Droplet motion driven by humidity gradients during evaporation and condensation.

The motion of droplets on solid surfaces in response to an external gradient is a fundamental problem with a broad range of applications, including water harvesting, heat exchange, mixing and printing. Here we study the motion of droplets driven by a humidity gradient, i.e. a variation in concentration of their own vapour in the surrounding gas phase. Using lattice-Boltzmann simulations of a diffuse-interface hydrodynamic model to account for the liquid and gas phases, we demonstrate that the droplet migrates towards the region of higher vapour concentration. This effect holds in situations where the ambient gradient drives either the evaporation or the condensation of the droplet, or both simultaneously. We identify two main mechanisms responsible for the observed motion: a difference in surface wettability, which we measure in terms of the Young stress, and a variation in surface tension, which drives a Marangoni flow. Our results are relevant in advancing our knowledge of the interplay between gas and liquid phases out of thermodynamic equilibrium, as well as for applications involving the control of droplet motion.

Tuning contact line dynamics on slippery silicone oil grafted surfaces for sessile droplet evaporation.

Controlling the dynamics of droplet evaporation is critical to numerous fundamental and industrial applications. The three main modes of evaporation so far reported on smooth surfaces are the constant contact radius (CCR), constant contact angle (CCA), and mixed mode. Previously reported methods for controlling droplet evaporation include chemical or physical modifications of the surfaces via surface coating. These often require complex multiple stage processing, which eventually enables similar droplet-surface interactions. By leveraging the change in the physicochemical properties of the outermost surface by different silicone oil grafting fabrication parameters, the evaporation dynamics and the duration of the different evaporation modes can be controlled. After grafting one layer of oil, the intrinsic hydrophilic silicon surface (contact angle (CA) ≈ 60°) is transformed into a hydrophobic surface (CA ≈ 108°) with low contact angle hysteresis (CAH). The CAH can be tuned between 1° and 20° depending on the fabrication parameters such as oil viscosity, volume, deposition method as well as the number of layers, which in turn control the duration of the different evaporation modes. In addition, the occurrence and strength of stick-slip behaviour during evaporation can be additionally controlled by the silicone oil grafting procedure adopted. These findings provide guidelines for controlling the droplet-surface interactions by either minimizing or maximising contact line initial pinning, stick-slip and/or constant contact angle modes of evaporation. We conclude that the simple and scalable silicone oil grafted coatings reported here provide similar functionalities to slippery liquid infused porous surfaces (SLIPSs), quasi-liquid surfaces (QLS), and/or slippery omniphobic covalently attached liquid (SOCAL) surfaces, by empowering pinning-free surfaces, and have great potential for use in self-cleaning surfaces or uniform particle deposition.

Droplet Self-Propulsion on Slippery Liquid-Infused Surfaces with Dual-Lubricant Wedge-Shaped Wettability Patterns.

Young's equation is fundamental to the concept of the wettability of a solid surface. It defines the contact angle for a droplet on a solid surface through a local equilibrium at the three-phase contact line. Recently, the concept of a liquid Young's law contact angle has been developed to describe the wettability of slippery liquid-infused porous surfaces (SLIPS) by droplets of an immiscible liquid. In this work, we present a new method to fabricate biphilic SLIP surfaces and show how the wettability of the composite SLIPS can be exploited with a macroscopic wedge-shaped pattern of two distinct lubricant liquids. In particular, we report the development of composite liquid surfaces on silicon substrates based on lithographically patterning a Teflon AF1600 coating and a superhydrophobic coating (Glaco Mirror Coat Zero), where the latter selectively dewets from the former. This creates a patterned base surface with preferential wetting to matched liquids: the fluoropolymer PTFE with a perfluorinated oil Krytox and the hydrophobic silica-based GLACO with olive oil (or other mineral oils or silicone oil). This allows us to successively imbibe our patterned solid substrates with two distinct oils and produce a composite liquid lubricant surface with the oils segregated as thin films into separate domains defined by the patterning. We illustrate that macroscopic wedge-shaped patterned SLIP surfaces enable low-friction droplet self-propulsion. Finally, we formulate an analytical model that captures the dependence of the droplet motion as a function of the wettability of the two liquid lubricant domains and the opening angle of the wedge. This allows us to derive scaling relationships between various physical and geometrical parameters. This work introduces a new approach to creating patterned liquid lubricant surfaces, demonstrates long-distance droplet self-propulsion on such surfaces, and sheds light on the interactions between liquid droplets and liquid surfaces.

