Cortical and subcortical contributions to state- and strength-based perceptual judgments

peer reviewe

Combining the Mg/Ca of the ostracod Cyprideis torosa with its ontogenic development for reconstructing a 28 kyr temperature record for Lake Banyoles (NE Spain)

Cyprideis torosa is a ubiquitous ostracod found in fresh to hypersaline waters, and commonly in large numbers across the Mediterranean region. Single valves of 51 adult specimens of C. torosa were separated from carapaces that were collected from Lake Banyoles in NE Spain at a depth of 5 m. The Mg/Ca of the valves was compared with known temperatures necessary for successive instar valve calcification, the latter being based on a four-year ecological study of C. torosa collected at Dievengat in northern Belgium by Carlo Heip in 1968–72. Hence, we were able to link the Mg/Ca of fossil valves of C. torosa recovered for a 28 kyr sequence at La Draga, cored on the fringe of Lake Banyoles, with the ontogenic observations of Heip, and reconstruct mean summer temperatures as well as optimal calcification temperature for C. torosa. Principal findings are: (1) the Holocene registered the highest temperatures with also very broad fluctuations; (2) three cold phases are clearly identified at 26.7–23.2, 21.6–20.3 and 16.2–14.3 ka BP; and (3) a prolonged warm phase that lasted about two millennia commenced at 19.5 ka BP and was followed by a progressive temperature decline well over three millennia. Surprisingly the Last Glacial Maximum was not the coldest phase. We finally compare our results with sea-surface temperature (SST) reconstructions from cores from the western Mediterranean Sea. Our record from La Draga clearly matches events recorded in the Alboran Sea that display SST changes obtained from the UK'37 index. The Heinrich 1 and 2 events around 16 and 28 ka BP coincide with significant low temperature excursions at Banyoles, and palynological records in the marine cores which define semi-arid conditions on land match the low temperature record in our core.The coring and analyses were funded by the European Euromaar Project and the Belgian Services fédéraux des affaires scientifiques, techniques et culturelles (SSTC)

Abrupt changes of temperature and water chemistry in the late Pleistocene and early Holocene Black Sea

Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 9 (2008): Q01004, doi:10.1029/2007GC001683.New Mg/Ca, Sr/Ca, and published stable oxygen isotope and 87Sr/86Sr data obtained on ostracods from gravity cores located on the northwestern Black Sea slope were used to infer changes in the Black Sea hydrology and water chemistry for the period between 30 to 8 ka B.P. (calibrated radiocarbon years). The period prior to 16.5 ka B.P. was characterized by stable conditions in all records until a distinct drop in δ 18O values combined with a sharp increase in 87Sr/86Sr occurred between 16.5 and 14.8 ka B.P. This event is attributed to an increased runoff from the northern drainage area of the Black Sea between Heinrich Event 1 and the onset of the Bølling warm period. While the Mg/Ca and Sr/Ca records remained rather unaffected by this inflow; they show an abrupt rise with the onset of the Bølling/Allerød warm period. This rise was caused by calcite precipitation in the surface water, which led to a sudden increase of the Sr/Ca and Mg/Ca ratios of the Black Sea water. The stable oxygen isotopes also start to increase around 15 ka B.P., although in a more gradual manner, due to isotopically enriched meteoric precipitation. While Sr/Ca remains constant during the following interval of the Younger Dryas cold period, a decrease in the Mg/Ca ratio implies that the intermediate water masses of the Black Sea temporarily cooled by 1–2°C during the Younger Dryas. The 87Sr/86Sr values drop after the cessation of the water inflow at 15 ka B.P. to a lower level until the Younger Dryas, where they reach values similar to those observed during the Last Glacial Maximum. This might point to a potential outflow to the Mediterranean Sea via the Sea of Marmara during this period. The inflow of Mediterranean water started around 9.3 ka B.P., which is clearly detectable in the abruptly increasing Mg/Ca, Sr/Ca, and 87Sr/86Sr values. The accompanying increase in the δ 18O record is less pronounced and would fit to an inflow lasting ∼100 a.This research was funded by the DFG grants LA 1273/2-1, LA 1273/2, and WE 992/47-3. RCOM 0517

