Move it! Visual feedback enhances validity of preferential looking as a measure of individual differences in vocabulary in toddlers.

Forty toddlers aged 20 to 24 months were presented with 32 pairs of images with the auditory stimulus Look followed by the name of the target image (e.g. Look . . . tree) in an intermodal preferential looking (IPL) paradigm. The same series of 16 items was presented first with one image as target and then with the other member of the pair as target. Half the children were given feedback, in the form of movement of the target image at the end of the trial, while the other half were presented with static images. IPL performance was quantified in terms of number of words showing at least 15% increase in proportion of looking time in the post-naming interval. Looking preference for the named item was correlated with parental report of vocabulary, this effect being stronger for those receiving feedback. The correlation with parental report of vocabulary comprehension was .65 for those receiving feedback, but only .37 for those with no feedback. It is concluded that the preferential looking task, which has been widely used in group studies, has the potential to act as a reliable index of comprehension level in individual children, especially when movement feedback is used to maintain attention.

Behavioral correlates of the distributed coding of spatial context.

Hippocampal place cells respond heterogeneously to elemental changes of a compound spatial context, suggesting that they form a distributed code of context, whereby context information is shared across a population of neurons. The question arises as to what this distributed code might be useful for. The present study explored two possibilities: one, that it allows contexts with common elements to be disambiguated, and the other, that it allows a given context to be associated with more than one outcome. We used two naturalistic measures of context processing in rats, rearing and thigmotaxis (boundary-hugging), to explore how rats responded to contextual novelty and to relate this to the behavior of place cells. In experiment 1, rats showed dishabituation of rearing to a novel reconfiguration of familiar context elements, suggesting that they perceived the reconfiguration as novel, a behavior that parallels that of place cells in a similar situation. In experiment 2, rats were trained in a place preference task on an open-field arena. A change in the arena context triggered renewed thigmotaxis, and yet navigation continued unimpaired, indicating simultaneous representation of both the altered contextual and constant spatial cues. Place cells similarly exhibited a dual population of responses, consistent with the hypothesis that their activity underlies spatial behavior. Together, these experiments suggest that heterogeneous context encoding (or "partial remapping") by place cells may function to allow the flexible assignment of associations to contexts, a faculty that could be useful in episodic memory encoding.