IRLEN FILTERS AND READING STRATEGIES:
THE EFFECT OF COLOURED FILTERS ON READING ACHIEVEMENT,
SPECIFIC READING STRATEGIES AND PERCEPTION OF ABILITY.
Gregory L. Robinson and Robert N. Conway
Special Education Centre
University of Newcastle
Dr. G.L. Robinson,
Special Education Centre,
University of Newcastle,
Summary: The effect of tinted nonoptical (Irlen) lenses was investigated in this study, with 29 experimental subjects and a control group of 31 subjects. Assessment of reading four months after the initial screening showed a significant improvement in reading rate and comprehension, but not in accuracy. A significant decrease in the number of pauses while reading was also noted for the experimental group, as well as increases in correlation between word repetition and reading rate and accuracy. The experimental group also showed significantly improved scores on a scale of attitude to school tasks.
While recent research has placed less importance on the association between visual difficulties and reading problems, the effects of orthographic representation, especially for phonological awareness cannot be overlooked (Ehri, 1989; Ehri & Wilce, 1985; Foorman & Liberman, 1989; Lovett, 1987; Rourke, 1989; Wagner, 1988).
The possibility that inadequate visual processing is a factor in reading disability has gained further attention as a result of Irlen's (1983) suggestion of a visual-perceptual dysfunction unrelated to those skills normally assessed by eye examination. This dysfunction was considered by Irlen (1983) to be associated with an excess sensitivity of the retina to particular frequencies of the light spectrum. Persons with this dysfunction which Irlen (1983) called Scotopic Sensitivity Syndrome, report print and background distortions when undertaking reading or writing tasks which may include blurring or movement of print, restricted span of recognition, and problems with sustaining focus (Whiting, 1985). Such difficulties are reported despite a full optometric or opthalmological examination, with appropriate lenses fitted where required. The distortions described by Irlen (1983) and Whiting (1985) are similar to those reported in a number of other investigations (Lovegrove, 1984: Meares, 1980; Stein & Fowler, 1985), especially the problem of restricted span of recognition (Bouma & Legein, 1977; Legein & Bouma, 1982; McIntyre, Murray, Cronin, & Blackwell, 1978).
Irlen (1983) claimed that the distortions reported by subjects with this visual-perceptual dysfunction are lessened by the use of tinted, nonoptical lenses, which filter out those frequencies of the light spectrum to which a person may be uniquely sensitive. Some symptoms reported by subjects, such as doubling and movement of words and shadows or halos around words may suggest a retinal-sensory after-imaging effect which may be exaggerated by extended reading. The possibility of this effect has been discussed by Riding and Pugh (1977), Sakitt (1976), and Stanley and Hall (1973) who suggested sensory images might persist longer for reading disabled children than for average readers. Such an effect may also be similar to that described by Lovegrove, Martin, and Slaghuis (1986) as a deficit in the transient visual subsystem which inhibits the overlapping of visual images between consecutive eye fixations, thereby preventing blurring or doubling.
The transient system is considered to be involved in eye movement and would thus direct the eye to a particular location of words on a page. Once the location has been fixed, another visual system (the sustained system) is activated to extract the visual detail of letters and words. It is claimed that in some people the visual detail of the sustained system may persist after the eye has moved to a new fixation point thereby causing overlapping of images (Brannan & Williams, 1988, Solman, Cho, & Dain, 1992; Spafford & Grosser, 1991; Williams & Bologna, 1985; Williams, Brannan, & Latrigue, 1987; with colour filtering, claimed to improve the ability of the transient system to inhibit the visual images of the sustained system (Solman, Dain, & Keech; 1991, Williams, Lecluyse, & Rock Faucheux; 1992).
