Absence Of Priming Research Articles

Exploiting Mass Spectrometry to Unlock the Mechanism of Nanoparticle-Induced Inflammasome Activation.

Nanoparticles (NPs) elicit sterile inflammation, but the underlying signaling pathways are poorly understood. Here, we report that human monocytes are particularly vulnerable to amorphous silica NPs, as evidenced by single-cell-based analysis of peripheral blood mononuclear cells using cytometry by time-of-flight (CyToF), while silane modification of the NPs mitigated their toxicity. Using human THP-1 cells as a model, we observed cellular internalization of silica NPs by nanoscale secondary ion mass spectrometry (nanoSIMS) and this was confirmed by transmission electron microscopy. Lipid droplet accumulation was also noted in the exposed cells. Furthermore, time-of-flight secondary ion mass spectrometry (ToF-SIMS) revealed specific changes in plasma membrane lipids, including phosphatidylcholine (PC) in silica NP-exposed cells, and subsequent studies suggested that lysophosphatidylcholine (LPC) acts as a cell autonomous signal for inflammasome activation in the absence of priming with a microbial ligand. Moreover, we found that silica NPs elicited NLRP3 inflammasome activation in monocytes, whereas cell death transpired through a non-apoptotic, lipid peroxidation-dependent mechanism. Together, these data further our understanding of the mechanism of sterile inflammation.

Are syntactic representations similar in both reading and listening? Evidence from priming in first and second languages.

It is unclear to what extent natural differences between reading and listening result in differences in the syntactic representations formed in each modality. The present study investigated the occurrence of syntactic priming bidirectionally from reading to listening, and vice versa to examine whether reading and listening share the same syntactic representations in both first language (L1) and second language (L2). Participants performed a lexical decision task in which the experimental words were embedded in sentences with either an ambiguous or a familiar structure. These structures were alternated to produce a priming effect. The modality was manipulated whereby participants (a) first read part of the sentence list and then listened to the rest of the list (reading-listening group), or (b) listened and then read (listening-reading group). In addition, the study involved two within-modality lists in which participants either read or listened to the whole list. The L1 group showed within-modal priming in both listening and reading as well as a cross-modal priming effect. Although L2 speakers showed priming in reading, the effect was absent in listening and weak in the listening-reading condition. The absence of priming in L2 listening was attributed to difficulties in L2 listening rather than to an inability to produce abstract priming.

The effect of seed priming with melatonin on improving the tolerance of Zea mays L. var saccharata to paraquat-induced oxidative stress through photosynthetic systems and enzymatic antioxidant activities

Melatonin is essential in improving plant's biotic as well as abiotic stress tolerance, especially detoxification of herbicides. The purpose of the present research study was studying the probable positive impacts of melatonin on the enhancement of the growth as well as oxidative stress tolerance in sweet corn (Zea mays L. var saccharata). For this purpose, the effects of seven treatments of priming (hydro priming with water (H), melatonin (M) priming with 25, 50, 100, 150 and 200 μM and non-priming (D)) and three doses of paraquat (PQ: 0, 5 and 7.5 L per hectare of recommended dose (5 L per hectare)) on physiological as well as biochemical responses belong to sweet corn were probed according to a completely randomized factorial design involving three replicates. The obtained results provided the indication that applying PQ, particularly at high levels (7.5 L ha−1), in the absence of priming, enhanced the rate of herbicide injury by 49.2%, as compared with 5 L ha−1, by increasing free radical production rate and membrane lipids' peroxidation, in addition to inhibiting the process of photosynthesis. Seed priming with melatonin positively impacted PQ exposed plants, even under the enhanced concentration of PQ (7.5 L ha−1). The maximum protection for the sweet corn plants could be observed at M150. Co-application of melatonin (M150) and PQ herbicide (7.5 L ha−1) reduced H2O2, MDA and herbicide injury by 3.0, 2.1 and 4.6 times, respectively, while it increased SOD, CAT, APX and POD by 2.9, 4.6, 2.4 and 2.0 times, respectively, as compared with D treatments. The obtained results provided the indication that melatonin priming could raise tolerance to oxidative stress which is triggered by PQ in sweet corn with the enhancement of antioxidant enzymes' activity and reduction of herbicide injury.

