Controlling the Helical Pitch of Foldamers Through Terminal Functionality: A Solid State Study.

Developing new methods to control the size and shape of the helical structures adopted by foldamers is highly important as the secondary structure displayed by these supramolecular scaffolds often dictates their activity and function. Herein, we report on a systematic study demonstrating that the helical pitch of ortho-azobenzene/2,6-pyridyldicarboamide foldamers can be readily controlled through the nature of the terminal functionality. Remarkably, simply through varying the end group of the foldamer, and without modifying any other structural features of the scaffold, the helical pitch can be over doubled in magnitude (from 3.4 Å to 7.3 Å). Additionally, crystallographic analysis of a library ten foldamers has identified general trends in the influence of a range of terminal functionalities, including carboxylbenzyl (Cbz), diphenylcarbamyl (N(Ph)2), ferrocene (Fc) and tert-butyloxycarbonyl (Boc), in controlling the folding behaviour of these supramolecular scaffolds. These studies could prove useful in the future development of functional foldamers which adopt specific sizes and shapes.

Dual, Photo-Responsive and Redox-Active Supramolecular Foldamers.

We report on dual, light-responsive and redox-active foldamers that demonstrate reversible and robust stimuli-induced behaviour. Herein, UV/Vis, 1H NMR and circular dichroism (CD) spectroscopy and cyclic voltammetry have been used to establish the reversibility and highly robust nature of the light- and redox-driven behaviour of these new foldamers with minimal levels of fatigue observed even upon multiple cyclic treatments with irradiative/non-irradiative and oxidative/reductive conditions. This proof-of-concept work paves the way towards the creation of novel stimuli-responsive foldamers of increasing sophistication capable of demonstrating reversible and robust responses to multiple distinct stimuli.

Automated Assignment of 15N And 13C Enrichment Levels in Doubly-Labeled Proteins.

Uniform enrichment of 15N and 13C in proteins is commonly employed for 2D heteronuclear NMR measurements of the three-dimensional protein structure. Achieving a high degree of enrichment of both elements is important for obtaining high quality data. Uniform labeling of proteins and glycoproteins expressed in higher organisms (yeast or mammalian cell lines) is more challenging than expression in Escherichia coli, a prokaryote that grows on simple, chemically defined media but does not provide appropriate eukaryotic modifications. It is difficult to achieve complete incorporation of both heavy isotopes, and quality control measures are important for quantitating the level of their enrichment. Mass spectrometry measurements of the isotopic distribution of the intact protein or its proteolytic fragments provide the means to assess the enrichment level. A mass accuracy of 1 ppm or better is shown to be required to distinguish the correct combination of 13C and 15N enrichment due to subtle shifts in peak centroids with differences in the underlying, but unresolved, isotopic fine structure. A simple computer program was developed to optimize the fitting of experimental isotope patterns to statistically derived distributions. This method can determine the isotopic abundance from isotope patterns and isotopologue masses in conventional MS data for peptides, intact proteins, and glycans. For this purpose, MATLAB's isotope simulator, isotopicdist, has been modified to permit the variation of 15N and 13C enrichment levels and to perform a two-dimensional grid search of enrichment levels of both isotopes. We also incorporated an alternate isotope simulator, js-emass, into MATLAB for use in the same fitting program. Herein we benchmark this technique on natural abundance ubiquitin and uniformly [15N,13C]-labeled ubiquitin at both the intact and peptide level, outline considerations for data quality and mass accuracy, and report several improvements we have made to the previously reported analysis of the [15N,13C]-enriched human IgG Fc domain, a glycoprotein that has been expressed in Saccharomyces cerevisiae.

Nanoscale ultrastructures increase the visual conspicuousness of signalling traits in obligate cleaner shrimps.

Signal theory predicts organisms should evolve signals that are conspicuous to intended receivers in natural signalling environments. Cleaner shrimps remove ectoparasites from reef fish clients and many signal their intent to clean by whipping long, white antennae. As white is a reliably conspicuous colour in aquatic environments, we hypothesized that selection has acted to increase broad-spectrum antennal reflectance in cleaners. Using scanning electron microscopy, optical models and reflectance measurements, we found that the antennae in three obligate cleaner species from two families (Palaemonidae and Lysmatidae) had thick (∼6 µm) chitinous layers or densely packed high refractive index spheres (300-400 nm diameter), which models show increase reflectance (400-700 nm). Two facultative and non-cleaning species had no visible antennae ultrastructure beyond the chitinous exoskeleton. Antennae reflectance was significantly higher in obligate cleaners than in facultative and non-cleaning species. Our results suggest that some obligate cleaners may have evolved ultrastructures that increase the conspicuousness of their antennae as signals.

iGWAS: Image-based genome-wide association of self-supervised deep phenotyping of retina fundus images.

