnitude of the unconditional stimulus, in that rates and latencies of both key pecks (which are directed movements toward the key) and gapes (which are independent of the bird's position and key properties) varied with pellet size. Gape measures were unique in that two dimensions (response strength and topography) of a single response class varied simultaneously with magnitude.

Systematic changes in gaping during the ontogeny of pecking in ring doves (Streptopelia risoria)

Food pecking in the ring dove is a skilled prehensile response that is similar to, but simpler than, many other prehensile responses. Previous work has shown that this response is initially poorly executed and requires experience for its accurate direction and coordination. The response involves two components: the thrusting of the bird's head toward food, and the opening and closure of the beak around food. Here, this second component, called gape, is followed through development with a precise measurement system. Four squabs moved through a similar sequence of three gape topographies, each of which is more efficient in picking up seed, during development. The present outcome, together with other work, argues for a substantial contribution of experience with pecking to the development of food pecking. We discuss the implications of these findings for understanding the ontogeny of motor control and for understanding how experience affects behavioral development.

Autoshaping the pigeon's gape response: acquisition and topography as a function of reinforcer type and magnitude

The pigeon's key-pecking response is experimentally dissociable into transport (head movement) and gape (jaw movement) components. During conditioning of the key-pecking response, both components come under the control of the conditioned stimulus. To study the acquisition of gape conditioned responses and to clarify the contribution of unconditioned stimulus (reinforcer) variables to the form of the response, gape and key-contact responses were recorded during an autoshaping procedure and reinforcer properties were systematically varied. One group of 8 pigeons was food deprived and subgroups of 2 birds each were exposed to four different pellet sizes as reinforcers, each reinforcer signaled by a keylight conditioned stimulus. A second group was water deprived and received water reinforcers paired with the conditioned stimulus. Water- or food-deprived control groups received appropriate water or food reinforcers that were randomly delivered with respect to the keylight stimulus. Acquisition of the conditioned gape response frequently preceded key-contact responses, and gape conditioned responses were generally elicited at higher rates than were key contacts. The form of the conditioned gape was similar to, but not identical with, the form of the unconditioned gape. The gape component is a critical topographical feature of the conditioned key peck, a sensitive measure of conditioning during autoshaping, and an important source of the observed similarities in the form of conditioned and consummatory responses.

Jaw muscle (EMG) activity and amplitude scaling of jaw movements during eating in pigeon (Columba livia)

During each phase of the pigeon's eating sequence, jaw opening amplitude (gape) is adjusted to the size of the food object; first prior to contact (Grasping), again in positioning the food (Stationing), and finally, during its movement through the oral cavity (Intraoral Transport). Part I of this study examined jaw movement kinematics during ingestion of different size food pellets to determine the relative contribution of velocity and rise time variables. Part II specified the muscle activity patterns mediating each phase of the eating sequence, and determined how these patterns are modulated to produce adjustments of gape size. The relative contribution of velocity and rise time variables to the control of gape differs in each phase of the eating sequence. However, for any pellet size, variations in opening rise time may function in a compensatory manner to minimize gape "undershooting". Each phase of the eating sequence is mediated by a characteristic muscle activity pattern. The adjustment of gape size to pellet size involves systematic modulation of this pattern, and the parameters modulated differ in the different phases in a manner which may reflect the functional requirements of each phase.

Organization of the cerebellum in the pigeon (Columba livia): I. Corticonuclear and corticovestibular connections

The projections of the cerebellar cortex upon the cerebellar nuclei and the vestibular complex of the pigeon have been delineated using WGA-HRP as an anterograde and retrograde tracer. Injections into individual cortical lobules (II-IXa) produce a pattern of ipsilateral terminal labeling of both the cerebellar and vestibular nuclei. The pattern of corticonuclear projections indicates both a rostrocaudal and a mediolateral organization with respect to the lobules and is consistent with a division of the cerebellar nuclei into a medial (CbM) and a lateral (CbL) nucleus. The retrograde experiments indicate that these nuclei receive projections, respectively, from Purkinje cells within medial (A) and lateral (C) longitudinal zones, which alternate with longitudinal zones (B, E) projecting upon the vestibular complex. Purkinje cells in (vestibulocerebellar) lobules IXb-X show only limited projections upon the cerebellar nuclei, but do project extensively upon the cerebellovestibular process (PCV), as well as upon the medial, superior, and descending vestibular nuclei. As the injection site shifts from medial to lateral, there is a corresponding shift in focus of the projection within PCV from areas bordering CbM to those abutting CbL. The topographic organization of corticovestibular projections is less clear-cut than those of the corticonuclear projections. Lobules II-X project upon the lateral vestibular nucleus (anterior lobe) or the dorsolateral vestibular nucleus (posterior lobe). These projections originate from either side of the lateral (C) zone. Projections originating from the medialmost (B) zone are interrupted in lobules VI and VII. The anterior and posterior portions of the lateralmost (E) zone overlap along lobules VI and VII. In addition, the E zone of the anterior lobe is the source of projections upon the medial, the descending, and the superior vestibular nuclei. Projections from the auricle and adjacent lateral unfoliated cortex (F zone) focus upon the infracerebellar nucleus, the medial tangential nucleus, and the medial division of the superior vestibular nucleus. The data suggest that the cerebellar cortex of the pigeon, like that of mammals, may be subdivided into a mediolaterally oriented series of longitudinal zones, with Purkinje cells in each zone projecting ipsilaterally to specific cerebellar nuclei or vestibular regions. For cortical regions exclusive of the auricle and lateral unfoliated cortex, three such zones (A, B, and C) are defined that are comparable in their efferent targets with the A, B, and C zones of mammals. There does not appear to be a D zone in the pigeon. The results are discussed in relation to comparative data on amphibians, reptiles, and mammals.

Prehension in the pigeon. II. Kinematic analysis

During eating, the pigeon's jaw functions as a prehensile organ, i.e., as an effector organ involved in the grasping and manipulation of objects. The preceding paper provided a descriptive account of the jaw opening movements associated with each phase of the eating behavior sequence. For two of these movements, Grasping and Mandibulation, the amplitude of jaw opening is adjusted to pellet size. In the present study a kinematic analysis of these movements was carried out to clarify the motor control mechanisms mediating these adjustments. The analysis was carried out within the conceptual framework provided by a "pulse-control" model of targeted movement. For each of the movements the extent to which opening amplitude, its first and second derivatives and its rise time are scaled to pellet size was determined. Relationships among these kinematic variables were then examined in order to distinguish between "pulse-height" and "pulse-width" strategies. In addition, the possibility that "corrective adjustments" to the trajectory are made during its execution was also explored using a multiple regression analysis developed by Gordon and Ghez (1987a, b). For both movements, peak opening amplitude, acceleration and velocity are scaled to pellet size and these variables account for most of the variance in opening amplitude. The kinematic analysis suggests that critical parameters of the trajectory are determined ("programmed") prior to its initiation. Moreover, pigeons, like cats and humans, appear to utilize a "pulse-height" strategy for the control of amplitude scaling during targeted movements.(ABSTRACT TRUNCATED AT 250 WORDS)