The development of responses to people and a toy in infants with down syndrome

The behavior of eight infants with Down syndrome was observed biweekly from 8 to 24 weeks and monthly up to 48 weeks. At each visit the infants were presented with their mother, a female stranger, and a rattle puppet that were alternately active and passive. Each condition lasted 60 s. The results showed that by 4 months of age the infants began to differentiate, in the proportion of time they looked, smiled, and vocalized, between people and the toy. They did not discriminate, however, between mother and female stranger and between the active and passive adults until the second half of the first year. In particular, whereas normal infants usually show distress toward passive or “still-face” adults, the infants in this study continued to vocalize, at times even with smiling faces. The implications of these atypical aspects of the social development of infants with Down syndrome for their subsequent nonverbal communicative development are discussed.     

Neonatal imitation, gaze aversion, and mother-infant interaction

A relationship between elicited imitation in neonates and social interaction has been proposed by several investigators. The present work examines if such a relationship can be found when studying neonatal imitation, gaze aversion, and mother-infant interaction. Thirty-two infants were observed at 2 to 3 days, 3 weeks, and 3 months of age. Imitation of tongue protrusion and mouth opening was assessed in all three observations. In addition, a face-to-face interaction between mother and child was included when the child reached 3 months of age. The most striking result was a negative relationship between the infants' brief gaze aversion observed at 3 months of age while interacting with their mothers and the infants' imitative reactions at 2 to 3 days, 3 weeks, and 3 months of age. Behaviorally, these patterns indicate that high-imitating infants tend to display fewer episodes of brief gaze aversion when interacting with their mothers.     

Positive and negative reinforcement effects on behavior in a three-person microsociety

Three-person groups, either of males or of females, resided for 6 to 12 days in a continuously programmed environment. Subjects followed a behavioral program that determined the sequential and contingent relations within an inventory of activities. The program consisted of positive reinforcement days and avoidance days. During a positive reinforcement day, each work unit completed by a subject incremented a group account. The account was divided evenly among the three participants at the conclusion of the study. During a negative reinforcement day, no money was earned, and the group was assigned work unit criterion that, if completed, prevented a reduction in accumulated earnings. During negative reinforcement days, subjects made aggressive verbal responses, which differed in magnitude among the four groups. These differences were evident in several distinct behavioral measures. Performances on components of the work unit were not demonstrably affected by the reinforcement schedules in effect, although during the avoidance condition one subject stopped working and another subject's productivity declined.     

Reinforcement of probe responses and acquisition of stimulus control in fading procedures

Stimulus control of pigeons' key pecking was transferred from colors to lines by the method of stimulus fading. Fading was conducted with the addition of probes consisting of the line stimuli presented alone at each fading level. Probe responding was used to measure stimulus-control acquisition by the lines. Effects of reinforcement and nonreinforcement of probe responding upon acquisition of stimulus control were assessed using a single-organism repeated-acquisition design in which three fades were conducted serially. Probe responding was not reinforced in the first and third fade but was in the second. Reinforcement of probe responding substantially reduced the number of fading levels needed to complete fading. The outcome of a control experiment ruled out the possibility of accounting for these results in terms of the specific stimuli used in each fade or in terms of the sequential exposure to the three discriminations. Although probes permitted measurement of stimulus-control acquisition in fading, a measurement/acquisition interaction was also present.     

How accurate are memories of traffic accidents? Increased false memory levels among motorcyclists when confronted with accident-related word lists

Previous studies have found that false memories increase when people receive stimuli which is related to their knowledge base. In the current set of four experiments, we examined how accident experience affected false memory production among motorcyclists using different types of false memory word lists. Specifically, Experiments 1, 2, and 3 were conducted involving motorcyclists with and without accident experience, whereas Study 4 was conducted on non-motorcyclists without accident experience. In all experiments, participants were given associatively-related word lists known to foster false memory creation. Different types of word lists were used consisting of accident-related words, emotionally-negative words, and neutral words. Levels of false memory were measured using recall and recognition tests. We found consistent results in Experiments 1, 2, and 3 in which among motorcyclists, accident-related words produced higher levels of false memory than emotionally-negative and neutral words. This pattern was not observed in Experiment 4 where non-motorcyclists were involved. Our results shed light on the role of previous experience on false memory formation. One implication could be that the police should be careful with reports of motorcyclists' experiences about their accidents as motorcyclists may spontaneously come up with false, but related details concerning these experiences.