E and the proportion of suspect selections to measure lineup fairness from mock-witness choices and the two-high threshold eyewitness identification model to measure the biased selection of the suspects directly from eyewitness identification decisions. Results obtained in the mock-witness task and the model-based analysis of data obtained in the eyewitness task converged in showing that simultaneous lineups with morphed fillers were significantly more unfair than simultaneous lineups with non-morphed fillers. However, mock-witness and eyewitness data converged only when the eyewitness task mimicked the mock-witness task by including pre-lineup instructions that (1) discouraged eyewitnesses to reject the lineups and (2) alerted eyewitnesses that a photograph might stand out from the other photographs in the lineup. When a typical eyewitness task was created by removing these two features from the pre-lineup instructions, the morphed fillers no longer lead to unfair lineups. These findings highlight the differences in the cognitive processes of mock witnesses and eyewitnesses and they demonstrate the importance of measuring lineup fairness directly from eyewitness identification decisions rather than indirectly using the mock-witness task.The mock-witness task is typically used to evaluate the fairness of lineups. However, the validity of this task has been questioned because there are substantial differences between the tasks for mock witnesses and eyewitnesses. Unlike eyewitnesses, mock witnesses must select a person from the lineup and are alerted to the fact that one lineup member might stand out from the others. It therefore seems desirable to base conclusions about lineup fairness directly on eyewitness data rather than on mock-witness data. To test the importance of direct measurements of biased suspect selection in eyewitness identification decisions, we assessed the fairness of lineups containing either morphed or non-morphed fillers using both mock witnesses and eyewitnesses. We used Tredoux’s  One reason for wrongful convictions is that unfair lineups increase the likelihood of misidentifications of innocent suspects3. A lineup is considered fair when all fillers (distractors who are known to be innocent) serve as plausible alternatives to the suspect in the lineup such that there is no way to distinguish the suspect from the other lineup members without relying on memory for the culprit. Fair lineups provide protection of the innocent suspect because good fillers siphon misidentifications away from the innocent suspect5. This protective mechanism is absent in unfair lineups in which the suspect stands out from the other lineup members based on physical appearance or other distinct characteristics of the suspect’s photograph6. It is clear from prior studies that unfair lineups dramatically increase the risk of mistakenly identifying the suspect in comparison to fair lineups8. For this reason, it is important to understand the numerous factors that can influence lineup fairness. However, progress will only be made when the fairness of a lineup is measured in a valid way.Mistaken eyewitness identification is a consistent and leading cause of wrongful convictions. In the United States, eyewitness misidentifications have contributed to 70 % of the more than 375 wrongful convictions uncovered by DNA-based exonerations9 to assess lineup fairness10. In this task, persons who did not witness the crime—so-called mock witnesses—are asked to view the lineup and to choose the lineup member they believe to be the police suspect. One possibility is that mock witnesses are provided with the witness’s description of the culprit as the basis for their choices . Alternatively, mock witnesses are not provided with any additional information other than the indication that the suspect might stand out from the other lineup members; armed with this information, mock witnesses are simply asked to indicate who they think the suspect is . This most basic evaluation of lineup fairness can be used to investigate whether there are cues that make the suspect stand out from the other lineup members that are unrelated to the facial appearance of the culprit15. For example, in photo lineups the facial photograph of the suspect may stem from a different source  than the photographs of the fillers that may be taken from special databases16. Sometimes, the photographs of the fillers may even be digitally manipulated17. Therefore, a simple inspection of the characteristics of the photographs such as brightness, contrast, color balance or softness could reveal who the suspect is (more on this below). Given that mock witnesses have not seen the face of the culprit, they cannot make an identification that is based on memory. Instead, they have to rely on inferences that are either informed by a description of the culprit or based on other clues available in the lineup. A lineup is fair if the mock-witness choices are evenly distributed among the lineup members . A lineup is unfair if disproportionately many mock witnesses select the suspect9. Based on the choices of mock witnesses, several formal measures of lineup fairness can be computed. These measures reflect either the effective lineup size  or the bias with which the suspect is selected18. Effective lineup-size measures indicate the number of lineup members that could plausibly be considered as the culprit. One of the most popular effective lineup-size measures is Tredoux’s E19. The proportion of suspect selections9 is a popular measure of the bias with which the suspect is selected. This measure reflects the extent to which the suspect stands out from the other lineup members.Eyewitness researchers have typically used the mock-witness task20. Nevertheless, it has become increasingly common in experimental research to rely on the mock-witness task10 as it provides a seemingly straightforward solution to the problem of how to assess the fairness of lineups. However, the validity of the mock-witness task has been criticized on the grounds that there are substantial differences between the tasks of mock witnesses and eyewitnesses21.The mock-witness task was originally developed to measure lineup fairness in real criminal cases in which the suspect’s guilt is unknown to the police, not for measuring lineup fairness in laboratory experiments22]. However, in order to avoid this loss of data, mock witnesses are typically denied the option to reject the lineup. Instead, mock witnesses are usually forced to guess who the suspect is . In contrast, eyewitnesses are encouraged to reject the lineup if they are unsure as to whether or not the culprit is in the lineup. More specifically, eyewitnesses are typically given two-sided pre-lineup instructions that emphasize the fact that it is equally important to select the culprit in culprit-present lineups and to reject culprit-absent lineups . This is also the procedure recommended by several guidelines for how lineups should be conducted28. Two-sided instructions decrease the probability of selecting one of the lineup members based on guessing, which is highly desirable in eyewitness tasks because the reduction of guessing-based selections reduces false identifications of innocent suspects that could lead to wrongful convictions32.First, mock witnesses are typically encouraged or even forced to choose one of the lineup members while lineup rejections are discouraged or even prevented, respectively. If participants are discouraged from rejecting the lineup but ignore or defy these instructions, their data are excluded from analysis . When no description is presented, mock witnesses are explicitly told to choose the person who looks most distinctive or stands out from the other lineup members . Both types of instructions can be expected to encourage non-memory-based comparisons among the lineup members which may make participants sensitive to unfairness cues, possibly to the degree to which participants notice cues they would not have noticed otherwise. When participants are not provided with a description of the culprit’s face, it is impossible to search for the culprit in the lineup and the only remaining strategy is to carefully compare the photographs in the lineup to identify the face that stands out. This is markedly different from the memory-based identification task of eyewitnesses who have to match each lineup member to their memory representation of the culprit in order to decide whether or not one person represents the culprit33. Any features that are unrelated to the identity of the culprit such as brightness, contrast, color balance and softness of the photographs are irrelevant to this task and may be thus ignored by the eyewitnesses. Given these striking differences between the mock-witness task and the eyewitness task, the processes underlying the observed behavior may well differ between mock witnesses and eyewitnesses. It is thus unclear whether the mock-witness task can be used to draw valid conclusions about eyewitness identification decisions.Second, the task of a mock witness differs necessarily from that of an eyewitness. Given that mock witnesses have not seen the face of the culprit, they cannot make a memory-based decision but have to perform a non-memory-based comparison of the faces in the lineup. Unlike eyewitnesses, mock witnesses are thus alerted to the fact that one person might stand out from the other lineup members. When using a description-based mock-witness