The ontogeny of long‐term memory over the first year‐and‐a‐half of life

Abstract

This research documents the development of long-term memory in human infants from 2 months through the end of the first year-and-a-half of life. In the initial study phase, we trained 6- to 18-month-old human infants in an operant task and tested them after increasing delays until they exhibited no retention for 2 successive weeks. In the second phase, their data were combined with data previously obtained from 2- to 6-month-olds in an equivalent task. The resulting function revealed that the duration of retention increases monotonically between 2 and 18 months of age. This increase was not due to age differences in original learning. This is the first systematic analysis of the course of long-term memory across an extended period of infant development that is based on standardized parameters of training and testing. It provides a reference function against which measures of retention from infants of different ages that are obtained in different memory tasks with different parameters can be meaningfully compared.

Contextual determinants of anger and other negative expressions in young infants.

“…We found that 90% of infants responded at least 50% above baseline for at least 2 consecutive minutes (Hartshorn et al, 1998), and all exceeded 25% of baseline in the final 2 min. Only 2 infants who did not meet the criterion met the Hartshorn et al (1998) criterion (50% above baseline in Minutes 2-3 or Minutes 3-4, respectively), but they responded below baseline during 3 of the 4 remaining minutes.…”

“…Because the criterion assessed minimum response levels, maximum (peak) and final learning levels of infants in this paradigm were typically greater. Infants who met the minimum criterion were also likely to meet a commonly accepted learning criterion of contingency mastery, that is, 1.5 × baseline for 2 consecutive minutes (Hartshorn et al, 1998).Frustration measures-The two aspects of the frustration response assessed were changes in arm response and changes in facial expression. Both were examined because the different frustration conditions might have affected the relation between arm responses and expressions.…”

“…The criterion was neither too easy nor too difficult and compared favorably with other commonly used indices of contingency mastery (Hartshorn et al, 1998). For example, all of the subjects meeting the current criterion sustained response increments at least 25% above baseline for at least 2 consecutive minutes during the contingency phase, and 90% were at least 50% above baseline in any 2 consecutive minutes.…”

“…On average, infants meeting the criterion achieved a response rate that was more than three times their base rate (M = 3.03, SD = 1.09) at the end of the contingency phase. In contrast, nonlearners were not significantly above baseline in the final 2 min of learning (M = 0.78, SD = 0.23).The criterion was neither too easy nor too difficult and compared favorably with other commonly used indices of contingency mastery (Hartshorn et al, 1998). For example, all of the subjects meeting the current criterion sustained response increments at least 25% above baseline for at least 2 consecutive minutes during the contingency phase, and 90% were at least 50% above baseline in any 2 consecutive minutes.…”

When do infants begin recognizing familiar words in sentences?

“…Using these paradigms this team of researchers found that in the first year of life there is a dramatic increase in memory retention (see Hartshorn et al, 1998a). In addition, the ability to recall an event from a related ' prime' or associated contingency or cue increases as a function not only of age, but also of the duration of the prime (Hsu, Rovee-Collier, Hill, Grodkiewicz & Joh, 2005): Hsu et al (2005) found that the duration of a prime needed to reactivate a memory decreased logarithmically with age.…”