Existing imaging genetics studies have been mostly limited in scope by using imaging-derived phenotypes defined by human experts. Here, leveraging new breakthroughs in self-supervised deep representation learning, we propose a new approach, image-based genome-wide association study (iGWAS), for identifying genetic factors associated with phenotypes discovered from medical images using contrastive learning. Using retinal fundus photos, our model extracts a 128-dimensional vector representing features of the retina as phenotypes. After training the model on 40,000 images from the EyePACS dataset, we generated phenotypes from 130,329 images of 65,629 British White participants in the UK Biobank. We conducted GWAS on these phenotypes and identified 14 loci with genome-wide significance (p<5×10-8 and intersection of hits from left and right eyes). We also did GWAS on the retina color, the average color of the center region of the retinal fundus photos. The GWAS of retina colors identified 34 loci, 7 are overlapping with GWAS of raw image phenotype. Our results establish the feasibility of this new framework of genomic study based on self-supervised phenotyping of medical images.

Distinct CD16a features on human NK cells observed by flow cytometry correlate with increased ADCC.

Natural killer (NK) cells destroy tissue that have been opsonized with antibodies. Strategies to generate or identify cells with increased potency are expected to enhance NK cell-based immunotherapies. We previously generated NK cells with increased antibody-dependent cell mediated cytotoxicity (ADCC) following treatment with kifunensine, an inhibitor targeting mannosidases early in the N-glycan processing pathway. Kifunensine treatment also increased the antibody-binding affinity of Fc γ receptor IIIa/CD16a. Here we demonstrate that inhibiting NK cell N-glycan processing increased ADCC. We reduced N-glycan processing with the CRIPSR-CAS9 knockdown of MGAT1, another early-stage N-glycan processing enzyme, and showed that these cells likewise increased antibody binding affinity and ADCC. These experiments led to the observation that NK cells with diminished N-glycan processing capability also revealed a clear phenotype in flow cytometry experiments using the B73.1 and 3G8 antibodies binding two distinct CD16a epitopes. We evaluated this "affinity profiling" approach using primary NK cells and identified a distinct shift and differentiated populations by flow cytometry that correlated with increased ADCC.

A comprehensive assessment of selective amino acid 15N-labeling in human embryonic kidney 293 cells for NMR spectroscopy.

A large proportion of human proteins contain post-translational modifications that cannot be synthesized by prokaryotes. Thus, mammalian expression systems are often employed to characterize structure/function relationships using NMR spectroscopy. Here we define the selective isotope labeling of secreted, post-translationally modified proteins using human embryonic kidney (HEK)293 cells. We determined that alpha-[15N]- atoms from 10 amino acids experience minimal metabolic scrambling (C, F, H, K, M, N, R, T, W, Y). Two more interconvert to each other (G, S). Six others experience significant scrambling (A, D, E, I, L, V). We also demonstrate that tuning culture conditions suppressed V and I scrambling. These results define expectations for 15N-labeling in HEK293 cells.

Backgrounds and the evolution of visual signals.

Color signals which mediate behavioral interactions across taxa and contexts are often thought of as color 'patches' - parts of an animal that appear colorful compared to other parts of that animal. Color patches, however, cannot be considered in isolation because how a color is perceived depends on its visual background. This is of special relevance to the function and evolution of signals because backgrounds give rise to a fundamental tradeoff between color signal detectability and discriminability: as its contrast with the background increases, a color patch becomes more detectable, but discriminating variation in that color becomes more difficult. Thus, the signal function of color patches can only be fully understood by considering patch and background together as an integrated whole.

Uniform [13C,15N]-labeled and glycosylated IgG1 Fc expressed in Saccharomyces cerevisiae.

