Contingency learning in 9-month-old infants with Down syndrome.

The ability of ten 9-month-old infants with Down syndrome to acquire a contingency in which arm movements were reinforced with auditory and visual stimulation was assessed. Unlike a group of infants without identifiable disabilities, those with Down syndrome did not learn the contingency. Examination of the performance of individual infants with Down syndrome indicated that some infants did master the contingency. In addition, there was a relation between contingency performance and scores on the Mental Development Index of the Bayley Scales of Infant Development. Results were discussed in terms of the possibility that some infants with Down syndrome experience a decline in conditionability with age and the relation between conditionability and mental development.

Conditioning and long-term memory in three-month-old infants with Down syndrome.

The learning and memory of twenty 3-month-old infants with Down syndrome was compared with that of 20 infants without handicaps using an operant conditioning task known as mobile conjugate reinforcement. The infants were trained for 2 days to produce movement in an overhead crib mobile by kicking and were reexposed to this task a week later. Both groups successfully acquired the contingency and displayed reliable long-term retention. In addition, the conditioning and retention-test performance of the two groups of infants did not differ.

Amount of training and retention by infants.

In studies of animals and adult humans, more training typically leads to better retention. The generality of this finding was assessed in two studies with human infants in which amount of training was manipulated in two different ways. In the first study, 3-month-olds were trained for either 1, 2, or 3 sessions, each 9 min long; in the second, they were trained for a single session that was either 6, 9, 12, or 18 min long. Retention of independent groups was measured after delays ranging from 1 to 21 days. In both studies, different amounts of training did not yield group differences on any of the standard measures of acquisition or after a retention interval of 1 day. After intervals of a week or longer, however, more training led to better retention. Across studies, the long-term retention of groups that were trained for the same amount of time differed. We speculate that subjects learn different things in these two training regimens.

Infant temperament and subject loss due to crying during operant conditioning.

Infants who failed to complete a 2-day operant-conditioning task were compared with a stratified random sample of those who did on measures of infant temperament and several demographic characteristics. A discriminant-function analysis revealed that female infants who cried differed from female infants who did not cry on measures of duration of orienting and latency to approach sudden or novel stimuli. Reliable prediction of crying and noncrying could not, however, be made for males. No sex differences emerged in the incidence of crying or in the number of sessions completed. Partially successful females (i.e., those completing 1 of the 2 sessions) could reliably be discriminated from those who cried during the first session on measures of age at testing and maternal ratings of smiling behavior. The results of this study suggest that, as with habituation studies, subject loss in operant-conditioning studies is influenced by individual differences among the infants which may or may not adversely affect external validity.

Twilight activity and antipredator behavior of young fowl housed in artificial or natural light.

Twenty-four-hr patterns of running wheel activity (Experiment 1) and death feigning, an antipredator behavior (Experiment 2), were studied in domestic chicks housed outside, in natural lighting, or indoors, with light onset and offset timed to coincide with the upper limbs of local sunrise and sunset, respectively. Although chicks housed outside were more active and displayed stronger death feigning reactions, the daily patterns of each activity were highly similar in the two groups. Activity peaked during the period corresponding to evening twilight and was negligible during the morning twilight period; in contrast, death feigning peaked during the morning twilight period. Activity measures indicated that chicks on the artificial light schedule had learned to anticipate dark by day 5, and subsequent ontogenetic changes in activity occurred exclusively in the evening twilight phase.

The effect of crying on long-term memory in infancy.

The influence of crying on infants' long-term memory for a learned response was investigated in 3 experiments. In each, infants were trained to move a crib mobile containing 10 identical objects by means of kicking and were then exposed to a reinforcer containing only 2 of these components. This shift in component numerosity produced crying in 53% of the infants. Infants who cried in response to the reward shift evidenced no retention of the contingency 1 week later (Experiment 1) but did have excellent retention at 1 day (Experiment 2). In Experiment 3, a brief reactivation treatment alleviated forgetting at 3 weeks regardless of the presence of crying in response to the change in mobiles. An unexpected recency effect characterized the efficacy of the reactivation treatment. The results indicate that crying in response to the violation of a reward-expectation habit functions as an amnesic agent to produce accelerated forgetting.

Noncontingent stimulation, stimulus familiarization, and subsequent learning in young infants.

2 experiments assessed the effects of prior noncontingent or familiarization experience on subsequent operant conditioning (kick-produced mobile movement) in young infants. In Experiment 1, infants received either long- or short-term noncontingent exposure to their own rotating mobile or simply viewed this mobile for several days while it remained motionless. In Experiment 2, long-term exposure was provided by the same novel mobile used for subsequent training. In both experiments, prior noncontingent experience did not interfere with subsequent conditioning. In Experiment 2, however, simple long-term familiarization with the training mobile precluded "evidence" of learning. The results indicated that infants develop expectancies regarding how stimuli occurring in particular contexts should behave based on their prior experiences with these stimuli.

Expectancies and memory retrieval in three-month-old infants.

The ability of 3-month-olds to acquire generalized expectancies of reward and the role of these expectancies in memory retrieval was assessed in 2 experiments. In both, infants learned to activate the components of a crib mobile by kicking and were trained with mobiles containing either the same (invariant) or different (variable) components in successive daily sessions. In Experiment 1, infants exhibited positive transfer over both the invariant and variable stimulus series. However, there was a trend toward disruption of retrieval when infants were tested with a familiar set of components following training on a variable stimulus series. In Experiment 2, infants were trained for 2 sessions with mobile components that either did or did not change between sessions. In a 24-hour retention test, mobile components that either continued or violated the serial order established during the preceding sessions were presented as retrieval cues. Infants again exhibited positive transfer over both variable and invariant series when the test stimulus was predicted by the serial order of training stimuli, but violations of either expected order produced a retention deficit. These results were interpreted as suggesting that very young infants develop generalized expectancies of reward that are based on the serial pattern in which events occur.