Validity of forensic cartridge-case comparisons.

This article presents key findings from a research project that evaluated the validity and probative value of cartridge-case comparisons under field-based conditions. Decisions provided by 228 trained firearm examiners across the US showed that forensic cartridge-case comparison is characterized by low error rates. However, inconclusive decisions constituted over one-fifth of all decisions rendered, complicating evaluation of the technique's ability to yield unambiguously correct decisions. Specifically, restricting evaluation to only the conclusive decisions of identification and elimination yielded true-positive and true-negative rates exceeding 99%, but incorporating inconclusives caused these values to drop to 93.4% and 63.5%, respectively. The asymmetric effect on the two rates occurred because inconclusive decisions were rendered six times more frequently for different-source than same-source comparisons. Considering probative value, which is a decision's usefulness for determining a comparison's ground-truth state, conclusive decisions predicted their corresponding ground-truth states with near perfection. Likelihood ratios (LRs) further showed that conclusive decisions greatly increase the odds of a comparison's ground-truth state matching the ground-truth state asserted by the decision. Inconclusive decisions also possessed probative value, predicting different-source status and having a LR indicating that they increase the odds of different-source status. The study also manipulated comparison difficulty by using two firearm models that produce dissimilar cartridge-case markings. The model chosen for being more difficult received more inconclusive decisions for same-source comparisons, resulting in a lower true-positive rate compared to the less difficult model. Relatedly, inconclusive decisions for the less difficult model exhibited more probative value, being more strongly predictive of different-source status.

Suppression of crystallization in saline drop evaporation on pinning-free surfaces.

For sessile droplets of pure liquid on a surface, evaporation depends on surface wettability, the surrounding environment, contact angle hysteresis, and surface roughness. For non-pure liquids, the evaporation characteristics are further complicated by the constituents and impurities within the droplet. For saline solutions, this complication takes the form of a modified partial vapor pressure/water activity caused by the increasing salt concentration as the aqueous solvent evaporates. It is generally thought that droplets on surfaces will crystallize when the saturation concentration is reached, i.e., 26.3% for NaCl in water. This crystallization is initiated by contact with the surface and is thus due to surface roughness and heterogeneities. Recently, smooth, low contact angle hysteresis surfaces have been created by molecular grafting of polymer chains. In this work, we hypothesize that by using these very smooth surfaces to evaporate saline droplets, we can suppress the crystallization caused by the surface interactions and thus achieve constant volume droplets above the saturation concentration. In our experiments, we used several different surfaces to examine the possibility of crystallization suppression. We show that on polymer grafted surfaces, i.e., Slippery Omniphobic Covalently Attached Liquid-like (SOCAL) and polyethyleneglycol(PEGylated) surfaces, we can achieve stable droplets as low as 55% relative humidity at 25 °C with high reproducibility using NaCl in water solutions. We also show that it is possible to achieve stable droplets above the saturation concentration on other surfaces, including superhydrophobic surfaces. We present an analytical model, based on water activity, which accurately describes the final stable volume as a function of the initial salt concentration. These findings are important for heat and mass transfer in relatively low humidity environments.

Silicone Oil-Grafted Low-Hysteresis Water-Repellent Surfaces.

Wetting plays a major role in the close interactions between liquids and solid surfaces, which can be tailored by modifying the chemistry as well as the structures of the surfaces' outermost layer. Several methodologies, such as chemical vapor deposition, physical vapor deposition, electroplating, and chemical reactions, among others, have been adopted for the alteration/modification of such interactions suitable for various applications. However, the fabrication of low-contact line-pinning hydrophobic surfaces via simple and easy methods remains an open challenge. In this work, we exploit one-step and multiple-step silicone oil (5-100 cSt) grafting on smooth silicon substrates (although the technique is suitable for other substrates), looking closely at the effect of viscosity as well as the volume and layers (one to five) of oil grafted as a function of the deposition method. Remarkably, the optimization of grafting of silicone oil fabrication results in non-wetting surfaces with extremely low contact angle hysteresis (CAH) below 1° and high contact angles (CAs) of ∼108° after a single grafting step, which is an order of magnitude smaller than the reported values of previous works on silicone oil-grafted surfaces. Moreover, the different droplet-surface interactions and pinning behavior can additionally be tailored to the specific application with CAH ranging from 1 to 20° and sliding angles between 1.5 and 60° (for droplet volumes of 3 µL), depending on the fabrication parameters adopted. In terms of roughness, all the samples (independent of the grafting parameters) showed small changes in the root-mean-square roughness below 20 nm. Lastly, stability analysis of the grafting method reported here under various conditions shows that the coating is quite stable under mechanical vibrations (bath ultrasonication) and in a chemical environment (ultrasonication in a bath of ethanol) but loses its low-pinning characteristics when exposed to saturated steam at T ∼ 99 °C. The findings presented here provide a basis for selecting the most appropriate and suitable method and parameters for silicone oil grafting aimed at low pinning and low hysteresis surfaces for specific applications.

