The authors evaluated patients with Fragile X-associated Tremor/Ataxia Syndrome (FXTAS), a neurodegenerative disorder associated with a CGG repeat expansion in the premutation range in the fragile X mental retardation 1 gene (FMR1).
Neurological, psychiatric, and neuropsychological evaluations were completed on 15 males with FXTAS.
Seven cases were diagnosed with dementia; seven were diagnosed with mood and/or anxiety disorders. Twelve subjects demonstrated deficits on neuropsychological testing.
Physicians assessing dementia patients are urged to consider this newly-described syndrome, especially in patients with dementia associated with a movement disorder and in patients with family history of mental retardation. If FXTAS is a possible diagnosis, the physician may obtain FMR1 DNA testing; patients who are positive on DNA testing should have an MRI, be referred to neurology, and receive genetic counseling
FXTAS; fragile X premutation; dementia; anxiety disorder; mood disorder
Integration of local elements into a coherent global form is a fundamental aspect of visual object recognition. How the different hierarchically organized stages of visual analysis develop in order to support object representation in infants remains unknown. The aim of this study was to investigate structural encoding of natural images in 4- to 6-month-old infants and adults. We used the steady-state visual evoked potential (ssVEP) technique to measure cortical responses specific to the global structure present in object and face images, and assessed whether differential responses were present for these image categories. This study is the first to apply the ssVEP method to high-level vision in infants. Infants and adults responded to the structural relations present in both image categories, and topographies of the responses differed based on image category. However, while adult responses to face and object structure were localized over occipitotemporal scalp areas, only infant face responses were distributed over temporal regions. Therefore, both infants and adults show object category specificity in their neural responses. The topography of the infant response distributions indicates that between 4 and 6 months of age, structure encoding of faces occurs at a higher level of processing than that of objects.
object perception; face processing; lateral occipital cortex; image structure; steady-state evoked potentials
Fragile X syndrome is the most common cause of inherited intellectual impairment and the most common single-gene cause of autism. Individuals with fragile X syndrome present with a neurobehavioural phenotype that includes selective deficits in spatiotemporal visual perception associated with neural processing in frontal–parietal networks of the brain. The goal of the current study was to examine whether reduced resolution of spatial and/or temporal visual attention may underlie perceptual deficits related to fragile X syndrome. Eye tracking was used to psychophysically measure the limits of spatial and temporal attention in infants with fragile X syndrome and age-matched neurotypically developing infants. Results from these experiments revealed that infants with fragile X syndrome experience drastically reduced resolution of temporal attention in a genetic dose-sensitive manner, but have a spatial resolution of attention that is not impaired. Coarse temporal attention could have significant knock-on effects for the development of perceptual, cognitive and motor abilities in individuals with the disorder.
crowding; flicker; magnocellular; Mooney; contrast sensitivity
Conscious visual perception of the constantly changing environment is one of the brain’s most critical functions. In virtually every moment of every daily activity, the visual system is confronted with the task of accurately representing and interpreting scenes that change rapidly over time. Adults can judge the identity and order of changing images presented at a rate of up to 10 Hz (~50 ms per image); this limit reflects a finite temporal resolution of attention. In the research reported here, although 6- to 15-month-old infants could detect the presence of rapid flicker without difficulty, their ability to segment individual alternating states within the flicker was severely limited: Fifteen-month-old infants had a temporal resolution of attention approximately one order of magnitude lower than that of adults (~1 Hz). Coarse temporal resolution constrains how infants perceive and utilize dynamic visual information and may play a role in the visual processing deficits found in individuals with neurodevelopmental disorders.
temporal individuation; Gestalt flicker fusion; contrast sensitivity
This study examined the effects of amblyopia on perceptual decision-making processes to determine the consequences of visual deprivation on development of higher-level cortical networks outside of visual cortex. A variant of the Eriksen flanker task was used to measure response time and accuracy for decisions made in the presence of response-selection conflict. Performance of adults with amblyopia was compared to that of neurotypical participants of the same age. Additionally, simple and choice reaction time tasks presented in the visual and the auditory modality were used to control for factors such as feature visibility, crowding, and motor execution speed. A selective deficit in response time for visual decisions was found when individuals with amblyopia used either the amblyopic or non-amblyopic (dominant) eye, and this deficit was independent of visual acuity, motor time, and performance accuracy. In trial conditions that provoked response-selection conflict, responses were significantly delayed in amblyopic relative to neurotypical participants, and were not subject to standard trial sequence effects. Our results indicate that, beyond the known effects of abnormal visual experience on visual cortex, suboptimal binocular input during a developmental critical period may also impact cortical connections to downstream areas of the brain, including parietal and frontal cortex, that are believed to underlie decision and response-selection processes.