Stimulus preference and its effect on visual habituation and dishabituation in four-month-old infants.

The rate of habituation and rehabituation and the magnitude of dishabituation were investigated in four-month-old infants (24 boys, 24 girls) as a function of stimulus preference. Infants were habituated to either a preferred or nonpreferred stimulus and rehabituated with the opposite stimulus. Infants initially viewing a preferred stimulus required more trials to habituate and fewer trials to rehabituate than those in the nonpreferred group. In addition, the magnitude of dishabituation was greater for infants in the latter group. The data were discussed in terms of the importance of stimulus preference in studies of infant habituation.

Memory retrieval: a time-locked process in infancy.

Three-month-old infants learned to activate an overhead crib mobile by operant footkicking and received a visual reminder of the event (a "reactivation treatment") 2 weeks later, after forgetting had occurred. Subsequent manifestation of the association was a monotonic increasing function of time since the reactivation treatment, and performance of infants tested 8 hours after the remainder was related to the time spent sleeping in the interim (r = 0.75). These data demonstrate that normal retrieval is time-dependent. Moreover, individual data suggest that retrieval may be continuous rather than discontinuous.

The effects of distributed training on retention of operant conditioning in human infants.

Long-term retention of operant footkicking acquired in the mobile conjugate reinforcement paradigm was assessed as a function of the distribution of training time. In the first study, 3-month-old infants were trained for either one 18-min session or for two 9-min or three 6-min sessions separated by 24-hr intervals. All infants exhibited retention during a test administered immediately after training, but only those trained in a single session continued to perform the conditioned response during cued-recall tests 7 or 14 days later. Infants trained in three sessions showed no evidence of remembering the contingency even after a week. A warm-up decrement, seen in the day-to-day performance of infants in the distributed conditions, was eliminated in the second study by the interpolation of a nonreinforcement period at the outset of daily sessions. This procedure also enhanced long-term retention such that infants trained in three 6-min sessions now remembered the contingency for 14 days and did not differ from infants who had received a single 18-min session. Whether distributed training facilitates or impairs long-term retention appears to depend on the opportunity for infants to acquire a sufficient number (or kind) of effective retrieval cues during original learning.

Effect of varying sucrose concentration on macrobehavioral aspects of licking in the rat.

Rats (eight male, eight female) were trained to lick 32% and 4% sucrose solutions for three minutes per day on four consecutive days. Measures of the number of licks revealed robust positive and negative contrast effects. Analysis of the burst-pause pattern of licking revealed that the decrease in licking characteristic of the negative contrast effect resulted from a decrease in the number of bursts, while the increase in licking characteristic of the positive contrast effect was the result of a shortening of the interburst interval.

Immediate and long-term memory for reinforcement context: the development of learned expectancies in early infancy.

Infants were pretrained to move crib mobiles containing 6 or 10 identical objects by means of footkicking and were then exposed to a reinforcer containing only 2 objects. Relative to infants with no prior history of reinformcement with either of the "larger mobiles, infants shifted to the "smaller" mobile had higher kick rates, and, in addition, their visual attention decreased and negative vocalizations increased. These effects were not transient but persisted 24 hours later in infants experiencing the larger (10- to 2-object) shift. The results suggested that infants develop reward-expectation habits which continue to influence behavior for periods of at least 24 hours.

Reactivation of infant memory.

Three-month-old infants learned to activate a crib mobile by means of operant footkicks. Retention of the conditioned response was assessed during a cued recall test with the nonmoving mobile. Although forgetting is typically complete after an 8-day retention interval, infants who received a reactivation treatment--a brief exposure to the reinforcer 24 hours before retention testing--showed no forgetting after retention intervals of either 2 or 4 weeks. Further, the forgetting function after a reactivation treatment did not differ from the original forgetting function. These experiments demonstrate that (i) "reactivation" or "reinstatement" is an effective mechanism by which early experiences can continue to influence behavior over lengthy intervals and (ii) memory deficits in young infants are best viewed as retrieval deficits.

Effect of handling on positive and negative contrast effects.

The effects of early handling on the exhibition of positive and negative contrast effects were investigated. Over two 4-day testing sessions, animals were given alternating 1-min access periods to 2 bottles containing either 32 or 4% sucrose solutions. Measures of lick rate and latency to switch bottles revealed that both handled and nonhandled animals exhibited contrast effects of equal magnitudes. The results did not support an emotional interpretation of contrast effects but were interpreted as support for the perceptual theory of this phenomenon.

Contrast effects in the rat: a developmental study.

Two experiments investigated and development of positive and negative contrast effects in the consummatory behavior of juvenile and adult rats. Over a 4-day session, animals were given alternating 30-sec presentations of 2 bottles containing either 32 or 4% sucrose solutions. In Experiment I, different groups of rats were tested both cross-sectionally and longitudinally using a cohort-sequential design. Cross-sectionally, animals at all ages exhibited both types of contrast and demonstrated increasing positive contrast effects with greater age. Discrepancies between the longitudinal and cross-sectional samples were found to be due to the repeated testing procedure of the former design. Experiment II replicated the positive and negative contrast effects in the juvenile animals, indicating that the processes responsible for contrast effects are operating in the rat at a very early age.