The sustained and transient systems theory has recently been further revised and incorporated in the conceptual framework of parvocellular and magnocellular processing in the primate visual system (Breitmeyer, 1989; Livingstone & Hubel, 1987). The implication is that dyslexics have an abnormality in the magnocellular subsystem, which normally should act to inhibit the parvocellular system after each saccade, thereby erasing the image of the previous system (Lovegrove, Garzia, & Nicholson, 1990). Livingstone, Rosen, Drislane, and Galaburda (1991) found that reading disabled subjects had diminished evoked potentials for rapid low-contrast stimuli, but normal responses to slow or high-contrast stimuli. Such abnormalities were consistent with a defect in the magnocellular pathway. This possibility was further corroborated in the study by comparing in autopsy brains of five dyslexic and five control persons. Abnormalities were found in the magnocellular but not the parvocellular layers for the dyslexic individuals. Lehmkuhle, Garzia, Turner, Hash and Baro (1993) also reported visual evoked potentials were larger for eight reading disabled children than 13 normally achieving controls, which was claimed to suggest that the magnocellular visual pathway is slowed for reading disabled children.
A number of studies have investigated the extent to which use of colour filtering will generalise to improved reading achievement. While these studies have produced more positive than negative results, there has been criticism of all studies for lack of methodological soundness (Lea & Hailey, 1990; Stanley, 1990). Initial investigations used coloured transparencies rather than the full Irlen procedure. Two positive studies were reported, with O'Connor, Sofo, Kendall, and Olsen (1990) showing significant gains in rate, accuracy and comprehension of reading and Robinson and Miles (1987) finding significantly higher mean scores for word matching, letter recognition and number recognition tasks. Saint John and White (1988) however found no significant differences in rate or accuracy of reading for 11 poor readers, although they were not screened for symptoms of scotopic sensitivity and thereby may not have been responsive to the use of colour (Howell & Stanley, 1988).
Recent investigations of the effect of colour filtering on reading have tended to use the full Irlen procedure rather than coloured transparencies, with positive results being obtained in nine studies, negative results obtained in three studies, and mixed results reported in two studies. The positive studies reported significant improvements in rate, accuracy and comprehension of reading over periods of four months to two years of use (Adler & Attwood, 1987; Fricker, 1989; Hannell, Gole, Dibden, Rooney, Pidgeon, & McGlinchey, 1989; Kreuttner & Strum, 1990; Robinson & Conway, 1990), with surveys of Irlen lens users reporting approval ratings of 82% to 93% over one to twelve months of use (Burgess, 1990; Irlen, 1983; McLachlan, Yale, & Wilkins, in press; Whiting & Robinson, 1988). The mixed result studies reported significant improvement in some reading subskills but not in others (Blaskey, Scheiman, Parisi, Ciner, Gallaway, & Selznick, 1990; Kyd, Sutherland, & McGettrick, 1992). The negative result studies did not find improvement in a timed letter recognition task (Winter, 1987), or significant gains in rate, accuracy and comprehension of reading when assessed immediately (Cotton & Evans, 1990), and over one school term of use (Gole, Dibden, Pearson, Pidgeon, Hannell, Fitzgerald, Kortman, & McGlinchey, 1989).
In addition to studies of the effects of colour on reading achievement, positive results have also been reported for reducing the number of eye fixations and regressions per line of print while reading (Holland, Tyrrell, & Wilkins, 1991), for visual search tasks and binocular coordination (Wilkins & Neary, 1991), and for eye strain from fluorescent lighting (Wilkins & Wilkinson, 1991).