Effect of priming on germination traits and antioxidant enzymes of pumpkin (Cucurbita pepo L.) seeds with different vigor under drought stress

In order to investigate the effect of priming on aspects of germination of aged pumpkin seeds under drought stress, a factorial experiment was conducted based on a completely randomized design with four replications in the laboratory. Treatments included of aging (control, 85% and 75% of control germination), drought stress (0, -0.75 and -1.5 MPa), and priming (control, hydro, gibberellin, GR24, benzyl aminopurine and spermidine). Results of mean comparison showed that the lowest germination percentage (43.6%), protein (0.82 mg.g-1Fw), radical length (RL, 9.24 mm), plumule length (PL, 1.19 mm), relative water content (RWC, 35.5%), carotenoid (1.253 mg.g-1Fw), catalase (CAT, 7.03 µmol.gmin-1.mgprotein-1), peroxidase (POX, 47.72 µmol.gmin-1.mgprotein-1) and superoxide dismutase activity (SOD, 53.48 mmol.gmin-1.mgprotein-1) were related to drought treatment with an intensity of -1.5 MPa and with 75% aging in the absence of priming. Also, the lowest content of malone dialdehyde (MDA, 3.75 mmol.g-1Fw) and proline (1.573 µg.g-1Fw) were obtained in the absence of drought and aging with priming by spermidine. The highest germination percentage (98.03%) and protein (9.54 mg.g-1Fw) were obtained in gibberellin treatment, RL (15.73 mm) and PL (4.26 mm) in priming with GR24 hormone, RWC (83.64%), carotenoid (6.277 mg.g-1Fw), CAT (40.44 µmol.gmin-1.mg protein-1), POX (95.71 µmol.gmin-1.mgprotein-1) and SOD activity (131.68 µmol.gmin-1.mg protein-1) in priming with spermidine with Non-drought stress and aging conditions. The highest MDA (32.42 mmol.g-1Fw) and proline (0.55 µg.g-1Fw) were observed in drought with an intensity of -1.5 MPa and 75% aging in the absence of priming.

Salt Priming as a Smart Approach to Mitigate Salt Stress in Faba Bean (Vicia faba L.).

The present investigation aims to highlight the role of salt priming in mitigating salt stress on faba bean. In the absence of priming, the results reflected an increase in H2O2 generation and lipid peroxidation in plants subjected to 200 mM salt shock for one week, accompanied by a decline in growth, photosynthetic pigments, and yield. As a defense, the shocked plants showed enhancements in ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR), peroxidase (POX), and superoxide dismutase (SOD) activities. Additionally, the salt shock plants revealed a significant increase in phenolics and proline content, as well as an increase in the expression levels of glutathione (GSH) metabolism-related genes (the L-ascorbate peroxidase (L-APX) gene, the spermidine synthase (SPS) gene, the leucyl aminopeptidase (LAP) gene, the aminopeptidase N (AP-N) gene, and the ribonucleo-side-diphosphate reductase subunit M1 (RDS-M) gene). On the other hand, priming with increasing concentrations of NaCl (50–150 mM) exhibited little significant reduction in some growth- and yield-related traits. However, it maintained a permanent alert of plant defense that enhanced the expression of GSH-related genes, proline accumulation, and antioxidant enzymes, establishing a solid defensive front line ameliorating osmotic and oxidative consequences of salt shock and its injurious effect on growth and yield.

Taking Advantage of Pathogen Diversity and Immune Priming to Minimize Disease Prevalence in Host Mixtures: A Model.

Host mixtures are a promising method for agroecological plant disease control. Plant immunity is key to the success of host mixtures against polymorphic pathogen populations. This immunity results from priming-induced cross-protection, whereby plants able to resist infection by specific pathogen genotypes become more resistant to other pathogen genotypes. Strikingly, this phenomenon was absent from mathematical models aiming at designing host mixtures. We developed a model to specifically explore how priming affects the coexistence of two pathogen genotypes in host mixtures composed of two host genotypes and how it affects disease prevalence. The main effect of priming is to reduce the coexistence region in the parameter space (due to the cross-protection) and to generate a singular mixture of resistant and susceptible hosts corresponding to the maximal reduction disease prevalence (in absence of priming, a resistant pure stand is optimal). The epidemiological advantage of host mixtures over a resistant pure stand thus appears as a direct consequence of immune priming. We also showed that there is indirect cross-protection between host genotypes in a mixture. Moreover, the optimal mix prevents the emergence of a resistance-breaking pathogen genotype. Our results highlight the importance of considering immune priming to design optimal and sustainable host mixtures.

