Friday, March 28th, 2025

Time	Event
10:48p	On variability in local field potentials Neuronal coding and decoding would be compromised if neuronal responses were highly variable. Intriguingly, neuronal spike counts (SCs) show a reduction in across-trial variance (ATV) in response to sensory stimulation, when SC variance is normalized by SC mean, that is, when using the Fano factor 1. Inspired by this seminal finding, ATV has also been studied in electroencephalography (EEG) signals, revealing effects of various stimulus and cognitive factors as well as disease states. Here, we empirically show that outside of evoked potentials, the ATV of the EEG or local field potential (LFP) is very highly correlated to the intra-trial variance (ITV), which corresponds to the well-known power metric. We propose that the LFP power, rather than the raw LFP signal, should be considered with regard to putative changes of its variability. We quantify LFP power variability as the standard deviation of the logarithm of the power ratio between an active and a baseline condition, normalized by the mean of that log(power ratio), that is the coefficient of variation (CV) of the log(power ratio). This CV(log(power ratio)) is reduced for gamma and alpha power when they are enhanced by stimulation, and it is enhanced for alpha power when it is reduced by stimulation. This suggests a potential inverse relation between changes in band-limited power and the corresponding CV. We propose that the CV(log(power ratio)) is a useful metric that can be computed for numerous existing and future LFP, EEG or MEG datasets, which will provide insights into those signals' frequency-specific variability and how they might be used for neuronal coding and decoding. (Comment on this)
10:48p	Working memory readout varies with frontal theta rhythms Increasing evidence suggests that attention varies rhythmically, phase-locked to ongoing cortical oscillations. Here, we report that the phase of theta oscillations (3 to 6 Hz) in the frontal eye field (FEF) is associated with temporal and spatial variation of the read-out of information from working memory (WM). Non-human primates were briefly shown a sample array of colored squares. A short time later, they viewed a test array and were rewarded for identifying which square changed color (the target). Better performance (accuracy and reaction time) varied systematically with the phase of local field potential (LFP) theta at the time of test array onset as well as the target location. This is consistent with theta scanning across the FEF and thus visual space from top to bottom. Theta was coupled, on opposing phases, to both spiking and beta (12 to 20 Hz). These results could be explained by a wave of activity that moves across the FEF, modulating the readout of information from WM. (Comment on this)
11:17p	The development of visual acuity and crowding: Finding the balance between fine detail and 'gist' processing The adult visual system is characterised by high-resolution foveal vision and a peripheral field limited by crowding, the disruption to object recognition in clutter that gives a summary 'gist' in place of fine detail. In children, crowding is elevated in the fovea, with estimates of the age where foveal crowding drops to adult-like levels varying widely from 5 to 12+ years. As crowding restricts key processes like reading, better characterisation of this developmental trajectory is critical. We developed methods optimised to measure crowding in children, whereby adults and typically developing children aged 3-13 years (n=119) judged the orientation of a foveal 'VacMan' target either in isolation or surrounded by 'ghost' flankers. Stimulus sizes and separation were scaled adaptively. In the isolated condition, acuity (measured as gap-size thresholds) dropped rapidly to adult-like levels at 5-6 years. Thresholds rose when flankers were added, demonstrating foveal crowding at all ages. These elevations were highest at 3-4 years and persisted at 5-6 years, dropping to adult-like levels at 7-8 years. A meta-analysis of our thresholds and those from 11 prior studies reveals the same overall developmental trajectory, despite widely varying stimuli and procedures, with some divergent estimates likely driven by measurement confounds such as underestimated adult crowding levels. We further demonstrate that developmental foveal crowding shows the same selectivity for target-flanker similarity as peripheral crowding, consistent with common mechanisms. This prolonged development of crowding reveals a shifting balance in the visual system between the processing of fine detail vs. the 'gist' of the scene. (Comment on this)

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