Pharmacological suppression of corticosterone secretion in response to a physical stressor does not prevent the delayed persistent increase in circulating basal corticosterone concentration

Elevated basal plasma corticosterone concentrations have been observed for several days after the cessation of severe stress. In the present study, we examined whether or not the acute plasma corticosterone response to stress is necessary to elicit increased basal plasma corticosterone concentrations the following day. Pretreatment with metyrapone (100 m a g , intraperitoneal)1 h before inescapable stress (40 2mA tail shocks delivered over a 1-h period) (IS)blocked the acute plasma corticosterone response to IS. However, elevated basal plasma corticosterone concentrations still emerged the next day. These results suggest that the corticosterone response to stress, and its attendant feedback, are not necessary to produce persistent hypothalamic-pituitary-adrenal axis (HPAA) activation.     

Reinforcement by an imprinting stimulus versus water on simple schedules in ducklings

Ducklings (5 to 28 days old) were trained to peck a pole on fixed-ratio, fixed-interval, and multiple schedules using brief presentation of an imprinting stimulus as the response-contingent event. Other ducklings of the same age were trained similarly except that reinforcement consisted of access to water. With water reinforcement the typical fixed-ratio (“break-run”), fixed-interval (“scallop”), and multiple schedule response patterns were readily established and consistently maintained. With the imprinting stimulus these schedule effects were inconsistent in some subjects and virtually nonexistent in others, despite extended training. Schedule control with the imprinting stimulus was not improved by the use of a reinforcement signaling procedure which enhances responding reinforced by electrical brain stimulation on intermittent schedules. However, the overall rates of responding and the extinction functions generated after reinforcement with water versus the imprinting stimulus were comparable. These findings imply that control by temporal and discriminative stimuli may be relatively weak when a young organism's behavior is reinforced by presentation of an imprinting stimulus.     

Auditory basis of maternal attachment in ducklings (Anas platyrhynchos) under simulated naturalistic imprinting conditions

The presence of broodmates during the imprinting process results in peer imprinting that interrupts a visually mediated maternal attachment. We sought to determine the conditions in which group-trained mallard ducklings (Anas platyrhynchos) acquire a maternal attachment. At 48 hr of age, ducklings were allowed to follow a vocal, stuffed mallard hen individually or in groups of 4. Individual ducklings showed a preference for the silent, familiar mallard over an unfamiliar pintail. Ducklings trained in groups did not show a preference. When the mallard maternal call was present during testing, group-trained ducklings overwhelmingly responded to it regardless of whether it came from the familiar mallard or an unfamiliar pintail. Training ducklings in groups, which simulates the natural social context of imprinting, results in peer imprinting. Thus, early in development the young become visually imprinted to each other, and the maternal call mediates attachment to the mother.     

Social interaction with siblings is necessary for visual imprinting of species-specific maternal preferences in ducklings (Anas platyrhynchos)

This study was conducted to examine the influence of various social rearing experiences on the development of imprinted visual maternal preferences in domestic mallard ducklings (Anas platyrhynchos) during the first 3 days of postnatal life. Twenty-four-hour-old ducklings were allowed to follow a stuffed mallard hen for 30 min. This experience resulted in a visual preference for the familiar mallard hen over an unfamiliar stuffed redhead (Aythya americana) hen in simultaneous choice tests at 48 hr and 72 hr only if the ducklings were reared in conditions allowing unrestricted social interaction with siblings, as would normally occur in nature. No visual preference for the familiar mallard model was found at 48 hr or at 72 hr if ducklings were reared in social isolation but allowed to see another duckling, reared with one duckling, or reared in a group of ducklings but denied the opportunity for direct social interaction. These results demonstrate the importance of normal social experience in the development of the visual imprinting of filial behavior in ducklings. Imprinting studies have traditionally employed isolation rearing and ignored the precocial bird's natural social context. Thus, the present findings raise doubts about the appropriateness of the usual methods of studying imprinting in the laboratory for an understanding of the process of filial imprinting in nature.     

Isolation-induced aggression in newly hatched ducklings.