The Effects of Online Status on Self-Other Processing as Revealed by Automatic Imitation

High status individuals have been found to be less attuned to the behavior of others in the social environment. An important question is whether social status in an online setting affects social information processing in a way that resembles the known effects of real-world status on such processing. We examined differences in automatic imitation between Instagram “leaders” and “followers.” In Experiment 1, we found that followers exhibited more automatic imitation than leaders. Experiment 2 sought to establish whether this effect depended on status being salient, or whether it would occur spontaneously in the absence of priming. Results confirmed that thinking about status prior to the task is necessary for producing the pattern of effects in which high status individuals exhibit less automatic imitation than lower status individuals. We discuss our findings in relation to the effects of online status on self-other processing as assessed in the automatic imitation task.

Defining an Upstream VEGF (Vascular Endothelial Growth Factor) Priming Signature for Downstream Factor-Induced Endothelial Cell-Pericyte Tube Network Coassembly.

In this work, we have sought to define growth factor requirements and the signaling basis for different stages of human vascular morphogenesis and maturation. Approach and Results: Using a serum-free model of endothelial cell (EC) tube morphogenesis in 3-dimensional collagen matrices that depends on a 5 growth factor combination, SCF (stem cell factor), IL (interleukin)-3, SDF (stromal-derived factor)-1α, FGF (fibroblast growth factor)-2, and insulin (factors), we demonstrate that VEGF (vascular endothelial growth factor) pretreatment of ECs for 8 hours (ie, VEGF priming) leads to marked increases in the EC response to the factors which includes; EC tip cells, EC tubulogenesis, pericyte recruitment and proliferation, and basement membrane deposition. VEGF priming requires VEGFR2, and the effect of VEGFR2 is selective to the priming response and does not affect factor-dependent tubulogenesis in the absence of priming. Key molecule and signaling requirements for VEGF priming include RhoA, Rock1 (Rho-kinase), PKCα (protein kinase C α), and PKD2 (protein kinase D2). siRNA suppression or pharmacological blockade of these molecules and signaling pathways interfere with the ability of VEGF to act as an upstream primer of downstream factor-dependent EC tube formation as well as pericyte recruitment. VEGF priming was also associated with the formation of actin stress fibers, activation of focal adhesion components, upregulation of the EC factor receptors, c-Kit, IL-3Rα, and CXCR4 (C-X-C chemokine receptor type 4), and upregulation of EC-derived PDGF (platelet-derived growth factor)-BB, PDGF-DD, and HB-EGF (heparin-binding epidermal growth factor) which collectively affect pericyte recruitment and proliferation. Overall, this study defines a signaling signature for a separable upstream VEGF priming step, which can activate ECs to respond to downstream factors that are necessary to form branching tube networks with associated mural cells.

Priming Is Dispensable for NLRP3 Inflammasome Activation in Human Monocytes In Vitro.

Interleukin (IL)-18 and IL-1β are potent pro-inflammatory cytokines that contribute to inflammatory conditions such as rheumatoid arthritis and Alzheimer’s disease. They are produced as inactive precursors that are activated by large macromolecular complexes called inflammasomes upon sensing damage or pathogenic signals. NLRP3 inflammasome activation is regarded to require a priming step that causes NLRP3 and IL-1β gene upregulation, and also NLRP3 post-translational licencing. A subsequent activation step leads to the assembly of the complex and the cleavage of pro-IL-18 and pro-IL-1β by caspase-1 into their mature forms, allowing their release. Here we show that human monocytes, but not monocyte derived macrophages, are able to form canonical NLRP3 inflammasomes in the absence of priming. NLRP3 activator nigericin caused the processing and release of constitutively expressed IL-18 in an unprimed setting. This was mediated by the canonical NLRP3 inflammasome that was dependent on K+ and Cl− efflux and led to ASC oligomerization, caspase-1 and Gasdermin-D (GSDMD) cleavage. IL-18 release was impaired by the NLRP3 inhibitor MCC950 and by the absence of NLRP3, but also by deficiency of GSDMD, suggesting that pyroptosis is the mechanism of release. This work highlights the readiness of the NLRP3 inflammasome to assemble in the absence of priming in human monocytes and hence contribute to the very early stages of the inflammatory response when IL-1β has not yet been produced. It is important to consider the unprimed setting when researching the mechanisms of NLRP3 activation, as to not overshadow the pathways that occur in the absence of priming stimuli, which might only enhance this response.