Effects of cleaning methods upon preservation of stable isotopes and trace elements in shells of Cyprideis torosa (Crustacea, Ostracoda): implications for palaeoenvironmental reconstruction

The trace element (Sr/Ca and Mg/Ca) and stable isotope (δ¹⁸O and δ¹³C) geochemistry of fossil ostracod valves provide valuable information, particularly in lacustrine settings, on palaeo-water composition and palaeotemperature. The removal of sedimentary and organic contamination prior to geochemical analysis is essential to avoid bias of the results. Previous stable isotope and trace element work on ostracod shells has, however, employed different treatments for the removal of contamination beyond simple ‘manual’ cleaning using a paint brush and methanol under a low-power binocular microscope. For isotopic work pre-treatments include chemical oxidation, vacuum roasting and plasma ashing, and for trace element work sonication, chemical oxidation and reductive cleaning. The impact of different treatments on the geochemical composition of the valve calcite has not been evaluated in full, and a universal protocol has not been established. Here, a systematic investigation of the cleaning methods is undertaken using specimens of the ubiquitous euryhaline species, Cyprideis torosa. Cleaning methods are evaluated by undertaking paired analyses on a single carapace (comprising two valves); in modern ostracods, whose valves are assumed to be unaltered, the two valves should have identical geochemical and isotopic composition. Hence, when one valve is subjected to the chosen treatment and the other to simple manual cleaning any difference in composition can confidently be assigned to the treatment method. We show that certain cleaning methods have the potential to cause alteration to the geochemical signal, particularly Mg/Ca and δ¹⁸O, and hence have implications for palaeoenvironmental reconstructions. For trace element determinations we recommend cleaning by sonication and for stable isotope analysis, oxidation by hydrogen peroxide. These methods remove contamination, yet do not significantly alter the geochemical signal

Direct gaze partially overcomes hemispatial neglect and captures spatial attention

Direct gaze has been shown to be a particularly important social cue, being preferentially processed even when unconsciously perceived. Results from several visual search tasks further suggest that direct gaze modulates attention, showing a faster orientation to faces perceived as looking toward us. The present study aimed to analyze putative modulation of spatial attention by eye gaze direction in patients with unilateral neglect. Eight right hemisphere stroke patients with neglect performed a target cancellation paradigm. Patients were instructed to cross all open-eyed pictures amidst closed eyed distractors. Target images were either in direct or averted gaze. Participants performed significantly better when observing targets with direct gaze supporting the hypothesis that this gaze direction captures attention. These findings further suggest that perception of direct gaze is able to diminish the visuospatial impairment seen in neglect patients

Les caractéristiques de la thermoluminescence des quartz différencient le Weichsélien supérieur du Wechsélien inférieur des loess d'Europe centrale

Thèse de doctorat en sciences -- UCL, 199

Quantification of paleotemperature changes during isotopic stage 2 in the La Draga continental sequence (NE Spain) based on the Mg/Ca ratio of freshwater ostracods

Past summer temperature changes are quantified from the La Draga sequence (Banyoles, NE Spain) during Stage 2 (24-10 ka BP), using trace-element content in lacustrine ostracod valves. The high resolution results from this new method are compared to summer paleotemperature reconstructions from sequences from the North Atlantic area, providing a discussion about the magnitudes of some temperature changes. In NE Spain and offshore Portugal, the coldest part of Stage 2 is not documented at the classical date of similar to 18 C-14 ka BP (similar to 21.5 calendar ka BP) but rather occurred later date of ca. 17-15 ka cal. BP In the North Atlantic area, the onset of the Bolling/Allerod interstadials was relatively synchroneous at similar to 14.6 ka cal. BP, although the magnitude of the Bolling/Allerod improvement was more important in the southern area than in the northern area. The duration of the Younger Dryas is discussed. Even if different durations are reported from calendar ages, it seems that the summer temperature cooling of the Younger Dryas was similar around the North Atlantic area. (C) 1996 Elsevier Science Lt