Alex R. Wade

Motion perception involves both bottom–up sensory processing and top–down perceptual interpretation. Using magnetoencephalography frequency tagging and source-space multivariate pattern analysis, we decoded the perceived direction of both real and bistable apparent motion from cortical activity in 11 human participants (six males, five females). Real motion direction was decoded with near-ceiling accuracy across frequencies in both whole-brain and visual cortex analyses, whereas apparent motion direction was decoded just above chance from the visual cortex (56.0%, p = 0.011, Cohen's d = 0.94) when combining the 5 and 7.5 Hz harmonics. Activation patterns showed a larger relative hMT ⁺ contribution for apparent than real motion, and cross-classification did not generalize direction information between conditions. These results identify a measurable cortical signature of subjective motion direction but also show that it is relatively diffuse and only weakly bound to the retinotopic cortex.

The absence of input from one sense can lead to a greater emphasis on the remaining senses, resulting in heightened performance. Numerous behavioral studies demonstrate that adults who have been deaf from an early age have superior visual sensitivity, particularly to far-peripheral stimuli. We asked whether the increased demand on peripheral vision throughout development that comes with early, profound deafness might be reflected in changes in early visual brain structures. Using functional MRI, we mapped visual field representations in 16 early, profoundly D/deaf adults and 16 hearing age-matched controls. D/deaf individuals exhibited a larger representation of the far-peripheral visual field in both the primary visual cortex and the lateral geniculate nucleus of the thalamus. Importantly, this was not due to a total expansion of the visual map, as there was no difference between groups in overall size of either structure, but a smaller representation of the central visual field in the D/deaf group, suggesting a redistribution of neural resources. Here, we demonstrate that the demands placed on vision due to lifelong deafness can sculpt first level visual map input, to increase neural processing resources for far-peripheral visual stimuli.

Glycogen synthase kinase 3β (GSK3β) is important in neuronal development and maintenance, acting as a key regulator by controlling a broad range of cellular processes. The effects of its dysregulation range from impairments in axonal transport and energy metabolism to synapse formation and neuronal plasticity. However, how such cellular defects link to neuronal dysfunction is less well studied despite the links between GSK3β and various neurological conditions, such as Alzheimer’s and Parkinson’s diseases, mood disorders and autism. Here we used a steady-state visually evoked potential (SSVEP) assay with Drosophila to measure the effect of altering GSK3β expression on neuronal function. We recorded SSVEPs from flies that expressed constitutively active or inactive (kinase-dead) variants of GSK3β and showed that the visual responses of these flies differed from those of controls. This was indicated by increased response latency and reduced photoreceptor maximum response ( R _max ). Importantly, multivariate pattern classification can distinguish between over- and inactive GSK3β conditions. Taken together, we show that SSVEPs provide a powerful tool for future studies to link the molecular and cellular functions of GSK3β with their effects on neuronal function. Furthermore, we introduce a monitoring protocol that ensures the quality of datasets to support future fly SSVEP experiments.

Important parts of the visual pathway occur in relatively small subcortical structures that are often difficult to identify and segment using standard structural scans in MRI (e.g. T1 and T2 scans). Studies of the Lateral Geniculate Nucleus (LGN) often use proton density (PD) scan protocols, repeated up to 40 times, then manually segment the LGN structure from the average image. Efficiency is crucial when conducting MRI scans: minimising time spent on structural scanning can increase time available for complementary functional MRI scans and/or reduce scanning costs. In this study we asked how segmentation accuracy depended on the number of PD repeats. Four raters segmented the LGN of five participants, using different numbers of PD scans in the average image (1, 2, 4, 8, 16, 24, 32, 40), and an additional experienced expert rater segmented the LGN for just the 40PD average for all participants. We compared how the rater LGN masks at each scan average level overlapped with the expert masks. One rater performed the segmentation for the 40PD average on four separate days, to measure intra-rater variability across repeats. We also used a state-of-the-art automated segmentation process to compare the reliability to manual segmentation. We found that the average overlap between rater masks and the expert masks increased up to the 16PD scan average level, after which there was no additional benefit to including more PD scans. The automated segmentation masks were comparable to the overlap between the raters (40PD) and expert masks.

Introduction: The growing ubiquity of smartphones with around-the-clock access to social media has sparked concerns regarding their impacts on sleep, mental health, and cognition, particularly among young people. A rapid research response is crucial given the potential, yet still unclear, threats, and evidence-based solutions are needed to educate young people on how to use smartphones as part of a healthy lifestyle. Methods: We assessed the feasibility of a 21-day smartphone and social media (SSM) ban among 12-year-olds at a UK school, featured in the Channel 4 documentary: “Swiped: The School that Banned Smartphones”. Twenty-six Year-8 pupils (15 males, 11 females) participated, with pre-and post-ban assessments of sleep, wellbeing, and cognitive abilities (attention and working memory), alongside continuous objective monitoring of sleep and wellbeing via wearables. Results: By the end of the ban, self-reported sleep onset latency significantly decreased by ~20 minutes, and total sleep duration significantly increased by ~1 hour. Wearable sleep data followed this trend but was not statistically significant. Improved sleep coincided with significant attention gains, though working memory showed no change. Anxiety symptoms and negative mood significantly declined, while symptoms of depression exhibited a small, nonsignificant reduction. Wearable data also indicated small (but nonsignificant) improvements in heart rate variability (HRV), a physiological marker of emotional wellbeing. Social connectedness remained unchanged.Conclusion: This study highlights the feasibility of implementing collective SSM bans. Preliminary findings suggest such “detox” approaches may help schools educate young people on the benefits of reduced screen time, particularly for sleep and wellbeing.

