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Coding Processes in Skilled And Less Skilled Readers
L. P. Haines, Ph.D. and
C. K. Leong, Ph.D.
Department for the Education of Exceptional Children University of Saskatchewan Saskatoon, Saskatchewan
Canada
The term coding refers to the abstract, internal representation in memory of events and relations between events. It relates to the structure of memory, its components and their organizations within a system. Coding is thus concerned with the central question of "what is learned?"
For reading, Gibson and Levin's (1975, p.5) definition is as concise and comprehensive as any: "reading is extracting information from text.'" Downing and Leong (1982, p. 4) broaden this to: "Reading is the inter- pretation of symbols." Symbols extend both in time and in space and include musical notations, cartographic symbols, Braille, ambient prints such as labels and displays on video machines and, of course, different writing systems. Whichever definition is used, readers must: (a) decode written symbols to sound, (b) have recourse to the internal lexicon or the internal, abstract, mental dictionary to extract meaning from the printed word from semantic memory and (c) incorporate this memory into their language learning system.
In this report we have confined our attention to two experiments converging on lexical access or reading words for meaning. Following Coltheart, Davelaar, Jonasson and Besner (1977), we have attempted to study the nature of the access code and the access procedure in skilled and less skilled readers. Access code refers to the nature of the information extracted from the printed word, and access procedure refers to the way in which the internal representation is used to find the word's entry in the internal lexicon. As English is a phonemically-based orthography, the question often revolves around these views: (a) that the access code during reading is phonological and indirect, (b) that the access code is visual and direct and (c) that there are dual phonological and visual codes.
The authors want to thank the teachers and children of Roland Michener School, Saskatoon for their co-operation. For this cooperative project L. P. Haines carried out the study; C. K. Leong wrote the report. Both authors share any shortcomings.
67
ANNALS OF DYSLEXIA
In this context, phonological and visual coding should not be taken to mean opposites. These processes range along a continuum: phonological to non-phonological; visual to non-visual. In what follows we review briefly the arguments for and against phonological coding (see Downing and Leong, 1982, Chapter 9 for detailed discussions). We then report on two interrelated experiments with readers involving a vocalization or naming latency task and a lexical decision task (deciding if a string of letters is a word or a nonword).
It may be said that phonological coding is an abstract, internal representation, the output dimensions (transforms) of which carry into categories of speech or language units such as phonemes, mor- phophonemes and syllables. Phonological coding may be pre-lexical as a necessary preliminary to lexical access; or it may be post-lexical or gener- ated from locating the lexical entry. Evidence on the pre- and post-lexical access is not clear-cut, as much depends on the experimental paradigm and the nature of the tasks used. The question can be seen as whether or not in accessing printed words there is any transformation into some form of speech-based code which could be an articulatory, acoustic, auditory or a more abstract code (see Kleiman, 1975). Outlined below are the main arguments for phonological coding and visual coding, and a summing up.
Phonological Coding in Lexical Access
(a) Short-Term Memory Studies Conrad (1962, 1964) reasoned that if subjects used a phonological
code, then silent reading of phonologically similar items would lead to impairment in recall. He indeed found that when subjects were shown such letters as B, C, D, P, T, V and were required to write them down, the errors they made were similar to the kinds of errors made in identifying the names of the letters heard in "white noise." He also studied deaf subjects and suggested their ineffective phonological code might explain in part why they read poorly (note the counter-argument that despite this deficiency deaf individuals do learn to read and some read reasonably efficiently).
(b) Electromyographic Studies The electromyographic technique (EMG), a procedure of inserting
electrodes into the speech musculature to measure and record electrical activities in the speech muscle of the laryngeal area, is often used to show covert oral behaviour during even silent reading (see Edfeldt, 1960; McGuigan, 1970). Of the body of literature on EMG and related studies, it is fair to refer to Conrad's (1972, p. 209) summary: "What is far from proved is that articulation is necessarily involved in silent reading."
68
CODING PROCESSES
(c) Lexical Decision Tasks Involving Homophonic Words The rationale for this kind of study is that when subjects are asked to
decide if a letter string forms a word, it takes longer to reject a nonword string like BRUME if that string sounds like a real word. Apparently this task requires the subjects to obtain access to their internal lexicon in order to arrive at a correct decision. A series of experiments by Rubenstein, Lewis and Rubenstein (1971) showed that reaction time (RT) for correct responses for legal nonsense (e.g. DRILP, MELP) was longer than re- sponse latency for illegal nonsense of higher pronounceability (e.g. TRUCP), which in turn was longer than the response latency for illegal nonsense of lower pronounceability (e.g. TRITV). This was taken as evidence that the phonological representation of a letter string was being compared with a subset of phonological representations stored in lexical memory. The large difference in reaction time between legal and illegal types supports the hypothesis that deciding if a string is a nonword when it is orthographically and phonologically illegal does not require the exhaustive search of the internal lexicon that is necessary for considering legal nonsense words.
