Early Arbitrary Object Memory May Set the Stage for Episodic Memory in Toddlers

1. The experiment had 6 trials - 2 familiarization trials (1 per room) and 4 test trials (2 per room). During familiarization children were shown where the toy was hidden, and that the other three containers were empty. On each test, children were asked in each room “do you remember where the toys are in here?” and their first search coded. Materials and Procedures Abstract This experiment was adapted from a non-human animal experiment (Eacott & Norman, 2004) which showed that “what-where-context” memory relies on the hippocampus. • Two uniquely decorated rooms (rainbow room and cloud castle), each containing the same 4 containers (basket, box, bag, and bin) arranged in unique configurations. • 2 toys (e.g. shapes and shape sorter) - 1 unique toy set per room In each room, a toy was hidden in one of the containers. The hiding place differed in each room, so that on each trial children had to remember the correct toy-container association in that context, to correctly find the toys. X Cloud Castle Early Arbitrary Object Memory May Set the Stage for Episodic Memory in Toddlers Frances Balcomb, Nora S. Newcombe, Katrina Ferrara, Jule Grant, Sarah M. Hittenger, Temple University Results Overview Children in Experiment 1 were divided at the median (20.5 months) into an older (n=14) and younger (n=16) cohort. The origins of episodic memory are poorly understood. Children do not show mature source memory and autobiographical memory until the age of 5 or 6 years. Infants show declarative memory, but it may be semantic. In adults, episodic memory has been linked to the ability to remember associations between objects, and research with elderly subjects reveals deficits in such memory, except when supported by familiar semantic relationships. Episodic memory relies on the hippocampus, and evidence from spatial learning work suggests that the hippocampus develops rapidly between 16-24 months. Perhaps the emergence of episodic memory is preceded by the ability to remember increasingly complex associations between objects, supported by the hippocampus. Two experiments explore associative object memory in toddlers. In both experiments, children learn different configurations of objects, using a variety of cues in unique arrays (person, place, objects), and their memory for specific configurations is tested. In experiment 1, children are provided with an explicit memory cue, but in experiment 2 they are only indirectly cued. Data from both experiments suggests that the ability to make arbitrary object-object associations emerges at about 20 months, but only when children are provided with explicit recall cues. Cued memory - correct first searches: Older children (m=.79, sd=.23) > younger (m=.39, sd=.32, F(24)=1.5 p=.002). Older children were also significantly better than chance. (See Figure 1). In the cued condition, there was a significant correlation between age and proportion of correct searches in the cued condition (r=.67, p<.001) (See Figure 2). Uncued memory - correct first searches: Older children (m=.64, sd=.38) > did not differ significantly from chance (See Figure 1). Cued vs. Uncued: Older cued and older uncued groups did not differ significantly. (See Figure 1). Familiarization (2 trials, 6 min each) : Children were encouraged to explore freely for 3 minutes. After that, if they had not found the toys, the experimenter encouraged them to open all 4 containers. The trial ended when a knock on the door sounded, prompting children to open the door, revealing a different experimenter, who took children to the other room. 2. Test trials (4 trials, 2.5 min each) a. Children entered each room for 2.5 minutes. b. On entering, they were handed a toy and asked - “do you remember where the [toy] was? Where did we play in here?” c. Children searched until they found the toy or until 1 min elapsed, after which point they were cued. Research Questions Experiment 1 - Cued Memory After familiarization, children’s memory for the toy’s location in each room was prompted with an explicit verbal and object cue in each room. For example, in the Rainbow Room, children were handed a ball and asked “do you remember where the balls are?” In Cloud Castle children were handed a block and asked “do you remember where the blocks are?” After 1 minute, if children had not found the toy the experimenter showed them the correct container, encouraging them to approach and open it. • Does early episodic-like memory emerge as arbitrary object memory between 16-24 months? • Does early episodic-like memory appear to develop on the same timecourse as place learning? Figure 2: Correlation between Age and proportion correct searches in Exp 1 (cued) Figure 1: Mean proportion correct searches in Exp 1 and 2 Discussion • Children’s ability to make arbitrary object associations develops rapidly from 16-24 months, the same time period that children show marked changes in place learning. • However, this ability requires a high level of redundant cueing at recall. • Both place learning and episodic memory rely on the hippocampus. This fact, taken in convergence with the data from the non-human animal literature suggesting that context-dependent memory performance relies on an intact hippocampus, suggests that what is being revealed are the very early underpinnings of episodic memory. Experiment 2 - Uncued Memory After familiarization, children’s memory for the toy’s location in each room was prompted with a general verbal cue only in each room. In both rooms children were not handed any object, and were asked “do you remember where the toys are in here?” After 1 minute, if children had not found the toy they were handed the object and given an explicit verbal cue. Age, place learning and total language were correlated partialling out total # of searches Future directions To what extent do children rely on different contextual cues in memory tasks like this? Can children use contextual information in a task like this to make unique future predictions, in addition to recall? Does performance on spatial navigation tasks correlate with performance on early episodic-like memory tasks such as this? Participants X Experiment 1: 26 children, aged 16-24 months Experiment 2: 9 children, aged 20-24 months Data coding Children’’s first search was coded as correct (1) or incorrect (0) and the proportion of correct searches (of all 4 test trials) was calculated. Rainbow Room