Parallel Advantage: Further Evidence for Bottom-up Saliency Computation by Human Primary Visual Cortex

Finding a target among uniformly oriented non-targets is typically faster when this target is perpendicular, rather than parallel, to the non-targets. The V1 Saliency Hypothesis (V1SH), that neurons in the primary visual cortex (V1) signal saliency for exogenous attentional attraction, predicts exactly the opposite in a special case: each target or non-target comprises two equally sized disks displaced from each other by 1.2 disk diameters center-to-center along a line defining its orientation. A target has two white or two black disks. Each non-target has one white disk and one black disk, and thus, unlike the target, activates V1 neurons less when its orientation is parallel rather than perpendicular to the neurons’ preferred orientations. When the target is parallel, rather than perpendicular, to the uniformly oriented non-targets, the target’s evoked V1 response escapes V1’s iso-orientation surround suppression, making the target more salient. I present behavioral observations confirming this prediction.

Pectis loiolae (Asteraceae: Tageteae): New Species Registered in a Natural Monument at an Archaeological Site in Northeast Brazil

Abstract— Pectis comprises about 90 species distributed in North America, Mexico, the Caribbean, South and Central America, and the Pacific Islands. In Brazil, the genus is represented by 14 species that mainly occur in the Cerrado and five species that are endemic to the Caatinga domain. During field expeditions to the Lajedo de Soledade archaeological site, in the state of Rio Grande do Norte, Brazil, a new species of Pectis was found on rocky outcrops (lajedos) in the Caatinga. Pectis loiolae sp. nov. grows on limestone rocks in sedimentary substrate and is recognized by its prostrate habit with ascending branches terminating in a solitary capitulum, apex of the involucral bracts rounded, apiculate, and green becoming vinaceous in the apical 1/3, corolla of ray flowers (5) with abaxial surface vinaceous and adaxial white, disk flowers 8‐10, and presence of stylopodium in the disk flowers. A morphological description, illustration, distribution map, habitat, conservation status, and a key for all Brazilian Pectis species are presented herein.

Attention cueing in rivalry: insights from pupillometry

We used pupillometry to evaluate the effects of attention cueing on perceptual bi-stability, as reported by adult human observers. Perceptual alternations and pupil diameter were measured during two forms of rivalry, generated by presenting a white and a black disk to the two eyes (binocular rivalry) or splitting the disks between eyes (interocular grouping rivalry). In line with previous studies, we found that subtle pupil size oscillations (about 0.05 mm) tracked alternations between exclusive dominance phases of the black or white disk. These oscillations were larger for perceptually stronger stimuli: presented to the dominant eye or with physically higher luminance contrast. However, cueing of endogenous attention to one of the rivaling percepts did not affect pupil oscillations during exclusive dominance phases. This was in spite of the reliable effects of endogenous attention on perceptual dominance, which shifted in favor of the cued percept by about 10%. The results were comparable for binocular and interocular grouping rivalry. Cueing only had a marginal modulatory effect on pupil size during mixed percepts in binocular rivalry. This may suggest that, rather than acting by modulating perceptual strength, endogenous attention primarily acts during periods of unresolved competition, which is compatible with attention being automatically directed to the rivaling stimuli during periods of exclusive dominance and thereby sustaining perceptual alternations.

Increasing turbidity in the North Sea during the 20^th century due to changing wave climate

Data on Secchi disk-depth (the depth at which a standard white disk lowered into the water just becomes invisible to a surface observer) show that water clarity in the North Sea declined during the 20th century, with likely consequences for marine primary production. However, the causes of this trend remain unknown. Here we analyze the hypothesis that changes in the North Sea's wave climate were largely responsible, by increasing the concentrations of suspended particulate matter (SPM) in the water column through re-suspension of seabed sediments. First, we analyzed the broad-scale statistical relationships between SPM and bed shear stress due to waves and tides. We used hindcasts of wave and current data to construct a space-time dataset of bed shear stress between 1997 and 2017 across the northwest European Continental Shelf, and compared the results with satellite-derived SPM concentrations. Bed shear stress was found to drive most of the inter-annual variation in SPM in the hydrographically mixed waters of the central and southern North Sea. We then used a long-term wave reanalysis to construct a time series of bed shear stress from 1900 to 2010. This shows that bed shear stress increased significantly across the shelf over this period, explaining more than half of the observed decline in water clarity over this period. Wave-driven processes are rarely included in projections of climate change impacts on marine ecosystems, but our analysis indicates that this should be reconsidered for shelf sea regions.

