Using sequential structure to improve visuomotor control

In daily life, people make rapid, goal-directed movements to interact with their environment. Since these movements are goal-directed, the outcome of the movement is important. A plan is typically formulated to make the movement using visual information about target location before the movement is initiated. However, in dynamic environments people need to track the location of an object if it moves during the reach. Additionally, it would be beneficial to motor performance to learn the distribution of target locations over multiple reaches. In this paper we develop a simple model that describes how people might exploit the sequential structure over a series of trials to improve rapid visuomotor control. We then present empirical data from a sequential tracking task that investigates how people's knowledge of the location of objects is updated over trials to improve pointing performance. The model is able to predict when people will hit and miss targets with reasonable success. Interestingly, the results suggest that not only are people able to use sequential information but also look for it even when it does not exist.Anna Ma-Wyatt and Daniel Navarr

Debris Disks: Probing Planet Formation

Debris disks are the dust disks found around ~20% of nearby main sequence stars in far-IR surveys. They can be considered as descendants of protoplanetary disks or components of planetary systems, providing valuable information on circumstellar disk evolution and the outcome of planet formation. The debris disk population can be explained by the steady collisional erosion of planetesimal belts; population models constrain where (10-100au) and in what quantity (>1Mearth) planetesimals (>10km in size) typically form in protoplanetary disks. Gas is now seen long into the debris disk phase. Some of this is secondary implying planetesimals have a Solar System comet-like composition, but some systems may retain primordial gas. Ongoing planet formation processes are invoked for some debris disks, such as the continued growth of dwarf planets in an unstirred disk, or the growth of terrestrial planets through giant impacts. Planets imprint structure on debris disks in many ways; images of gaps, clumps, warps, eccentricities and other disk asymmetries, are readily explained by planets at >>5au. Hot dust in the region planets are commonly found (<5au) is seen for a growing number of stars. This dust usually originates in an outer belt (e.g., from exocomets), although an asteroid belt or recent collision is sometimes inferred.Comment: Invited review, accepted for publication in the 'Handbook of Exoplanets', eds. H.J. Deeg and J.A. Belmonte, Springer (2018

Humans use different statistics for sequence analysis depending on the task

Despite its long history (Luce, 1986) the study of sequential effects has mostly been confined to simple binary tasks such as two-alternative forced choice tasks (2AFC). Here we present experimental results from a choice task with three rather than two alternatives (3AFC) as well as a novel model that can explain them. We find that humans change the statistics they use to analyse a sequence depending on the task constraints, relying on first-order transition probabilities in a 2AFC but event relative frequencies (i.e., zeroth-order transition probabilities) in a 3AFC.Dinis Gökaydin, Anna Ma-Wyatt, Daniel Navarro, Amy Perfor

The effects of ageing and visual field loss on pointing to visual targets

Purpose: To investigate the effect of ageing on visuomotor function and subsequently evaluate the effect of visual field loss on such function in older adults. Methods: Two experiments were performed: 1) to determine the effect of ageing on visual localisation and subsequent pointing precision, and 2) to determine the effect of visual field loss on these outcome measures. For Experiment 1, we measured visual localisation and pointing precision radially at visual eccentricities of 5, 10 and 15u in 25 older (60–72 years) and 25 younger (20–31 years) adults. In the pointing task, participants were asked to point to a target on a touchscreen at a natural pace that prioritised accuracy of the touch. In Experiment 2, a subset of these tasks were performed at 15u eccentricity under both monocular and binocular conditions, by 8 glaucoma (55–76 years) and 10 approximately agematched controls (61–72 years). Results: Visual localisation and pointing precision was unaffected by ageing (p.0.05) and visual field loss (p.0.05), although movement time was increased in glaucoma (p = 0.01). Conclusion: Visual localisation and pointing precision to high contrast stimuli within the central 15u of vision are unaffected by ageing. Even in the presence of significant visual field loss, older adults with glaucoma are able perform such tasks with reasonable precision provided the target can be perceived and movement time is not restricted.Nikki J. Rubinstein, Andrew J. Anderson, Anna Ma-Wyatt, Mark J. Walland, Allison M. McKendric

Nightly treatment of primary insomnia with prolonged release melatonin for 6 months: a randomized placebo controlled trial on age and endogenous melatonin as predictors of efficacy and safety

&lt;p&gt;Background: Melatonin is extensively used in the USA in a non-regulated manner for sleep disorders. Prolonged release melatonin (PRM) is licensed in Europe and other countries for the short term treatment of primary insomnia in patients aged 55 years and over. However, a clear definition of the target patient population and well-controlled studies of long-term efficacy and safety are lacking. It is known that melatonin production declines with age. Some young insomnia patients also may have low melatonin levels. The study investigated whether older age or low melatonin excretion is a better predictor of response to PRM, whether the efficacy observed in short-term studies is sustained during continued treatment and the long term safety of such treatment.&lt;/p&gt; &lt;p&gt;Methods: Adult outpatients (791, aged 18-80 years) with primary insomnia, were treated with placebo (2 weeks) and then randomized, double-blind to 3 weeks with PRM or placebo nightly. PRM patients continued whereas placebo completers were re-randomized 1:1 to PRM or placebo for 26 weeks with 2 weeks of single-blind placebo run-out. Main outcome measures were sleep latency derived from a sleep diary, Pittsburgh Sleep Quality Index (PSQI), Quality of Life (World Health Organzaton-5) Clinical Global Impression of Improvement (CGI-I) and adverse effects and vital signs recorded at each visit.&lt;/p&gt; &lt;p&gt;Results: On the primary efficacy variable, sleep latency, the effects of PRM (3 weeks) in patients with low endogenous melatonin (6-sulphatoxymelatonin [6-SMT] ≤8 μg/night) regardless of age did not differ from the placebo, whereas PRM significantly reduced sleep latency compared to the placebo in elderly patients regardless of melatonin levels (-19.1 versus -1.7 min; P = 0.002). The effects on sleep latency and additional sleep and daytime parameters that improved with PRM were maintained or enhanced over the 6-month period with no signs of tolerance. Most adverse events were mild in severity with no clinically relevant differences between PRM and placebo for any safety outcome.&lt;/p&gt; &lt;p&gt;Conclusions: The results demonstrate short- and long-term efficacy and safety of PRM in elderly insomnia patients. Low melatonin production regardless of age is not useful in predicting responses to melatonin therapy in insomnia. The age cut-off for response warrants further investigation.&lt;/p&gt