While many studies have produced positive results and there have been numerous anecdotal reports of beneficial effects for some individuals, the findings to date do not fully settle the issue of possible causal mechanisms or of positive and enduring effects for reading achievement. The discrepancies in findings may reflect that print distortions reported by experimental subjects in many studies may not be the only factor in poor reading achievement. A similar conclusion (due to discrepant results) has been reached for the likely influence of optical defects on reading achievement (Bond, Tinker, & Wasson, 1979; Spache, 1976), with more recent studies (Simons & Grisham, 1987; Stolzenberg, Ritty, Cohen, & Liebegmann, 1989) suggesting that binocular abnormalities may, for some children, be only one contributing factor in reading difficulty. Other possible factors may include poor word recognition skills, which may still need to be developed once print distortions are reduced (Blaskey, et al. 1990; Kyd, et al. 1992; Robinson, 1990; Robinson & Conway, 1990), as well as willingness and motivation to read (Wong, 1986). Established reading strategies such as guessing of words from single letter cues may also restrict the development of phonic analysis (Robinson & Conway, 1990). Such strategies may have been developed to compensate for word identification problems (Bouma & Legein, 1980; Mazer, McIntyre, Murray, Till, & Blackwell, 1983).
The reduction in the span of visual recognition reported by many users of Irlen lenses (Irlen, 1983, Robinson & Conway, 1990) may be of particular importance. Reduced span may hinder word recognition and comprehension as prior parafoveal exposure can influence the identification of a fixated word (Jennings & Underwood, 1984, Legein & Bouma, 1982) and may also influence (in conjunction with semantic context) the guidance of eye fixations needed for flexible scanning to process meaning (Fisher & Shebliske, 1985). Poor readers have been found to have a restricted field of vision (Eames, 1957) and to make significantly more fixations and backward regressions per line than normal readers (Foss & Hakes, 1978; Griffin, Walton, & Ives, 1974; Mazer et al. 1983; Pavlides, 1985). The number of fixations and regressions has been reported to improve for users of Irlen lenses (Holland, et al. 1991). It could be hypothesised that a reduced span of recognition may hinder the organisation of text into meaningful phrase units by restricting word identification and limiting the flexibility of eye fixations needed to process meaning.
This hypothesis may be supported by investigations which report that readers with poor speed and accuracy have difficulty identifying meaningful phrase units (Clay & Imlach, 1971; Lovett, 1986), which could restrict the effective integration of text for comprehension (Lovett, 1986). Studies of the effects of Irlen filters have indicated increases in reading speed and comprehension (Adler & Attwood, 1987; Fricker, 1989; Robinson & Conway, 1990) which could imply that increased speed of word identification may facilitate comprehension, as words neeed to be identified quickly so that word groupings which denote units of meaning can be formed before words fade from short term memory (Andrews, 1989; Bresnitz, 1987; Just & Carpenter, 1980; Kirby & Williams, 1991; Liberman & Shankweiler, 1985; Lunzer & Gardiner, 1979; Oakhill & Garnham, 1988). The restriction in span of recognition and other distortions of print reported by users of Irlen lenses may lead to slow, word-by-word recognition as previously discussed, which could limit the use of semantic context and restrict meaningful integration of text. Conversely, reductions in such distortions may facilitate reading fluency and in turn give greater access to semantic context for comprehension and word identification.
The sample consisted of 29 experimental and 31 control children, referred to the Special Education Centre at the University of Newcastle for assistance with reading or study problems. Subjects were placed into experimental and control groups on the basis of significant symptoms of scotopic sensitivity using the Irlen Differential Perceptual Schedule (IDPS, Irlen, 1983). The experimental group ranged in age from 9.1 yrs. to 9.7 yrs. (M=139 mths, SD=25 mths.) with an average reading age on the Neale Analysis of Reading Ability (Neale, 1966) of 8.8 yrs. and an average discrepancy of chronological age from reading age discrepancy of 1.7 yrs. The control group ranged in age from 9.1 yrs. to 14.8 yrs., with an average reading age of 9.4 yrs. (M=144 mths, SD=21.5 mths) and an average discrepancy of chronological age from reading age of 1.9 yrs. No significant differences existed between the groups at the pretest.
While all subjects had intelligence quotients within the average range, it was considered that such scores for subjects in this study may not be a valid indication of academic potential. Scores on such tests may be influenced by reading ability (Bishop & Butterworth, 1980; Prior, 1989, Stanovich, 1991), with visual processing subtests such as Coding and Picture Completion on the WISC-R (Wechsler, 1974) likely to be compromised for the experimental group.