Despite the prevalence and importance of glycoproteins in human biology, methods for isotope labeling suffer significant limitations. Common prokaryotic platforms do not produce mammalian post-translation modifications that are essential to the function of many human glycoproteins, including immunoglobulin G1 (IgG1). Mammalian expression systems require complex media and thus introduce significant costs to achieve uniform labeling. Expression with Pichia is available, though expertise and equipment requirements surpass E. coli culture. We developed a system utilizing Saccharomyces cerevisiae, [13C]-glucose, and [15N]-ammonium chloride with complexity comparable to E. coli. Here we report two vectors for expressing the crystallizable fragment (Fc) of IgG1 for secretion into the culture medium, utilizing the ADH2 or DDI2 promoters. We also report a strategy to optimize the expression yield using orthogonal Taguchi arrays. Lastly, we developed two different media formulations, a standard medium which provides 86-92% 15N and 30% 13C incorporation into the polypeptide, or a rich medium which provides 98% 15N and 95% 13C incorporation as determined by mass spectrometry. This advance represents an expression and optimization strategy accessible to experimenters with the capability to grow and produce proteins for NMR-based experiments using E. coli.

Prevalence of Heart Failure With Preserved Ejection Fraction in Patients Undergoing Atrial Fibrillation Ablation Based on Resting and Post-Tachycardia Pacing Left Atrial Pressure.

Atrial fibrillation (AF) and heart failure with preserved ejection fraction (HFpEF) are frequent co-morbid conditions. In patients with symptomatic AF and preserved left ventricular ejection fraction the clinical diagnosis of HFpEF may be difficult, as history, examination, and echocardiography are not sensitive or specific. This study sought to assess the prevalence of HFpEF in patients undergoing AF ablation utilizing resting and post-tachycardia pacing left atrial pressure (LAP) measurements. This retrospective cohort study consisted of consecutive patients with symptomatic AF and preserved left ventricular ejection fraction who had invasive hemodynamic assessment (IHA) of LAP under resting and post-tachycardia pacing conditions while undergoing AF ablation from 2020 to 2022 at a tertiary care academic medical center. Elevated LAP was defined as ≥15 mm Hg at rest and ≥15 mm Hg post-tachycardia pacing. Patients were stratified into 3 groups: (1) normal resting and post-tachycardia pacing LAP (control group), (2) elevated resting LAP (apparent HFpEF), (3) normal resting but elevated post-tachycardia pacing LAP (occult HFpEF). A total of 78 patients were included with age 64.6 ± 9.1 years, 28 (36%) female, body mass index 33.3 ± 6.5 kg/m2, 5 (6%) paroxysmal and 73 (94%) persistent AF, and CHA2DS2-VASc 3.0 ± 1.5. IHA categorized 31 (40%), 32 (41%), and 15 patients (19%) into groups 1, 2, and 3 respectively. Notably, while only 9 patients (12%) were diagnosed with HFpEF based on clinical evaluation, 47 patients (60%) were diagnosed by IHA. IHA in patients undergoing AF ablation suggests a high prevalence of clinically undiagnosed HFpEF through a novel methodology measuring resting and post-tachycardia pacing LAP.

Successful Medical and Surgical Management of Recalcitrant Acanthamoeba Keratitis, Scleritis, and Culture-Positive Scleral Abscess.

PURPOSE: The purpose of this study was to describe the management of a case of recurrent scleritis and Acanthamoeba -positive scleral abscess in a patient after the use of miltefosine for recalcitrant Acanthamoeba keratitis. METHODS: This is a case study. RESULTS: In this study, we report a case of advanced Acanthamoeba keratitis with resultant corneal perforation with therapeutic keratoplasty and associated scleritis who later developed a scleral abscess after treatment with oral miltefosine. The scleral abscess was positive for Acanthamoeba cysts and trophozoites, and after treatment for an additional several months, the patient had complete resolution of her disease. CONCLUSIONS: Acanthamoeba scleritis is a rare complication associated with Acanthamoeba keratitis. It has traditionally been treated as an immune reaction and associated inflammation, especially with the use of miltefosine. Management can require a multitude of different approaches, and in this situation, it has been demonstrated that scleritis can be infectious and that conservative management can be effective.

Mettl14-mediated m6A modification ensures the cell-cycle progression of late-born retinal progenitor cells.

