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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

Motion Segmentation Task used in Experiment 2. The fully coherent prime was presented in either the same or opposite direction to the partially coherent test. The stationary prime was used as a control condition. The blank stimulus between the prime and test was presented for 96 ms and the test stimulus was presented for 160 ms (10 animation frames).
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Figure 2: Motion Segmentation Task used in Experiment 2. The fully coherent prime was presented in either the same or opposite direction to the partially coherent test. The stationary prime was used as a control condition. The blank stimulus between the prime and test was presented for 96 ms and the test stimulus was presented for 160 ms (10 animation frames).

Mentions: The apparatus and adaptive psychophysical procedure used were the same as those used in Experiment 1. In the global motion task, the RDK used as both the prime and the test had 300 white dots (luminance: 20 cd/m2) presented on a dark background (luminance: 0.54 cd/m2). The stimulus was displayed within a borderless area subtending 13.35° × 13.35° presented in the middle of the computer screen. Dot density was 3.83 dots/deg2 and dot life time was three animation frames (50 ms). The dot life time was increased from Experiment 1 from the results of pilot testing. The motion primes were presented at 100% coherence, with one moving to the left and the other moving to the right. The baseline control stimulus was a stationary RDK with no dot displacement. Each of these stimuli was presented for 96 ms. When extinguished these were replaced with a blank low luminance field (0.54 cd/m2) for 32 ms. This field was replaced with the partially coherent test stimulus, which was presented for 10 animation frames (160 ms). The method used is shown in Figure 2.


Why do adults with dyslexia have poor global motion sensitivity?

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

Motion Segmentation Task used in Experiment 2. The fully coherent prime was presented in either the same or opposite direction to the partially coherent test. The stationary prime was used as a control condition. The blank stimulus between the prime and test was presented for 96 ms and the test stimulus was presented for 160 ms (10 animation frames).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: Motion Segmentation Task used in Experiment 2. The fully coherent prime was presented in either the same or opposite direction to the partially coherent test. The stationary prime was used as a control condition. The blank stimulus between the prime and test was presented for 96 ms and the test stimulus was presented for 160 ms (10 animation frames).
Mentions: The apparatus and adaptive psychophysical procedure used were the same as those used in Experiment 1. In the global motion task, the RDK used as both the prime and the test had 300 white dots (luminance: 20 cd/m2) presented on a dark background (luminance: 0.54 cd/m2). The stimulus was displayed within a borderless area subtending 13.35° × 13.35° presented in the middle of the computer screen. Dot density was 3.83 dots/deg2 and dot life time was three animation frames (50 ms). The dot life time was increased from Experiment 1 from the results of pilot testing. The motion primes were presented at 100% coherence, with one moving to the left and the other moving to the right. The baseline control stimulus was a stationary RDK with no dot displacement. Each of these stimuli was presented for 96 ms. When extinguished these were replaced with a blank low luminance field (0.54 cd/m2) for 32 ms. This field was replaced with the partially coherent test stimulus, which was presented for 10 animation frames (160 ms). The method used is shown in Figure 2.

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