242 research outputs found
When and where do feed-forward neural networks learn localist representations?
According to parallel distributed processing (PDP) theory in psychology,
neural networks (NN) learn distributed rather than interpretable localist
representations. This view has been held so strongly that few researchers have
analysed single units to determine if this assumption is correct. However,
recent results from psychology, neuroscience and computer science have shown
the occasional existence of local codes emerging in artificial and biological
neural networks. In this paper, we undertake the first systematic survey of
when local codes emerge in a feed-forward neural network, using generated input
and output data with known qualities. We find that the number of local codes
that emerge from a NN follows a well-defined distribution across the number of
hidden layer neurons, with a peak determined by the size of input data, number
of examples presented and the sparsity of input data. Using a 1-hot output code
drastically decreases the number of local codes on the hidden layer. The number
of emergent local codes increases with the percentage of dropout applied to the
hidden layer, suggesting that the localist encoding may offer a resilience to
noisy networks. This data suggests that localist coding can emerge from
feed-forward PDP networks and suggests some of the conditions that may lead to
interpretable localist representations in the cortex. The findings highlight
how local codes should not be dismissed out of hand
A promising new tool for literacy instruction: The morphological matrix
There is growing interest in the role that morphological knowledge plays in literacy acquisition, but there is no research directly comparing the efficacy of different forms of morphological instruction. Here we compare two methods of teaching English morphology in the context of a memory experiment when words were organized by affix during study (e.g., a list of words was presented that all share an affix, such as , , , , etc.) or by base during study (e.g., a list of words was presented that all share a base, such as , , , ). We show that memory for morphologically complex words is better in both conditions compared to a control condition that does not highlight the morphological composition of words, and most importantly, show that studying words in a base-centric format improves memory further still. We argue that the morphological matrix that organizes words around a common base may provide an important new tool for literacy instruction
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