Advances in TVA-based visual attention research - Part II: Clinical profiles, effects of manipulations and neural correlates

Tourette syndrome (TS) is a neurodevelopmental disorder involving the basal ganglia and connecting fronto-striatal pathways. TS is characterised by motor and vocal tics, as well as a high comorbidity with attention-deficit/hyperactivity disorder (ADHD) and obsessive compulsive disorder (OCD). In some studies, TS has been associated with cognitive impairments, but the degree to which this is driven by comorbid disorders is unclear. Here we present a parametric investigation of visual attention in TS based on a Theory of Visual Attention (TVA) while correcting for comorbidity. We tested 187 TS patients aged 11-25 years (M = 18.25) and 47 healthy controls aged 14-24 years (M = 18.39) with a TVA-based whole report paradigm to derive individual estimates of visual short-term memory span, visual processing speed, and the temporal threshold of perception. The TS patients were further divided into four subgroups based on comorbidity status: TS-only, TS+ADHD, TS+OCD, and TS+ADHD+OCD. We found no differences between the full patient group and the healthy controls, nor between TS-only and the healthy controls. However, comorbid ADHD appears to be associated with lower processing speed, while comorbid OCD may positively affect the capacity of short-term memory. Thus, a diagnosis of TS alone does not seem to influence visual attention negatively. These findings are discussed in relation to previous studies of cognition in TS and to TVA-based investigations in children and adolescents with neurodevelopmental disorders.

Multiple sclerosis (MS) is characterized by both visual and cognitive deficits. White and grey matter pathologies caused by the disease can affect the visual system at any point from peripheral to central processing stages. In recent TVA-based studies assessing MS patients, a marked decrease of visual processing capacity was found. In particular, the parameter reflecting visual threshold was increased at later disease stages and related to cognitive ability. However, possible relationships to markers of sensory visual dysfunction were not considered in these studies. In the present study, therefore, we assessed visual processing capacity in a whole report paradigm based on TVA in a sample of 60 MS patients. Data on visual contrast sensitivity and visual evoked potentials were collected as measures reflecting the degree of visual impairment. Significant correlations were found between these measures and TVA parameters visual threshold and processing rate, but not visual short-term memory storage capacity. The implications of these results for TVA-based assessment of visual processing capacity as a tool for identifying cognitive impairment in MS will be discussed.

Little is known about plasticity in the human adult visual cortex. Aim of this study was to better understand the nature of neuroplastic changes in the visual cortex. Studies with up to 150 minutes of monocular deprivation have shown to alter visual perception in adult humans. In this study we used long term monocular deprivation about 7 days with intervals of 1, 3, 5 and 14 days to test for short- and long-term structural and functional changes in brain visual networks by structural and functional MRI. TVA (theory of visual attention)-based assessment was used for sensitive investigation of functional changes in short-term memory and visual attention.

Visual processing speed, as assessed with whole report paradigms based on the theory of visual attention, decreases in healthy older compared to younger adults and more so in patients with amnestic Mild Cognitive Impairment (aMCI) at high risk for developing Alzheimer dementia. In a series of studies we showed that auditory cues increase visual processing speed for a limited period of time, in healthy younger and older participants. Such phasic adaptation is relevant in order to optimize performance in conditions where fast reactions to visual stimuli are required. It is not known, however, whether patients with aMCI also show such active perception effects. We will demonstrate that also aMCI patients can, to some degree, counteract their overall reduction in processing speed, when presented with auditory alerting cues.

Aging impacts both visual short-term memory (vSTM) capacity and thalamo-cortical connectivity. According to the Neural Theory of Visual Attention, vSTM depends on the structural connectivity between posterior thalamus and visual occipital cortices (PT-OC). We tested whether aging modifies the association between vSTM capacity and PT-OC structural connectivity. To do so, 66 individuals aged 20 to 77 years were assessed by diffusion-weighted imaging used for probabilistic tractography and performed a psychophysical whole-report task of briefly presented letter arrays, from which vSTM capacity estimates were derived. We found reduced vSTM capacity, and aberrant PT-OC connection probability in aging. Critically, age modified the relationship between vSTM capacity and PT-OC connection probability: in younger adults, vSTM capacity was negatively correlated with PT-OC connection probability while in older adults, this association was positive. Furthermore, age modified the microstructure of PT-OC tracts suggesting that the inversion of the association between PT-OC connection probability and vSTM capacity with aging might reflect age-related changes in white-matter properties. Accordingly, our results demonstrate that age-related differences in vSTM capacity links with the microstructure and connectivity of PT-OC tracts.

When attention is unguided, perceptual performance is generally better for stimuli appearing in the central as compared to the peripheral region. To what extent the eccentricity effect depends on task demands and individual factors, is still a matter of debate. In the current study, we investigated the effect of top-down allocation of attention and working memory span on the eccentricity bias in two experiments. In the first experiment, participants (N=24) performed a probed change detection task in which we simultaneously presented two target letters in central vision (at 5° eccentricity) and two target letters in peripheral vision (at 10° eccentricity). In line with previous findings, we observed a significant eccentricity effect when participants were asked to distribute their attention across the visual field. This effect diminished when cued to one level of eccentricity in the left and/or right visual field, both when the probe letter appeared at the validly and when it appeared at the invalidly cued location. In the second experiment, participants (N=56) performed an unguided whole/partial report task where 4 or 8 target letters appeared at three different eccentricity levels (4°, 7°, 10° of visual angle). Working memory span was measured by a digital Corsi Block Tapping Task and ranged between 3.40 and 7.60. We observed a significant effect of eccentricity, which was not modulated by working memory span. In summary, our findings demonstrated that the ability to process information in the peripheral visual field can be flexibly modulated by top-down allocation of attention.