Newly hatched Khaki Campbell ducklings (Anas platyrhynchos domesticus) were initially housed in pairs and subsequently transferred to isolated housing conditions. Subjects living with another bird displayed filial behavior and little aggression upon encountering another duckling in a test arena. In contrast, ducklings housed in isolation exhibited aggressive pecking in addition to filial behavior when another duckling was subsequently encountered. In Experiment 2, ducklings were housed with an imprinting object (i.e., an object that elicits attachment behavior), but they were otherwise isolated from other birds. These subjects displayed little aggression when they were subsequently reunited with a conspecific, indicating that the aggression-precluding effects of social housing are not limited to the particular social stimulus with which the ducklings are housed. In Experiment 3, ducklings were again housed with an imprinting object, but this time the object was behind glass, thereby precluding tactile contact with it. Since these birds also exhibited little aggression when reunited with a conspecific, it is apparent that visual stimulation from an imprinting object is sufficient in itself to preclude subsequent aggression. These findings suggest that stimulation that elicits attachment behavior is the critical factor mediating isolation-induced aggression.     

Ability and effort weights in pay level and pay increase decisions

It was hypothesized that ability, effort, and the interaction between ability and effort would influence pay level and pay increase decisions. An experiment was conducted with 66 human resource professionals to test this hypothesis. The results indicate that pay level decisions are influenced primarily by ability, and pay increase decisions are influenced primarily by the interaction between ability and effort. The results are discussed in the context of the traditional compensation model which suggests that ability should influence pay level, but not pay increase, and that effort should influence pay increase, but not pay level. It was concluded that the distinction currently being made between person and job based pay plans may not be meaningful.Portions of this paper were presented to the PHR division of the Southern Management Association, Atlanta, November, 1991.The authors wish to thank Marcia Miceli, Eileen Hogan, and Don Eskew, for their helpful comments on earlier drafts.     

Wavelength generalization and preference in monochromatically reared ducklings

Two experiments determined the effects of early color experience on gradients of wavelength generalization. In each experiment, one group of ducklings was raised in monochromatic (589 nanometers) sodium-vapor light and a second group, in white light. In Exp. I, ducklings pecked a key transilluminated by 589 nanometers. In a subsequent test, the group raised in white light produced steeper gradients. However, several monochromatically reared ducklings produced gradients as steep as those for the white-reared ducklings. In Exp. II, ducklings pecked a white line. In a subsequent test, using a fully illuminated key, subjects in both groups responded more often to "green" (510, 530, 550, or 570 nanometers) than to "non-green" wavelengths (490, 589, 610, or 650 nanometers). Ducklings raised in monochromatic light preferred shorter "green" wavelengths than ducklings raised in white light. This difference between the "green" preferences for the two groups accounted for most of the differences between the gradients of wavelength generalization obtained from the two groups in Exp. I after training at 589 nanometers.     

Classical aversive conditioning of catecholamine and corticosterone responses.

Some earlier work, not rigorously controlled, suggested that conditional increases in sympathoadrenal stress hormones could occur. The purpose of this experiment was to test this idea further using an appropriately controlled design. To do this, we subjected rats living in a tether-type apparatus to differential fear conditioning. Chronic catheterization allowed us to sample blood before and after conditional stimulus probes without having to touch the rats. No evidence for conditional changes in norepinephrine and corticosterone was found. In contrast, differential conditioning of epinephrine responses was found. The conditional response, however, was not a simple one in that conditional increases in epinephrine following CS+ probes were not always seen. These data support the idea that learned changes in hormonal stress respondents can occur. But they leave open the question of why clear cut conditional changes in these visceral systems are so difficult to obtain.     

Stimulus factors in the isolation-induced aggression of Bobwhite quail and Khaki Campbell ducklings

Two studies examined the relative abilities of conspecific-derived visual and tactile stimulation to modulate the occurrence of isolation-induced aggression in Bobwhite quail and Khaki Campbell ducklings. In Experiment 1, subjects were permitted visual stimulation from conspecifics but were deprived of conspecific tactile stimulation. In both species, these subjects subsequently showed significantly less aggression towards conspecifics than birds that had been deprived of both visual and tactile stimulation from conspecifics. In Experiment 2, one group of subjects was permitted conspecific tactile stimulation but was deprived of conspecific visual stimulation. Again for both species, these subjects subsequently exhibited significantly less aggressive behavior towards conspecifics than did subjects that had been both visually and tactually de-prived. In sum, the present research suggests that both tactile and visual stimulation from a conspecific are individually sufficient to reduce isolation-induced aggression in these precocial buds.     