The Rubenstein et al. (1971) study was replicated by Coltheart, et al. (1977) who obtained slightly different results. These authors suggested that phonological recoding might play a role in the rejection of nonword items, but they doubted if similar recoding was carried out for words. Thus Coltheart et al. argued against the joint assertion that the role of the lexicon is phonological and that the access procedure is serial search. In a further study, Davelaar, Coltheart, Besner and Jonasson (1978) proposed that lexical access is a parallel process with the interplay of phonological and visual coding during lexical access. More recently, there seems to be greater acceptance of this dual coding, parallel processing hypothesis.
(d) Experiments With Non-Alphabetic Script In an early study, Erickson, Mattingly and Turvey (1972) used a
probed short-term memory paradigm with Oriental university students to examine possible phonological coding with the morphemic Chinese component or Kanji characters of the Japanese syllabary. Results show that the subjects resorted to a phonetic strategy as there was a significant difference in their identification of phonetically similar characters and those with no systematic similarity. Tzeng, Hung and Wang (1977) asked subjects to judge whether or not a sentence printed in Chinese characters made sense. This task was done more slowly when the characters in a phrase were phonologically similar than when they were not. Tzeng et al. suggested that phonetic similarities of Chinese characters interfered with the subjects" performance on both a short-term memory task and a sentence judgment task. Some recent evidence on lexical decision tasks on Serbo-Croatian letter strings also shows that phonological coding is automatic, rapid and obligatory (Lukatela and Turvey, 1980). Serbo-
69
ANNALS OF DYSLEXIA
Croatian is considerably more transparent than English in that individual letters have phonetic representations that remain consistent throughout changes in the context in which they are embedded. Turvey and associ- ates emphasized that the full implications of their data for a theory of word recognition remain to be further explored.
The above is just a sketch from experimental evidence outlining the main arguments for phonological coding during lexical access.
Visual Coding in Lexical Access
Counter-arguments can be advanced to buttress the claim for visual access. These sources of evidence are summarized below.
(a) Effect of Homophonic and Heterophonic Words Good examples of these kinds of studies are those carried out by
Baron (1973, 1977), Bradshaw and Nettleton (1974), Green and Shallice (1976) and Frederiksen and Kroll (1976), among others. Baron (1973) asked university students to examine if phonologically and visually congruent phrases of the kind MY NEW CAR; phonologically congruent but visually incongruent phrases (e.g. MY KNEW CAR); and phono- logically and visually incongruous phrases (e.g. OUR NO CAR) made sense or not and measured reaction time to these classifications. The results led Baron to suggest that visual analysis is faster than phonemic encoding for skilled readers and is thus normally used when readers are free to choose their strategies of analysis. In a subsequent study Baron (1977) found some evidence for the use of the indirect phonemic path and suggested the probability of this indirect path being used in parallel with the direct path.
In an analogous study using heterophonic words (words similar in spelling but dissimilar in pronunciation such as MOWN--DOWN), Brad- shaw and Nettleton (1974) measured latencies for initiating and com- pleting the vocalization of the pair, the first member alone and the second member alone. Results show that words could be recognized, identified or stored without phonological recoding. Green and Shallice (1976) exam- ined the problem of whether or not phonological recoding during reading is obligatory or optional. Their experimental materials included rhyming versus non-rhyming words (e.g. DOTE, STOAT vs. POISE, WISE) and correctly and incorrectly spelled words (e.g. URGE and ERGE) and the experimental subjects (university students) were asked to make a se- mantic decision about these words. From their results Green and Shallice argued for the direct visual route to semantic representation. They pointed out that the questions of obligatory or optional use of phono- logical recoding in reading should take the form of the argument as put
70
CODING PROCESSES
forward by Kleiman (1975) that for phonological recoding to occur the activity is more likely to be at the working memory stage. In a detailed analysis of the effects of orthographic structure of words on naming latencies, Frederiksen and Kroll (1976) proposed that in reading, abstract phonological representation is not developed prior to articulation and is not a prerequisite for lexical retrieval.