task, participants are typically asked to choose the person who best fits the culprit’s description which implies that the description fits one person better than the others ). Alternatively, participants may not select a lineup member based on guessing with probability 1 − g, which results in a correct rejection of the lineup in culprit-absent lineups.The model tree in the lower half of Fig. 32 and by fitting the model to published data obtained in various laboratories34. Both approaches support the validity of the model by demonstrating that all parameters predictably reflect experimental manipulations of the processes they were designed to measure. A brief overview of the validation results for the biased-suspect-selection parameter b seems in order because this parameter is of central importance to the present study. Parameter b has been shown to sensitively reflect the unfairness of a lineup in which the suspect’s face stood out from the fillers’ faces because it was the only face without large birthmarks32. In addition, the biased-suspect-selection parameter b has been shown to be larger in unfair lineups with low suspect-filler similarity than in fair lineups with high suspect-filler similarity; parameter b has also been shown to be larger when the suspect’s face stood out from the fillers due to distinctive facial features such as scars, bruisings, nose piercings and tattoos than when the suspect’s face did not stand out34.The 2-HT eyewitness identification model has been extensively validated using novel experiments designed specifically for the purpose of testing the model’s validity38. To solve this problem, face-morphing software can be used to increase the selection of faces that can be used in the lineup40. What is more, the morphing process protects the identity of the fillers which is legally required, for instance, in Germany: Photographs must be digitally manipulated so that the persons originally depicted in the photographs are no longer recognizable before these photographs may legally be used as filler photographs in lineups41. The downside of this practice is that it often produces morphing artifacts such as shadows, double edges, ghosting effects or blurring and lets the image appear softer43. In morphed lineups, the photograph of the suspect might therefore stand out from the fillers because it is the only photograph in the lineup that has not been digitally manipulated. Witnesses could thus use the absence of morphing artifacts as the cue to the identity of the suspect which might lead to a biased selection of the suspect.In the experiments reported here, we measured the fairness of lineups containing either morphed or non-morphed photographs of fillers (hereinafter referred to as morphed and non-morphed lineups). This morphing manipulation is of applied relevance. Assembling lineups is often a challenging task because pertinent databases often do not provide enough facial photographs that match the description of the culpritE and the proportion of suspect selections. To anticipate, the results of the mock-witness task indicate that morphed simultaneous lineups are more unfair than non-morphed simultaneous lineups. In Experiments 2 to 4, we examined the effect of the morphing manipulation on eyewitness identification decisions using the 2-HT eyewitness identification model to measure biased suspect selection. In Experiment 2, we began by adding to the eyewitness task two features that are typical of the mock-witness task but highly unusual for the eyewitness task with the result that this version of the eyewitness task closely resembled the mock-witness task. These two features were then removed successively in Experiments 3 and 4 with the goal to identify the factors that may underlie the differences in the conclusions drawn based on data from the mock-witness task and the eyewitness task. Specifically, in Experiment 2, it was tested whether the biased-suspect-selection parameter b of the 2-HT eyewitness identification model reflects the unfairness of morphed lineups when participants (1) are discouraged from rejecting the lineups and (2) are alerted that a photograph might stand out from the other photographs in the lineup. When the eyewitness task thus closely resembled the mock-witness task, the eyewitness task led to the same conclusions as the mock-witness task: Biased suspect selection was enhanced in morphed simultaneous lineups in comparison to non-morphed simultaneous lineups. In the subsequent experiments, the procedure was brought closer to the standard procedure of typical eyewitness tasks. In Experiment 3, we removed the discouragement of lineup rejections. In Experiment 4, we removed both the discouragement of lineup rejections and the instruction to look for the photograph that stands out from the rest of the photographs. To anticipate, the results indicate that those who criticized the validity of the mock-witness task  are correct: When the procedure was brought closer to the standard procedure of the eyewitness task, the effects of the morphing manipulation on biased suspect selection vanished. Specifically, the effect of the morphing manipulation on biased suspect selection was only descriptively present but not statistically significant in Experiment 3 and completely absent in Experiment 4. The results thus suggest that the mock-witness task has limited validity for drawing conclusions about eyewitness identification decisions. Instead, it is preferable to derive conclusions about lineup fairness directly from eyewitness identification decisions.In the present series of experiments, we examined the effect of the morphing manipulation in the mock-witness and eyewitness tasks. Whether morphed lineups are unfair was tested in Experiment 1 using the traditional mock-witness task, thereby relying on two classical measures of lineup fairness based on mock-witness choices, Tredoux’s E and the proportion of suspect selections—to measure the fairness of morphed and non-morphed simultaneous lineups in Experiment 1. However, in Experiment 2, the 2-HT eyewitness identification model was used to measure biased suspect selection in an eyewitness task that was modified to resemble the mock-witness task. To anticipate, the results obtained in the mock-witness task in Experiment 1 and the model-based analysis of eyewitness identification decisions in Experiment 2 converged in showing that morphed simultaneous lineups were significantly more unfair than non-morphed simultaneous lineups.In comparison to the eyewitness task, the mock-witness task provides an impoverished data structure because mock witnesses are hindered from rejecting the lineup and have actually not seen the culprit so that mock-witness lineups are essentially culprit-absent lineups. With only two of the six data categories of the eyewitness task left, it is not possible to use the 2-HT eyewitness identification model introduced above to analyze the data of the mock-witness task. Therefore, we relied on traditional mock-witness measures—Tredoux’s SoSci Survey44 and were made available via https://www.soscisurvey.de. Participation was possible with a laptop or desktop computer, but not with a smartphone. All participants were recruited from the online research panel of Gapfish, Berlin, Germany (https://gapfish.com). Participants received a small monetary compensation for their participation.All experiments reported here were conducted online. They were implemented using n = 91) or saw the lineups more than once due to repeated participation (n = 7). The final data set contained data from 753 participants  aged between 18 and 69 years . The sample was characterized by a diversified level of education. We had aimed for a sample size of at least 750 valid datasets and ended data collection at the end of the day on which this criterion was met. Participants were randomly assigned to either the morphed lineup condition (n = 385) or the non-morphed lineup condition (n = 368).Of the 851 participants who completed the socio-demographic questionnaire at the beginning of the experiment, 98 participants had to be excluded from the analysis because they did not complete the experiment or withdrew their consent to use their data . Participants were asked to indicate which lineup member was most likely to be the suspect in each lineup to help evaluate the fairness of the lineups. The instructions read: “We want to verify that the suspect’s photograph does not stand out from the other lineup members. If the photograph stands out, then you can recognize the suspect even if you are a person who had not seen the recording. Therefore, please look at all photographs carefully. Please select the person that you think is the suspect by clicking on the ‘Yes, is suspected’ button that belongs to the particular face”.Participants subsequently saw four separate lineups, each consisting of one suspect and five morphed or non-morphed fillers  were selected for each suspect pair. These faces were obtained from three face databases: The Center for Vital Longevity Face Database , the FEI Face Database  and the Radboud Faces Database . All fillers were selected based on their similarity (as determined by the authors) to the corresponding suspects in terms of hair color, hairstyle and stature as well as their suitability for morphing . Using MorphAge , each filler from Set A was morphed with one filler from Set B by marking landmarks on one face  and matching each landmark to the