Eyewitness confidence and decision time reflect identification accuracy in actual police lineups.

OBJECTIVE: Although there are many lab-based studies demonstrating the utility of confidence and decision time as indicators of eyewitness accuracy, there is almost no research on how well these variables function for lineups in the real world. In two experiments, we examined confidence and decision time associated with real lineups that had been conducted using research-based recommendations. HYPOTHESES: We expected that how confident an eyewitness sounded and how quickly that eyewitness made their identification would be associated with whether that eyewitness identified a suspect or a filler. We also hypothesized that people's interpretations of eyewitness confidence could be easily influenced by additional, biasing information. METHOD: Using audio recordings of these lineups, we examined (a) participants' subjective ratings of how confident an eyewitness sounded at the time of the identification and (b) objective data regarding how quickly the eyewitness made the identification decision. We also manipulated what additional information, if any, participants received in Experiment 2. RESULTS: In both experiments, decision time and confidence predicted whether the eyewitnesses identified the suspect or a known-innocent filler, and when decision time and confidence diverged, it is likely that the eyewitness identified a filler. In Experiment 2, we found that people's interpretations of eyewitness's confidence statements could be biased. When observers believed that the witness picked a filler rather than a suspect, or vice versa, this changed how confident they thought the witness sounded. CONCLUSIONS: Confidence and decision time should both be collected when administering real lineups, but objective decision time data may be the most useful because people's perceptions of confidence are easily altered. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Self-Assembled, Hierarchical Structured Surfaces for Applications in (Super)hydrophobic Antiviral Coatings.

A versatile method for the creation of multitier hierarchical structured surfaces is reported, which optimizes both antiviral and hydrophobic (easy-clean) properties. The methodology exploits the availability of surface-active chemical groups while also manipulating both the surface micro- and nanostructure to control the way the surface coating interacts with virus particles within a liquid droplet. This methodology has significant advantages over single-tier structured surfaces, including the ability to overcome the droplet-pinning effect and in delivering surfaces with high static contact angles (>130°) and good antiviral efficacy (log kill >2). In addition, the methodology highlights a valuable approach for the creation of mechanically robust, nanostructured surfaces which can be prepared by spray application using nonspecialized equipment.

The Liquid Young's Law on SLIPS: Liquid-Liquid Interfacial Tensions and Zisman Plots.

Slippery liquid-infused porous surfaces (SLIPS) are an innovation that reduces droplet-solid contact line pinning and interfacial friction. Recently, it has been shown that a liquid analogue of Young's law can be deduced for the apparent contact angle of a sessile droplet on SLIPS despite there never being contact by the droplet with the underlying solid. Since contact angles on solids are used to characterize solid-liquid interfacial interactions and the wetting of a solid by a liquid, it is our hypothesis that liquid-liquid interactions and the wetting of a liquid surface by a liquid can be characterized by apparent contact angles on SLIPS. Here, we first present a theory for deducing liquid-liquid interfacial tensions from apparent contact angles. This theory is valid irrespective of whether or not a film of the infusing liquid cloaks the droplet-vapor interface. We show experimentally that liquid-liquid interfacial tensions deduced from apparent contact angles of droplets on SLIPS are in excellent agreement with values from the traditional pendant drop technique. We then consider whether the Zisman method for characterizing the wettability of a solid surface can be applied to liquid surfaces created using SLIPS. We report apparent contact angles for a homologous series of alkanes on Krytox-infused SLIPS and for water-IPA mixtures on both the Krytox-infused SLIPS and a silicone oil-infused SLIPS. The alkanes on the Krytox-infused SLIPS follow a linear relationship in the liquid form of the Zisman plot provided that the effective droplet-vapor interfacial tension is used. All three systems follow a linear relationship on a modified Zisman plot. We interpret these results using the concept of the critical surface tension (CST) for the wettability of a solid surface introduced by Zisman. In our liquid surface case, the obtained critical surface tensions were found to be lower than the infusing liquid-vapor surface tensions.