(b) Stroop Effect The Stroop (1935) word-color interference task has been used by a
number of researchers (see Ehri, 1976, 1977; Posnansky and Rayner, 1977; Rosinski, 1977) to show that grade school and university readers can access word meaning without phonological recoding. A good example is the study by Posnansky and Rayner (1977). In a series of experiments with materials of the kind: HORSE (word condition), HCNRE (nonword with preservation of overall word shape condition), HGPLE (nonword with preservation of initial and final letters condition), PYNRK (nonword with preservation of neither word shape nor letters condition) and RADIO (Stroop word condition), Posnansky and Rayner varied visual- threshold exposure durations for these materials to examine stages of word processing. They found that in all the experiments, nonwords that preserved more of the visual features of the picture label resulted in faster naming times than those that did not, especially when the stimuli were presented at brief exposure durations. They suggested that the results support the visual feature stage model more than the phonemic recoding stage model for word identification.
(c) Studies of Deep Dyslexia In their research program, Marshall and Newcombe (Marshall, 1976;
Marshall and Newcombe, 1966, 1973, 1977; Newcombe and Marshall, 1981) discussed detailed individual cases of one form of the acquired dyslexias--deep dyslexia. A comprehensive review of the phenomenon is given by Coltheart, Patterson and Marshall (1980). In general, the "reading" errors of patients with deep dyslexia are characterized by: (a) predominantly semantic substitution errors (e.g. SPEAK read as TALK, SICK read as ILL), (b) visual errors (e.g. BEG read as LEG), (c) derivational errors (e.g. COURAGE read as COURAGEOUS), (d) difficulties with low imagery words, (e) difficulties with function words and (f) difficulties in deriving sound from print especially nonsense words. These "central" errors likely derive from the disturbance of the central lexicon which explains the semantic relationship between the stimulus word and the error response. Coltheart (1980) commented: "The reading of the deep dyslexic thus reflects the operation of a partially impaired left-hemisphere reading system" (p. 326) and further: " ' . . . what is lost in deep dyslexia is access from print to the left-hemisphere lexicon, i.e. orthographic access
71
A N N A L S O F D Y S L E X I A
to this lexicon" (p. 352). Reference to an orthographic strategy should not be taken to mean a holistic approach as mixed letter case presentations
D (e.g. o or cAbiNeT) did not interfere with the reading performance of
G . . . . . deep ~iyslexlcs. While care should be taken in interpreting the findings of deep dyslexia and their differing symptom complexes from develop- mental dyslexia, there are also similarities (Newcombe and Marshall, 1981). As to extrapolations to "normal" reading, Allport (1977) very aptly pointed out that the central errors of deep dyslexic patients indicate some means of access to the semantic system for visually presented words that does not require obligatory phonological recoding.
Summing Up of Evidence
Evidence shows that the phonological route is likely used in proc- essing non-words since the faster visual route would not be helpful. On the other hand, the non-lexical route of grapheme-phoneme correspon- dence cannot be used with irregular words such as SWORD because they do not conform to grapheme-phoneme rules. In the preceding sections arguments for both phonological and visual coding have been presented. There is, however, also growing evidence for the dual coding and mul- tiple paths theory in word processing (see Barron and Baron, 1977; Davelaar, et al. 1978; Downing and Leong, 1982; Shulman and Davison, 1977, among others). From available literature, it also seems that learning the grapheme-phoneme (or print to sound) correspondence is an abstract task and one not readily available to young readers or to those with reading problems. What is needed is to determine the advantages of the phonological versus the visual route for readers of different reading abilities and for different materials in lexical access. Information of this kind will better answer the question of whether the phonological route is obligatory or optional and the conditions under which one route is preferred over the other.
In an attempt to provide an answer to the above questions, two converging experiments were undertaken to examine word processing of skilled and less skilled elementary school readers. Experimental subjects consisted of a total of 72 children with 24 children at each of grades 4, 6 and 8 with sex and reading ability equally represented. The first experi- ment involved measuring vocalization latency to visually presented indi- vidual three-, four- and five-letter words and pseudowords equated for word frequency, syllable structure and intraword redundancy. The sec- ond experiment was a lexical decision task which required the children to make word/nonword decisions to singly presented items from a mixed list of the two word types and pseudowords, with yes/no latency as the dependent measure.