corresponding point on the other face. Both faces of fillers from Set A and Set B were blended in a 50:50 ratio . This procedure generated five morphed fillers for each suspect pair  were chosen from the Center for Vital Longevity Face Database9, participants were not given the option to reject the lineup. Once the participants had selected a person, they could proceed to the next lineup by pressing the “Next” button. The order in which the lineups appeared was randomly determined for each participant. After completing the four lineup trials, participants were debriefed and thanked for their participation. The experiment took about 10 min.The four lineups were presented one after another in a simultaneous format. In each lineup, all six faces were shown together in a single row with the option to respond “Yes, is suspected” appearing underneath each photograph. The position of the suspect and the five fillers was randomized. Implementing the typical mock-witness taskE, which provides an estimate of the number of plausible lineup members19. Tredoux’s E takes on a minimum value of 1 and a maximum value of k, the number of lineup members . Each lineup member who receives fewer choices than expected by chance will cause a reduction of the value of Tredoux’s E, starting from k and approaching 1. Tredoux’s E was calculated separately for each of the four morphed and non-morphed lineups before an average effective size was computed separately for the morphed and the non-morphed lineup condition that is reported below (details on the data underlying these effective sizes are reported in the Open Science Framework repository at https://osf.io/zaybc/). Second, the average proportion of suspect selections was calculated for both morphed and non-morphed lineups as a measure of biased selection of the suspect9. This measure is straightforward to interpret: If the mock-witness choices are equally distributed across the lineup members , a lineup would be considered perfectly fair. If a disproportionate number of mock witnesses pick out the suspect, a lineup is considered unfair. Thus, a greater proportion of participants choosing the suspect from morphed lineups than from non-morphed lineups would indicate that the morphed lineups are more biased toward the suspect than the non-morphed lineups.For each lineup, the distribution of mock-witness choices across the six lineup members was determined. Based on these mock-witness data, lineup fairness was computed in two ways. First, effective lineup size was assessed using Tredoux’s E was higher for the non-morphed lineup condition (M = 4.51) than for the morphed lineup condition (M = 3.44), indicating that the morphed lineups were more unfair than the non-morphed lineups. The same conclusion can be reached when calculating the proportion of suspect selections in both conditions. The average proportion of suspect selections was significantly higher in the morphed lineup condition (M = 47.5 %) than in the non-morphed lineup condition (M = 25 %), as determined by a z-test for proportions .The average Tredoux’s The results obtained in the traditional mock-witness task indicate that the morphed lineups were more unfair than the non-morphed lineups. These results thus lead to the conclusion that the police should stop using this morphing technique as it leads to artifacts that make the suspect stand out from the other lineup members. However, it has yet to be shown whether or not these findings are limited to the mock-witness task. Therefore, the purpose of Experiments 2 to 4 was to examine the effects of the same morphing manipulation on eyewitness identification decisions in simultaneous and sequential lineups.It cannot be taken for granted that the mock-witness choices validly reflect the processes that determine eyewitness identification decisions. Therefore, it has to be tested whether the morphing manipulation affects eyewitness identification decisions to the same extent as it affects mock-witness choices. As noted above, the mock-witness task differs from a typical eyewitness task in at least two significant ways. Unlike eyewitnesses, mock witnesses (1) are required to choose one of the lineup members and (2) are alerted to the fact that one lineup member might stand out from the others. Therefore, the aim of the following series of experiments was to test, across experiments, whether evidence for the unfairness of the morphed lineups emerged depending on whether these two features were present in the eyewitness task.b sensitively reflects the biased selection of suspects34 and can thus be used to assess the unfairness of lineups. If the biased-suspect-selection parameter b is sensitive to the morphing manipulation used in Experiment 1, the estimate of parameter b should be higher for simultaneous morphed lineups than for simultaneous non-morphed lineups.As the next step, we aimed at testing whether the unfairness effects of the morphing manipulation could be demonstrated in eyewitness identification decisions when the eyewitness task was modified to mimic the mock-witness task—that is, when participants (1) were discouraged from rejecting the lineup and (2) were alerted to the fact that the suspect may stand out from the fillers. The eyewitness task provides a richer data structure than the mock-witness task because suspect identifications, filler identifications and lineup rejections in both culprit-present and culprit-absent lineups can be observed. It is thus important to rely on a measurement model that takes the full data structure of the eyewitness task into account. The 2-HT eyewitness identification model capitalizes on the full range of data categories that can be observed in the eyewitness task. It has been successfully demonstrated that the model’s parameter 48. However, in some countries such as the UK and Germany, the sequential presentation has become the standard way of conducting police lineups50. The second aim of Experiment 2 was thus to test the effect of the morphing manipulation on biased suspect selection in sequential lineups. Here it is useful that the 2-HT model has been demonstrated to validly reflect biased selection in both simultaneous and sequential lineups32. Previous research has demonstrated that sequential lineups provide some protection against biased suspect selection in unfair lineups52. For example, in simultaneous lineups, a photograph that differs from the other photographs in brightness, contrast, color balance or softness may pop out from the others. In sequential lineups, witnesses cannot compare the photographs side-by-side. Therefore, it may be less salient that one photograph stands out from the others in sequential lineups. There is thus reason to expect that the morphing manipulation is less likely to affect eyewitness identification decisions in sequential lineups than in simultaneous lineups. As a consequence, biased selection of the suspect may only be enhanced in simultaneous morphed lineups in comparison to simultaneous non-morphed lineups but may not differ between morphed and non-morphed sequential lineups.An additional aspect not mentioned so far is that the mock-witness technique has been proposed to evaluate the fairness of simultaneous lineups but it is of limited use in estimating the fairness of sequential lineupsn = 120), incorrectly answered the attention-check question (n = 11) or watched the video more than once due to repeated participation (n = 20). The final data set contained data from 783 participants  aged between 18 and 69 years . The sample was characterized by a diversified level of education. We had aimed for a sample size of at least 750 valid datasets and stopped data collection at the end of the day on which this criterion was met. A sensitivity analysis using G*Power53 showed that with a sample size of N = 783, four eyewitness identification decisions and an alpha error probability of 0.05, it was possible to detect even small effects of the morphing manipulation on the biased-suspect-selection parameter b of effect size w = 0.06 with a statistical power (1 − beta error probability) of 0.95. Participants were randomly assigned to one of the four lineup conditions: the morphed simultaneous lineup condition (n = 199), the non-morphed simultaneous lineup condition (n = 190), the morphed sequential lineup condition (n = 196) and the non-morphed sequential lineup condition (n = 198).Of the 934 participants who completed the socio-demographic questionnaire at the beginning of the experiment, 151 participants had to be excluded from the analysis because they did not complete the experiment or withdrew their consent to use their data  verbally and physically attacked a fan of the rival soccer club Borussia Dortmund (henceforth referred to as the victim) at a bus stop. The hooligans and their victim wore typical fan clothing of the soccer clubs . The four culprits poked fun at the victim, insulted him and tossed his personal belongings around. At the end of the video, the culprits pushed the victim to the ground. The four culprits continued to verbally and physically abuse the victim. Once the culprits noticed another pedestrian approaching (not visible in the videos), they ran away shouting loudly. Note that in many other lineup studies, participants are only exposed to a single culprit at encoding and thus to a single lineup at test . However, to increase the efficiency of data collection, we followed the lead of other researchers  and presented