Secchi depth in the Oslofjord–Skagerrak area: theory, experiments and relationships to other quantities

The Secchi depth and its relationships to other properties of the sea water in the Oslofjord–Skagerrak area have been investigated. White and black disks of different sizes have been applied, and the Secchi depth has been observed with the naked eye, through colour filters and with a water telescope. Spectral luminances and illuminances have been calculated from recordings of radiance and irradiance, and attenuation coefficients have been determined. A theoretical expression for the Secchi depth based on luminances has been tested against field observations, and it is found that the field results for the product of Secchi depth and attenuation coefficients are on average only 4% less than the predicted value for the white disk. For the Secchi depths observed through colour filters or for the black disk, the average field results are more than 30% smaller than the theoretical estimates. The reduction in the disk diameter from 30 to 10 cm should theoretically reduce the Secchi depths by 13–22%, while the field observations show an average reduction of 10–20%. Similarly we find from theory that the removal of sun glitter should increase the Secchi depth by 12%, while the observed increase is 14% on average for the white disk. Our overall conclusion is that the theoretical expression works well for the white disk, but less so for the colour filter observations and the black disk. Statistical relationships between Secchi depths and attenuation coefficients have been determined, and it is found that the root-mean-square errors relative to the mean value are smaller for the beam attenuation coefficients (12–24%, white disk) than for the vertical attenuation coefficients (16–65%, white disk). The depth of the 1% level of surface quanta irradiance (PAR) can be estimated with a relative root-mean-square error of 23% from observations of the white Secchi depth. Similar estimates of chlorophyll a and total suspended material will have rms errors in the range 40–90%. Our conclusion becomes that the Secchi depth observation is a very useful tool for checking the value and order of magnitude of other related quantities in the Oslofjord–Skagerrak area.

Relationship between Respiratory Load Perception and Perception of Nonrespiratory Sensory Modalities in Subjects with Life-Threatening Asthma

Subjects with life-threatening asthma (LTA) have reported decreased sensitivity to inspiratory resistive (R) loads. It is unknown if decreased sensitivity is specific for inspiratoryRloads, other types of respiratory loads, or a general deficit affecting sensory modalities. This study hypothesized that impairment is specific to respiratory stimuli. This study tested perceptual sensitivity of LTA, asthmatic (A), and nonasthmatic (NA) subjects to 4 sensory modalities: respiratory, somatosensory, auditory, visual. Perceptual sensitivity was measured with magnitude estimation (ME): respiratory loads ME, determined using inspiratoryRand pressure threshold (PT) loads; somatosensory ME, determined using weight ranges of 2–20 kg; auditory ME, determined using graded magnitudes of 1 kHz tones delivered for 3 seconds bilaterally; visual ME, determined using gray-to-white disk intensity gradations on black background. ME for inspiratoryRloads lessened for LTA over A and NA subjects. There was no significant difference between the 3 groups in ME for PT inspiratory loads, weight, sound, and visual trials. These results demonstrate that LTA subjects are poor perceivers of inspiratoryRloads. This deficit in respiratory perception is specific to inspiratoryRloads and is not due to perceptual deficits in other types of inspiratory loads, somatosensory, auditory, or visual sensory modalities.

Anomalous Induction of Brightness and Surface Qualities: A New Illusion Due to Radial Lines and Chromatic Rings

When a chromatic (eg light-blue) annulus surrounds the central gap of an Ehrenstein figure so as to connect the inner ends of the radial lines, a striking new lightness effect emerges: the central white disk has both a self-luminous quality (brighter than in the regular Ehrenstein figure) and a surface quality (dense, paste-like). Self-luminous and surface qualities do not ordinarily appear co-extensively: hence, the brightness induction is called anomalous. In experiment 1, subjects separately scaled self-luminous and surface properties, and in experiment 2, brightness was nulled by physically darkening the central gap. Experiments 3 and 4 were designed to evaluate the importance of chromatic versus achromatic properties of the annulus; other aspects of the annulus (width or the inclusion of a thin black ring inside or outside the chromatic annulus) were tested in experiments 5–7. In experiments 8–12, subjects rated the brightness of modified Ehrenstein figures varying the radial lines (number, length, width, contrast, arrangement). Variation of these parameters generally affected brightness enhancement in the Ehrenstein figure and anomalous brightness induction in a similar manner, but was stronger for the latter effect. On the basis of these results, anomalous brightness induction is attributed to a surface induction process triggered by an interaction between illusory brightness enhancement (due to the radial lines) and border ownership (due to the blue annulus).