Sheila Gillard Crewther

Multisensory processing has long been recognized to enhance perception, cognition, and actions in adults. However, there is currently limited understanding of how multisensory stimuli, in comparison to unisensory stimuli, contribute to the development of both motor and verbally assessed working memory (WM) in children. Thus, the current study aimed to systematically review and meta-analyze the associations between the multisensory processing of auditory and visual stimuli, and performance on simple and more complex WM tasks, in children from birth to 15 years old. We also aimed to determine whether there are differences in WM capacity for audiovisual compared to unisensory auditory or visual stimuli alone after receptive and spoken language develop. Following PRISMA guidelines, a systematic search of PsycINFO, MEDLINE, Embase, PubMed, CINAHL and Web of Science databases identified that 21 out of 3968 articles met the inclusion criteria for Bayesian meta-analysis and the AXIS risk of bias criteria. The results showed at least extreme/decisive evidence for associations between verbal and motor reaction times on multisensory tasks and a variety of visual and auditory WM tasks, with verbal multisensory stimuli contributing more to verbally assessed WM capacity than unisensory auditory or visual stimuli alone. Furthermore, a meta-regression confirmed that age significantly moderates the observed association between multisensory processing and both visual and auditory WM tasks, indicating that verbal- and motor-assessed multisensory processing contribute differentially to WM performance, and to different age-determined extents. These findings have important implications for school-based learning methods and other educational activities where the implementation of multisensory stimuli is likely to enhance outcomes.

Currently, the human myopia epidemic is estimated to affect nearly 3 billion persons, yet experimental refractive error research is still hampered by the lack of a plausible theoretical mechanism explaining how the eye detects defocus and grows to minimise error (emmetropization). Applied lens defocus, either positive or negative, to animals including human, induces rapid changes in both refraction and axial length. Such changes have been linked to the rate of transfer of fluid from the vitreous chamber across the Retinal Pigment Epithelium (RPE). However, the theoretical basis of sensing the sign of defocus still eludes, as does the physiological operationalisation of this defocus signal. We propose that the signal for the sign of defocus is contained within the pattern of temporal modulation of light on the retina during the myriad saccadic eye movements performed every minute. This pattern is generated by a combination of the ocular point spread function for the defocused eye, narrow cone photoreceptor acceptance of light and the modification of photoreceptor directionality by the retinal shear that accompanies saccadic eye movements. Thus, under conditions of defocus, performing a saccade across a simple visual grating produces an out of focus dynamic stimulus pattern on the retina which is sawtooth-like, the profile being dependent on the sign of defocus. Positive lens defocus induces a fast-OFF/slow-ON sawtooth-like luminance modulation transfer function, while negative lens defocus results in a fast-ON/slow-OFF temporal pattern. Such patterns produce relative incremental or decremental changes in the trans-epithelial electrical potential and consequent changes in fluid absorption across the RPE. Thus, rearing with positive lens defocus is associated with an increase in trans-epithelial potential, increasing trans-epithelial absorption and decreasing vitreous chamber size, while rearing with a negative lens decreases the trans-epithelial electrical potential and decreases RPE fluid absorption, increasing eyeball size. In both cases, retinal images become more in-focus, and the refractive error tends to zero. The resultant is emmetropization, modifying eyeball size in response to applied defocus in a stable negative feedback fashion.

Background: Vision is rarely appraised either acutely or during recovery, following acute ischemic stroke. Our previous study found significant deficits in visual function after 2 to 3 days in ~68% of hospitalized mild-to-moderate acute ischemic stroke (AIS) patients with no comorbid eye disease. The purpose of this study was to evaluate recovery in vision after 2–6 months in a subgroup of the original participants.Methods: Visual assessments were performed within the first week of admission and 2–6 months later. Testing was achieved on an iPad and included visual acuity (VA), VA-in-noise, visual field, visual neglect, and time to complete an eye–hand coordination (EHC) task. All cases were radiologically confirmed, and 10 had left hemisphere lesions. The outcomes were compared to 20 age-matched healthy controls who were tested and retested over a similar duration using the same vision tests. The testing took 12 min.Results: During the first week of admission, 19/20 (95%) AIS patients returned normal visual acuity (>6/12 VA, p = 0.11), yet 11/20 (55%) had reduced VA-in-noise (p < 0.000).Visual neglect was present in 2/20 cases. Visual field defects were present in 16/20 (80%, p < 0.001), with 7/16 (44%) being unaware of their visual field loss. All of the patients chose to use their dominant right hand despite 10 having left hemisphere lesions and 13/20 (65%, p < 0.001) returning longer times to complete the EHC tracing tasks. After 2–6 months of recovery, all stroke patients returned normal visual attention, although 3/20 (15%) continued to show reduced VA in the presence of noise masks. Seven out of 20 (35%) retained visual field defects, and 8/20 (40%, three right and five left hemisphere lesions) had visuomotor impairment. Posterior circulation territory strokes and left hemisphere lesions were more likely to result in a persistent visual field loss and visuomotor deficit.Conclusion: Given that stroke is the leading cause of neurological disability affecting over 110 million people, our findings highlight the necessity for both acute and longitudinal vision assessments subsequent to mild stroke. Exposing the persistent limitations in visual functions could aid in identifying suitability for driving and the visuomotor rehabilitation of stroke survivors.Clinical Trial Registration: https://www.ANZCTR.org.au/ACTRN12618001111268.aspx, identifier ACTRN12618001111268.