Improving face identification of mask-wearing individuals.

Research has consistently shown that concealing facial features can hinder subsequent identification. The widespread adoption of face masks due to the COVID-19 pandemic has highlighted the critical and urgent need to discover techniques to improve identification of people wearing face coverings. Despite years of research on face recognition and eyewitness identifications, there are currently no evidence-based recommendations for lineup construction for cases involving masked individuals. The purpose of this study was to examine identification accuracy of a masked perpetrator as a function of lineup type (i.e., unmasked or masked lineups) and perpetrator presence (i.e., absent or present). In both experiments, discriminability was superior for masked lineups, a result that was due almost exclusively to higher hits rates in target-present conditions. These data suggest that presenting a masked lineup can enhance identification of masked faces, and they have important implications for both eyewitness identification and everyday face recognition of people with face coverings.

Friction Coefficients for Droplets on Solids: The Liquid-Solid Amontons' Laws.

The empirical laws of dry friction between two solid bodies date back to the work of Amontons in 1699 and are pre-dated by the work of Leonardo da Vinci. Fundamental to those laws are the concepts of static and kinetic coefficients of friction relating the pinning and sliding friction forces along a surface to the normal load force. For liquids on solid surfaces, contact lines also experience pinning and the language of friction is used when droplets are in motion. However, it is only recently that the concept of coefficients of friction has been defined in this context and that droplet friction has been discussed as having a static and a kinetic regime. Here, we use surface free energy considerations to show that the frictional force per unit length of a contact line is directly proportional to the normal component of the surface tension force. We define coefficients of friction for both contact lines and droplets and provide a droplet analogy of Amontons' first and second laws but with the normal load force of a solid replaced by the normal surface tension force of a liquid. In the static regime, the coefficient of static friction, defined by the maximum pinning force of a droplet, is proportional to the contact angle hysteresis, whereas in the kinetic regime, the coefficient of kinetic friction is proportional to the difference in dynamic advancing and receding contact angles. We show the consistency between the droplet form of Amontons' first and second laws and an equation derived by Furmidge. We use these liquid-solid Amontons' laws to describe literature data and report friction coefficients for various liquid-solid systems. The conceptual framework reported here should provide insight into the design of superhydrophobic, slippery liquid-infused porous surfaces (SLIPS) and other surfaces designed to control droplet motion.

Slippery Liquid-Like Solid Surfaces with Promising Antibiofilm Performance under Both Static and Flow Conditions.

Biofilms are central to some of the most urgent global challenges across diverse fields of application, from medicine to industries to the environment, and exert considerable economic and social impact. A fundamental assumption in anti-biofilms has been that the coating on a substrate surface is solid. The invention of slippery liquid-infused porous surfaces─a continuously wet lubricating coating retained on a solid surface by capillary forces─has led to this being challenged. However, in situations where flow occurs, shear stress may deplete the lubricant and affect the anti-biofilm performance. Here, we report on the use of slippery omniphobic covalently attached liquid (SOCAL) surfaces, which provide a surface coating with short (ca. 4 nm) non-cross-linked polydimethylsiloxane (PDMS) chains retaining liquid-surface properties, as an antibiofilm strategy stable under shear stress from flow. This surface reduced biofilm formation of the key biofilm-forming pathogens Staphylococcus epidermidis and Pseudomonas aeruginosa by three-four orders of magnitude compared to the widely used medical implant material PDMS after 7 days under static and dynamic culture conditions. Throughout the entire dynamic culture period of P. aeruginosa, SOCAL significantly outperformed a typical antibiofilm slippery surface [i.e., swollen PDMS in silicone oil (S-PDMS)]. We have revealed that significant oil loss occurred after 2-7 day flow for S-PDMS, which correlated to increased contact angle hysteresis (CAH), indicating a degradation of the slippery surface properties, and biofilm formation, while SOCAL has stable CAH and sustainable antibiofilm performance after 7 day flow. The significance of this correlation is to provide a useful easy-to-measure physical parameter as an indicator for long-term antibiofilm performance. This biofilm-resistant liquid-like solid surface offers a new antibiofilm strategy for applications in medical devices and other areas where biofilm development is problematic.

