Reexamination of contextual conditioning with massed versus distributed unconditioned stimuli

Sprague-Dawley rats were placed in the black compartment of a 2 compartment choice apparatus and received a series of unsignaled footshocks at fixed intertrial intervals (ITIs), with ITI duration varied across groups. Contextual conditioning was assessed using place preference and freezing tests. In Experiments 1 and 3, time spent in the unshocked, white compartment in a preference test decreased monotonically with increasing ITI. In Experiment 2, less freezing occurred in the 3-s than in the 60-s groups. An inverted U-shaped relationship between ITI and freezing emerged when a full range of ITIs was used in Experiment 3. The results have implications for the learning-performance distinction and suggest that short ITIs may promote contextual conditioning.     

Effects of massed versus distributed practice on gross and fine motor proficiency of educable mentally handicapped adolescents

Gross and fine motor proficiency were studied in a sample of 52 educable mentally handicapped students (M = 15.8 yr.), half of whom were assigned to 15 30-sec. trials, a relatively massed practice schedule with 5 sec. between trials, and half to a distributed practice schedule with 30-sec. rests. 5 trials were given 24 hr. later. All subjects performed the stabilometer balance task to measure gross motor proficiency and a 45-rpm pursuit rotor task to measure fine motor proficiency. No significant differences with regard to the practice schedule used early in learning were found, however, boys scored significantly higher on the pursuit rotor than girls.     

Extinction of a conditioned emotional response: massed and distributed exposures

Using the lick-suppression methodology of Jacobs, Buttrick & Kennedy (Pavlovian Journal of Biological Science, 23, 29-34, 1988), a conditioned emotional response (CER) was established in 24 rats using off-the-baseline pairings of a light (the conditional stimulus) and brief footshock (the unconditioned stimulus). Following conditioning, the rats were assigned to one of three extinction groups differing in whether they received massed or distributed off-the-baseline exposure to the conditional stimulus. The effects of differential treatment were assessed on-the-baseline on test days, when the extinction of the CER was monitored. Rats receiving a single, long exposure to the conditional stimulus showed greater resistance to extinction than the rats in the distributed groups. They also showed a difference pattern of CER extinction. The results were discussed and compared to similar studies that have explored the massed vs distributed dimension, both in CER and avoidance-extinction (using response prevention or flooding). The relation of animal studies to parallel human studies using exposure therapy was also discussed.     

Distributed and massed practice effects on motor performance and learning of autistic children

The purpose of this study was to examine the effect of massed and distributed practice upon the learning by 8 autistic children of rotary pursuit tracking at 20 rpm. The massed practice group of four completed 10 30-sec. trials with 5-sec. rests for 10 consecutive days on the Photoelectric Pursuit Rotor. The distributed practice group completed 10 30-sec. trials with 30-sec. rests for 10 consecutive days on the same device. The results of a 2 x 10 x 10 (group x practice days x trials) analysis of variance with repeated measures on the last two factors indicated that learning occurred for both groups but no differences between groups were significant. It is suggested that further investigations into the applicability of motor learning principles to special populations be conducted using larger groups.     

Fetal habituation performance: Gestational age and sex effects

Habituation is the decrement in response to repeated stimulation. Fetal habituation performance may reflect the functioning of the central nervous system (CNS) prenatally. However, basic characteristics of the prenatal habituation phenomena remain unclear, such as the relationship with gestational age (GA) and fetal sex. The current study investigated the relationship between habituation performance and both fetal sex and advancing gestational age, by comparing habituation performance at 31 and 35 weeks GA within a sample of 74 singleton pregnancies, all with normal neonatal outcomes. A vibroacoustic stimulus was used to habituate the fetus and motor responses were monitored via ultrasound. The criterion for habituation was defined as no response to five consecutive stimulus presentations. Prenatal habituation performance was found to demonstrate a developmental trend, with an increased proportion of fetuses habituating with advancing gestational age and requiring fewer stimulus presentations to satisfy the habituation criterion. Fetal sex also appears to have a moderating influence on gestational changes in habituation performance. Hence, the ongoing maturation of the fetal CNS does appear to be reflected in fetal habituation performance, indicating the need to consider the composition of fetal samples in terms of both gestational age and sex. Variability in interfetal performance was found to be high and clinical applications remain speculative.     

Building blocks of self-control: increased tolerance for delay with bundled rewards

Impulsive choice can be defined as temporary preference for a smaller-sooner reward (SS) over a larger-later reward (LL). Hyperbolic discounting implies that impulsive choices will occur less when organisms choose between a series of SSs versus LLs all at once than when they choose between single SS versus LL pairs. Eight rats were exposed to two conditions of an intertemporal choice paradigm using sucrose solution as reward. In both conditions, the LL was 150 microl delayed by 3 s, while the SS was an immediate reward that ranged from 25-150 microl across sessions. Preference for the LL was greater when the chosen reward was automatically delivered three times in succession (bundled) than when it was chosen singly and delivered after each choice. For each of the 8 rats, the estimated SS amount that produced indifference was higher in the bundled condition than in the single condition. Because bundling in humans may be based on the perception that one's current choice is predictive of future choices, the data presented here may demonstrate an important building block of self-control.     

Development of children's mental representations: effects of age, sex, and school experience

In the present study mental representations in drawings by 158 young children, ages 2 1/2 to 6 yr. old were analysed. The aim was to investigate whether the accuracy of mental representations increased with age and how this development progressed. Also tested were whether the inferred mental representations differed for boys and girls and whether preschool experience affected the drawings. As expected, mental representation increased in complexity with age as measured by Goodenough's score, and girls' mental representations (drawings) were significantly more elaborate than boys. Moreover, attending school early seemed to affect mental representations of the 3-yr.-olds but not the 4-yr.-olds. Results are discussed in terms of internal and external factors in mental representation in drawing a man.     

Children's memory of events: effects of stress,age, time delay and location of interview

To examine the ability of children aged between 4 and 12 years to recall a stressful event (venipuncture) compared with a non-stressful event (demonstration of venipuncture), recall was tested after 6–8 weeks. Half also had recall tested after 2–7 days. Testing took place where the stressful event occurred (n=122) or at a neutral location (n=127). Children who experienced the stressful event were less likely to give inaccurate responses in free recall or to acquiesce to suggestive misleading questions. Apart from incorrect responses in free recall, correct responses increased and incorrect responses decreased with increasing age. Recall after 2–7 days was superior to recall after 6–8 weeks. Those who had an early and a late interview had better recall at the late interview than those who had a late interview only. The location of interview showed no effects on recall. © 1998 John Wiley & Sons, Ltd.