72
CODING PROCESSES
Experiment1
There have been previous studies of the effect of word characteristics on vocalization latency with adult subjects (e.g. Frederiksen and Kroll, 1976) and with children (e.g. Perfetti and Hogaboam, 1975). The major finding of the Perfetti and Hogaboam vocalization latency study in third and fifth grade good and poor readers was that they could be maximally different on the pronunciation latency of low frequency words and pseudowords and that this discrimination was greater for grade three than for grade five children. While this study provides an indication of the role of phonological recoding, it does not address adequately the question of the unit of processing. Thus Experiment 1 in the present study was designed to examine the effects of predictability, lexical membership and stimulus length upon pronunciation latency for skilled and less skilled readers in the fourth, sixth and eighth grades. The stimuli were carefully matched for syllable length, frequency of occurrence and orthographic redundancy to control for possible confounding effects. The rationale for this experiment was that equivalent performance on "predictable" and "unpredictable" words would reflect visual coding in lexical access while an advantage of predictable over unpredictable words would indicate that phonological recoding was the preferred strategy. A strict phono- logical recoding model would predict equivalent performance for pre- dictable words and pseudowords along with poorer performance on the unpredictable words, while the dual coding model would predict equiv- alent performance for the two word types with both superior to the pseudowords.
Method Subjects. Subjects consisted of a total of 72children selected from
grades 4, 6 and 8 in a large elementary school. There were 24 children in each grade and each group of 24 was divided into skilled and less skilled readers on the basis of the Canadian Test of Basic Skills (CTBS) Form 3M (King, 1977). The sexes were equally represented for each reading ability level for each grade. The chronological ages in months for the different grades were: grade 4 (skilled readers: M = 110.58, SD = 3.40; less skilled readers: M = 108.66, SD = 3.73); grade 6 (skilled readers: M = 134.50, SD = 3.15; less skilled readers: M = 136.08, SD = 4.75); grade 8 (skilled readers: M = 158.00, SD = 4.44; less skilled readers: M = 157.33, SD = 3.90). The grade equivalent CTBS reading score was as follows: grade 4 (skilled readers: M = 5.73, SD = .19; less skilled readers: M = 3.63, SD = .38); grade 6 (skilled readers: M = 8.11, SD = . 19; less skilled readers: M = 5.63, SD = .46); grade 8 (skilled readers: M = 10.13, SD = .32; less skilled readers: M = 7.73, SD = .65). It can be seen that high and low reading ability groups were closely matched for age. For reading levels the less
73
ANNALS OF DYSLEXIA
skilled readers were about six months below the appropriate reading grade placement at the time of the experiments while the skilled readers showed the expected increment in reading from grade to grade.
Materials. The stimulus lists of predictable and unpredictable words followed Venezky's (1970) analysis of English vocabulary. Very briefly, predictable words are those words with a vowel or vowel cluster mapping onto its most frequently occurring phonemic correspondence (e.g. GET, NEAR, STAND). Unpredictable words are those with a vowel cluster mapping onto a less frequently occurring phonemic correspon- dence (e.g. ONE, MOVE, LEARN). In addition, pseudowords or letter strings matching the vowel or vowel cluster of the predictable and unpredictable words (e.g. LOD, LOAT, BRESH) were also used. The predictable, unpredictable and pseudowords were carefully controlled for syllable structure with the use of monosyllabic items, for sequential and positional redundancy (see M. Mason, 1975), for letter frequency (see Mayzner and Tresselt, 1965) and for word frequency (see Carroll, Davies and Richman, 1971). For each of the three types of stimuli there were six three-letter strings, six four-letter strings and six five-letter strings pre- ceded by practice examples. The full list of the predictable words, unpre- dictable words and pseudowords is shown in Appendix 1.
The stimulus materials were typed with IBM Delegate 10 pitch type and centered on white index cards 121/2 x 10 cm., which were then laminated. A Lafayette Model U-1 two-field illumination tachistoscope interfaced with a specially designed voice-activated relay system and a Hunter Model 120A Series D Klockounter was used to measure the vocalization latencies in milliseconds.
Procedure. The 72 children in the three grades were tested indi- vidually for sessions of approximately 45 minutes duration. Each child was seated in front of the tachistoscope and asked to say out loud the word or "nonsense word" (pseudoword) immediately upon its ap- pearance. The onset of the vocal response would terminate the stimulus field and stop the timer simultaneously. In this way, an accurate meas- urement of the elapsed time between the onset of a stimulus and initiation of a vocal response is provided. The experimental session consisted of 54 trials (six items for each of three types and each of three lengths) and the three word types were presented in different random orders to the children. For the different pseudowords, pronunciation of vowels as either their most frequent or their less frequent versions were scored as c o r r e c t .
