Research paper: An Evaluation of a Visual Biofeedback Intervention in Dyslexic Adults (2004)
by: Elizabeth Liddle, Georgina Jackson and Stephen Jackson, School of Psychology, University of Nottingham, United Kingdom
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Summary of Results
The results of this study indicate firstly, that the system tested produced significant improvements in fluency on literacy tasks, as measured by timed tests of naming, single word reading and copying, with improvements in naming speed and single word reading being individually significant.
NOTE: Timed test indicates fluency in literacy tasks. It also is interpreted as a gain in task automaticity.
The results indicate that the system induced a significant decrease in the LF/HF ratio relative to baseline, indicating a shift in autonomic balance from the sympathetic to the parasympathetic ANS.
NOTE: The LF/HF ratio in our study shows a shift towards a relaxation level increase and that is represented by a parasympathetic increase. Parasympathetic means the relaxation increase after one session.
The results indicate that the system induced changes in the performance of a lateralized visual-spatial task, particularly at levels of difficulty where there was scope for change.
Ad 1) Literacy Measures
The Dyslexia Adult Screening Test (DAST) in the study measures:
- Rapid Naming
- One Minute Reading
- One Minute Writing
For all three timed tests, the entire sample of participants showed significant mean improvements at post-test:
“… significant improvements were found in reading and naming speed in the treatment group relative to the placebo group.”
As reading is a complex skill in which success breeds success, and lack of fluency deprives the dyslexic reader of the reading experience that in the non-dyslexic developing reader rapidly leads to development of further fluency, it is possible that a system that even temporarily optimizes the attentional state required for speedy word recognition may substantially increase the gradient of any learning curve resulting from either appropriate tuition or from reading itself.
The research paper showed improvements in 1 minute reading and rapid naming. The Error bars in the related bar charts represent 95% confidence intervals. For 1 minute reading, the Y-axis represents the increase in number of words read correctly in 1 minute. For rapid naming the Y-axis represents the change in the number of seconds taken to name all the items on the card. For both these measures the intervention group showed significantly more improvement than the placebo group.
Ad 2) LF/HF ratio – HRV recordings
The heart-rate variability data for each subject at each session was subjected to spectral analysis in order to calculate the power of constituent frequencies (expressed as the area under the curve) in the LF band (0.03-0.15Hz) assumed to reflect sympathetic ANS influence, and in the HF band (0.15-0.5Hz) assumed to reflect parasympathetic ANS influence (Cerutti et al., 2001). The LF power was then divided by the HF power in order to arrive at an index of autonomic balance (LF/HF ratio). These ratios showed a skewed distribution in the sample. Natural logarithms of the ratios produced a normalized distribution and were used in statistical tests.
In all three of these ANOVAs multivariate tests showed a significant group effect.
The reaseach study contains a bart chart with the changes in LF/HF ratio from baseline across sessions for the two groups. The Y-axis represents the magnitude of the change from baseline in the log transformed LF/HF ratios. The three successive sessions are plotted along the X-axis. The error bars represent 95% confidence intervals; where the error bars do not cross zero, the change is significantly greater than zero. The LF/HF ratio in participants who received the intervention showed a trend to decrease from baseline after one treatment, culminating in a significant net downward change, p<0.001, after three treatments.
These results support the conclusion that the intervention leads to a significant reduction in the LF/HF ratio, after as little as one treatment session, and that these effects are observable at least 2-5 days after a treatment session.
The results are interpreted as indicating that the treatment induces a shift in autonomic balance in favor of the parasympathetic ANS, and that this shift is also reflected in increased efficiency of left cerebral hemisphere circuits implicated in the perceptual-motor processes required for naming and reading fluency.