Page 75 - Foundations of Cognitive Psychology : Core Readings

74 Jay L. McClelland, David E.Rumelhart, and Geoffrey E.Hinton

Figure 4.9
An example of a nonword display that might be presented to the interactive activation model of
word recognition and the response of selected units at the letter and word levels.The letter units
illustrated are detectors for letters in the second input position.

structure of English.We illustrate this feature of the model with the example
showninfigure 4.9, wherethe nonword YEAD is shown in degraded form so
that the second letter is incompletely visible.Given the information about this
letter, considered alone, either E or F would be possible in the second position.
Yetour modelwilltendtocompletethisletterasan E.
The reason for this behavior is that, when YEAD is shown, a number of
words are partially activated.There is no word consistent with Y, E or F, A,and
D, but there are words which match YEA_ (YEAR, for example) and others
which match _EAD (BEAD, DEAD, HEAD,and READ, for example).These and
other near misses are partially activated as a result of the pattern of activation
at the letter level.While they compete with each other, none of these words
gets strongly enough activated to completely suppress all the others.Instead,
these units act as a group to reinforce particularly the letters E and A.There are