Schedules of electric shock presentation in the behavioral control of imprinted ducklings

The behavioral effects of various schedules of electric shock presentation were investigated during and after the imprinting of Peking ducklings to moving stimuli. The behavior of following a moving imprinted stimulus was differentially controlled by a multiple schedule of punishment and avoidance that respectively suppressed and maintained following behavior. Pole-pecking, reinforced by presentations of the imprinted stimulus, was suppressed by response-produced shock (punishment); various schedules of response-independent shock and delayed punishment had an overall minimal effect. The delivery of response-independent shock in the presence of one of two stimuli, both during and after imprinting, resulted in a marked reduction in choice of the stimulus paired with shock. The experiments provide no support for a differentiation of imprinting from learning on the basis of the behavioral effects of aversive stimuli. Instead, as is the case with other organisms, the schedule under which shock is delivered to imprinted ducklings appears to be an important determinant of the temporal patterning of subsequent behavior.     

Development of species identification in ducklings: I. Nature of perceptual deficit caused by embryonic auditory deprivation.

In simultaneous choice tests with normal and filtered maternal calls, devocal-isolated ducklings were much more likely than vocal-communal ducklings to select the mallard maternal call in which the higher frequencies were severely attenuated, thus indicating their relative insensitivity to the higher frequency components of the maternal call. On the other hand, the devocal ducklings were as adept as vocal ducklings in selecting the normal mallard maternal cal1 when it was pitted against a low-frequency attenuated mallard call. Thus, the perceptual deficiency resulting from embryonic and postnatal auditory deprivation is selective in the sense of being relegated to the higher frequency components of the maternal call. Devocalization prevents the embryo and hatchling from hearing their own vocalizations all of which happen to be in the high-frequency range (greater than or equal to 1,500 Hz).     

Development of species identification in ducklings: III. Maturational rectification of perceptual deficit caused by auditory deprivation.

Mute ducklings, devocalized as embryos and maintained in auditory isolation, manifest a selective high-frequency perceptual deficit vis-à-vis the maternal call of their species at 24 hr after hatching. Since it takes a rather specific auditory experiential input to rectify this high-frequency insensitivity at 24 hr, it was predicted that, in the absence of auditory experience, devocal-isolated ducklings would fail to show sufficient endogenously mediated improvement to bring them up to the level of perceptual competence of vocal-communal ducklings at any age. This hypothesis proved wrong in that the proportion of devocalized ducklings showing a preference for the normal maternal call over the greater than 825-Hz attenuated one became equivalent to the vocal ducklings at 48 hr after hatching, as did their ability to discriminate the normal maternal call from greater than 1,800-Hz attenuated maternal call. At 65 hr, however, the devocalized ducklings' performance deteriorated back to the level observed at 24 hr. Embryonic exposure to the (sibling) contact-contentment call prevents the perceptual deficit at 24 hr and the deterioration at 65 hr.     

Persistence of acquired behavioral control in the context of imprinting

Newly hatched Khaki Campbell ducklings (Anas platyrhynchos domesticus) were exposed to a moving object that immediately suppressed distress vocalizations occurring in a novel environment. The static visual and auditory features of this object acquired the ability to suppress distress vocalizations after eight 20-min sessions of exposure to the object in motion. The acquired suppressive properties of these features were found to persist throughout thirty 20-min sessions given over 10 days. During these sessions, the ducklings were continually exposed to the static features in the absence of visual movement. In a second experiment, the ability of these features in the absence of visual movement. In a second experiment, the ability of these features to serve as reinforcement for a pecking response was shown to persist for up to 56 hr. In one duckling, presentations of the static visual features did not maintain pecking behavior. However, it was shown that pecking responses could be re-instated in this duckling by introducing novel stimuli to the environment.     

Long-term potential for imprinting in ducks and chickens

In the first of five experiments, three of four adult ducks who had been reared in visual isolation gradually developed strong approach responses towards a moving panel of colored lights. Experiment 2 provided evidence that the ducks' approach response reflected the same sort of social attachment that is typically formed to moving objects by newly hatched ducklings. Experiment 3 revealed that the fourth duck would not approach the moving stimulus even after additional exposure to it, but would approach a conspecific after group housing had been enforced for seven days. In Experiment 4, none of five adult chickens who had been reared in visual isolation developed approach responses towards the moving stimulus, even though in Experiment 5, newly hatched chicks approached the stimulus quite readily. Taken together, these findings (a) indicate that ducks retain the ability to form filial-type attachments to novel objects throughout their lives, and (b) offer preliminary evidence that chickens do not retain this ability into adulthood.