For humans, visual tracking of moving stimuli often triggers catch-up saccades during smooth pursuit. The switch between these continuous and discrete eye movements is a trade-off between tolerating sustained position error (PE) when no saccade is triggered or a transient loss of vision during the saccade due to saccadic suppression. de Brouwer et al. (2002b) demonstrated that catch-up saccades were less likely to occur when the target re-crosses the fovea within 40-180 ms. To date, there is no mechanistic explanation for how the trigger decision is made by the brain. Recently, we proposed a stochastic decision model for saccade triggering during visual tracking (Coutinho et al., 2018) that relies on a probabilistic estimate of predicted PE (PE pred). Informed by model predictions, we hypothesized that saccade trigger time length and variability will increase when pre-saccadic predicted errors are small or visual uncertainty is high (e.g., for blurred targets). Data collected from human participants performing a double step-ramp task showed that large pre-saccadic PE pred (Ͼ10°) produced short saccade trigger times regardless of the level of uncertainty while saccade trigger times preceded by small PE pred (Ͻ10°) significantly increased in length and variability, and more so for blurred targets. Our model also predicted increased signal-dependent noise (SDN) as retinal slip (RS) increases; in our data, this resulted in longer saccade trigger times and more smooth trials without saccades. In summary, our data supports our hypothesized predicted error-based decision process for coordinating saccades during smooth pursuit.

No abstract

Background: The COVID-19 pandemic caused significant morbidity and mortality in people who inject drugs (PWID). Upper extremity soft tissue infections are frequently associated with intravenous drug use (IVDU) due to poor compliance with aseptic technique. In Canada, multiple safe injection sites providing clean injection supplies closed, leaving many PWID with no alternatives to inject safely. It was hypothesized that these closures will correspond with increased morbidity and mortality among PWID. The main objective of this study was to determine the effect of the COVID-19 pandemic on the incidence of upper extremity infections in PWID. Methods: This was a retrospective chart review study. The primary outcome of interest was the frequency of upper extremity infections in PWID. Data were filtered to include only those patients presenting to the emergency department between March to June of 2019 and 2020. Chi-squared analysis was used to compare the number of IVDU patients among patients with upper extremity skin infections between these time periods. Results: The number of IVDU patients treated for upper extremity infections in Hamilton significantly increased during the pandemic, relative risk = 2.0 (95% confidence interval [CI]: 1.3-2.9, P = .0012,) while total upper extremity infections numbers have decreased overall. During the pandemic, PWID made up a larger proportion of upper extremity infections ( χ2 = 10.444, P = .00123). Demographic data such as age and sex of IVDU patients presenting with upper extremity infection was not significantly affected by the pandemic. Conclusions: The effect of the pandemic on accessing harm reduction services has led to evident increases in morbidity as described by this study. Further research on the impact of closures in PWID is needed to quantify these harms and work toward mitigation strategies.

These topical anesthetics seem ineffective in controlling the pain associated with frenotomy. Clinicians should continue to search for an effective treatment for this procedure.