Priming quantifier scope: Reexamining the evidence against scope inversion

In a study of quantifier-scope priming, Chemla and Bott (2015) found evidence suggesting that, while representations of quantifiers’ relative scope can be primed, a scope inversion operation cannot. We identify a confound in their materials. In Experiment 1, we replicate their finding with this confound intact. In Experiment 2, we remove the confound and find that all priming disappears. This confound demonstrates how structural priming paradigms can be sensitive to many dimensions of similarity, pointing to a need for task-specific controls. We conclude that the prior study does not provide evidence concerning the priming of either relative scope representations or operations. While priming of scope representations has been independently found in other paradigms, the jury is still out on Chemla and Bott’s more novel finding – the absence of priming of a scope inversion operation.

The mental timeline is gradually constructed in childhood.

When reasoning about time, English-speaking adults often invoke a "mental timeline" stretching from left to right. Although the direction of the timeline varies across cultures, the tendency to represent time as a line has been argued to be ubiquitous and primitive. On this hypothesis, we might predict that children also spontaneously invoke a spatial timeline when reasoning about time. However, little is known about how and when the mental timeline develops, or to what extent it is variable and malleable in childhood. Here, we used a sticker placement task to test whether preschoolers and kindergarteners spontaneously map temporal events (breakfast, lunch, and dinner) and deictic time words (yesterday, today, tomorrow) onto lines, and to what degree their representations of time are adult-like. We found that, at age 4, preschoolers were able to arrange temporal items in lines with minimal spatial priming. However, unlike kindergarteners and adults, most preschoolers did not represent time as a line spontaneously, in the absence of priming, and did not prefer left-to-right over right-to-left lines. Furthermore, unlike most adults, children of all ages could be easily primed to adopt an unconventional vertical timeline. Our findings suggest that mappings between time and space in children are initially flexible, and become increasingly automatic and conventionalized in the early school years.

Wednesday's Meeting Really Is on Friday: A Meta-Analysis and Evaluation of Ambiguous Spatiotemporal Language.

Experimental work has shown that spatial experiences influence spatiotemporal metaphor use. In these studies, participants are asked a question that yields different responses depending on the metaphor participants use. It has been claimed that English speakers are equally likely to respond with either variant in the absence of priming. Related studies testing non-spatial experiences demonstrate varied results with a wide range of primes. Here, the effects of eye movement and stimuli presentation modality on comprehension of this question are investigated in different formats. In addition, the results of prior reported controls are re-analyzed in a meta-analysis to verify reliable ambiguity of the test question. Results suggest that English speakers have a baseline preference for the Moving Ego metaphor variant, with a stronger preference in verbal rather than written presentation. The findings have implications both for (re)interpretation of prior studies' results and future study designs.

Initial activation state, stimulation intensity and timing of stimulation interact in producing behavioral effects of TMS

Behavioral effects of transcranial magnetic stimulation (TMS) have been shown to depend on various factors, such as neural activation state, stimulation intensity, and timing of stimulation. Here we examined whether these factors interact, by applying TMS at either sub- or suprathreshold intensity (relative to phosphene threshold, PT) and at different time points during a state-dependent TMS paradigm. The state manipulation involved a behavioral task in which a visual prime (color grating) was followed by a target stimulus which could be either congruent, incongruent or partially congruent with the color and orientation of the prime. In Experiment 1, single-pulse TMS was applied over the early visual cortex (V1/V2) or Vertex (baseline) at the onset of the target stimulus – timing often used in state-dependent TMS studies. With both subthreshold and suprathreshold stimulation, TMS facilitated the detection of incongruent stimuli while not significantly affecting other stimulus types. In Experiment 2, TMS was applied at 100ms after target onset –a time window in which V1/V2 is responding to visual input. Only TMS applied at suprathreshold intensity facilitated the detection of incongruent stimuli, with no effect with subthreshold stimulation. The need for higher stimulation intensity is likely to reflect reduced susceptibility to TMS of neurons responding to visual stimulation. Furthermore, the finding that in Experiment 2 only suprathreshold TMS induced a behavioral facilitation on incongruent targets (whereas facilitations in the absence of priming have been reported with subthreshold TMS) indicates that priming, by reducing neural excitability to incongruent targets, shifts the facilitatory/inhibitory range of TMS effects.