Neural progenitor cells lengthen their cell cycle to prime themselves for differentiation as development proceeds. It is currently not clear how they counter this lengthening and avoid being halted in the cell cycle. We show that N6-methyladenosine (m6A) methylation of cell-cycle-related mRNAs ensures the proper cell-cycle progression of late-born retinal progenitor cells (RPCs), which are born toward the end of retinogenesis and have long cell-cycle length. Conditional deletion of Mettl14, which is required for depositing m6A, led to delayed cell-cycle exit of late-born RPCs but has no effect on retinal development prior to birth. m6A sequencing and single-cell transcriptomics revealed that mRNAs involved in elongating the cell cycle were highly enriched for m6A, which could target them for degradation and guarantee proper cell-cycle progression. In addition, we identified Zfp292 as a target of m6A and potent inhibitor of RPC cell-cycle progression.

Bilateral punctate keratitis and hurricane keratopathy following apremilast therapy.

Purpose: To report a unique case of bilateral punctate keratitis consistent with hurricane keratopathy during apremilast therapy. Observations: A 49-year-old female presented with severe, painful, bilateral, punctate keratitis following five months of apremilast therapy. The past ocular history was noncontributory. The past medical history included psoriasis refractory to topical corticosteroids. The patient subsequently received systemic apremilast therapy and noted improvement in her psoriatic rash. Five months later the patient presented to an outside eye care provider complaining of three weeks of progressive photophobia associated with pain and redness in both eyes. On examination, the patient had decreased visual acuity with diffuse conjunctival injection and punctate epithelial erosions in a whorl-like pattern in both eyes. The remainder of the ophthalmic exam was unremarkable. The patient was started on topical moxifloxacin drops, erythromycin ointment, and preservative free artificial tears, but did not improve. Apremilast was then discontinued and topical prednisolone was added once per day. Ten weeks after discontinuation of apremilast and topical steroid therapy, the patient had recovered normal vision with an intact and normal corneal epithelium. Conclusions and Importance: This is the first case report of cornea epithelial keratitis resembling hurricane keratopathy associated with apremilast treatment and should be recognized as a possible side effect of therapy with this class of drug.

Electrostatic polarization fields trigger glioblastoma stem cell differentiation.

Over the last few years it has been understood that the interface between living cells and the underlying materials can be a powerful tool to manipulate cell functions. In this study, we explore the hypothesis that the electrical cell/material interface can regulate the differentiation of cancer stem-like cells (CSCs). Electrospun polymer fibres, either polyamide 66 or poly(lactic acid), with embedded graphene nanoplatelets (GnPs), have been fabricated as CSC scaffolds, providing both the 3D microenvironment and a suitable electrical environment favorable for CSCs adhesion, growth and differentiation. We have investigated the impact of these scaffolds on the morphological, immunostaining and electrophysiological properties of CSCs extracted from human glioblastoma multiform (GBM) tumor cell line. Our data provide evidence in favor of the ability of GnP-incorporating scaffolds to promote CSC differentiation to the glial phenotype. Numerical simulations support the hypothesis that the electrical interface promotes the hyperpolarization of the cell membrane potential, thus triggering the CSC differentiation. We propose that the electrical cell/material interface can regulate endogenous bioelectrical cues, through the membrane potential manipulation, resulting in the differentiation of CSCs. Material-induced differentiation of stem cells and particularly of CSCs, can open new horizons in tissue engineering and new approaches to cancer treatment, especially GBM.

Using implementation science frameworks to translate and adapt a pregnancy app for an emerging Latino community.

BACKGROUND: Digital mobile health (mHealth) applications are a popular form of prenatal education and care delivery in the U.S.; yet there are few Spanish language options for native speakers. Furthermore, existing applications do not consider cultural differences and disparities in healthcare access, including those specific to emerging Latino communities. OBJECTIVE: To adapt and translate an English-language pregnancy mobile health app to meet the language and cultural needs of Spanish-speaking Latino immigrants living in the United States. METHODS: We use a multi-step process, grounded in implementation science frameworks, to adapt and translate the contents of an existing pregnancy app. Interviews with stakeholders (n = 12) who advocate for the needs of pregnant individuals in an emerging Latino community were used to identify domains of possible disparities in access to prenatal care. We then conducted semi-structured interviews with peripartum Spanish-speaking Latino users (n = 14) to understand their perspectives within those domains. We identified a list of topics to create educational material for the modified app and implemented a systematic translation approach to ensure that the new version was acceptable for immigrants from different countries in Latin America. RESULTS: The interviews with stakeholders revealed seven critical domains that need to be addressed in an adapted prenatal app: language and communication, financial concerns, social support, immigration status, cultural differences, healthcare navigation, and connection to population-specific community resources that offer Spanish language services. The interviews with peripartum Spanish-speaking Latino women informed how the existing content in the app could be adjusted or built upon to address these issues, including providing information on accessing care offered in their native language and community support. Finally, we used a systematic approach to translate the existing application and create new content. CONCLUSION: This work illustrates a process to adapt an mHealth pregnancy app to the needs of an emerging Latino community, by incorporating culturally sensitive Spanish language content while focusing on addressing existing health disparities.

