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Why do adults with dyslexia have poor global motion sensitivity?

Conlon EG, Lilleskaret G, Wright CM, Stuksrud A - Front Hum Neurosci (2013)

Bottom Line: When the motion of the prime and test were presented in opposite directions, coherence thresholds were reduced in both groups.No group threshold differences were found.We concluded that the global motion processing deficit found in adults with dyslexia can be explained by undersampling of the target motion signals.

View Article: PubMed Central - PubMed

Affiliation: Griffith Health Institute, School of Applied Psychology, Griffith University Gold Coast, QLD, Australia.

ABSTRACT
Two experiments aimed to determine why adults with dyslexia have higher global motion thresholds than typically reading controls. In Experiment 1, the dot density and number of animation frames presented in the dot stimulus were manipulated because of findings that use of a high dot density can normalize coherence thresholds in individuals with dyslexia. Dot densities were 14.15 and 3.54 dots/deg(2). These were presented for five (84 ms) or eight (134 ms) frames. The dyslexia group had higher coherence thresholds in all conditions than controls. However, in the high dot density, long duration condition, both reader groups had the lowest thresholds indicating normal temporal recruitment. These results indicated that the dyslexia group could sample the additional signals dots over space and then integrate these with the same efficiency as controls. In Experiment 2, we determined whether briefly presenting a fully coherent prime moving in either the same or opposite direction of motion to a partially coherent test stimulus would systematically increase and decrease global motion thresholds in the reader groups. When the direction of motion in the prime and test was the same, global motion thresholds increased for both reader groups. The increase in coherence thresholds was significantly greater for the dyslexia group. When the motion of the prime and test were presented in opposite directions, coherence thresholds were reduced in both groups. No group threshold differences were found. We concluded that the global motion processing deficit found in adults with dyslexia can be explained by undersampling of the target motion signals. This might occur because of difficulties directing attention to the relevant motion signals in the random dot pattern, and not a specific difficulty integrating global motion signals. These effects are most likely to occur in the group with dyslexia when more complex computational processes are required to process global motion.

No MeSH data available.


Related in: MedlinePlus

Coherent motion thresholds for the effects of dot density and the number of animation frames presented for the groups with (n = 21) and without dyslexia (n = 22) in each of the four experimental conditions. Error bars represent ±1 standard error.
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Figure 1: Coherent motion thresholds for the effects of dot density and the number of animation frames presented for the groups with (n = 21) and without dyslexia (n = 22) in each of the four experimental conditions. Error bars represent ±1 standard error.

Mentions: The influence of dot density and the number of animation frames presented on coherence thresholds for the reader groups is shown in Figure 1. These data were analyzed using a 2 (group: dyslexia or control) × 2 (dot density: low or high) × 2 (animation frames: five or eight) mixed factorial ANOVA. The assumptions of the analysis were met. A significant main effects was found for reader group, F(1, 41) = 15.80, p < 0.001; = 28. Regardless of the condition, the group with dyslexia (M = 47.09; 95%CI = 41.87–52.03) had higher coherence thresholds than controls (M = 32.74; 95%CI = 27.65–37.84). Significant main effects were also found for dot density, F(1, 41) = 18.81, p < 0.001; = 0.31, and the number of animation frames presented, F(1, 41) = 10.66, p = 0.002; = 0.21. These were modified by a significant interaction between dot density and the number of animation frames presented, F(1, 41) = 8.68, p = 0.005, = 0.17. There were no other significant interactions found.


Why do adults with dyslexia have poor global motion sensitivity?

Conlon EG, Lilleskaret G, Wright CM, Stuksrud A - Front Hum Neurosci (2013)

Coherent motion thresholds for the effects of dot density and the number of animation frames presented for the groups with (n = 21) and without dyslexia (n = 22) in each of the four experimental conditions. Error bars represent ±1 standard error.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3860316&req=5

Figure 1: Coherent motion thresholds for the effects of dot density and the number of animation frames presented for the groups with (n = 21) and without dyslexia (n = 22) in each of the four experimental conditions. Error bars represent ±1 standard error.
Mentions: The influence of dot density and the number of animation frames presented on coherence thresholds for the reader groups is shown in Figure 1. These data were analyzed using a 2 (group: dyslexia or control) × 2 (dot density: low or high) × 2 (animation frames: five or eight) mixed factorial ANOVA. The assumptions of the analysis were met. A significant main effects was found for reader group, F(1, 41) = 15.80, p < 0.001; = 28. Regardless of the condition, the group with dyslexia (M = 47.09; 95%CI = 41.87–52.03) had higher coherence thresholds than controls (M = 32.74; 95%CI = 27.65–37.84). Significant main effects were also found for dot density, F(1, 41) = 18.81, p < 0.001; = 0.31, and the number of animation frames presented, F(1, 41) = 10.66, p = 0.002; = 0.21. These were modified by a significant interaction between dot density and the number of animation frames presented, F(1, 41) = 8.68, p = 0.005, = 0.17. There were no other significant interactions found.

Bottom Line: When the motion of the prime and test were presented in opposite directions, coherence thresholds were reduced in both groups.No group threshold differences were found.We concluded that the global motion processing deficit found in adults with dyslexia can be explained by undersampling of the target motion signals.

View Article: PubMed Central - PubMed

Affiliation: Griffith Health Institute, School of Applied Psychology, Griffith University Gold Coast, QLD, Australia.

ABSTRACT
Two experiments aimed to determine why adults with dyslexia have higher global motion thresholds than typically reading controls. In Experiment 1, the dot density and number of animation frames presented in the dot stimulus were manipulated because of findings that use of a high dot density can normalize coherence thresholds in individuals with dyslexia. Dot densities were 14.15 and 3.54 dots/deg(2). These were presented for five (84 ms) or eight (134 ms) frames. The dyslexia group had higher coherence thresholds in all conditions than controls. However, in the high dot density, long duration condition, both reader groups had the lowest thresholds indicating normal temporal recruitment. These results indicated that the dyslexia group could sample the additional signals dots over space and then integrate these with the same efficiency as controls. In Experiment 2, we determined whether briefly presenting a fully coherent prime moving in either the same or opposite direction of motion to a partially coherent test stimulus would systematically increase and decrease global motion thresholds in the reader groups. When the direction of motion in the prime and test was the same, global motion thresholds increased for both reader groups. The increase in coherence thresholds was significantly greater for the dyslexia group. When the motion of the prime and test were presented in opposite directions, coherence thresholds were reduced in both groups. No group threshold differences were found. We concluded that the global motion processing deficit found in adults with dyslexia can be explained by undersampling of the target motion signals. This might occur because of difficulties directing attention to the relevant motion signals in the random dot pattern, and not a specific difficulty integrating global motion signals. These effects are most likely to occur in the group with dyslexia when more complex computational processes are required to process global motion.

No MeSH data available.


Related in: MedlinePlus