Lecture 4 - Denis Mareschal (Birkbeck College)
Co-ordination of Multiple Object Representations:
A Connectionist Account of Object Permanence

Thesis: Computationial modeling lies at the heart of developmental psychology because the study of transitional mechanisms is one of the mot important, yet understudied, facets of developmental psychology.

The Modelling Approach

Models complement empirical studies by highlighting...

Thus, model building involves "sucessive aproximations to reality" (Rumelhart & McClelland) with each new generation building on the findings of the past. Indeed, in developmental psychology, particularly in the pst several years, many conectionist models have appeared.

Steps to modeling

Examine the Area: Object Permanence

Piaget first discovered that infants less than seven months don't actively search for hidden objects. However, Baillergeon and Spelke (using passive preferential looking/surprise tasks) found that indeed children as young as three months had maintained some sort of mental representation (memory) for the hidden object and were surprised if it wasn't there.

WHY IS THERE SUCH A DEVELOPMENTAL LAG
BETWEEN ACTION AND PERCEPTION?

Model: Connectionist Network

Network: Has retinal preprocessor with feature detectors. Has and integration network with what and where sections (trained via unsupervised learning), and also has a Trajectory prediction with recurrent nodes.

This network observes four different types of objects, at 3 speeds either passing behind an occluder or not.

Results: First, the model predicts trajectories very well and can predict the exact position and projected location of the object, even when it has no direct perceptual input (ie. when the object is behind the screen). Likewise, the network can also keep track of the features of objects which are hidden, and will "reach for " desired objects. In addition, the network, and children, will notice if one object dissappears and a different object appears soon after. Most importantly: the network exhibits a developmental lag in reaching

Why is there the developmental lag? Because the Integration network also has feature information to process. Thus, the lack of salient features means the activation of the reaching portion of the network isn't high enough any more to elicit the responce, where as the trajectory network only has to predict.

 

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 Last Modified: Sep 20, 1999