Results and Discussion A 3 (grade level) × 2 (reading ability) x 3 (stimulus type) × 3
(stimulus length) analysis of variance with repeated measures on the last two factors was performed on the mean response latencies for each cell of the above matrix. Prior to this analysis the few outliers with response
74
CODING PROCESSES
latencies greater than 3 SD from the cell mean were eliminated and replaced by the corresponding cell means. Table I shows the means and standard deviations of the reaction time (RT) values for the children by grade, reading ability, stimulus type and stimulus length.
There was a highly significant main effect for grade IF (2,66) = 11.84, p < .0011. A trend analysis (Keppel, 1973) showed a significant linear component IF (1,66) = 23.50, p < .001] but no quadratic trend IF (1,66) = • 17, p > .051. There was no significant interaction between grade and any other variable in the analysis. The significant main effect for grade shows a linear decrease in pronunciation latency with increasing grade level across different conditions• The highly significant main effect for reading ability [F (1,66) = 17.14, p < .0011 shows that the skilled readers con- sistently used shorter pronunciation latencies than less skilled readers. A significant main effect was also obtained for stimulus type IF (2,132) = 107.55, p < .001]. Orthogonal decomposition of this effect revealed a highly significant pseudoword versus predictable word, unpredictable word comparison [F (1,66) = 215.03, p < •0011 and a nonsignificant predictable word versus unpredictable word comparison IF (1,66) = •08, p > .05]. The main effect for stimulus length IF (2,132) = 15.26, p < .0011 was also significant with increasing pronunciation latency for increase in stimulus length as shown in a trend analysis IF (1,66) = 21.63, p < .011.
Of the interactions, only the reading ability by stimulus type inter- action and the stimulus length by stimulus type interactions were sig- nificant [F (2,132) = 6.78, p < .01 and F (4,264) = 3.55, p < .01 respect- ively]. With the two significant interactions, interpretation of the main effects for the three grades (grades 4, 6 and 8), the two reading abilities (skilled and less skilled readers), the three stimulus types (predictable and unpredictable words, pseudowords) and stimulus lengths (three-, four- and five-letter words and nonwords) must be qualified somewhat.
The mean response latencies and the number of pronunciation errors on stimulus type as a function of grade level are shown in Figure I while the mean pronunciation latencies and error rates on stimulus length as a function of grade level are shown in Figure 2.
Inspection of error rates shown in Figure 1 suggests no effect for grade but an increase in errors for both stimulus type and reading ability. These observations were confirmed by a non-significant effect for grade [F (2,66) = .58, p > .05], a significant stimulus type effect IF (2,132) = 88.02, p < .0011 and a significant reading ability effect IF (1,66) = 19.55, p < •001]. The finding that error rate did not increase across grades suggests that the significant main effect for grade in the pronunciation latency analysis does not reflect a speed-accuracy trade-off. Skilled read- ers made significantly fewer vocalization errors than less skilled readers and thus their better performance in the latency analysis was not accom- plished at the expense of accuracy. Orthogonal decomposition of the stimulus type main effect for errors showed a significant predictable
75
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589
656
604
611
616
737
707
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(127
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(112
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20)
(149
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(175
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2 75
8 77
0 77
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9 81
9 94
8 10
25
1084
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(159
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40)
(155
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21)
(321
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24)
(324
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61)
546
522
562
546
544
533
671
644
695
(60)
(5
6)
(74)
(6
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(67)
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(76)
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1 64
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1 65
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5 97
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(99)
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(365
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493
501
543
504
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512
631
654
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CODING PROCESSES
u) =¢ 0 70 I¢ 60 uJ 50 I,i. 40 0
w
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GRADE LEVEL
Figure 1. Mean pronunciation latency and number of errors on stimulus type as a function of grade level for skilled readers and less skilled readers (T1 = predictable words, T2 = unpredictable words, T3 = pseudowords)
word, unpredictable word versus pseudoword comparison [F (1,66) = 96.15, p < .001] and a significant predictable word versus unpredictable word comparison IF (1,66) = 27.69, p < .001]. This finding is at slight variance with the latency analysis which revealed similar performance on the two word types but increased latency on the pseudowords.
The significant main effects for grade and reading ability reflect the expected decline in pronunciation latency in the higher grades and the superior performance of skilled readers over that of less skilled readers. The finding of a linear but not a quadratic trend for grade suggests that
77
ANNALS OF DYSLEXIA
SKILLED READERS LESS SKILLED READERS u~ 7O
I ill 50 . - ~.. 4O L3 ~ ~ " ' - ~
~, 800
700p L5
Figure 2.