All subjects had undertaken an optical or opthalmological examination within the year prior to being screened and had prescription lenses fitted when required. It was thus assumed that identified symptoms were unlikely to be confused with problems of a refractive or accomodative nature.
The sample covered a wide range of cultural background and socioeconomic status (as indicated by parents' occupations). A variety of school situations in the Newcastle urban and Hunter Valley rural areas were represented, including both public and private school systems. Subjects were also monitored to ensure that no significant changes in the extent of remediation support occurred during the study period.
All subjects were assessed initially for symptoms of scotopic sensitivity using the I D P S by staff attached to the Special Education Centre. This schedule has three sections, (1) a questionnaire relating to reading and writing performance, light sensitivity, depth perception, and symptoms of eye strain; (2) a series of visual tasks; and (3) an assessment of the extent to which performance on these visual tasks and on reading tasks is improved by the use of coloured plastic overlays. The questionnaire related to the subject's reading and writing strategies including rereading of lines, skipping of words or lines, loss of place, poor writing quality, and lack of efficiency in board- or book-copying activities. Questions relating to eye strain and light sensitivity include rubbing of eyes, excessive blinking while reading, watering of eyes, avoidance of bright lights, and shading of the page while reading.
The first visual task requires the subject to count the number of squares in specific rows on grid patterns superimposed on pictures of cubes and to answer questions about difficulties in performance and the nature of any visual distortion experienced. Symptoms claimed to indicate scotopic sensitivity on the cube tasks include incorrect counting of squares, loss of place, reported movement and blurriness of lines, and reported eye strain. A further visual task involved the observation of music lines and the answering of questions concerning their distortion. Symptoms claimed to indicate scotopic sensitivity include reported crookedness and movement of lines, lines waving, merging together, and disappearing.
The third section of the I D P S involves placing coloured plastic overlays over the cubes and music lines as well as over a page of print to ascertain the extent to which specific colours may reduce the reported visual distortions. For the page of print, questions relate to print and background distortions including blurring of print, shadows and halos around words, spacing of letters and words, and movement of print. Questions are also asked concerning eye comfort, ease of reading and reading endurance.
Validity studies of the I D P S have been undertaken by Haag (1984) and Miller (1984). Haag (1984) found significant differences in scores on all sections between reading disabled and normally achieving students (performance tasks, p<.01; diagnostic questions, p<.05). Miller (1984) also identified significant differences (p<.01) in scores between students of low and high reading ability.
On the basis of I D P S scores, subjects were placed into an experimental group (significant symptoms) or a control group (few or no symptoms). Within two weeks of screening on the I D P S, experimental subjects undertook a diagnostic analysis to identify and supply the specific frequency and density coloured filter reported to reduce most distortions.
At the time of screening, all subjects were also tested on the Neale Analysis of Reading Ability, Form A (Neale, 1966) and asked to complete the Student's Perception of Ability Scale (Boersma & Chapman, 1978). The Neale Analysis of Reading Ability has three parallel forms, each with six passages of prose, graded in difficulty to form a continuous reading scale for children aged 6 to 13 years. The reader is assessed on reading accuracy, reading rate, and reading comprehension. Parallel forms reliabilities within specific age groups are quoted as 0.96 to 0.98 for accuracy and 0.92 to 0.98 for comprehension, with reading subscales being validated by factor analysis and by high validity coefficients (0.95) between subscale scores and scores on other standardised reading tests.
Subjects' oral reading of the Neale passages were audiotaped and for analysis of reading behaviour and errors. The analysis identified the frequency of occurrence of the following behaviours.
- Pauses or hesitations of more than five seconds in attempting to read a word.
- Refusal to read a word.
- Attempts to analyse sound components of a word.
- Self-correction of a word read incorrectly.
- Repetition of a word or word cluster.
