On the Low Energy (< keV) O+ Ion Outflow directly into the Inner Magnetosphere

&lt;p&gt;The development of low energy (&lt; keV) O+ ions in the inner magnetosphere is a crucial issue for various aspects of magnetospheric dynamics: i) Recent studies have suggested that low energy O+ can be locally accelerated to few keV energies inside geosynchronous orbit, and thus can constitute a significant source of the storm-time ring current O+ that could dominate the energy density during storms, ii) Mass loaded densities are important for accurate location of the plasmapause, which, in turn, is necessary for meaningful calculation of the field line resonance radial frequency profiles of ULF hydromagnetic waves in plasmasphere, iii) since O+ is only of ionospheric origin, its outflow from ionosphere into the magnetosphere is a manifestation of fundamental processes concerning energy and mass flow within the coupled Magnetosphere &amp;#8211; Ionosphere system. Although a lot of progress has been made on O+ outflow at high latitudes and its subsequent transport and acceleration within the magnetotail and plasma sheet, the source of low-energy O+ within the inner magnetosphere remains a compelling open question. The Helium Oxygen Proton and Electron (HOPE) mass spectrometer instrument aboard Van Allen Probes, which move in highly elliptical, low inclination orbits with apogee of 5.8 RE, has repeatedly detected field aligned flux enhancements of eV to hundreds of eV O+ ions, which indicate O+ outflow directly into the inner magnetosphere. We systematically investigate, throughout the duration of the Van Allen Probes mission (2012 &amp;#8211; 2019), the occurrence of such events with respect to L and MLT, the dependence of their directionality (bi-directional or unidirectional) and the lowest and highest energies involved on L, MLT and MLAT. We categorize the outflow events with respect to plasmapause location (when its determination is possible) and identify whether there is enhancement of O+ density. This categorization is important because if the outflows occur close to the plasmapause location, and depending on the density enhancement they cause, they could be responsible for the formation of O+ torus, whose source has been under debate for years. Finally, in order to identify the physical processes that lead to the ionospheric outflow, we also examine whether there are dipolarizations and/or enhancements of the field-aligned poynting flux associated with these outflow events.&lt;/p&gt;

Impact of microsaccades on visual shape processing

Sensitivity to subtle changes in the shape of visual objects has been attributed to the existence of global pooling mechanisms that integrate local form information across space. While global pooling is typically demonstrated under steady fixation, other work suggests prolonged fixation can lead to a collapse of global structure. Here we ask whether small ballistic eye movements that naturally occur during periods of fixation affect the global processing of radial frequency (RF) patterns - closed contours created by sinusoidally modulating the radius of a circle. Observers were asked to discriminate the shapes of circular and RF modulated patterns while fixational eye movements were recorded binocularly at 500Hz. Microsaccades were detected using a velocity-based algorithm, allowing trials to be sorted according to the relative timing of stimulus and microsaccade onset. Results revealed clear peri-saccadic changes in shape discrimination thresholds. Performance was impaired when microsaccades occurred close to stimulus onset, but facilitated when they occurred shortly afterwards. In contrast, global integration of shape was unaffected by the timing of microsaccades. These findings suggest that microsaccades alter the discrimination sensitivity to briefly presented shapes but do not disrupt the spatial pooling of local form signals.

Eccentricity Effect of Deformation Detection for Radial Frequency Patterns With Their Centers at Fixation Point

We measured the eccentricity effect of deformation thresholds of circular contours for two types of the radial frequency (RF) patterns with their centers at the fixation point: constant circular contour frequency (CCF) RF patterns and constant RF magnified (retino-cortical scaling) RF patterns. We varied the eccentricity by changing the mean radius of the RF patterns while keeping the centers of the RF patterns at the fixation point. Our peripheral stimulus presentation was distinguished from previous studies which have simply translated RF patterns at different locations in the visual field. Sensitivity for such shape discrimination fell off as the moderate and high CCF patterns were presented on more eccentric sites but did not as the low CCF patterns. However, sensitivity held constant as the magnified RF patterns were presented on more eccentric sites, indicating that the eccentricity effects observed for the high and moderate CCF patterns were neutralized by retinocortical mapping. Notably, sensitivity for the magnified RF patterns with large radii (4°–16°) presented in the peripheral field revealed a similar RF dependence observed for RF patterns with small radii (0.25°–1.0°) presented at the fovea in previous studies.

Numerosity and cumulative surface area are perceived holistically as integral dimensions

Human and non-human animals have the remarkable capacity to rapidly estimate the quantity of objects in the environment. The dominant view of this ability posits an abstract numerosity code, uncontaminated by non-numerical visual information. The present study provides novel evidence in contradiction to this view by demonstrating that number and cumulative surface area are perceived holistically, classically known as integral dimensions. Whether assessed explicitly (Experiment 1) or implicitly (Experiment 2), perceived similarity for dot arrays that varied parametrically in number and cumulative area was best modeled by Euclidean, as opposed to city-block, distance within the stimulus space, comparable to other integral dimensions (brightness/saturation and radial frequency components), but different from separable dimensions (shape/color and brightness/size). Moreover, Euclidean distance remained the best-performing model, even when compared to models that controlled for other magnitude properties (e.g., density) or image similarity. These findings suggest that numerosity perception entails the obligatory processing of non-numerical magnitude.