"1- | ~ I "1" ! I !
4 8 4 6 8
GRADE LEVEL Mean pronunciation latency and number of errors on stimulus length as a function of grade level for skilled and less skilled readers (L3 = three letters, L4 = four letters, Ls = five letters)
word processing speed continues to develop to at least the grade eight level. Further, the magnitude of the processing speed between skilled and less skilled readers observable at the fourth grade level does not diminish over the grades, at least not to grade eight. Besides their inefficiency in processing words as shown by longer vocalization laten- des, less skilled readers also made more errors. The finding of equivalent performance on the predictable and unpredictable words with both superior to pseudowords would suggest that both direct visual access and phonological coding were used in the pronunciation task. It is likely that
78
CODING PROCESSES
some words might have been processed by direct access while others underwent phonological recoding. That the less skilled readers made an increasing number of errors on the unpredictable words and pseudo- words seems to show the greater reliance of these children on the phonological route and also their greater difficulty with this strategy. The present results also reveal an overall increase in pronunciation latency with word length, with no difference between three- and four-letter stimuli but significantly greater time interval needed to initiate pro- nunciation of five-letter items.
Experiment 2
It has been pointed out that a naming task such as that used in Experiment I might bias readers towards phonological coding and that this bias is likely to be magnified with good readers. To remedy this bias and to examine further word recognition processes in readers, Experi- ment 2 used the lexical decision paradigm which requires subjects to give yes~no responses according to whether items are words or nonwords. The advantage of this paradigm over the naming task is that lexical access is necessary as a basis for the correct decision and response output factors are minimized by requiring only a yes~no reply. The lexical decision task has been used extensively with adult subjects as a means of word recognition processes and a good example is the study by Frederiksen and Kroll (1976).
Method Subjects. The same 72 children from grades 4, 6 and 8 participated as
in Experiment 1. Materials. The same stimulus materials of predictable words, un-
predictable words and pseudowords as in Experiment 1 were used. Procedure. Again, the 72 children were tested with the same in-
strumentation as in Experiment 1 for sessions of about 45 minutes per child. The same 54 items of words and pseudowords were then presented in random order to each child, who was asked to say "yes" to a word and "no" to a nonword and the yes/no response latencies were used as dependent variables.
Results and Discussion As with Experiment 2, a 3 (grade level) x 2 (reading ability) x 3
(stimulus type) x 3 (stimulus length) analysis of variance with repeated measures on the last two factors was performed on the lexical decision mean latencies for all correct responses. As with the first experiment, the few outliers with lexical decision latencies greater than 3 SD from the cell mean were replaced with the corresponding cell means. Table II shows
79
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27)
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CODING PROCESSES
the means and standard deviations of reaction time (RT) for the children by grade, reading ability, stimulus type and stimulus length.
There was a highly significant main effect for grade IF (2,66) = 22.92, p < .001]. A trend analysis showed a significant linear component IF (1,66) = 45.72, p < .001] but no quadratic shape to the curve [F (1,66) = .32, p > .05]. The significant effect for grade indicates the expected decline in lexical decision times for higher grades. The main effect for reading ability IF (1,66) = 15.65, p < .001] was highly significant. Stimu- lus type was also highly significant [F (2,132) = 68.65, p < .001]. Ortho- gonal decomposition of this type effect showed a significant pseudoword versus predictable word, unpredictable word comparison [F (1,66) = 131.20, p < .001] and a significant predictable word versus unpredictable word source IF (1,66) -- 6.10, p < .05]. The main effect for stimulus length was significant [F (2,132) = 4.19, p < .05].
While the main effects were significant, interpretation of these re- sults must be qualified with reference to four significant interactions between the variables. The only interaction involving the grade variable was between grade and stimulus type [F (4,132) = 3.06, p < .05]. This came about mainly because of the greater reduction in response time over grades for the pseudowords relative to the two word types. The sig- nificant interaction between stimulus type and reading ability [F (2,132) = 8.38, p < .001] may have arisen from a greater decrement in response latency on the unpredictable words and pseudowords for the unskilled readers relative to the skilled readers. Orthogonal comparisons revealed a significant difference in the predictable word versus pseudoword com- parison for skilled readers relative to less skilled readers IF (1,66) -- 13.43, p < .001], accounting for 98 per cent of the interaction variance. The difference in the predictable word, pseudoword versus unpredictable word comparisons for the two reading ability levels was not significant [F (1,66) = .42, p > .05]. The results taken together support the observation that the decline in performance on the unpredictable words and pseudo- words is greater for less skilled readers than for skilled readers. The significant interaction between stimulus length and stimulus type [F (4,264) = 8.00, p < .001] might be due to the dissimilarity of the unpre- dictable word plot relative to the predictable words and pseudowords. A further significant interaction was found between or among stimulus type, stimulus length and reading level [F (4,264) = 3.48, p < .001]. Further analyses revealed that the contribution of the predictable words and pseudowords to the three-way interaction is minimal and that differ- ent performance patterns for the skilled and less skilled readers are observable on the unpredictable words.
