Figure 1: A pr ototyp ical exa mple of a three-layer feed forward network, used by Plunkett and M archm an (1 991 ) to simulate learning the past-tense of En glish verbs. The inpu t units encode representations of the three phonemes of the present tense of the artificial words used in this simulation. Th e netwo rk is trained to produce a representation of the phonemes employed in the past tense form and the suffix (/d/, /ed/, or /t/) (...) used on regular verbs. To run the network, each input unit is assigned an activation value o f 0 or 1 , dep ending on whethe r the featu re is present or not. Eac h input unit is conne cted to each of the 30 hidden units by a we ighted conn ection and p rovid es an inp ut to each hidden unit equal to the product of the input unit's activation and the weight. Each hidd en unit's activation is then determined by summing ov er the va lues co ming fro m each inp ut unit to deter mine a netinput, and then applying a non-linear function (e.g., the logistic function 1/(1+e^netinput). Th is whole proced ure is. (shrink)

This paper argues that an ecological approach to psychology of the sort advanced by J. J. Gibson provides a coherent and powerful alternative to the computational, information-processing, paradigm. The paper argues for two principles. Firstly, one cannot begin to understand what internal information processing an organism must accomplish until one understands what information is available to the organism in its environment. Secondly, an organism can process information by acting on or manipulating physical structures in its environment. An attempt is made (...) to show how these principles can be extended to cognition as a whole. It is suggested that these principles may have a foundation in evolutionary biology. (shrink)