Environmental light entrains many physiological and behavioural processes to the 24 h solar cycle. Such light-driven circadian rhythms are centrally controlled by the suprachiasmatic nucleus (SCN), which receives information from the short-wavelength-sensitive intrinsically photosensitive retinal ganglion cells. The SCN synchronizes local clocks throughout the body affecting sleep/wake routines and the secretion of neuroendocrine-linked hormones such as melatonin from the pineal gland and cortisol via the hypothalamic pituitary adrenal (HPA) axis. Although the effects of light parameters on melatonin have been recently reviewed, whether the experimental variation of the spectral power distribution and intensity of light can induce changes in cortisol rhythms remains unclear. Thus, this systematic review evaluated the effects of daytime exposure to lights of different spectral wavelength characteristics and luminance intensity on the cortisol levels in healthy individuals. A search of the PubMed, Web of Science, EMBASE, CINAHL, Medline, PsycINFO and Cochrane Library databases on 19 June 2023 identified 3418 articles, of which 12 studies (profiling 337 participants) met the inclusion and risk of bias criteria. An analysis of the literature indicated that exposure to bright lights of any colour during the late night or early morning can induce significant increases in cortisol secretion relative to time-matched dim light comparison conditions. Furthermore, exposure to bright lights with stronger short-wavelength (blue/green) components in the early morning typically induced greater increases in cortisol relative to lights with stronger long-wavelength (red) components. Thus, the circadian regulation of cortisol is sensitive to the wavelength composition of environmental lighting, in line with the more commonly studied melatonin. As such, wavelength characteristics should be optimized and reported in light intervention studies (particularly for the investigation of cortisol-associated disorders and HPA axis function), and exposure to short-wavelength light during sensitive periods should be carefully considered in constructed environments (e.g., bedroom and classroom lighting and device screens).

Proficiency of multisensory processing and motor skill are often associated with early cognitive, social, and language development. However, little research exists regarding the relationship between multisensory motor reaction times (MRTs) to auditory, visual and audiovisual stimuli, and classical measures of receptive language and expressive vocabulary development in school-age children. Thus, this study aimed to examine the concurrent development of performance in classical tests of receptive (Peabody Picture Vocabulary Test; abbreviated as PPVT) and expressive vocabulary (Expressive Vocabulary Test; abbreviated as EVT), nonverbal intelligence (NVIQ) (determined with the aid of Raven’s Colored Progressive Matrices; abbreviated as RCPM), speed of visual–verbal processing in the Rapid Automatic Naming (RAN) test, Eye–Hand Co-ordination (EHC) in the SLURP task, and multisensory MRTs, in children (n = 75), aged between 5 and 10 years. Bayesian statistical analysis showed evidence for age group differences in EVT performance, while PPVT was only different for the youngest group of children aged 5–6, supporting different developmental trajectories in vocabulary acquisition. Bayesian correlations revealed evidence for associations between age, NVIQ, and vocabulary measures, with decisive evidence and a higher correlation (r = 0.57 to 0.68) between EVT, MRT tasks, and EHC visuomotor processing. This was further supported by regression analyses indicating that EVT performance was the strongest unique predictor of multisensory MRTs, EHC, and RAN time. Additionally, visual MRTs were found to predict both receptive and expressive vocabulary. The findings of the study have important implications as accessible school-based assessments of the concurrent development of NVIQ, language, and multisensory processing; and hence as rapid and timely measures of developmental and neurodevelopmental status.

Parkinson’s disease (PD) is a chronic and progressive age-related neurodegenerative disease affecting up to 3% of the global population over 65 years of age. Currently, the underlying physiological aetiology of PD is unknown. However, the diagnosed disorder shares many common non-motor symptoms associated with ageing-related neurodegenerative disease progression, such as neuroinflammation, microglial activation, neuronal mitochondrial impairment, and chronic autonomic nervous system dysfunction. Clinical PD has been linked to many interrelated biological and molecular processes, such as escalating proinflammatory immune responses, mitochondrial impairment, lower adenosine triphosphate (ATP) availability, increasing release of neurotoxic reactive oxygen species (ROS), impaired blood brain barrier integrity, chronic activation of microglia, and damage to dopaminergic neurons consistently associated with motor and cognitive decline. Prodromal PD has also been associated with orthostatic hypotension and many other age-related impairments, such as sleep disruption, impaired gut microbiome, and constipation. Thus, this review aimed to present evidence linking mitochondrial dysfunction, including elevated oxidative stress, ROS, and impaired cellular energy production, with the overactivation and escalation of a microglial-mediated proinflammatory immune response as naturally occurring and damaging interlinked bidirectional and self-perpetuating cycles that share common pathological processes in ageing and PD. We propose that both chronic inflammation, microglial activation, and neuronal mitochondrial impairment should be considered as concurrently influencing each other along a continuum rather than as separate and isolated linear metabolic events that affect specific aspects of neural processing and brain function.