Risk heatmaps as visual displays: Opening movie studios after the COVID-19 shutdown.

Upon shutting down operations in early 2020 due to the COVID-19 pandemic, the movie industry assembled teams of experts to help develop guidelines for returning to operation. It resulted in a joint report, The Safe Way Forward, which was created in consultation with union members and provided the basis for negotiations with the studios. A centerpiece of the report was a set of heatmaps displaying SARS-CoV-2 risks for a shoot, as a function of testing rate, community infection prevalence, community transmission rate (R0), and risk measure (either expected number of cases or probability of at least one case). We develop and demonstrate a methodology for evaluating such complex displays, in terms of how well they inform potential users, in this case, workers deciding whether the risks of a shoot are acceptable. We ask whether individuals making hypothetical return-to-work decisions can (a) read display entries, (b) compare display entries, and (c) make inferences based on display entries. Generally speaking, respondents recruited through the Amazon MTurk platform could interpret the display information accurately and make coherent decisions, suggesting that heatmaps can communicate complex risks to lay audiences. Although these heatmaps were created for practical, rather than theoretical, purposes, these results provide partial support for theoretical accounts of visual information processing and identify challenges in applying them to complex settings.

Metabolic15N labeling of the N-glycosylated immunoglobulin G1 Fc with an engineered Saccharomyces cerevisiae strain.

The predominant protein expression host for NMR spectroscopy is Escherichia coli, however, it does not synthesize appropriate post-translation modifications required for mammalian protein function and is not ideal for expressing naturally secreted proteins that occupy an oxidative environment. Mammalian expression platforms can address these limitations; however, these are not amenable to cost-effective uniform 15 N labeling resulting from highly complex growth media requirements. Yeast expression platforms combine the simplicity of bacterial expression with the capabilities of mammalian platforms, however yeasts require optimization prior to isotope labeling. Yeast expression will benefit from methods to boost protein expression levels and developing labeling conditions to facilitate growth and high isotope incorporation within the target protein. In this work, we describe a novel platform based on the yeast Saccharomyces cerevisiae that simultaneously expresses the Kar2p chaperone and protein disulfide isomerase in the ER to facilitate the expression of secreted proteins. Furthermore, we developed a growth medium for uniform 15 N labeling. We recovered 2.2 mg/L of uniformly 15 N-labeled human immunoglobulin (Ig)G1 Fc domain with 90.6% 15 N labeling. NMR spectroscopy revealed a high degree of similarity between the yeast and mammalian-expressed IgG1 Fc domains. Furthermore, we were able to map the binding interaction between IgG1 Fc and the Z domain through chemical shift perturbations. This platform represents a novel cost-effective strategy for 15 N-labeled immunoglobulin fragments.

The Severity of the Co-infection of Mycoplasma pneumoniae in COVID-19 Patients.

