Children with FXS Have Difficulty Fixing Visual Attention, Study Finds

Ana Pena, PhD avatar

by Ana Pena, PhD |

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Young children with fragile X syndrome have trouble fixing their attention in a visual clue compared to typically developing children, a study has found.

Researchers believe problems in a cognitive skill known as visual orienting are caused by deficits in the parietal function of the brain, which mediates visual engagement, and emerge early in children affected by the disease.

Their study, “Impaired Attention Orienting in Young Children With Fragile X Syndrome” was published in the journal Frontiers in Psychology.

Fragile X syndrome is the most common inherited disorder causing intellectual disability. Affected individuals usually have motor and language delays, as well as behavioral abnormalities including autistic behaviors, anxiety disorders, and attention deficit/hyperactivity disorders.

One of the deficits observable in children with fragile X is in dynamic visual attention — the ability to rapidly detect and focus on a given visual stimulus. Early in development, infants with fragile X can have trouble visually exploring their environment and focusing their attention.

Underlying these impairments are thought to be deficits in brain circuits involved in attention processing, specifically those on the parietal lobes of the brain.

These are two regions located closer to the center of the brain that are involved in sensing and perceiving, as well as integrating sensory stimuli, primarily with the visual system.

One key component of visual attention processing is orienting, which is the ability to shift attention from one stimulus to another. Efficient and flexible orienting is essential for selecting and processing information, and is a skill that typically emerges in infancy.

Unlike other cognitive impairments studied in fragile X, problems in visual orienting never have been characterized in young children affected by the disease.

To address that, researchers from the University of California studied the attention orienting skills in young children with fragile X, relative to typically developing children.

For assessing visual engagement and disengagement, children were submitted to a gap-overlap task.

This test makes use of two conditions. In the “gap” condition, a central stimulus is displayed so as to fix the viewer’s attention in a given point, but then disappears before a peripheral stimulus appears

In the “overlap” condition, the central stimulus still remains visible when the peripheral stimulus appears so that both stimuli overlap. As a result, they both compete for the viewer’s attention, resulting in slower saccadic responses, the quick, simultaneous movements of both eyes that people do when shifting their visual point of fixation.

When participants are tested on both conditions, a “gap effect” emerges. It takes longer to shift to the peripheral target in overlap versus gap conditions because the viewer must actively disengage from the central stimulus in order to orient toward the peripheral one.

This effect can be used as an index of visual orienting efficiency, reflecting the strength of visual disengagement and engagement.

Researchers in this study measured the gap effect in 18 infants and toddlers with fragile X (7 months to 5.6 years of age), as compared to normally developing children — namely, 20 children matched to the mental age of fragile X patients (ages 5 months to 4.5 years) and 20 children chronologically age-matched (ages 6 months to 5.6 years).

To record eye movements researchers employed an eye tracker LCD which displayed both the stimuli and recorded gaze data during the task.

The data showed that both groups of typically developing children (mental age- and chronological age-matched) displayed the expected gap effect, being slower to orient their attention toward the peripheral targets on overlap versus gap conditions. For instance, chronological age-matched children took 0.31 seconds in overlap verus 0.24 seconds in gap tests.

In contrast, children with FXS had no significant gap effect. They shifted their attention to the peripheral target at the same speed regardless of the presence or absence of a central stimulus — 0.31 seconds in overlap and 0.28 seconds in gap.

“This finding suggests that attention engagement is impaired in FXS and lends behavioral support to our broader hypothesis that visual processing deficits in FXS are rooted in fronto-parietal dysfunction.” researchers wrote.

It adds to the view that FXS is a disorder “involving early and basic attention-mediated visual processing deficits” and suggests “potential targets for attention training in this population,” the researchers noted.

Future research should investigate how the variability in the type of FMR1 mutations underlying fragile X can affect patients visual attention deficits.