our participants with a video showing four culprits. This procedure allowed us to generate four data points per participant instead of just one. Also note that multiple-culprit crimes are in fact quite frequent62. For instance, in 2008, 25 % of all crimes committed in the UK involved four or more culprits .The same two parallel videos were used (henceforth referred to as Video A and Video B) as in the validation experiments of Winter et al.The two parallel videos had the same content , but the culprits and the victims differed between the two videos. Care was taken to select the actors in such a way that the victim of Video A resembled the victim of Video B as closely as possible and that each of the four culprits of Video A resembled one of the four culprits of Video B in hair color, hairstyle and stature . Note that the same eight faces had served as suspects in Experiment 1 to ensure comparability between the experiments. It was randomly determined whether participants watched Video A or Video B. Both videos were 130 s long and showed a clear view of the culprits’ faces. The videos were presented in a resolution of 885 × 500 pixels.Participants could start the video by clicking on the “Start” button. They were unable to proceed to the next page until they had watched the whole video. After the video had finished, participants had to answer a 10-alternatives attention-check question  to test whether participants had been paying attention to the video. The order of the response options was randomized.. As in Experiment 1, participants were informed that “Each lineup consists of six pictures, one recent photo of the suspect and five photos taken from face databases”. They were also made aware of the possibility that the suspect might stand out from the other lineup members: “It is possible that the suspect stands out from the other lineup members. If the suspect stands out, then you can recognize the suspect even if you have not seen the video. Therefore, please look at all photos carefully”. Lineup rejections were discouraged by instructing the participants: “It is very likely that every lineup contains a culprit. Therefore, even if you are uncertain about whether or not the culprit is in the lineup, choose the picture that stands out among the others. Then you will almost certainly identify the culprit. To do this, click on the ‘Yes, was present’ button that belongs to that face. Only if you are very certain that the persons do [simultaneous lineups]/person does [sequential lineups] not represent any of the culprits, click on the ‘No, none of these persons was present’ [simultaneous lineups]/‘No, this person was not present’ [sequential lineups] button”. Participants were not made aware of the number of lineups that were about to follow.Participants who had correctly answered the attention-check question were asked to identify the four culprits: “The video you just watched showed aggressive FC Bayern München hooligans. You will be asked to identify these hooligans. For this purpose, we are going to show you some lineups”32 was used to manipulate the suspect’s guilt. Specifically, if participants had seen Video A, two culprits of Video A  served as the culprits in the culprit-present lineups, while two culprits of Video B  served as the innocent suspects in the culprit-absent lineups. If participants had seen Video B, two culprits of Video B served as the culprits in the culprit-present lineups while two culprits of Video A served as the innocent suspects in the culprit-absent lineups. This approach had two advantages: First, culprit-absent lineups contained a designated innocent suspect to whom the fillers had been matched. This situation represents a more ecologically valid lineup procedure than using only fillers in culprit-absent lineups. This is so because, in practice, the photographs of the suspects (whose guilt or innocence is unknown) are taken from other sources  than the photographs of the fillers which are usually taken from face databases and may be digitally altered. Second, culprit-present and culprit-absent lineups included the identical filler faces; only the identity of the suspect was changed. Which of the two suspects served as the culprit or innocent suspect depended on the random assignment to one of the two videos (see above). In that way, it was ensured that, on average, the degree of fairness was the same in culprit-present and culprit-absent lineups. A similar approach, the single-lineup procedure, has been proposed by Oriet and Fitzgerald64. In contrast to the crossed lineup procedure used here, the single lineup procedure implies showing all participants the same lineup after having seen one of two videos, one that contains the suspect in the lineup while the other contains a person who is not presented in the lineup but matches the physical description of the suspect. As in Experiment 1, all photographs were presented at a resolution of 142 × 214 pixels.Participants saw a total of four separate lineups, two were randomly selected to be culprit-present lineups and the other two were culprit-absent lineups. The lineups consisted of the same faces as in Experiment 1. Each lineup consisted of the facial photographs of six persons, one suspect face and either five morphed or five non-morphed filler faces see Fig. . The cro65. It also corresponds to the identification procedure in the simultaneous lineups in which it was possible for participants to revise their decision before clicking the “Next” button. After each decision, participants were asked to indicate their level of confidence in their judgment in the same manner as in the simultaneous lineup conditions. A lineup was counted as rejected if participants identified none of the lineup members. The order with which the lineups were presented was randomized, as was the position of the lineup members in each lineup. After their response to the fourth lineup, participants were debriefed and thanked. The experiment took about 10 min.Participants were randomly assigned to either the simultaneous or the sequential lineup conditions. In the simultaneous lineup conditions, the six faces were shown together in one row. Participants made a decision by either clicking on the “Yes, was present” button underneath a face to identify a person as a culprit or by clicking on the “No, none of these persons was present” button located to the right of each lineup to reject the lineup. After having made a decision, participants were asked to express how confident they were in their judgments in order to approximate the procedure to that of a real police lineup. Then they could initiate the presentation of the next lineup by clicking on the “Next” button. In the sequential lineup conditions, the faces were presented one at a time. For each of the six faces, participants decided whether or not the depicted face belonged to one of the culprits by clicking on either the “Yes, was present” button underneath the face or the “No, this person was not present” button located to the right of the face. A decision was required before participants could proceed to the next lineup member. If participants identified more than one face within a single lineup, only the last identification decision was counted. This procedure is legally prescribed in several jurisdictions such as Germany or the United StatesmultiTree66. The alpha error probability was set to 0.05. The observed response frequencies and proportions for Experiments 2, 3 and 4 are reported in Table 34 for conditions that can be expected to affect the probability of culprit-absence detection]. Therefore, the parameter representing culprit-absence detection (dA) was set to be equal across the four lineup conditions. Second, there was no a priori reason why the ability to detect the presence of the culprit should differ between the morphed and non-morphed lineups. However, previous results that were obtained with the same stimulus materials and procedure32 suggest that culprit-presence detection is somewhat better in simultaneous than in sequential lineups. Therefore, the culprit-presence-detection parameter dP was set to be equal between the simultaneous morphed and non-morphed conditions and between the sequential morphed and non-morphed conditions. Third, there was no a priori reason why guessing-based selection should differ between the morphed and non-morphed lineups. However, previous results32 suggest that guessing-based selection is enhanced in sequential in comparison to simultaneous lineups. Therefore, the guessing-based-selection parameter g was set to be equal between the simultaneous morphed and non-morphed conditions and between the sequential morphed and non-morphed conditions. The asymptotically chi-square distributed likelihood-ratio goodness-of-fit statistic (with degrees of freedom reported in parentheses)  indicated that the base model incorporating these restrictions fit the data, G2(7) = 2.55, p = 0.924.Four instances of the model illustrated in Fig. b to be equal between these conditions. If the model with this restriction fits significantly worse to the data than the base model , we would have to reject the equality assumption implied by the restriction and would conclude that parameter b differs between conditions.In an MPT model such as the 2-HT eyewitness identification model, hypotheses can be tested directly at the level of the parameters representing the postulated processes. For instance, the hypothesis that biased