Background and objective The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel coronavirus that causes coronavirus disease 2019 (COVID-19) infection, with symptoms ranging from mild upper respiratory illness to multisystem organ failure, and even death. Since its discovery in December 2019, the SARS-CoV-2 virus has led to a global pandemic, rapidly spreading to countries around the world, with millions of reported deaths to date. As researchers around the world continue to analyze and interpret the data gathered regarding the novel virus, it is evident that its co-infection with various bacterial pathogens is associated with a worse overall prognosis. One such bacterial pathogen, Mycoplasma pneumoniae (M. pneumoniae), has been associated with an increase in inpatient mortality, length of hospital stay, and need for mechanical ventilation. The aim of this study was to evaluate the characteristics and outcomes of patients co-infected with SARS-CoV-2 and M. pneumoniae. We sought to determine if this co-infection led to increased incidence of ventilatory support, intensive care unit (ICU) stay, and mortality. Materials and Methods A multi-center retrospective study was conducted involving patients aged 18 years and older. We compared the incidence of in-hospital mortality, ICU stay, and mechanical ventilation support between COVID-19-positive patients with and without M. pneumoniae co-infection. Based on the collected data, a binary logistic regression model was implemented to assess the correlation between mortality and ventilatory support, while linear regression was used to study the length of stay (LOS) independent variable. Results A total of 1,208 patients with a positive SARS-CoV-2 test were identified. Among them, 604 (50%) had an M. pneumoniae co-infection. LOS (95% CI for the coefficient estimate [0.86, 1.05], p<0.001), need for mechanical ventilation (95% CI for the odds ratio [2.60, 6.02], p<0.001), and inpatient mortality (95% CI for the odds ratio [1.43, 2.97], p<0.001) among those co-infected were significantly higher compared to COVID-19 patients without concomitant M. pneumoniae infection. Conclusion COVID-19 with a concomitant M. pneumoniae infection was found to have worse outcomes and overall prognosis when compared to individuals with independent disease states. Based on retrospective data gathered from a large multicenter database, the rates of mortality, ventilatory support, and length of hospital stay were significantly worse in patients with a co-infection of SARS-CoV-2 and M. pneumoniae.

The Clinical Utility of the MOCA in iNPH Assessment.

Objectives: We sought to estimate reliable change thresholds for the Montreal Cognitive Assessment (MoCA) for older adults with suspected Idiopathic Normal Pressure Hydrocephalus (iNPH). Furthermore, we aimed to determine the likelihood that shunted patients will demonstrate significant improvement on the MoCA, and to identify possible predictors of this improvement. Methods: Patients (N = 224) presenting with symptoms of iNPH were given a MoCA assessment at their first clinic visit, and also before and after tap test (TT) or extended lumbar drainage (ELD). Patients who were determined to be good candidates for shunts (N = 71, 31.7%) took another MoCA assessment following shunt insertion. Reliable change thresholds for MoCA were derived using baseline visit to pre-TT/ELD assessment using nine different methodologies. Baseline characteristics of patients whose post-shunt MoCA did and did not exceed the reliable change threshold were compared. Results: All nine of reliable change methods indicated that a 5-point increase in MoCA would be reliable for patients with a baseline MoCA from 16 to 22 (38.4% of patients). Furthermore, a majority of reliable change methods indicated that a 5-point increase in MoCA would be reliable for patients with a baseline MoCA from 14 to 25. Reliable change thresholds varied across methods from 4 to 7 points for patients outside of this range. 10.1% had at least a 5-point increase from baseline to post-TT/ELD. Compared to patients who did not receive a shunt, patients who received a shunt did not have lower average MoCA at baseline (p = 0.88) or have better improvement in MoCA scores after the tap test (p = 0.17). Among shunted patients, 23.4% improved by at least 5 points on the MoCA from baseline to post-shunt. Time since onset of memory problems and post-TT/ELD gait function were the only clinical factors significantly associated with having a reliable change in MoCA after shunt insertion (p = 0.019; p = 0.03, respectively). Conclusions: In patients with iNPH, clinicians could consider using a threshold of 5 points for determining whether iNPH-symptomatic patients have experienced cognitive benefits from cerebrospinal fluid drainage at an individual level. However, a reliable change cannot be detected for patients with a baseline MoCA of 26 or greater, necessitating a different cognitive assessment tool for these patients.

Influence of visual background on discrimination of signal-relevant colours in zebra finches (Taeniopygia guttata).

Colour signals of many animals are surrounded by a high-contrast achromatic background, but little is known about the possible function of this arrangement. For both humans and non-human animals, the background colour surrounding a colour stimulus affects the perception of that stimulus, an effect that can influence detection and discrimination of colour signals. Specifically, high colour contrast between the background and two given colour stimuli makes discrimination more difficult. However, it remains unclear how achromatic background contrast affects signal discrimination in non-human animals. Here, we test whether achromatic contrast between signal-relevant colours and an achromatic background affects the ability of zebra finches to discriminate between those colours. Using an odd-one-out paradigm and generalized linear mixed models, we found that higher achromatic contrast with the background, whether positive or negative, decreases the ability of zebra finches to discriminate between target and non-target stimuli. This effect is particularly strong when colour distances are small (less than 4 ΔS) and Michelson achromatic contrast with the background is high (greater than 0.5). We suggest that researchers should consider focal colour patches and their backgrounds as collectively comprising a signal, rather than focusing on solely the focal colour patch itself.