- Substitution of a word which is visually (graphically) similar to the correct word.
- Substitution of a word which has sound components (phonics) similar to the correct word.
- Substitution of a word which is syntactically acceptable for the correct word.
- Substitution of a word which is semantically acceptable for the correct word.
- Substitution of "nonsense" words or non words for the correct word.
- Use of the final letter only of a word as the basis for
The above criteria were based on observations of the reading performance of children showing both significant symptoms and no symptoms on the I D P S, and studies of reading errors in good and poor readers (Burke, 1976; Harding, Beech & Sneddon, 1985; Hood, 1976).
The Student's Perception of Ability Scale requires subjects to circle a "yes" or "no" response to each of 70 statements relating to areas of school performance (general ability, reading, spelling, writing, and mathematics). Specific assistance was given in reading the statements where required. Chapman and Boersma (1979) quote a test-retest reliability of 0.83 over a period of 4 to 6 weeks. Boersma and Chapman (1978) found a correlation between score and end of year grade point average of 0.489 (p<.001, n=630). Chapman and Boersma (1979) identified significantly lower scores on the scale for 81 learning disabled students when compared to 162 normally achieving controls (p<.001), with a similar result obtained for a different sample of 77 under achievers and 68 normal achievers (Chapman & Boersma, 1982).
Four months after the initial testing, all subjects were retested on the Neale Analysis of Reading Ability, Form B.and were also required to complete again the Student's Perception of Ability Scale.
All tests were administered by experienced research staff who had no knowledge of prior test results or of group status (experimental and control) of subjects. This anonymity was achieved for the reading test by use of audiotape of reading test performance as the basis for scoring and analysis.
The reading test and attitude questionnaire were administered and scored according to standardised instructions. One variation from the original test format occurred for the Neale test, with the colour of the background paper for test Form A changed from yellow to white (similar to Form B). This change was implemented to control for any potential variation in performance due to colour of the background (Whiting , 1985).
A reliability check on scoring categories of reading errors was applied by randomly sampling 15 subjects and rescoring their test profiles for error independent of knowledge of original results. This check identified an average category score correspondence of 94%.
The results for experimental and control group performance on the Neale Analysis of Reading (Neale, 1966) are presented followed by performance on the Student's Perception of Ability Scale (Boersma & Chapman, 1978), and reading performance and error analysis. A series of analyses of variance (2 variables X 2 times) with repeated measures on the last variable were conducted.
Rate. Table 1 presents mean rate both as a raw score (total time in seconds) and reading age in months. A significant main effect for time was found on raw scores (F 1,59=14.94; p<.05) and for age (F 1,59-10.96; p<.002).
Reading Rate, Accuracy, Comprehension
(Total correct words)
(Total words correct)
Accuracy. Table 1 also presents reading accuracy mean raw scores and reading age in months. A significant main effect for time was found for raw scores (F 1,60=10.24, p<.002) and age (F 1,60=8.27, p<.006). No significant interaction of group and time was found for either raw score or reading age.
Comprehension. Reading comprehension mean raw scores and ages in months are shown in Table 1. Significant main effects for time were obtained for both mean raw scores (F 1,60=7.57, p<.001. and reading comprehension age in months (F 1,60=28.65, p<.001). A significant interaction between groups and time was found for both raw score (F 1,60=5.86, p<.02) and reading comprehension age (F 1,60=12.69, p<.001).
Students' Perceived Ability. Students performance on the Student's Perception of Ability Scale is shown in Table 2. A significant main effect for time (F 1, 54=19.38, p<.001) and a interaction of group and time (F 1,54=8.98, p<.004) were found.
Students' Perceptions of Ability
(Total correct responses)
Analysis of errors in reading
An analysis of reading errors using the 11 predetermined categories of error was calculated. Table 3 shows means and standard deviations for pre- and posttest performance. An analysis of variance with repeated measures yielded significant differences for pauses.