DOM and bacterial growth efficiency in oligotrophic groundwater: absence of priming and co-limitation by organic carbon and phosphorus

DOM and bacterial growth efficiency in oligotrophic groundwater: absence of priming and co-limitation by organic carbon and phosphorus

A meta-analysis of syntactic priming in language production

Abstract We performed an exhaustive meta-analysis of 73 peer-reviewed journal articles on syntactic priming from the seminal Bock (1986) paper through 2013. Extracting the effect size for each experiment and condition, where the effect size is the log odds ratio of the frequency of the primed structure X to the frequency of the unprimed structure Y, we found a robust effect of syntactic priming with an average weighted odds ratio of 1.67 when there is no lexical overlap and 3.26 when there is. That is, a construction X which occurs 50% of the time in the absence of priming would occur 63% if primed without lexical repetition and 77% of the time if primed with lexical repetition. The syntactic priming effect is robust across several different construction types and languages, and we found strong effects of lexical overlap on the size of the priming effect as well as interactions between lexical repetition and temporal lag and between lexical repetition and whether the priming occurred within or across languages. We also analyzed the distribution of p-values across experiments in order to estimate the average statistical power of experiments in our sample and to assess publication bias. Analyzing a subset of experiments in which the primary result of interest is whether a particular structure showed a priming effect, we did not find evidence of major p-hacking and the studies appear to have acceptable statistical power: 82%. However, analyzing a subset of experiments that focus not just on whether syntactic priming exists but on how syntactic priming is moderated by other variables (such as repetition of words in prime and target, the location of the testing room, and the memory of the speaker), we found that such studies are, on average, underpowered with estimated average power of 53%. Using a subset of 45 papers from our sample for which we received raw data, we estimated subject and item variation and give recommendations for appropriate sample size for future syntactic priming studies.

Abstract 14850: Independent Role of the Priming and Triggering of the NLRP3 Inflammasome in the Heart

Introduction: The NLRP3 inflammasome is activated in the heart following ischemic injury, and it promotes cardiac dysfunction. Ischemic injury establishes both a priming signal (leading to transcription of inflammasome components) and a trigger (NLRP3 activation). Whether activation of NLRP3 (in absence of priming) represents the limiting step in the formation of the inflammasome in the heart is unknown. Hypothesis: Both priming and the triggering signals in the heart are necessary for the formation of the inflammasome and ensuing cardiac dysfunction. Methods: We induced systemic expression of a floxed mutant NLRP3-A350V, that is constitutively active, in 10 mice using a tamoxifen-inducible Cre recombinase, to create a condition in which NLRP3 is activated, in absence or presence of priming with low dose LPS (2 mg/kg). Molecular analyses were performed on the heart and the spleen (myeloid organ not dependent on priming) to measure caspase-1 activity using a fluorogenic assay, mRNA expression of the component of the inflammasome (caspase-1 and IL-1β), and echocardiography to measure left ventricular (LV) dimension and systolic function. Results: NLRP3-A350V mutant mice had increased caspase-1 activity in the spleen but not in the heart and had normal LV systolic function (Figure), showing that in NLRP3 activation without priming is insufficient to induce inflammasome formation in the heart nor LV systolic dysfunction. Priming with LPS induced the expression of the inflammasome components in the heart which in absence of NLRP3 activation (control mouse) had no effects on LV systolic function, whereas in the presence of NLRP3 activation (mutant mouse) led to reduced LV systolic function and premature death (Figure). Conclusions: The inflammasome formation in the heart requires a priming signal to be coupled with activation of NLRP3 in order to induce LV dysfunction.

