Figure 117

McClelland and Rumelhart's (1981) interactive activation model of visual word recognition. Adapted from Ellis (1984).

Letter vs. word identification

Common sense indicates that the recognition of a word on the printed page involves two successive stages:

1. Identification of the individual letters in the word.

2. Word identification.

However, the notion that letter identification must be complete before word identification can begin seems to be wrong. For example, consider the word superiority effect (Reicher, 1969). A letter string is presented very briefly followed by a pattern mask. The participant's task is to decide which of two letters was presented in a particular position (e.g., the third letter). The word superiority effect is defined by the fact that performance is better when the letter string forms a word than when it does not.

The word superiority effect suggests that information about the word presented can facilitate identification of the letters of that word. However, there is also a pseudo-word superiority effect: letters are better recognised when presented in pronounceable non-words (e.g., "MAVE") than in unpronounceable non-words (Cole, Rudinsky, Zue, & Reddy, 1980).

Interactive activation model

McClelland and Rumelhart (1981) put forward an influential interactive activation model of visual word recognition. The key assumptions of this model are as follows: "Visual word recognition involves a process of mutual constraint satisfaction between the bottom-up information gained about the features in the words and the top-down knowledge about word and letter identities" (Ellis & Humphreys, 1999, p. 315). The more detailed theoretical assumptions made by McClelland and Rumelhart (1981) are as follows (see Figure 11.7):

• There are recognition units at three levels: the feature level at the bottom; the letter level in the middle; and the word level at the top.

• When a feature in a letter is detected (e.g., vertical line at the right-hand side of a letter), activation goes to all the letter units containing that feature (e.g., H, M, N), and inhibition goes to all other letter units.

• Letters are identified at the letter level. When a letter in a particular position within a word is identified, activation is sent to the word level for all four-letter word units containing that letter in that position, and inhibition is sent to all other word units.

• Words are recognised at the word level. Activated word units increase the level of activation in the letterlevel units for the letters forming that word (e.g., activation of the word SEAT would increase activation for the four letters S, E, A, and T at the letter level) and inhibit activity of all other letter units.

• At each level in the system, activation of one particular unit leads to suppression or inhibition of competing units.

Bottom-up processes stemming directly from the written word proceed from the feature level through the letter level to the word level by means of activation and inhibition. Top-down processing is involved in the activation and inhibition processes going from the word level to the letter level. The word superiority effect occurs because of the top-down influences of the word level on the letter level. Suppose the word SEAT is presented, and the participants are asked whether the third letter is an A or an N. If the word unit for SEAT is activated at the word level, then this will increase the activation of the letter A at the letter level, and inhibit the activation of the letter N.

How can the pseudo-word superiority effect be explained? When letters are embedded in pronounceable non-words, there will generally be some overlap of spelling patterns between the pseudo-word and genuine words. This overlap can produce additional activation of the letters presented in the pseudo-word and thus lead to the pseudo-word superiority effect.


The interactive activation model has been very influential. It provides an interesting example of how a connectionist processing system (see Chapter 1) can be applied to visual word recognition. It accounts for various phenomena, including the word superiority effect and the pseudoword superiority effect.

According to the model, letters are coded in terms of their precise locations in the visual field. In fact, however, the evidence suggests that coding is actually based on the relative positions of letters rather than their precise positions. For example, Ellis and Humphreys (1999) pointed out that the following letter strings are often misread if seen only briefly:

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