Test a Witness's Memory of a Suspect Only Once.

Eyewitness misidentifications are almost always made with high confidence in the courtroom. The courtroom is where eyewitnesses make their last identification of defendants suspected of (and charged with) committing a crime. But what did those same eyewitnesses do on the first identification test, conducted early in a police investigation? Despite testifying with high confidence in court, many eyewitnesses also testified that they had initially identified the suspect with low confidence or failed to identify the suspect at all. Presenting a lineup leaves the eyewitness with a memory trace of the faces in the lineup, including that of the suspect. As a result, the memory signal generated by the face of that suspect will be stronger on a later test involving the same witness, even if the suspect is innocent. In that sense, testing memory contaminates memory. These considerations underscore the importance of a newly proposed recommendation for conducting eyewitness identifications: Avoid repeated identification procedures with the same witness and suspect. This recommendation applies not only to additional tests conducted by police investigators but also to the final test conducted in the courtroom, in front of the judge and jury.

Lattice Boltzmann Simulations of Multiphase Dielectric Fluids.

The dynamic effect of an electric field on dielectric liquids is called liquid dielectrophoresis. It is widely used in several industrial and scientific applications, including inkjet printing, microfabrication, and optical devices. Numerical simulations of liquid-dielectrophoresis are necessary to understand the fundamental physics of the phenomenon, but also to explore situations that might be difficult or expensive to implement experimentally. However, such modeling is challenging, as one needs to solve the electrostatic and fluid dynamics equations simultaneously. Here, we formulate a new lattice-Boltzmann method capable of modeling the dynamics of immiscible dielectric fluids coupled with electric fields within a single framework, thus eliminating the need of using separate algorithms to solve the electrostatic and fluid dynamics equations. We validate the numerical method by comparing it with analytical solutions and previously reported experimental results. Beyond the benchmarking of the method, we study the spreading of a droplet using a dielectrowetting setup and quantify the mechanism driving the variation of the apparent contact angle of the droplet with the applied voltage. Our method provides a useful tool to study liquid-dielectrophoresis and can be used to model dielectric fluids in general, such as liquid-liquid and liquid-gas systems.

Eyewitnesses' free-report verbal confidence statements are diagnostic of accuracy.

OBJECTIVES: We assessed recent policy recommendations to collect eyewitnesses' confidence statements in witnesses' own words as opposed to numerically. We conducted an experiment to test whether eyewitnesses' free-report verbal confidence statements are as diagnostic of eyewitness accuracy as their numeric confidence statements and whether the diagnostic utility of eyewitnesses' verbal and numeric confidence statements varies across witnessing conditions. HYPOTHESES: We hypothesized that eyewitnesses' verbal and numeric confidence statements are both significantly associated with identification accuracy among choosers and that their diagnostic utility holds across varying witnessing conditions. METHOD: In the first phase of the experiment, eyewitnesses (N = 4,795 MTurkers; 48.8% female; 50.8% male; .3% other; age M = 36.9) viewed a videotaped mock-crime and made an identification decision from a culprit-present or culprit-absent lineup. We manipulated witnessing conditions at encoding and retrieval to obtain varied levels of memory performance. In the second phase of the experiment, evaluators (N = 456 MTurkers; 35.5% female; 62.7% male .4% other; age M = 36.5) translated witnesses' verbal confidence statements to a numeric estimate and we used calibration and confidence-accuracy characteristic analyses to compare the diagnosticity of witnesses' verbal and numeric confidence statements across the two levels of memory performance. RESULTS: Witnesses' verbal and numeric confidence statements were significantly and nondifferentially diagnostic of eyewitness accuracy for both choosers and nonchoosers, and their diagnostic utility held across variations in witnessing conditions. CONCLUSIONS: These findings suggest the applied utility of collecting either verbal or numeric confidence statements from eyewitnesses immediately following an identification decision. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Controlling the breakup of toroidal liquid films on solid surfaces.

