Impaired Visual Search Affects Selective Attention in Rett Children, Study Shows

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by Jonathan Grinstein |

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The first evidence that selective attention — the ability to focus on or select an object in the environment — is compromised by Rett syndrome was presented in new research findings.

The article, “Impaired Visual Search in Children with Rett Syndrome,” was published in Pediatric Neurology.

Profound impairments in speech and motor control in Rett syndrome patients have been an obstacle in psychological testing. This has limited the understanding of how the brain is affected in this neurodevelopmental disorder.

Using eye-tracking technology, researchers have been able to bypass these obstructive impairments and identify specific deficits in recognition memory — the ability to recognize previously encountered events, objects, or people — in patients with Rett syndrome.

Additionally, they found evidence suggesting that the source of some of these difficulties may lie in impaired attention. However, how attention is affected in Rett patients is unclear.

Attention is made up of three core components:

  1. Sustained attention: maintaining focus on a target while ignoring distractors;
  2. Disengagement of attention: shifting focus while ignoring competing information;
  3. Selective attention: searching the visual field to find a target in an array of distractors.

To gain clarity into attention impairment in Rett syndrome children, researchers from Albert Einstein College of Medicine and the University of East London focused on selective attention by using gaze-based tasks — interactions based on looking steadily and intently.

They used an adapted eye-tracking version of the search task developed by University of Massachusetts researchers to study selective attention in Rett syndrome and healthy children.

The final sample included 28 females with clinically diagnosed classical Rett syndrome and a comparison group of 32 typically developing females, all in the age range of 2 to 12 years old.

The visual search task that the researchers used works like this:

First, a target (e.g. a red apple) is presented alone on a screen for a second and then disappears. After a second of a blank screen, the target reappears, but this time is randomly placed among distractors (e.g. blue apples and red cylinders). When the child looks at the target, the task concludes.

The team looked at the success rate of completing the task and the speed of completing the task in these two groups of children.

Participants did four practice runs of the task before being tested for the study 13 times, and each did this twice. The 13-test trials were presented with single- and conjunction-feature trials intermixed:

  • Single-feature trials: the distractors differed from the target in one feature (color or shape), creating a pop-out effect;
  • Conjunction-feature trials: the distractors differed in both features (color and shape), and finding the target is thought to require a serial search.

In the single-feature condition, the overall average success rate for the children with Rett syndrome was almost half that of the control group (48.7% compared to 83.6%). The typically developing group’s performance improved with age and screen size. On the contrary, children with Rett syndrome showed little evidence of being influenced by screen size or age, with scores staying the same as screen sizes and age increased.

In the single-feature condition, children with Rett syndrome took longer than the typically developing group to find the target, even when they were successful. This, however, was not influenced by age or screen size.

In the conjunction-feature condition, the overall average success rate for children with Rett syndrome was again lower ( 42.0%) than that of the typically developing group (  77.9%). Here, age-related improvements were observed for both groups.

In this condition, while having Rett syndrome did not influence how long it took to find the target, for both groups, as screen size increased, reaction time (or the time to find the target) slowed down.

“It is unclear what factors underlie the difficulties encountered by children with Rett syndrome, particularly in their success in finding the target,” researchers said.

“One possibility is that they have difficulty shifting and/or disengaging attention from the distractors. Another possibility is that visual search is impaired in children with Rett syndrome because they have difficulty distributing their attention across the screen. A related but as of yet uninvestigated possibility is that the efficient search in children with Rett syndrome is compromised by a tendency to focus on local, rather than global, features.”

These results reinforce the usefulness of gaze-based tasks to measure the behavior and brain function of Rett syndrome patients. However, the study was limited, as is common with rare disorders such as Rett syndrome, by small sample size. So, testing the usefulness of gaze-based tasks to measure behavior and brain function needs to be expanded.

Additionally, future testing is required to see if these eye-tracking tasks have the requisite sensitivity to be useful for characterizing Rett syndrome attention symptoms at the individual level. The researchers recommend that future work should focus on identifying the mechanisms that underlie selective attention and impaired visual search abilities in children with Rett syndrome.