visual development; amblyopia; strabismus; decision; response conflict; cognitive control
Conscious awareness of objects in the visual periphery is limited. This limit is not entirely the result of reduced visual acuity, but is primarily caused by crowding—the inability to identify an object when surrounded by clutter. Crowding represents a fundamental limitation of the visual system, and has to date been unexplored in infants. Do infants have a fine-grained “spotlight”, similar to adults, or a diffuse “lantern” that sets limits on what they can register in the periphery? An eye-tracking paradigm was designed to psychophysically measure crowding in 6- to 15-month-olds by showing pairs of faces at three eccentricities, in the presence or absence of flankers, and recording infants’ first saccade from central fixation to either face. Results reveal that infants can discriminate faces in the periphery, and flankers impair this ability as close as 3 degrees; the effective spatial resolution of visual perception increased with age but was only half that of adults.
inversion; crowding; attention; peripheral vision; Mooney face
Recent insight into the underlying molecular and cellular mechanisms of fragile X syndrome (FXS) has led to the proposal and development of new pharmaceutical treatment strategies, and the initiation of clinical trials aimed at correcting core symptoms of the developmental disorder. Consequently, there is an urgent and critical need for outcome measures that are valid for quantifying specific symptoms of FXS and that are consistent across time. We used eye tracking to evaluate test–retest reliability of gaze and pupillometry measures in individuals with FXS and we demonstrate that these measures are viable options for assessing treatment-specific outcomes related to a core behavioral feature of the disorder.
Face processing; Gaze; Fixation; FMR1 gene; fragile X syndrome; Outcome measure; Pharmacotherapy
An object or feature is generally more difficult to identify when other objects are presented nearby, an effect referred to as crowding. Here, we used Mooney faces to examine whether crowding can also occur within and between holistic face representations (C. M. Mooney, 1957). Mooney faces are ideal stimuli for this test because no cues exist to distinguish facial features in a Mooney face; to find any facial feature, such as an eye or a nose, one must first holistically perceive the image as a face. Through a series of six experiments we tested the effect of crowding on Mooney face recognition. Our results demonstrate crowding between and within Mooney faces and fulfill the diagnostic criteria for crowding, including eccentricity dependence and lack of crowding in the fovea, critical flanker spacing consistent with less than half the eccentricity of the target, and inner-outer flanker asymmetry. Further, our results show that recognition of an upright Mooney face is more strongly impaired by upright Mooney face flankers than inverted ones. Taken together, these results suggest crowding can occur selectively between high-level representations of faces and that crowding must occur at multiple levels in the visual system.
peripheral vision; spatial vision; object recognition; inversion; asymmetry
Our visual world is dynamic in nature. The ability to encode, mentally represent, and track an object's identity as it moves across time and space is critical for integrating and maintaining a complete and coherent view of the world. Here we investigated dynamic object processing in typically developing (TD) infants and infants with fragile X syndrome (FXS), a single-gene disorder associated with deficits in dorsal stream functioning. We used the violation of expectation method to assess infants’ visual response to expected versus unexpected outcomes following a brief dynamic (dorsal stream) or static (ventral stream) occlusion event. Consistent with previous reports of deficits in dorsal stream-mediated functioning in individuals with this disorder, these results reveal that, compared to mental age-matched TD infants, infants with FXS could maintain the identity of static, but not dynamic, object information during occlusion. These findings are the first to experimentally evaluate visual object processing skills in infants with FXS, and further support the hypothesis of dorsal stream difficulties in infants with this developmental disorder.
object tracking; occlusion; motion; dorsal/ventral visual streams; attention
Gaze avoidance is a hallmark behavioral feature of fragile X syndrome (FXS), but little is known about whether abnormalities in the visual processing of faces, including disrupted autonomic reactivity, may underlie this behavior. Eye tracking was used to record fixations and pupil diameter while adolescents and young adults with FXS and sex- and age-matched typically developing controls passively viewed photographs of faces containing either a calm, happy, or fearful expression, preceded by a scrambled face matched on luminance. Results provide quantitative evidence for significant differences in gaze patterns and increased pupillary reactivity when individuals with FXS passively view static faces. Such abnormalities have significant implications in terms of understanding causes of gaze avoidance observed in individuals with FXS.
face processing; fragile X syndrome; FMR1 gene; eye tracking; pupil reactivity