The breakup of a slender filament of liquid driven by surface tension is a classical fluid dynamics stability problem that is important in many situations where fine droplets are required. When the filament is resting on a flat solid surface which imposes wetting conditions the subtle interplay with the fluid dynamics makes the instability pathways and mode selection difficult to predict. Here, we show how controlling the static and dynamic wetting of a surface can lead to repeatable switching between a toroidal film of an electrically insulating liquid and patterns of droplets of well-defined dimensions confined to a ring geometry. Mode selection between instability pathways to these different final states is achieved by dielectrophoresis forces selectively polarising the dipoles at the solid-liquid interface and so changing both the mobility of the contact line and the partial wetting of the topologically distinct liquid domains. Our results provide insights into the wetting and stability of shaped liquid filaments in simple and complex geometries relevant to applications ranging from printing to digital microfluidic devices.

Psychological science on eyewitness identification and its impact on police practices and policies.

The development of forensic DNA testing has led to the discovery of hundreds of cases of mistaken eyewitness identification in which innocent people were convicted. Although these discoveries of wrongful convictions from mistaken identification based on DNA testing have been a surprise and shock to the legal system and the public, psychological scientists have been less surprised. This is because psychological scientists were "blowing the whistle" on the eyewitness identification problem for decades prior to forensic DNA testing. Today, most law enforcement agencies in the United States have adopted reformed policies and procedures on eyewitness identification that are based on research by experimental social and cognitive psychologists. This article describes core aspects of this research and how the research has managed to have this impact on the U.S. legal system. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Contact-Angle Hysteresis and Contact-Line Friction on Slippery Liquid-like Surfaces.

Contact-line pinning and dynamic friction are fundamental forces that oppose the motion of droplets on solid surfaces. Everyday experience suggests that if a solid surface offers low contact-line pinning, it will also impart a relatively low dynamic friction to a moving droplet. Examples of such surfaces are superhydrophobic, slippery porous liquid-infused, and lubricant-impregnated surfaces. Here, however, we show that slippery omniphobic covalently attached liquid-like (SOCAL) surfaces have a remarkable combination of contact-angle hysteresis and contact-line friction properties, which lead to very low droplet pinning but high dynamic friction against the motion of droplets. We present experiments of the response of water droplets to changes in volume at controlled temperature and humidity conditions, which we separately compare to the predictions of a hydrodynamic model and a contact-line model based on molecular kinetic theory. Our results show that SOCAL surfaces offer very low contact-angle hysteresis, between 1 and 3°, but an unexpectedly high dynamic friction controlled by the contact line, where the typical relaxation time scale is on the order of seconds, 4 orders of magnitude larger than the prediction of the classical hydrodynamic model. Our results highlight the remarkable wettability of SOCAL surfaces and their potential application as low-pinning, slow droplet shedding surfaces.

Self-propelled droplet transport on shaped-liquid surfaces.

The transport of small amounts of liquids on solid surfaces is fundamental for microfluidics applications. Technologies allowing control of droplets of liquid on flat surfaces generally involve the generation of a wettability contrast. This approach is however limited by the resistance to motion caused by the direct contact between the droplet and the solid. We show here that this resistance can be drastically reduced by preventing direct contact with the help of dual-length scale micro-structures and the concept of "liquid-surfaces". These new surfaces allow the gentle transport of droplets along defined paths and with fine control of their speed. Moreover, their high adhesion permits the capture of impacting droplets, opening new possibilities in applications such as fog harvesting and heat transfer.

Distinguishing Between Investigator Discriminability and Eyewitness Discriminability: A Method for Creating Full Receiver Operating Characteristic Curves of Lineup Identification Performance.

The conceptual frameworks provided by both the lineups-as-experiments analogy and signal detection theory have proven important to understanding how eyewitness lineups work. The lineups-as-experiments analogy proposes that when investigators use a lineup procedure, they are acting as experimenters and should therefore follow the same tried-and-true procedures that experimenters follow when executing an experiment. Signal detection theory offers a framework for distinguishing between factors that improve the trade-off between culprit and innocent-suspect identifications and factors that affect the frequency of suspect identifications. We integrate these two conceptual frameworks. We argue that an eyewitness lineup procedure is characterized by two simultaneous signal detection tasks. On one hand, the witness is tasked with determining whether the culprit is present in the lineup and identifying that person. On the other hand, the investigator knows which lineup member is the suspect and which lineup members are known-innocent fillers and is therefore tasked only with determining whether the suspect is the culprit. The investigator uses the witness's identification decision and associated level of confidence to decide whether the suspect is the culprit. We leverage this realization to demonstrate a method for creating full receiver operating characteristic curves for eyewitness lineup procedures.