(Michael I. Posner, Joe L. Lewis, and Carol Conrad)
A detailed analysis of the internal structures and mental operations involved in the process of reading might help us understand problems in acquiring the skill. This is a point that our keynote speaker [Gibson 1965] made several years ago. In the last few years there has been a considerable advance in the development of techniques used to isolate stages of processing and their interrelationships [Neisser 1967; Posner 1969; Sternberg, 1969]. This paper is an effort to review both the techniques and the results that might aid in elucidating the component processes in reading.
Let us be quite concrete. A young child who has never before seen the symbol "A" must be aware primarily of the visual form of the letter. But this is not so with an adult. Consciousness of the letter is suffused with past experience: its association to other visual forms (e.g., "a”), the phoneme /a/, its status as a vowel, and as the first letter of a list called the alphabet. Yet, even in the skilled reader, by appropriate
experimental technique, we can isolate the visual system processes from these other influences. We can, in fact, argue that the visual processes represent in the adult an isolable subsystem the properties of which can be studied.
Experiments showing that the visual process is an isolable subsystem of letter processing in the adult [Posner 1969] suggest that there are important psychological problems involved in passing from one subsystem to another (e.g., visual to name). Perhaps it is at the boundaries between any two isolable subsystems that special difficulties in cognitive processing lie. Indeed, the problem of coordinating modality-specific subsystems may represent one explanation of the difliculty in the seemingly simple translation from a visual word to the word name.
The idea of an isolable subsystem is a complex one [Miller 1970]. In the recent experimental literature there have been many eFforts to discover serial “stages" of processing [Clark and Chase 1971; E. E. Smith 1968; Sternberg 1959, Trabasso 1970]. These tasks tend to be ones in which one stage must depend directly upon the outcome of the prexious stage. There is still dispute about the details of these models (eg., whether the comparison stage is serial), but they have had sufficient success to show that internal mental operations can be isolated for study.
The words that you are presently reading are unique conngurations of print. The names that these words represent are abstractions in the sense that they stand for a variety of perceptually ditcferent visual forrns (eg., "PLANT, plant”) and auditory patterns [eg., the word plant spoken by a male or a female). The name of a word gains its meaning from the semantic structure to which it is related. The word plant may be related to a structure dealing with living things, or to one dealing with labor unions and assembly lines [Quillian 1969]. At one level the word is a visual code, at another a name, and at still another, an aspect of the overall semantic structure of which it is a part.
AN EXPERIMENTAL METHOD
The mental operations that transform one code into another can be observed in the time required for making classifications. Suppose that the subject is shown a pair of items and is asked to press, as quickly as possible, one key if they are "same" and another if they are "different." Figure 1 (left diagram) illustrates the results from an experiment in which items were letters and the definition of “same" was "both vowels” or "both consonants” [Posner and Mitchell 1967]. If the letters were identical in physical form ("A A"), the reaction time was faster than if they had only a name in common (e.g., "A a"), which in turn was faster than when items shared only the same class (e.g., “A e,” both vowels). A similar result [Schaeffer and Beller 1970] is shown (right diagram) for an experiment in which word pairs were used and the subject was required to press the key when both words were "living things" or both were "nonliving things". These figures illustrate the method measuring mental operations by the amount of time they require.
Can we isolate operations that are performed on visual information? The problem is how to determine if the operations performed on letters or words use visual representations rather than letter names or semantic information. Suppose that a pair of items is presented simultaneously. The subject is then required to press one key if the two items have the same name and another key if the names are different. If the two are physically identical (e.g. "A A") it is logically possible to base the match upon a visual form. On the other hand, for letters like "A a", which are not similar in physical form, the match is more likely to be based upon a learned correspondence between the visual forms such as the letter name.
Experimental data show that these logical distinctions apply to actual performances of subjects. The time for matching identical letters (e.g., "A A") is faster than that for upper and lower case forms of the same letters (e.g. "A a"). (...)
The isolability of visual and name processes, even for letters, allows us to study properties of the visual code independently of names. For example, it is now clear that any number of letters may be matched simultaneously, as long as they are physically identical. This means that the contact between external letters and their internal pattern recognizers can go in parallel and with no interference [Beller 1970; Donderi and Case 1970]. (...)
In her 1965 paper, Gibson argues that the primary units of analysis for reading are spelling patterns rather than single letters. It is possible now to show that these familiarity effects occur within the visual code and do not depend upon feedback from the letter names. Recent experiments have allowed us to study the influence of past experience upon mental operations within the visual system. If a subject is required to match two strings of letters to determine if they are physically identical, he can do so much faster if they form a familiar word than if they are nonsense strings [Eichelman 1970; Krueger 1970]. (...)
Moreover, the word can appears to form a unit. If the subject has to identify a single letter from a brief exposure, he can do so as efficiently when a words is presented as when a single letter is presented [Reicher 1969; Wheeler 1970]. It thus appears that having had past experience with certain sequences of letters allows us to perform matching and other visual operations upon them with great efficiency.
(...) In one study [Smith, Lott el al. 1969] it was found that subjects scanned a visual array just as rapidly whether the visual patterns were familiar ("PLANT, plant") or quite new ("pLaNt"), provided that the letters were equated for visibility. (...)
Nothing we have said suggests a solution to the more general problem of pattern recognition. We simply do not know how the input is brought into contact with the internal system. (...)
The concept of the name of a word or letter is an extremely important one for the psychology of reading. Many theories implicitly assume that the internal representation that stands for the name of a word is the same regardless of the modality through which the information was received [Morton 1969]. This assumption greatly simplifies an analysis of reading. The unique problem of reading would then involve mainly converting from a visual to a name code. From there on, comprehension would be based on mechanisms already present for listening. We have already reviewed one objection to this idea, namely, the view that meaning is connected directly to the visual forms. A second objection is that subjects can recall the channel of entry by which a stimulus was presented [Murdock 1967]. This objection, however, can be met by recognizing that the activation of a name code does not obliterate information about the past history of the input [Posner 1969].
Name Codes and Meaning
It is obvious that knowing the name of a word is not the same as knowing its meaning. James  commented on his point (Vol.I, p. 263), "it is more difficult to ascend to the meaning of word than to pass from one word to another; or to put it otherwise, it is harder to be a thinker than to be a rhetorician, and on the whole nothing is commoner than trains of words not understood." It is well known that the word associations of children often involve similarity of word sound, a type of association that is reduced in frequency later in life. If subjects are asked to signify that they have read a word, they respond much more quickly than when required to signify that they understand it [Wickens 1970]. (...)