suspect selection is higher in the morphed lineup conditions than in the non-morphed lineup conditions can be tested by restricting parameter b for morphed and non-morphed lineups as a function of lineup format. The probability of biased suspect selection was higher for morphed lineups than for non-morphed lineups when simultaneous lineups were used, ∆G2(1) = 5.31, p = 0.021, w = 0.04, in accordance with the mock-witness results of Experiment 1. However, biased suspect selection did not differ between morphed and non-morphed lineups when sequential lineups were used, ∆G2(1) = 2.04, p = 0.153, w = 0.03. In addition, the probability of biased suspect selection was significantly higher for morphed simultaneous than for morphed sequential lineups, ∆G2(1) = 21.89, p < 0.001, w = 0.08, but it did not differ between non-morphed simultaneous and sequential lineups, ∆G2(1) = 1.60, p = 0.207, w = 0.02.Figure dP), guessing-based selection (g) and culprit-absence detection (dA) as a function of lineup format are shown in Table b), we do not include an analysis or discussion of the other parameters here. However, we will provide a brief overview and interpretation of the results of Experiments 2 to 4 pertaining to culprit-presence detection and guessing-based selection in the General Discussion.The parameter estimates for culprit-presence detection , incorrectly answered the attention-check question (n = 13) or watched the video more than once due to repeated participation (n = 9). The final data set contained data from 760 participants  aged between 18 and 85 years . The sample was characterized by a diversified level of education. We had aimed for a sample size of at least 750 valid datasets and stopped data collection at the end of the day on which this criterion was met. A sensitivity analysis showed that with a sample size of N = 760 participants, four eyewitness identification decisions and an alpha error probability of 0.05, it was possible to detect even small effects of the morphing manipulation on the biased-suspect-selection parameter b of effect size w = 0.07 with a statistical power (1 − beta error probability) of 0.9553. As in Experiment 2, participants were randomly assigned to one of the four lineup conditions: the morphed simultaneous lineup condition (n = 197), the non-morphed simultaneous lineup condition (n = 180), the morphed sequential lineup condition (n = 195) and the non-morphed sequential lineup condition (n = 188).Of the 894 participants who completed the socio-demographic questionnaire at the beginning of the experiment, 134 had to be excluded from the analysis because they did not complete the experiment or withdrew their consent to use their data  = 3.58, p = 0.827.The same assumptions as in Experiment 2 were used to arrive at the base model. This base model fit the data, b for morphed and non-morphed lineups as a function of lineup format. Parallel to Experiment 2, the probability of biased suspect selection was descriptively higher for morphed simultaneous lineups compared to non-morphed simultaneous lineups, but in contrast to Experiment 2 this difference was no longer statistically significant, ∆G2(1) = 3.63, p = 0.057, w = 0.03. As in Experiment 2, biased suspect selection did not differ between morphed and non-morphed lineups when sequential lineups were used, ∆G2(1) = 1.49, p = 0.222, w = 0.02. Also as in Experiment 2, the probability of biased suspect selection was significantly higher for morphed simultaneous than for morphed sequential lineups, ∆G2(1) = 12.53, p < 0.001, w = 0.06, but it did not differ between non-morphed simultaneous and sequential lineups, ∆G2(1) = 0.42, p = 0.515, w = 0.01.Figure dP), guessing-based selection (g) and culprit-absence detection (dA) as a function of lineup format are shown in Table The parameter estimates for culprit-presence detection , incorrectly answered the attention-check question (n = 13), watched the video more than once due to repeated participation (n = 22) or a technical error occurred during the experiment (n = 7). The final data set contained data from 761 participants  aged between 18 to 80 years . The sample was characterized by a diversified level of education. We had aimed for a sample size of at least 750 participants and stopped data collection at the end of the day on which this criterion was met. A sensitivity analysis showed that with a sample size of N = 761 participants, four eyewitness identification decisions and an alpha error probability of 0.05, it was possible to detect even small effects of the morphing manipulation on the biased-suspect-selection parameter b of effect size w = 0.07 with a statistical power (1 − beta error probability) of 0.9553. Participants were randomly assigned to one of the four lineup conditions: the morphed simultaneous lineup condition (n = 183), the non-morphed simultaneous lineup condition (n = 200), the morphed sequential lineup condition (n = 194) and the non-morphed sequential lineup condition (n = 184).Of the 958 participants who completed the socio-demographic questionnaire at the beginning of the experiment, 197 participants had to be excluded from the analysis because they did not complete the experiment or withdrew their consent to use their data  = 6.61, p = 0.471.The same assumptions as in Experiments 2 and 3 were used to arrive at the base model. This base model fit the data, b for morphed and non-morphed lineups as a function of lineup format. Crucially, the descriptive difference between morphed and non-morphed simultaneous lineups that was still evident in Experiment 3 was absent in Experiment 4. This result is so clear from the sizes of the parameter estimates that it does not require a statistical test, but for completeness, we report here that the probability of biased suspect selection did not differ significantly between morphed simultaneous lineups and non-morphed simultaneous lineups, ∆G2(1) < 0.01, p = 0.992, w < 0.01. Further, as in Experiments 2 and 3, biased suspect selection did not differ between morphed and non-morphed lineups when sequential lineups were used, ∆G2(1) < 0.01, p = 0.950, w < 0.01. Finally, the probability of biased suspect selection differed neither between morphed simultaneous and sequential lineups, ∆G2(1) = 0.02, p = 0.898, w < 0.01, nor between non-morphed simultaneous and sequential lineups, ∆G2(1) < 0.01, p = 0.952, w < 0.01.Figure dP), guessing-based selection (g) and culprit-absence detection (dA) as a function of lineup format are shown in Table The parameter estimates for culprit-presence detection  and the data obtained in a variant of the eyewitness task that closely mimicked the mock-witness task (Experiment 2). Similar contradictions between mock-witness data and eyewitness results have been reported in other studies48. Together, these results support the assumption that mock-witness choices may not be a good basis for drawing conclusions about eyewitness identification decisions21.However, in Experiment 3, in which the pre-lineup instructions did not discourage participants from rejecting the lineup, the difference in the biased-suspect-selection parameter Given that the model-based analysis did not yield signs of a morphing unfairness when lineup rejections were not discouraged and participants were not alerted that a photograph might stand out from the other photographs in the lineup, it is possible to assume that these two procedural differences between the mock-witness task and the typical eyewitness task are two major reasons as to why mock-witness choices fail to align with eyewitness identification decisions in the standard eyewitness task: First, whereas mock witnesses are typically required to choose a lineup member, eyewitnesses may choose to reject the lineup. Second, mock witnesses are made aware of the possibility that one lineup member might stand out from the others. Eyewitnesses, in contrast, must make a memory-based identification decision by matching each individual face to their memory representation of the culprit in order to be able to decide whether the culprit is in the lineup. Therefore, the unfairness of the lineup is overestimated in the mock-witness task in comparison to the standard eyewitness task.20. This is so simply because there is currently no better alternative for assessing lineup fairness in practice where the goal is to ensure that a lineup is fair before it is presented to real witnesses. However, as the data presented here have shown, results obtained with mock witnesses may well differ from those obtained with eyewitnesses and thus should be used with caution. In lineup research, in contrast, a measurement model should be used which allows determining whether or not a lineup is unfair in the eyewitness identification situation proper. Otherwise, researchers may draw incorrect conclusions based on invalid fairness assessment procedures, which could lead practitioners to discard appropriate techniques for lineup construction. For instance, here we have shown that morphing artifacts affect mock-witness choices in simultaneous lineups. Such results may well lead policy makers to ban the morphing of photographs for lineup presentation and to eliminate this technique from the set of techniques the police is allowed to use in order to construct lineups. However, as we have shown, the same morphing artifacts that affect choices in situations in which participants have received instructions that are typical of the mock-witness task (Experiments 