Refractive errors (myopia and hyperopia) are the most common visual disorders and are severe risk factors for secondary ocular pathologies. The development of refractive errors has been shown to be associated with changes in ocular axial length, suggested to be induced by outer retinal elements. Thus, the present study systematically reviewed the literature examining retinal function as assessed using global flash electroretinograms (gfERGs) in human clinical refractive error populations. Electronic database searching via Medline, PubMed, Web of Science, Embase, Psych INFO, and CINAHL retrieved 981 unique records (last searched on the 29 May 2022). Single case studies, samples with ocular comorbidities, drug trials, and reviews were excluded. Demographic characteristics, refractive state, gfERG protocol details, and waveform characteristics were extracted for the eight studies that met the inclusion criteria for the review and were judged to have acceptable risk of bias using the OHAT tool (total N = 552 participants; age 7 to 50). Study synthesis suggests that myopia in humans involves attenuation of gfERG photoreceptor (a-wave) and bipolar cell (b-wave) function, consistent with the animal literature. Meaningful interpretation of the overall findings for hyperopia was limited by inconsistent reporting, highlighting the need for future studies to report key aspects of gfERG research design and outcomes more consistently for myopic and hyperopic refractive errors.

Although cognitive abilities have been shown to facilitate multisensory processing in adults, the development of cognitive abilities such as working memory and intelligence, and their relationship to multisensory motor reaction times (MRTs), has not been well investigated in children. Thus, the aim of the current study was to explore the contribution of age-related cognitive abilities in elementary school-age children (n = 75) aged 5–10 years, to multisensory MRTs in response to auditory, visual, and audiovisual stimuli, and a visuomotor eye–hand co-ordination processing task. Cognitive performance was measured on classical working memory tasks such as forward and backward visual and auditory digit spans, and the Raven’s Coloured Progressive Matrices (RCPM test of nonverbal intelligence). Bayesian Analysis revealed decisive evidence for age-group differences across grades on visual digit span tasks and RCPM scores but not on auditory digit span tasks. The results also showed decisive evidence for the relationship between performance on more complex visually based tasks, such as difficult items of the RCPM and visual digit span, and multisensory MRT tasks. Bayesian regression analysis demonstrated that visual WM digit span tasks together with nonverbal IQ were the strongest unique predictors of multisensory processing. This suggests that the capacity of visual memory rather than auditory processing abilities becomes the most important cognitive predictor of multisensory MRTs, and potentially contributes to the expected age-related increase in cognitive abilities and multisensory motor processing.

Inhibition of reaching and grasping actions as an element of cognitive control and executive function is a vital component of sensorimotor behaviour that is often impaired in patients who have lost sensorimotor function following a stroke. To date, there are few kinematic studies detailing the fine spatial and temporal upper limb movements associated with the millisecond temporal trajectory of correct and incorrect responses to visually driven Go/No-Go reaching and grasping tasks. Therefore, we aimed to refine the behavioural measurement of correct and incorrect inhibitory motor responses in a Go/No-Go task for future quantification and personalized rehabilitation in older populations and those with acquired motor disorders, such as stroke. An exploratory study mapping the kinematic profiles of hand movements in neurotypical participants utilizing such a task was conducted using high-speed biological motion capture cameras, revealing both within and between subject differences in a sample of healthy participants. These kinematic profiles and differences are discussed in the context of better assessment of sensorimotor function impairment in stroke survivors.

Optical clarity and efficient phototransduction are necessary for optimal vision, however, how the associated processes of osmoregulation and continuous fluid drainage across the whole eye are achieved remains relatively unexplored. Hence, we have employed elemental microanalysis of planed surfaces of light-adapted bulk frozen-hydrated chick eyes to determine the unique intracellular elemental localization, compositions, and hydration states that contribute to maintaining osmotic gradients and water flow from the vitreous, across the retina, retinal pigment epithelium (RPE), to choroid and sclera. As expected, the greatest difference in resultant osmotic concentration gradients, [calculated using the combined concentrations of sodium (Na) and potassium (K)] and tissue hydration [oxygen-defined water concentration], occurs in the outer retina and, in particular, in the RPE where the apical and basal membranes are characterized by numerous bioenergetically active, osmoregulating ion transport mechanisms, aquaporins, and chloride (Cl) channels. Our results also demonstrate that the high intracellular Na⁺and K⁺concentrations in the apical region of the RPE are partially derived from the melanosomes. The inclusion of the ubiquitous osmolyte taurine to the calculation of the osmotic gradients suggests a more gradual increase in the osmotic transport of water from the vitreous into the ganglion cell layer across the inner retina to the outer segments of the photoreceptor/apical RPE region where the water gradient increases rapidly towards the basal membrane. Thus transretinal water is likely to cross the apical membrane from the retina into the RPE cells down the Na⁺and K⁺derived osmotic concentration gradient and leave the RPE for the choroid across the basal membrane down the Cl⁻derived osmotic concentration gradient that is sustained by the well-described bioenergetically active RPE ion transporters and channels.