For pauses, a significant main effect was found for
time(F 1,51=12.4, p<=.001) together with a significant interaction of group and time (F 1,51=78.2, p<=.05). Although a significant main effect for time was found for refusals (F 1,51=46.8, p=.01), grapheme substitutions (F 1,51=41.7, p<=.005), and semantic substitutions (F 1,51=21.0, p<=.03), no significant interactions were found.
Analysis of Errors
While there are qualifications to interpretations of results of this study, some explanation is possible of the likely effects of print distortions on reading achievement and the effects of reported reduction of these distortions on specific reading strategies.
The significant increase in reading comprehension scores for the experimental group corresponds to similar experimental group gains from other studies (Kreuttner & Strum, 1990; O'Connor, et al. 1990; Robinson & Conway, 1990) as does the finding of a significant increase in rate of reading (Adler & Attwood, 1987; Fricker, 1989; Hannell, et al. 1989; Kreuttner & Strum, 1990; O'Connor, et al. 1990).
Gains in reading comprehension and rate may partly be a function of the extent to which reported reduction in print and background distortions allow more fluency. This fluency could provide more working memory space for the processing of continuous text rather than to the identification of individual words, thereby providing greater extraction of meaning (Andrews, 1989; Breznitz, 1987; Chan & Robinson, 1990; Daneman & Carpenter, 1980; Juel, Griffith, & Gough, 1986; Kirby & Williams, 1991; LaBerge & Samuels, 1974; Lovett, 1987; Perfetti, 1985; Stanovich, 1980, 1981, 1986; Wong, 1986). An increase in capacity to monitor meaning may also increase access to text context as a supplement to word recognition (Stanovich, 1986) or as a means of compensating for other word attack deficiencies (Bruck, 1988; Bouma & Legein, 1980).
There have been studies however which did not find increases in reading speed and comprehension (Cotton & Evans, 1990; Saint-John & White, 1988; Winter, 1987), which suggests that reductions in print distortions alone may not be sufficient to generate improved reading achievement. Improved print clarity may make basic reading skills easier to learn but for many poor readers these skills may still have to be taught. Previous studies have emphasized fact that prior word-attack skills, willingness to read, and inefficient reading strategies may all restrict the development of reading fluency, accuracy and comprehension (Blaskey et al., 1990; Bouma & Legein, 1980; Kyd et al., 1992; Mazer et al., 1983; Robinson & Conway, 1990). In particular Irlen filter subjects have been observed to frequently use a strategy of guessing based on single letter cues which may restrict the development of phonic analysis skills (Robinson & Conway, 1990).
The significant pre-post test reduction for the experimental group in number of pauses while reading parallels findings of increases in rate of reading and is also consistent with findings of increases in performance on visual search tasks using print (Holland, et al.,1991; Wilkins & Neary, 1991). The reduction in frequency of pauses could suggest that the experimental group are a visually based subgroup with a slower response latency for visual stimuli (Bouma & Legein, 1980; Lovett, 1987; Mazer, et al., 1983; Rourke, 1989), who respond to colour filters. The concept of a slower response latency as a causal factor in reading difficulty is consistent with the notion of a magnocellular defect in the visual pathway (Lehmkuhle, et al, 1993; Livingstone, et al., 1991) and with the possibility of a transient visual subsystem deficit which may be influenced by colour filters (Solman, et al., 1991; Williams, et al., 1992).
The pre-post test increases in correlation coefficients between word repetition and reading rate and accuracy for the experimental group could also suggest that a more detailed analysis of words and meaning may influence the increased reading achievement. An increase in word re-reading was observed by Robinson and Conway (1990), who suggested that improvements in clarity of print may facilitate the use of re-reading as a strategy for monitoring word recognition and meaning, thereby enhancing reading comprehension (Neville & Pugh, 1977; Oakan, Weiner & Cromer, 1971).