1 and 2) need not affect eyewitness identification decisions in a typical eyewitness task (Experiment 4). Given these results, there seems to be no reason to ban the morphing of photographs when constructing photo lineups, provided it can be ensured that witnesses receive standard lineup instructions and do not feel pressured to make an identification.Of course, the mock-witness task remains a valuable tool in actual criminal cases, that is, in the situation for which the task has been developed originally, as has been pointed out by Quigley-McBride and Wells32. This is a distinguishing feature of the present model given that previous research has shown that the mock-witness task is of limited use in estimating lineup fairness in sequential lineups48. It has previously been shown that unfair simultaneous lineups led to more identifications of innocent suspects than unfair sequential lineups, suggesting that sequential lineups provide more protection for the innocent suspect when the lineup is unfair52. This conclusion is supported by the findings reported here. The results of Experiments 2, 3 and 4 consistently showed no effect of the morphing manipulation on biased suspect selection in sequential lineups, even when the instructions closely resembled those of a mock-witness task. When lineup identifications are made under conditions that do not qualify as best practices—that is, when lineups are unfair and instructions encourage non-memory-based decisions—, sequential lineups provide some protection against unfairness in comparison to simultaneous lineups.We included both simultaneous and sequential lineups in the present series of experiments because the 2-HT eyewitness identification model is a tool for measuring lineup fairness in both types of lineup formats69—that is, a higher ratio of the proportion of correct culprit identifications to the proportion of false innocent-suspect identifications71. This result seemed to indicate that sequential lineups perform better than simultaneous lineups when the goal is to separate culprits from innocent suspects. However, it has been argued that the diagnosticity ratio is an inadequate measure of lineup performance because it confounds the ability to distinguish between a culprit and an innocent suspect with response bias . Receiver Operating Characteristic (ROC) analyses do not have this problem and have shown either that simultaneous lineups perform better than sequential lineups74 or that sequential and simultaneous lineups perform equally well77. ROC analyses are said to have the advantage of delivering a performance measure that is not confounded by response bias23. However, ROC analyses focussing on the partial area under the curve—that have become commonplace in lineup research—are based on the proportion of correct culprit identifications and false innocent-suspect identifications, as a consequence of which they do not exploit the information contained in filler identifications and lineup rejections separately; these data categories are combined based on the reasoning that both filler identifications and lineup rejections have no legal consequences . However, there is information to be gained when these two response categories are analyzed separately. For instance, a filler identification in a culprit-absent lineup is an error. A lineup rejection in a culprit-absent lineup is a correct response. Obviously, many such filler identifications and few lineup rejections indicate bad performance, whereas few such filler identifications and many lineup rejections indicate good performance. The 2-HT eyewitness identification model used here exploits this information in that it takes into account the full range of data categories available from lineup procedures  exclusively. We would now like to focus on the process of culprit-presence detection represented by parameter dP. An advantage of the 2-HT eyewitness identification model is that parameter dP is not confounded with lineup fairness34, that is, parameter dP is a pure measure of culprit-presence detection even in unfair lineups. In the model-based analyses reported here, the estimates of parameter dP were consistently higher in the simultaneous lineup conditions than in the sequential lineup conditions (see Table G2(1) = 8.25, p = 0.004, w = 0.05, and Experiment 4, ∆G2(1) = 4.80, p = 0.028, w = 0.04, but not in Experiment 3, ∆G2(1) = 3.78, p = 0.052, w = 0.04. A small superiority of simultaneous over sequential lineups was also found by Winter et al.32 when applying the 2-HT eyewitness identification model to both simultaneous and sequential lineups. This pattern in the results based on the 2-HT eyewitness identification model is in good agreement with the results of ROC-based analyses in which a superiority of simultaneous over sequential lineups was sometimes found  but not always .For quite some time, another advantage of sequential lineups seemed to be that, compared with simultaneous lineups, sequential lineups have often been found to be associated with a higher diagnosticity ratioas e.g.,7. Receive32, we also found a consistently higher probability of guessing-based selection (captured by parameter g) in sequential lineups in comparison to simultaneous lineups in Experiments 2, 3 and 4  lineup protocol that has been used here can be expected to produce relatively liberal responding and thus a higher prevalence of guessing-based selections among lineup members in the sequential lineup. However, this rather interesting aspect of the present study has to be further addressed in future experiments.Parallel to the results of Winter et al.20 have proposed an alternative method to measure lineup fairness directly from actual eyewitness data. Specifically, they have recommend calculating the resultant lineup fairness based on the innocent-suspect identifications and filler identifications in culprit-absent lineups. Given that it seems interesting to compare these resultant lineup-fairness measures with the biased-suspect-selection parameter b of the 2-HT eyewitness identification model, we calculated the average resultant proportion of suspect selections  and the average resultant Tredoux’s E for Experiments 2, 3 and 4. Note that these calculations are based only on the identifications in culprit-absent lineups whereas the 2-HT eyewitness identification model takes into account all data of both culprit-present lineups and culprit-absent lineups. As a result of being based on a reduced data set, we may expect more variability in the values calculated for the resultant-lineup fairness measures. Still, the resultant proportions of suspect selections reflect the unfairness of morphed opposed to non-morphed lineups in a way that is largely parallel to that of the biased-suspect-selection parameter b in the present series of experiments . In addition, the resultant proportions of suspect selections reflect the higher unfairness in simultaneous lineups than in sequential lineups. The resultant Tredoux’s E was calculated separately for each of the four simultaneous and sequential morphed and non-morphed lineups before an average resultant Tredoux’s E was computed for the simultaneous and sequential morphed and non-morphed lineup conditions, as in Experiment 1. The average resultant Tredoux’s E was descriptively smaller for morphed lineups than for non-morphed lineups in Experiment 2, but the data pattern is more variable in Experiments 3 and 4 . In all experiments, the resultant Tredoux’s E was descriptively smaller in simultaneous lineups than in sequential lineups .Recently, Quigley-McBride and Wells12]. Given that it cannot be taken for granted that the search processes are the same for these two different types of mock-witness tasks, future research should focus on whether the same conclusions can be obtained with the description-based mock-witness task.A limitation of the present research is that a cross-experiment comparison was used to demonstrate that morphing artifacts cause unfairness in an anomalous identification situation—comparable to that of mock witnesses—but do not enhance biased suspect selection in a standard eyewitness task. Future research could extend the present research by performing a within-experiment comparison to examine more directly how the morphing effect on biased suspect selection interacts with the different lineup conditions. Another limitation of the present study is that only one of the two possible types of mock-witness tasks was used here. Participants were asked to choose the person who stands out from the other lineup members. In another variant of the mock-witness task, participants are provided with a description of the culprit as the basis for their choice . The present series of experiments not only demonstrates that those who had questioned the usefulness of the mock-witness task48 were correct but also sheds light on the crucial differences between the mock-witness task and the eyewitness task that are responsible for the divergent effects. While the mock-witness task showed that morphed lineups were more unfair than non-morphed lineups, the morphing manipulation did not affect eyewitness identification decisions in a typical lineup procedure. This discrepancy was due to two task differences: First, unlike eyewitnesses, mock witnesses are not allowed to reject lineups. Second, mock witnesses are made aware of the possibility that one lineup member might stand out from the others. In contrast, eyewitnesses must match each lineup member to their memory representation of the culprit. In lineup research, it therefore seems desirable to measure lineup fairness directly from eyewitness data using a measurement model such as the 2-HT eyewitness identification model rather than to rely on mock-witness-based measures.Lineup fairness is a critical factor affecting the likelihood of misidentifications, yet there is surprisingly little research on how to determine the fairness of lineups. Traditionally, researchers have relied on the mock-witness task to evaluate lineup fairness


