3.1. Reading impairment
Because of the relative lack of information regarding reading dysfunction in schizophrenia and lack of consensus regarding “ideal” reading tests, four separate test batteries were used (GORT-4, CTOPP, WJ-III, and NDRT). An omnibus MANOVA demonstrated first that patients showed significant impairments in reading relative to controls across respective test batteries (). In order to identify specific subtests that were particularly sensitive to reading dysfunction, individual subtests were compared between patients and controls using Bonferroni-corrected t-tests. Significant between-group differences were found on the following measures: GORT-4-Rate, GORT-4-Fluency, GORT-4-ORQ, CTOPP-APA, WJ-III-BR and NDRT-C (). Scores on GORT-4-Rate, Comprehension and ORQ; CTOPP-PA, CTOPP-RN, CTOPP-APA, CTOPP-ARN, WJ-III-BR and NDRT-C were also significantly below adult population norms (p<0.01), as well as CTOPP-PM and NDRT-T (p<0.05). Significant correlations with NDRT-C were found for GORT-4-Rate and CTOPP-APA, respectively (r=0.82, n=29, p=0.001; r=0.63, n=29, p=0.001).
Means and standard deviations for reading measures for patients (n=19) and controls (n=10)
The NDRT-C assesses reading performance relative to grade appropriate norms. Grade equivalent reading scores were significantly reduced for patients (8.9±5.0) relative to years of education completed (12.4±2.3), with the mean difference being 3.4±3.8 years (paired t=3.9, df=18, n=19, p=0.001). In contrast, controls showed no significant difference between education level completed (15.2±0.85) and reading ability (15.2±3.4), leading to a significant group × diagnosis interaction (F=5.51, df=1,27, n=29, p=0.03).
As opposed to the significant deficits in specific reading functions, patients showed only a marginal deficit in WRAT3 reading scores vs. control (p<0.04) that did not survive Bonferroni correction. Further, patient WRAT3 scores were not significantly different from population norms (t=−0.35, p=0.73), consistent with prior literature.
3.2. Models of diagnostic classification
Several theoretical models for diagnosing reading impairment were used in order to classify participants on an individual basis. This idiographic approach was proposed to further elucidate differences between individuals distinguished as reading impaired or non-impaired.
Based upon available literature, five models were selected (Fletcher et al., 1992
; Aaron, 1995
; Boder, 1970
; Wolf and Bowers, 1999
; Ramus et al., 2003
) and participants were classified according to the criteria. Significantly more patients were identified as having a specific reading disability across models than controls (21–63% vs. 0–20%). Since multiple models were employed, it was decided a priori that individuals assigned to the “reading impaired” group would be classified as having reading deficiencies in at least 2 of the 5 models, which led to identification of nine patients as reading impaired.
As a final step, we defined an experimental diagnostic model using two tests, GORT-4-Rate and CTOPP-APA, which showed the greatest between-group differences. These tests tap orthographic and phonological awareness, respectively. Using deficient performance on these two tests, we identified 9 patients and no controls who met criteria for reading disturbance (Fisher exact test p=0.011). This group subsumed the individuals identified by other models, while nevertheless maintaining between-group specificity.
In order to validate group reading performance differences for our experimental model, we looked at group differences for percentile scores for NDRT-reading rate. Overall significant differences were found (F=4.1, df=2,28, n=29, p=0.03); with significant Bonferroni post hoc comparisons between impaired patients (12.7±16.3, n=9) and non-impaired patients (48.6±39.7, n=10, p=0.05), but not between impaired or non-impaired patients and non-impaired controls (45.1±28.0, n=10).
3.3. Reading impairment and visual processing
Within the patient group as a whole, GORT-4-Rate and Fluency deficits were significantly related to contrast sensitivity for low (0.5 c/deg) (r=0.56, n=18, p=0.01; r=0.64, n=18, p=0.004 respectively) but not medium (7 c/deg) (r=0.34, n=18, p=0.16; r=0.33, n=18, p=0.18), or high (21 c/deg) (r=0.31, n=18, p=0.21; r=0.27, n=18, p=0.27) spatial frequency stimuli.
In categorical analyses, mean contrast sensitivity measures at 0.5 c/deg were significantly reduced in the group of patients with reading impairment (43.7±18.4) compared to patients without (94.5±28.9) (F=11.48, n=28, p=0.001) (). By comparison, the patient groups showed no significant contrast sensitivity differences at 7 or 21 c/deg (97.8±31.2 vs. 118.6±50.1 and 4.0±2.1 vs. 5.0±5.0 respectively).
Contrast sensitivity by group.
3.4. Relationship to symptoms, neurocognitive and functional outcome measures
GORT-4-Comprehension correlated significantly and inversely with the PANSS Cognitive-factor score (r=−0.68, n=18, p=0.002). In contrast, neither the WAIS-3 Working Memory Index (r=0.12, n=12, p=0.71) nor the WAIS-3 Processing Speed Index (r=0.16, n=18, p=0.52) significantly predicted GORT-4 performance. No other significant relationships were found for reading tests with symptoms or neurocognitive tests.
GORT-4-Comprehension (r=0.64, n=19, p=0.003); GORT-4-ORQ (r=0.61, n=19, p=0.006); NDRT-T (r=0.63, n=19, p=0.004); and NDRT-C (r=0.63, n=19, p=0.004) were all also significantly correlated with ILS-PB scores, with higher levels of reading comprehension being associated with less need for community supervision.
Since significant differences were found between patient and comparison groups on education and SES, the analyses for between group differences were repeated using education or SES as covariates. Using MANCOVA, no significant between-group differences survived, suggesting that impairments in reading may have significantly influenced the reduced educational achievements and SES levels of the subjects since education and SES were significantly interrelated (r=0.74, p=<0.01). However, significant between group differences remained for five of six measures (GORT-Rate, GORT-Fluency, GORT-ORQ, CTOPP-APA, and NDRT-C) following covariation for parental SES.