Autoimmune susceptibility imposed by public TCRβ chains (BA2P.125)

Abstract The MHC is the largest genetic risk factor for autoimmunity. It imposes risk in association with a complementary autoantigen specific TCR repertoire. How this occurs is unresolved. Each individual’s TCR repertoire is largely unique, and should therefore not contribute to population-wide disease risk. However, due to biases in TCR recombination, a subset of α and β sequences are shared by most individuals, or public. If these public α or β chains modulate a TCRαβ heterodimer’s likelihood of productively engaging autoantigen-MHC, they could influence autoimmune susceptibility. We demonstrate that disease-associated regulatory and effector TCRβ repertoires in autoimmune encephalomyelitis preferentially incorporate public TCR. Some disease-associated public TCRβ, when transgenically expressed, could further endow T cells with autoantigen specificity in the absence of priming, and demonstrate a subordinate role of the non-shared, endogenous TCRα chains in autoantigen specificity. Further, 2 of 7 Tg public and 0 of 7 Tg private TCRβ isolated from high frequency CNS-infiltrating T cells, provoked spontaneous, early-onset autoimmunity when associated with endogenous TCRα. These findings support a disproportionate contribution of public TCR to immunopathology and implicate them, in association with risk-associated MHC, in disease susceptibility. They further suggest that subsets of public sequences may serve as disease-specific biomarkers or therapeutic targets in autoimmunity.

On One Leg: Trehalose Monoesters Activate Macrophages in a Mincle‐Dependent Manner

The C22 and C26 trehalose monoesters, each containing a single acyl chain, were synthesised in good overall yields and found to activate macrophages in a Mincle-dependent manner. The activities of the monoesters paralleled those of their diester counterparts, and both mono- and diesters could activate the immune response in the absence of priming. This is the first time that trehalose monoesters have been found to activate macrophages, and these studies thus provide an important framework for the rational design of other Mincle agonists.

On the Role of Dendritic Cells Versus Other Cells in Inducing Protective CD8+ T Cell Responses

Dendritic cells (and/or macrophages) are key transporters of antigen from extralymphatic tissue to secondary lymphatic organs. The phagocytized antigen is presented via MHC class II but not via class I, except for infections by intracellular viruses, bacteria, etc. (1–4). Class II-negative cells (e.g., fibroblasts) that get drained to secondary lymphatic organs (including spleen) induce MHC class I restricted CD8 T cells’ cell responses as efficiently as dendritic cells (5–7). So called crosspresentation is at least 105 times less efficient than direct presentation and therefore is practically not achievable under physiological conditions (5–8). If antigen accumulates in the endoplasmic (ER) reticulum because of transport problems, crosspresentation on to MHC class I can be demonstrated. This requires gigantic amounts of antigen accumulation in the ER, but this process has so far been difficult to quantitate in comparison to direct presentation (9). Positive demonstration of crosspresentation in experiments is sometimes based on use of excessive amounts of protein antigen (e.g., OVA) and/or the use of unphysiological (i.e., much too sensitive) detection method, e.g., using very high frequencies of transgenic T cells (e.g., OVA-specific tgCD8+ T cells). In some experiments, virus inactivation is not controlled properly, permitting abortive (but not virus productive) infections that seemingly suggest crosspresentation instead of direct presentation [e.g., Ref. (8)]. An insulin-producing allogeneic cell graft strictly transplanted under the kidney capsule is accepted for more than >200 days by the host, but is promptly rejected if at the time of transplantation, or a few days later, the same cells are also given i.p. or i.v. (10) Once accepted, the allogeneic strictly peripheral cell graft is highly resistant to rejection by a transplanted corresponding allogeneic skin graft (or dendritic cells). This skin graft is rejected in a primary fashion, signaling absence of direct or indirect priming by the original allogeneic cell graft indicating absence of priming by the original cell graft. This prompt skin rejection does not cause rejection of the insulin-producing cell graft (10). A strictly extralymphatic (7) tumor expressing a very strong and defined viral antigen (similar to insulin-producing self-beta-cells or allogeneic islet cells (10–12) can grow successfully to become lethal tumors. This depends on the condition that at the time of syngeneic tumor cell transplantation no (or too few) tumor cells escape/or drain to secondary lymphatic organs (7). This potentially early direct immunization is distinct from the late process of metastasis to secondary lymphatic organs that very often represent immune escape of tumor cells (e.g., MHC mutants, mutations of the T cell epitope, barrier formation by fibrin, coagulation, etc.)

The Persistence of Inattentional Blindness and the Absence of Priming by Natural Scenes

The Persistence of Inattentional Blindness and the Absence of Priming by Natural Scenes