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Motion Perception Deficits and Reading Impairment It’s the noise, not the motion A. Sperling, Z-L. Lu, F. Manis & M

Motion Perception Deficits and Reading Impairment It’s the noise, not the motion A. Sperling, Z-L. Lu, F. Manis & M. Seidenberg. Motion Coherence and Reading Impairment. Reading deficits have been linked to low level visual deficits and/or higher level visual attention deficits

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Motion Perception Deficits and Reading Impairment It’s the noise, not the motion A. Sperling, Z-L. Lu, F. Manis & M

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  1. Motion Perception Deficits and Reading ImpairmentIt’s the noise, not the motionA. Sperling, Z-L. Lu, F. Manis & M. Seidenberg

  2. Motion Coherence and Reading Impairment • Reading deficits have been linked to low level visual deficits and/or higher level visual attention deficits • Particularly, deficits in the magnocellular pathway have been claimed to disrupt the process of learning to read either by impairing low level visual perception or visual attention • The authors propose an alternative explanation based on the concept of noise exclusion at all levels of basic processing (i.e. both visual and auditory)

  3. Motion Coherence and Reading Impairment • In their view, deficits in magnocellular processing would be found in poor readers but would result from noise exclusion problems. • This gives two specific predictions: • In addition to magnocellular processing deficits, processing deficits would also occur in parvocellular processing in conditions of high noise. Some evidence for this in literature (Sperling et al., 2005) • Dyslexics will not show impairments in magnocellular conditions when noise is low – tested in this paper

  4. Motion Coherence and Reading Impairment Experiment 1 – Adults

  5. Motion Coherence and Reading Impairment • One patch (6.5 x 6.5 degs) of 300 dots (0.015 x 0.015 degs) on screen – participants had to indicate whether motion was to left or right • Luminance of background was 12.7 cd/m2; luminance of dots was 18.3 cd/m2; Weber contrast was 0.44 • Central fixation cross present throughout trial • Motion created by re-plotting a proportion of the dots 0.6 degs in a single direction (left or right) after 67 ms delay for 2 frames (0.9 degs/sec). • Auditory feedback given after each trial

  6. Motion Coherence and Reading Impairment • Three tests of motion coherence used: • Version 1 – motion in high external noise. All dots were light grey in luminance and colour. Levels of coherence ranged from 0.3 to 25% in 8 log steps. 30 trials at each level (240 trials in total) • Version 2 – Motion in low external noise. Signal and noise differentiated by colour of dots. Signal dots were red, noise dots were gray (equal luminance). Levels of coherence ranged from 0.1 to 15% in 8 steps. • Version 3 – Motion in no noise. Only signal dots were plotted – 8 densities of signal dots which matched the number of signal dots in Version 2.

  7. Motion Coherence and Reading Impairment • Psychometric curves were used to derive the coherence level at which participants could perform at 75% correct • Several participants could not perform at criteria for the task (>75% criterion at the highest level of coherence). Number of participants eliminated from each test was: • Version 1 – 5 poor readers and 6 good readers • Version 2 – 7 poor readers and 1 good reader • Version 3 – 5 poor readers and 4 good readers

  8. Mean = 8.8% Mean = 11.7% Floor Effects? Motion Coherence and Reading Impairment Experiment 1 – Adults “… on Version 3… distribution of thresholds was highly skewed”

  9. Motion Coherence and Reading Impairment • Hierarchical regression was used to determine which reading skills related to motion coherence Version 1 (controlling for spatial IQ) Word attack – 9% Orthographic Choice – 11.3% Version 2 No correlations Version 3 Verbal comprehension (IQ)

  10. Motion Coherence and Reading Impairment • Thus, adults with reading disabilities show poorer motion coherence ability when tested in high noise condition • Variance in motion coherence scores accounted for significant variance in word attack (?phonological and/or visual test) and orthographic choice (visual test) • No differences are found in low noise conditions (but floor effect and greater number of poor readers eliminated from these conditions) • Provides some limited support for their hypothesis

  11. Motion Coherence and Reading Impairment Experiment 2 – Children: Tests of Reading

  12. Motion Coherence and Reading Impairment Experiment 2 – Children: Language and IQ Tests

  13. Motion Coherence and Reading Impairment • One patch (6.5 x 6.5 degs) of 300 dots (0.015 x 0.015 degs) on screen – participants had to indicate whether motion was to left or right • Luminance of background was 13.7 cd/m2; luminance of dots was 20.1 cd/m2; Weber contrast was 0.47 • Central fixation cross present throughout trial • Motion created by re-plotting a proportion of the dots 0.6 degs in a single direction (left or right) after 67 ms delay for 2 frames (0.9 degs/sec). • Auditory feedback given after each trial

  14. Motion Coherence and Reading Impairment • Two tests of motion coherence used: • Version 1 – motion in high external noise. All dots were light grey in luminance and colour. Levels of coherence ranged from 2 to 30% in 8 log steps. 20 trials at each level (160 trials in total) • Version 2 – Motion in low external noise. Signal and noise differentiated by colour of dots. Signal dots were red, noise dots were gray (equal luminance). Levels of coherence ranged from 0.2 to 10% in 8 steps.

  15. Motion Coherence and Reading Impairment • Children who were good readers were significantly younger than those who were poor readers (mean difference = 12 months) • Psychometric curves were used to derive the coherence level at which participants could perform at 75% correct • Several participants could not perform at criteria especially in Version 1 (>80% criterion at the highest level of coherence). Number of participants eliminated was: • 11 poor readers and 4 good readers

  16. Mean = 7.2% Mean = 11.5% Floor Effects? Motion Coherence and Reading Impairment Experiment 2 – Children

  17. Motion Coherence and Reading Impairment • Hierarchical regression was used to determine which reading skills related to motion coherence Version 1 (controlling for Version 2 - noise) Word identification (reading) Elision scores (phonology) Both language measures Version 2 (controlling for Version 1 - motion) Orthographic Choice (orthography) Word Identification and attack (reading)

  18. Motion Coherence and Reading Impairment • Thus, children with both language and reading disabilities show poorer motion coherence ability when tested in high noise condition • Variance in noise accounted for significant variance in reading, phonological and language tests • Variance in motion accounted for significant variance in orthographic and reading scores (again – floor effects and differences in number of participants excluded) • Provides some limited support for their hypothesis and some evidence against!

  19. Motion Coherence and Reading Impairment Questions • How do threshold measures relate to performance well above threshold? • In the normal reading process, where does the noise that poor readers are failing to exclude come from? • How does this relate to both typical and atypical development of reading?

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