Peer-peer interaction among infants and toddlers with extensive daycare experience

Peer-peer interaction among 10–21- and 24–30-month-olds with extensive daycare experience was studied. Thirteen pairs of familiar agemates were formed, and each dyad was observed in a playpen with toys at their daycare center. Adult preparation and various constraints to peer-peer interaction were minimized. The nine behavioral measures included nonsocial, marginally social, and social play categories. The results revealed equivalent amounts of nonsocial behavior for both age groups, and marginally social behavior was not the dominant play activity at either age. Compared with the younger group, the older children engaged in less marginally social activity, more positive social behavior overall, and more sustained sociable interchanges. Neither age group had high levels of antisocial behavior, but the younger children tended to display more than the older. Support was found for the view that marginally social activity functions as a bridge from nonsocial to social behavior.     

Food and amphetamine self-administration by baboons: effects of alternatives.

The effects of the availability of an alternative reinforcer on responding maintained by food pellets or fluid solutions were examined in 6 adult male baboons (Papio cynocephalus anubis). During daily 23-hr experimental sessions, baboons had concurrent access to both food pellets and fluid, with responding maintained under fixed-ratio schedules of reinforcement that varied between the two commodities. The fixed-ratio requirement, or cost, for pellets was increased when (a) no fluid, (b) a dilute dextrose vehicle, (c) 0.002 mg/kg d-amphetamine, or (d) 0.004 mg/kg d-amphetamine was available. When given nonrestricted concurrent access to food pellets and amphetamine at minimal cost (FR 2), baboons self-administered sufficient amphetamine to decrease pellet intake. Increasing the response requirement for pellets decreased pellet intake at a similar rate regardless of the available fluid and increased fluid intake in a variable manner among baboons such that there were no statistically significant increases in fluid intake. In contrast, when access to pellets was restricted to 70% of maximal intake under nonrestricted conditions, increasing pellet cost decreased pellet intake and increased fluid intake more rapidly when the high amphetamine dose was available. Thus, amphetamine was more effective as an economic substitute for pellets when access to pellets was restricted. The response cost for vehicle and both amphetamine concentrations was increased when baboons had nonrestricted and restricted access to pellets. Increasing the response requirement for fluid delivery decreased intake of all three fluids similarly under both pellet-access conditions. The results indicate that substitution between commodities with minimal commonalities can be studied under controlled laboratory conditions and is dependent upon reinforcement schedule and commodity restrictions.     

Selective effects of barbiturate and amphetamine on information processing and response execution

In a 3 × 2 × 2 factoral experiment, 12 subjects carried out a choice reaction task with reaction time (RT) and movement time (MT) as response measures.Independent variables were drug treatment (amphetamine, barbiturate, placebo), visual stimulus degradation and S-R compatibility. Visual stimulus degradation and S-R compatibility showed additive effect on the RT, but did not affect the MT. This confirms that stimulus encoding, response selection and response execution represent independent processing stages. The two drugs had selective effects on the RT and the MT. Barbiturate (as compared to placebo) had no effect on the MT, but it lengthened the RT, and this effect was additive with the effects of S-R compatibility but showed an interaction with the effects of stimulus degradation. Amphetamine (as compared to placebo) shortened the MT, but there was no significant main effect of amphetamine on the RT although the interaction with the effect of S— compatibility was significant. These results suggest that barbiturate affects stimulus encoding whereas amphetamine affects response-related processes..     

A parametric evaluation of the hedonic and motoric effects of drugs: pimozide and amphetamine

This study uses a curve-fitting approach to evaluate the effects of drugs on reinforced responding in rats. The subjects obtained reinforcement according to a series of five different variable-interval schedules (a five-component multiple schedule). For each rat, pimozide, a neuroleptic, decreased response rate, and the decrease was associated with (1) a decrease in the estimated asymptotic response rate and (2) an increase in the rate of reinforcement necessary for half-asymptotic responding. That is, pimozide decreased the proportion of responding maintained by a given rate of reinforcement. In contrast, intermediate doses of amphetamine increased response rate and increased the proportion of responding maintained by a given rate of reinforcement. It was proposed that the response rate asymptote indexes motor capacity, and the rate of reinforcement necessary for half-asymptotic responding indexes reinforcement efficacy; accordingly, pimozide decreased motor capacity and reinforcement strength and amphetamine increased reinforcement strength.     

Conditioned suppression with extinction as the signalled stimulus

The key pecking of pigeons that was maintained by a 60-sec random-interval schedule of food reinforcement was suppressed during a variable-duration warning stimulus that signalled a 5-min extinction period. The onset of the extinction period immediately followed the termination of the warning signal and was independent of the subject's responses. All subjects eventually showed nearly complete suppression of responding during the warning stimulus.     

Maximum likelihood estimation of latent interaction effects with the LMS method

In the context of structural equation modeling, a general interaction model with multiple latent interaction effects is introduced. A stochastic analysis represents the nonnormal distribution of the joint indicator vector as a finite mixture of normal distributions. The Latent Moderated Structural Equations (LMS) approach is a new method developed for the analysis of the general interaction model that utilizes the mixture distribution and provides a ML estimation of model parameters by adapting the EM algorithm. The finite sample properties and the robustness of LMS are discussed. Finally, the applicability of the new method is illustrated by an empirical example. This research has been supported by a grant from the Deutsche Forschungsgemeinschaft, Germany, No. Mo 474/1 and Mo 474/2. The data for the empirical example have been provided by Andreas Thiele of the University of Frankfurt, Germany. The authors are indebted to an associate editor and to three anonymous reviewers ofPsychometrika whose comments and suggestions have been very helpful.     

Conditioned increases in locomotor activity produced with morphine as an unconditioned stimulus, and the relation of conditioning to acute morphine effect and tolerance

Rats administered 5 mg/kg morphine SO4, through subcutaneously implanted catheters, during each of several daily sessions in an open field showed a progressive increase in locomotor activity measured in the open field prior to each morphine administration. Since the increases in activity were not observed in rats given morphine in a different environment (home cage) and saline in the open field, it is concluded that the increases were due to conditioning. In addition, the increases in activity were retained over a 7-day rest period; they were also produced when a second opiate (5 microgram/kg etorphine HCl) was substituted for morphine, were not seen when 2 mg/kg naloxone HCl (ip) was administered during treatment, and were present in rats showing tolerance to opiate-produced hypoactivity. Morphine's direct effect on activity is believed to have a biphasic dose-response curve; therefore, the relation of dose to conditioning was also studied. Increases in activity were the only conditioned behaviors observed; they were present only at the higher doses (16, 4, and 1 vs. .25, .065, and 0 mg/kg), and they occurred whether or not the dose was associated with unconditioned hypoactivity. The discussion deals with the relation of conditioning and morphine tolerance, the question of whether the unconditioned stimulus of morphine conditioning is a compensatory or a direct effect of morphine, and the similarity of conditioned increases in activity produced by morphine and by other stimuli that are reinforcing.