Peripheral vestibular disorders affect 2.8–6.5% of people. Standard treatment is vestibular rehabilitation therapy, and virtual reality (VR) could improve outcomes. The objective of this study was to identify the commercially available VR video game that is most congruent to vestibular rehabilitation therapy.A term search “virtual reality racing” was performed on the App Store in March 2022. Results were screened for free point-of-view racing games compatible with Android and iOS devices. An investigator was filmed playing each game and videos were distributed to 237 physiotherapists. Physiotherapists completed a survey of 5-point Likert scale questions that assessed the video games vestibular rehabilitation potential. Survey responses were analyzed using Friedman Two-Way ANOVA  and paired samples sign test with Bonferroni correction.p < 0.001) better than Derby VR, and VRWBR replicated physiotherapist-prescribed exercises significantly (p < 0.001) better than VR X-Racer. There were no discernable significant differences between VRWBR and VRTR.The search yielded 58 games, 4 were included. Forty physiotherapists participated. VR Tunnel Race (VRTR) and VR Real World Bike Racing (VRWBR) had the greatest vestibular rehabilitation potential . VRTR replicated habituation exercises significantly (VRTR and VRWBR are the most congruent VR games to standard vestibular rehabilitation. VRWBR is preferable to VRTR with respect to ease of use and the ability to alter the amount of optokinetic stimulation. Prospective studies are needed to confirm the efficacy of these videos games and to determine if they could be used as solitary treatments.Trial registration: Not applicable. Peripheral vestibular disorders are highly morbid conditions that affect 2.8–6.5% of the population (women more frequently than men) and become more prevalent with age , 2. The Current treatments for peripheral vestibular disorders are pharmacological, surgical, or physical including repositioning maneuvers and standard vestibular rehabilitation (SVR). The latter involves a range of exercises that include habituation, substitution, and adaptation exercises, where there is moderate evidence in support of virtual reality (VR) as a mode of delivering these exercises . The intVR could serve as an adjunctive therapy to SVR and may address adherence issues while improving outcomes. VR is defined as technology that immerses the wearer into an interactive environment that mimics reality . This teHBVR video game exercises are thus a promising adjunct to SVR. However, there is a paucity of literature on which VR games are best suited for SVR, with Micarelli et al. utilizing a point-of-view VR racing game based on their judgment that it replicated SVR exercises , 20. HowVirtual reality is defined as the immersion of the user in a digital environment that mimics the real world . In conthttps://www.youtube.com/watch?v=79q7bh3PbsA&ab_channel=AustinHeffernan). Physiotherapists were asked to watch each game and provide a response on a five-point Likert scale to the statements listed in Fig. Sample videos of a member of the research team playing the eligible video games along with a screen recording of the video game itself were included in the survey Fig.  (https:/Physiotherapist recruitment was conducted using the Physiotherapy Association of British Columbia (PABC) website. Physiotherapists who self-identified as having training and/or experience in SVR were identified using the PABC website “Find a Physio” function. Eligible physiotherapists who held valid licensure with the College of Physiotherapists of British Columbia, were actively practicing, and who provided SVR were contacted through email to participate in the survey.a-priori alpha = 0.05) was used to compare the scored physiotherapists’ survey responses given for each of the video games assessed. If a statistically significant difference was identified, a paired samples sign test was used as a post hoc exploratory procedure to identify which video games differ based on the physiotherapists’ responses. Significance values for the sign test were adjusted by the Bonferroni correction for multiple tests, resulting in a significance level set at p < 0.002.Statistical analyses were performed using IBM SPSS Statistics version 24. Medians and interquartile ranges are reported for the scored physiotherapists’ responses to each video game’s survey statement and for global scores. Global scores were calculated for each survey, which is defined as the sum of the scored responses to each survey statement. A Friedman Two-Way ANOVA , VR Real World Bike Racing (VRWBR), Derby VR (DVR) and VR X-Racer (VRXR). A total of 237 physiotherapists were contacted and 40 17%) consented to complete the survey in full. Survey results indicated that the largest fraction of physiotherapist responses was “agree” for VRXR, DVR, VRTR, and VRWBR replicating gaze stabilization exercises, matching habituation exercises, being effective adjunctive therapies and for recommending these games to their patients (Table 7% consenp = 0.013), habituation exercise replication (p < 0.001), effective adjunctive therapy (p = 0.045) and physiotherapist prescribed exercise replication scores (p < 0.001) (Table p < 0.001) better than DVR however VRTR and VRWBR did not differ significantly in their ability to replicate habituation exercises (Table p < 0.001) better than VRXR there was once again no discernable difference between VRWBR and VRTR  Table . In term1) Table . Paired This is the first study that assessed licensed physiotherapists’ opinion on the vestibular rehabilitation potential of commercially available virtual reality videos games. They determined that VRWBR and VRTR were the two VR video games with the highest vestibular rehabilitation potential. Deciding between these two games could not be done based on study results and statistical analyses alone. While this study did not seek to determine user’s preferences for different videogames, their preferences will likely play a large role in treatment adherence, especially for older patients who are known to report reduced usability of new gaming technology . One of For many chronic peripheral vestibular disorders, it is established that vestibular rehabilitation improves symptom scores and quality of life, however studies comparing the relative importance of gaze stabilization, habituation, and substitution exercises for specific vestibular pathologies are scarce and of poor quality , 25. VRTGaze stabilization exercises involve head movements in the vertical plane (pitch) and horizontal plane (yaw) to induce vestibular adaptation and to achieve substitution through enhanced VOR gain . These eThe demonstrable differences between some virtual reality programs, and SVR leaves the opportunity for innovation. Recently, a smartphone-based gaming system for vestibular rehabilitation has been developed which consists of two games with graded levels of difficulty that utilize optokinetic stimulation and discrete head movements in the pitch and yaw planes to achieve rehabilitation . The gamThis study introduces the option of using VRWBR as an adjunctive treatment, however there are limitations to the conclusions drawn. The study by design is unable to provide a robust clinical recommendation for the use of VRWBR. A prospective randomized controlled clinical trial of VRWBR is required to arrive at a robust recommendation. The results are hindered by the lack of validated surveys that assess video games for their vestibular rehabilitation potential. The survey utilized in this study was created by medical students, a neurotologist, and a physiotherapist with a special interest in vestibular rehabilitation and was not subjected to validation testing prior to its use. The physiotherapists based their assessments on video recordings of an individual playing each video game; they did not personally use each video game. It is uncertain how this affects the accuracy of their responses. The licensed physiotherapists surveyed were recruited through the PABC website where physiotherapists can self-select interest/training areas. No attempt was made to select physiotherapists based on objective measures of vestibular education, knowledge, or documented experience. The low response rate is however likely a reflection of participant physiotherapists self selection as Balance and Dizziness Canada lists only 28 therapists in British Columbia who have completed at least one competency-certified formal exam or have taken multiple in-person post-professional courses without formal exams . Future In conclusion, according to the opinions of licensed physiotherapists, VRTR and VRWBR are the most congruent VR video games to SVR. These video games replicate both habituation and gaze stabilization exercises, could be effective adjunctive therapies to vestibular rehabilitation and would be recommended by physiotherapists to their patients. VRWBR is preferable to VRTR with respect to ease of use and the ability to alter the amount of optokinetic stimulation. Prospective studies are needed to confirm the efficacy of these videos games and to determine if they could be used as solitary treatments. These games could lay the foundation for the development of virtual reality video games that replicate vestibular rehabilitation exercises.