The mean lexical decision latencies and the number of errors for stimulus type as a function of grade level for the skilled and less skilled readers are shown in Figure 3. The mean lexical decision latencies and
81
ANNALS OF DYSLEXIA
U) SKILLED READERS LESS SKILLED READERS 0¢ ~ 6o
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GRADE LEVEL
Figure 3. Lexical decision latency means and number of errors for stimulus type as a function of grade level for skilled and less skilled readers
error rates for st imulus length as a function of grade level for the readers are displayed in Figure 4.
Examination of the panels of error numbers in Figure 3 suggests that error rates were similar across grades but that less skilled readers made more errors than their skilled peers, especially on pseudowords . For the error analysis grade was not significant [F (2,66) = .40, p > .05], while reading ability [F (1,66) = 6.25, p < . 05], s t imulus type IF (2,132) = 11.17, p
82
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CODING PROCESSES
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G R A D E L E V E L
Lexical decision latency means and number of errors for stimulus length as a function of grade level for skilled and less skilled readers
< .001] and stimulus type x reading ability interaction [F (2,132) --- 3.07, p < .05] all reached significance. These results suggest that superior per- formance in the higher grades and by skilled readers in the latency analysis was not achieved at the cost of more errors. Orthogonal de- composition of the stimulus type main effect showed a significant pseudoword versus predictable word, unpredictable word comparison [F (1,66) = 21.08, p < .001] and a nonsignificant predictable word versus
83
ANNALS OF DYSLEXIA
unpredictable word comparison IF (1,66) = 1.36, p > .05]. The stimulus type x reading ability interaction reflects the greater number of errors for less skilled than skilled readers on pseudowords. For errors as analyzed in Figure 4 there was no significant stimulus length effect [F (2,132) = 2.00, p < .05].
Without loss of generality, the results of Experiment 2 are in line with those of the pronunciation experiment. In both experiments it was shown that less skilled readers, more than skilled ones, tended to rely more on phonological recoding in word processing. Paradoxically, less skilled readers also experienced their greatest difficulty in processing through the phonological route, as evidenced by the relatively longer latencies on pseudowords and also the greater number of errors for the less skilled readers on unpredictable than predictable words.
General Discussion
The results of the above two experiments can be interpreted in a number of ways. Following the work of Perfetti and his associates at Pittsburgh (Hogaboam and Perfetti, 1978; Perfetti, 1977; Perfetti, Finger and Hogaboam, 1978; Perfetti and Hogaboam, 1975), we have examined the role of fast, accurate decoding of words in young readers. Our findings are in line with those of the Pittsburgh group in that:
(a) Less skilled readers showed longer vocalization latencies to context-free printed words and pseudowords.
(b) Less skilled readers showed slower lexical access. This is probably related to their difficulty with recoding letter strings and not so much with a poor lexicon.
(c) Less skilled readers were less efficient with phonological coding so essential to comprehension.
To some extent, the findings of longer vocMi~,ation latency or slower lexical access in less skilled readers can be explained by the very powerful model of automaticity proposed by LaBerge and Samuels (1974). In es- sence, this model implies that readers have to be alert to the source of information, to be selective and to use the limited capacity of attention to advantage. LaBerge and Samuels assumed that a person can attend to only one task at a time but can perform other activities simultaneously if these activities do not require attention or if they have attained auto- maticity. The criterion for deciding if a skill is automatic is whether or not it can function while attention is focussed on other acts. Another criterion is that, if two tasks are to be performed at the same time and each requires attention, can the tasks be performed simultaneously? If so, then at least one of the tasks is operating automatically. When readers attain auto-
84
CODING PROCESSES
maticity in reading subskiUs, they can concentrate on the meanings of what is read rather than on the mechanics of reading itself.