Many cells in the early human visual system respond to either chromatic or luminance contrast or a combination of both. In addition, depending on their location in the visual hierarchy, these cells may receive input from either one eye or both eyes. It is well understood that spatial luminance contrast patterns undergo binocular normalization: Inputs from each eye mutually suppress each other so that monocular and binocular percepts appear similar. Recent reports suggest that interocular normalization computations may depend on spatial and temporal frequency. Here, we examined the effect of chromaticity and spatial frequency on binocular normalization computations using a dichoptic frequency-tagged, steady-state visually evoked potential (SSVEP) paradigm. We found that normalization as indexed by changes in eye-tagged input SSVEP frequencies and intermodulation terms depends significantly on both spatial frequency and color. We also found that binocular combination must occur in neurons that carry half-wave rectified signals due to 1F combination frequencies being present. Overall, our results are not well explained by a model in which neurons that code low spatial frequency color are segregated anatomically in the centers of ocular dominance columns. Significant levels of binocular interaction must occur in neurons that code both color and luminance and in neurons sensitive to both low and high spatial frequencies.

Purpose: The apparent contrast of a visible central grating can be reduced by the presence of a surrounding grating—an effect known as surround suppression of contrast. Surround suppression is strong when the orientation of the surround matches that of the central probe and is strongest in the periphery. There is evidence that surround suppression at the fovea increases in strength with age, and that the orientation dependence of surround suppression is weakened. However, the range of visual stimuli that can produce this effect (and the implicated underlying mechanisms) requires further examination. This study aimed to characterise surround suppression at the fovea and its dependence on age. Visual stimuli with previously unexplored spatiotemporal parameters were used, designed to minimise contributions from spatially short‐range overlay masking and temporally transient masking mechanisms. Methods: In 20 younger (60 years) observers, psychophysical contrast‐matching thresholds were measured using stimuli centred on the fovea. Grating stimuli were presented with either no surround, a collinearly oriented surround or an orthogonally oriented surround. Using a staircase procedure, observers matched the contrast of these central target stimuli to the contrast of a separate reference stimulus. The points of subjective equality between target and reference stimuli were compared between the two surround orientations and between younger and older age groups. Results: Across all observers, weak foveal surround suppression was found that had little orientation tuning. No evidence for the strength of surround suppression increasing with age is reported. Conclusions: These findings suggest that the age‐related effects of surround suppression may be dependent on the spatiotemporal parameters of the stimulus used and encourage further exploration of the contrast masking mechanisms affected by age. The mild and weakly orientation‐tuned suppression may have been produced by a weak and temporally sustained suppression mechanism.

Much progress has been made in understanding how the brain combines signals from the two eyes. However, most of this work has involved achromatic (black and white) stimuli, and it is not clear if the same processes apply in color-sensitive pathways. In our first experiment, we measured contrast discrimination (“dipper”) functions for four key ocular configurations (monocular, binocular, half-binocular, and dichoptic), for achromatic, isoluminant L-M and isoluminant S-(L+M) sine-wave grating stimuli (L: long-, M: medium-, S: short-wavelength). We find a similar pattern of results across stimuli, implying equivalently strong interocular suppression within each pathway. Our second experiment measured dichoptic masking within and between pathways using the method of constant stimuli. Masking was strongest within-pathway and weakest between S-(L+M) and achromatic mechanisms. Finally, we repeated the dipper experiment using temporal luminance modulations, which produced slightly weaker interocular suppression than for spatially modulated stimuli. We interpret our results in the context of a contemporary two-stage model of binocular contrast gain control, implemented here using a hierarchical Bayesian framework. Posterior distributions of the weight of interocular suppression overlapped with a value of 1 for all dipper data sets, and the model captured well the pattern of thresholds from all three experiments.

The apparent contrast of a suprathreshold central stimulus can be reduced by a surrounding stimulus - a phenomenon known as surround suppression. When stimuli are presented at the fovea, this effect reportedly increases in strength with age. The underlying mechanism proposed for this age dependence, a change in the balance of inhibition and excitation in cortex, makes this phenomenon potentially interesting as a biomarker of neurological dysfunction. Here, we attempt to repeat these measurements, but we use stimuli designed to control for untuned overlay masking, a different form of suppression thought to be of pre-cortical origin. We measured contrast matching thresholds in twenty younger (< 30) and seventeen older (>60) observers. Across all observers, we find weak suppression that has little or no orientation tuning and, importantly, no dependence on age. Our findings contradict those from earlier studies and suggest that effects relating to age may be dependent on the temporal parameters of this stimulus, and could arise from effects on other pre-cortical mechanisms.