The association between word repetition and reading rate and accuracy could also be linked to the hypothesized facilitative effects of reported improvements in clarity of print and span of recognition on reading fluency, use of semantic context and meaningful integration of text. Increased span allows prior exposure to words, which may facilitate word recognition and the guidance of eye fixations for comprehension (Fisher & Shebliske, 1985). This in turn may assist the identification of meaningful phrases as units in reading (Clay & Imlach, 1971; Lovett, 1986) and facilitate integration of text (Andrews, 1989). Holland, et al. (1991) found a significant reduction in the number of eye fixations and regressions for line of print when using preferred colour filters.
The hypothesized trend in experimental subjects towards more detailed word analysis and more effective monitoring of print meaning is similar to trends identified in early developing readers.(Harding, et al., 1985; Watson, Sinclair, Cooney, & March, 1988; Willich, Prior, Cumming, & Spanos, 1988). Studies of oral reading errors by Beimiller (1970) and Cohen (1975) also suggested that early readers may develop from an initial sensitivity to global, contextual information to an intermediate stage where more attention is directed towards sound and letter features in words, with the final stage involving analysis of higher-order units of structure (Gibson, 1965).
This study, however did not show significant increases within the experimental group in other areas of miscue which could be related to improved word analysis, such as improvement in phonic acceptability of errors, as was previously found for developing readers (Beimiller, 1970; Harding, et al., 1985; Weber, 1970). This lack of response could relate to the fact that improved clarity of print is only likely to generalise to more effective phonic analysis-synthesis if the subject already has skill in phonic segmentation. Poor skills in sound analysis have been identified as a common characteristic of reading disabled children (Bruck, 1988; Bryant & Bradley, 1985; Stanovich, 1986; Wagner, 1988) and improved clarity of print may not generalise to more effective sound analysis in such cases unless accompanied by specific skills training in that area.
The significant improvement in raw scores on the perception of ability measure for the experimental group in this study parallels previous findings by Robinson and Conway (1990) and may be a significant factor in reading progress, as improved motivation could increase participation (Adelman, MacDonald, Nelson, Smith, & Taylor, 1990), with children more likely to make renewed efforts if they feel this effort will lead to success in reading (Paris & Oka, 1986). It is likely that a reciprocal causation exists between specific learning difficulties, motivation, and lack of sufficient reading practice (Stanovich, 1986, Wong, 1986). The improvement in raw scores on perceived ability in this study, however, was not as large as that in the Robinson and Conway (1990) study, which may reflect reduced media attention and a consequent reduction in expectation of success.
The patterns of improvement in reading achievement in this study parallel the results of previous studies by Robinson and Conway (1990), O'Connor, et al., (1990), and Fricker, (1989). In addition, the analysis of oral reading errors suggests changes in reading strategies by the experimental group which lead to more detailed word analysis and possibly a more effective monitoring of meaning. Such changes have been identified early in developing readers, with the implication that the experimental group is not different from their normally achieving peers but may be at a lower level on a continuum of normal reading development (Chan & Robinson, 1989; Prior, 1989; Willich, et al., 1988).
Despite these findings the difficulty of developing an effective placebo is still a significant limitation of studies of the Irlen procedure. The screening procedure requires that a subject identify a colour which is reported to reduce print and background distortions and which is then tried on a reading task. This procedure limits the usefulness of providing alternate colours, as subjects are likely to either identify the colour as the nonpreferred colour or state that the colour is now not giving the visual advantage previously perceived. One possible method of overcoming this problem might be to use placebo lenses which look similar to the preferred colour but which are significantly different in light tranmission value.
There is also a need to investigate further the nature of reading strategies, both pre- and post test use of Irlen lenses, in comparison to reading disabled subjects who do not have significant symptoms. Such investigation will help clarify the extent to which reading improvement using Irlen lenses may still depend on intervention programs specifically designed to overcome word-attack skill and also help identify reading-strategy deficits which may be specific to this group.
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