The present study provides some support for the LaBerge-Samuels postulate of automaticity. The focus of current literature in this area is more on speed of lexical access, on verbal knowledge from print rather than on overcoming competing attention. In one sense we are coming back to the great debate---the code emphasis and the meaning emphasis in reading. Both could be right, as reading is interactive and draws information from multiple sources. The crux is how fast and how auto- maticaUy children could decode or could comprehend. If they decode accurately but very slowly then their attention is directed away from comprehension. One possibility in remediation is practice on fast word recognition but there is insufficient evidence to support the efficacy of this approach, at least in the short run. However, it appears important to follow a systematic strategy of teaching word recognition subskills. In particular, a balanced code and meaning emphasis is needed to remedy the poor readers' inefficiency in using a phonological code. In this connection, Lesgold and Perfetti (1981) aptly sum up the role of coding in lexical access:
A less awkward model would assume that lexical access always activates phonemic codes. The only relevant strategic factor is whether a reader recodes in subword units and then uses that code to consult meaning and to place it in the text representation. The attractive feature of this proposal is that the activated phonemic code is available for later memory scanning. A name code is thus available for securing reference. By this proposal, reading skill includes the rapid activation of all lexical information, including phonemic infor- mation. In any given situation, activation of phonemic information may precede or follow activation of semantic information depending upon the depth of semantic analysis required and the familiarity of the word (pp. 404-405).
Thus word recognition is derived from information from multiple sources and poor readers may well use context to compensate for in- efficient word coding or recoding abilities (Perfetti, 1980; Stanovich, 1980). Put another way, the Perfetti and associates model of rapid lexical access in reading and the LaBerge and Samuels automaticity model of word encoding can be utilized to enhance semantic processes. This was demonstrated by Beck, Perfetti and McKeown (1982) in a long-term vocabulary instruction experiment. They instructed 27 grade 4 children on 104 words over a five-month period and compared these children with 39 controls matched on vocabulary and comprehension. After instruc-
85
ANNALS OF DYSLEXIA
tion, the experimental subjects were found to be superior to the controls on tasks ranging from semantic decisions to simple verification and memory for discourse. Thus, the compensatory-facilitative process could work either way--with context facilitating lexical access and word knowl- edge contributing to comprehension.
Another explanation can be derived from the related work of Mason (1978, 1980; Mason, Pilkington and Brandau, ]981). She found that highly skilled and less skilled college readers differed in the latency and accuracy in processing verbal materials. These results are consonant with the notion that the need to encode and process ordered information may be related to reading difficulties. Specifically, reading disorder is linked to the time needed to process the where of information. The time dimension is what Bakker (1972, p. 67) terms temporal order perception hypothesis, as reading difficulties occur when "the interaction between time and verbal code is disturbed." The important aspect is the interaction of perception and linguistic items. We are thus led back to the role of language awareness as proposed by I. Liberman and her associates in the Haskins Laboratories (see for example, I. Liberman and Shankweiler, 1979) and discussed by Leong and colleagues (see Downing and Leong, 1982, Chapter 6; Leong, 1982; Leong and Haines, 1978; Leong and Sheh, 1982). Emphasizing the interdependence of the perception of when and the perception of where, Mason et al. (1981) further suggested that alphabetic writing systems might be more vulnerable to spatial-temporal order perception deficit and thus might provide a clue to the greater prevalence of reading difficulties with such a language as English. Evi- dence is emerging (see Kavanagh and Venezky, 1980) that phonological recoding is needed at the working memory stage in early reading quite independently of orthography. Thus, the representation of print, sound and meaning is a fruitful source of investigation in both phonologically deep and shallow languages.
References
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COD1NG PROCESSES
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APPENDIX 1
Predictable, Unpredictable Words and Pseudowords for Experiments 1 and 2
Practice Examples Word Type
Length Predictable Unpredictable Pseudowords
(No. of letters) 3 get one lod 4 near move loat 5 stand learn bresh
Test Stimuli Word Type
Length Predictable Unpredictable Pseudowords
(No. of letters) 3
4
5
top, cow, sun, dew, bed, lag note, rush, near, room,
noun, dear broom, clear, found, least, stove, float
son, low, put, tob, gow, bup, sew, key, won tew, seg, jop done, bend, pour, bope, team, poud, bear, door, push lear, moop, dush
floor, great, touch, stoom, fream, heart, prove, houth, seach, broad trove, troak
Annals of Dyslexia, Vol. 33, 1983. Copyright© I983 by The Orton Dyslexia Society ISSN 0736--9387
89