The global healthcare crisis with the COVID-19 pandemic has placed a significant overwhelming demand for intubation procedures and the need for reliable and accessible video laryngoscopes. The purpose of this scoping and technological review is to provide a comprehensive overview of the current state of the art, covering the period from 2007 to 2022, pertaining to the manufacturing process, characteristics, and validation of video laryngoscopes produced using additive manufacturing techniques. Following the guidelines outlined in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR), an exhaustive search was conducted across nine prominent databases  and four patent databases , Google Patents). The main materials utilized for the impression, as well as the physical characteristics of the device are introduced at first. Crucial aspects to facilitate proper visualization of the anatomical structures during endotracheal intubation as the optimal angulation of the blade, the mechanical resistance of the device, traction force on the jaw, intubation time, and the experimental methods employed to validate its performance were reviewed in terms of their recent advances.The online version contains supplementary material available at 10.1186/s13643-023-02406-y. The global healthcare crisis with the COVID-19 pandemic evidenced the overwhelming demand for intubation procedures and the need for a video laryngoscope has become more pronounced. Additive manufacturing has emerged as a promising solution, enabling the rapid production and prototyping of video laryngoscopes .Fused deposition modeling (FDM) has been widely employed since 2013 , and polThe video laryngoscope blade is an essential part of the device. With a continuous curve in its design, initially described by Robert Macintosh in 1943 , it can The identified traction forces vary among the different devices, primarily depending on the design and type of material used in the construction of the equipment. However, these data are scarce, as authors do not always prioritize this type of assessment in their studies, which are mostly clinical studies, often neglecting the detailed analysis of the device's design and mechanics . Thus, aRegarding the validation process of manufactured devices, a series of experiments and tests are conducted to assess their performance and functionality. This includes the analysis of factors such as ease of use, maneuverability, intubation success rate, time required for intubation, and potential complications during the procedure , 9. AddiConsidering these factors, we provide a comprehensive overview of the characteristics and protocol validation of the 3D-printed equipment.The manuscript begins with a detailed account of the search strategies, descriptors used, databases employed, and eligibility criteria. Next, a flowchart illustrates the methods of study identification, screening, and inclusion. The results section provides an overview of the historical context and major trends in additive manufacturing for video laryngoscopes (VLPs). Additionally, aspects related to filament selection, forces applied for oral cavity opening, and equipment strength are discussed in this section. Furthermore, the literature’s suggested angulation values, equipment validation mechanisms, and industrial applicability are addressed. Finally, the discussion and conclusion sections offer our perspectives on future research directions. Authors are encouraged to follow this structure to effectively present their findings and insights.This scoping review adhered to the recommendations and checklist derived from the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) , 15. TheThe survey in databases employed Boolean operators “OR” and “AND” to identify relevant descriptors from MeSH, Emtree terms, and DeCS. The search terms included (Laryngoscopies) OR (Laryngoscopes) OR (Laryngoscope) OR (Laryngoscopy) OR  OR  OR (Intubation) OR (Laringoscopio) AND  OR  OR (3 D Printing). Another combination was employed for the Portuguese and Spanish databases, Scielo and Lilacs/Bireme (VHL), using terms (Laringoscopia) OR (Intubação) OR  OR  AND (Manufatura aditiva) OR (3D Impressão).Additionally, a patent search was conducted using the International Patent Classification (IPC) approach with codes A61 , A61B , and the groups and subgroups A61B1/267 (laryngoscopes), and A61B1/05 . A combined approach was utilized, employing IPC with the terms (Laryngoscope) OR (Laryngoscopy) AND (3D Printing) OR  OR , (Laringoscopia) OR (Intubação) OR  OR  AND (Manufatura aditiva) OR (3D Impressão).The eligibility criteria or inclusion in this review encompassed the manufacturing process of video laryngoscope equipment or its components using additive manufacturing techniques, either with or without the integration of micro-cameras or a borescope.Additionally, descriptive, and comparative studies examine the differences between commercially available video laryngoscopes and those produced through additive manufacturing were included, along with clinical trials utilizing mannequins for comparison and usability assessments.Articles solely focusing on the additive manufacturing of accessories, such as the blade, system function for commercial video laryngoscopes, traditional commercial laryngoscopes, or those intended for animal use, were excluded from consideration. No restrictions were imposed on publication dates or languages, and relevant articles and technological documents considered were translated into Portuguese for analysis  patents.The assessment of patents involves an evaluation of their titles, abstracts, claims, and drawings. A third reviewer examined the patent publications in the patent database. Furthermore, additional criteria, including the International Patent Classification (IPC) code, publication date, international registration (PCT), participation of international entities with technological significance, and commercial potential, were taken into account to determine their relevance. The sequence for identifying and selecting documents proceeded as follows:An electronic search was conducted in December 2021 and October 2023 resulting in an initial retrieval of 1588 publications. After removing duplicate entries and screening for relevance based on the title, 1507 publications were excluded as they did not meet the eligibility criterialeaving 86 studies for abstract evaluation. Further evaluation of the full text led to the exclusion of 59 studies, resulting in 22 studies met the inclusion criteria. In the patent database, the search retrieved 2502 patents. After reviewing the titles, abstracts, and drawings, 2484 were excluded.Among the remaining 18 patents, 10 were excluded based on the exclusion criteria, leaving 8 patent documents for analysis. Overall, 30 documents, including both studies and patents, were considered relevant to the search. Figure The search retrieved scientific articles dating back to 2007; however, only publications from 2016 onwards met the selection criteria, as did the patents. Of the selected articles, 15 mentioned the presence of a camera or endoscope, while the remaining 7 did not reference this accessory. In the technological database search, 8 patents mentioned the presence of an endoscope or microcamera. A technological approach identified a total of 19 publications, five originating from the USA and the remaining publications from emerging countries, including Brazil (2), Argentina (1), Equator (1), México (1), South Africa (2), and Turkey (1). Among the identified publications, the majority consisted of scientific articles , followed by four clinical randomized studies and one systematic review. The demographic data of the included articles can be found in Supplemental Table SThe trends in video laryngoscope (VLP) development through additive manufacturing have emerged relatively recently. Early publications primarily focused on the initial stages of producing laryngoscope prototypes for otolaryngology, utilizing processes like light-curing technology . NotablyThe utilization of fused deposition modeling (FDM) for impressions, particularly with the thermoplastic polymer ABS, has been highlighted as the favored approach for rapid prototyping. However, it is essential to note that ABS equipment should be confined to training exercises using simulators due to its carcinogenic properties and lack of compatibility with in vivo tissue , 17, 18.Since the advent of the COVID-19 pandemic in 2020, there has been a heightened emphasis on adopting environmentally friendly thermoplastic polymers. Polylactic acid (PLA) has emerged as a biocompatible, biodegradable thermoplastic polyester sourced from renewable materials that pose no harm to human health , 19. FurRecent explorations have delved into novel combinations of thermoplastic polymers, including polyethylene terephthalate glycol (PETG) , CCTREE This evolving landscape of thermoplastic material investigations provides a foundation for enhancing the development of video laryngoscopes (VLP) through additive manufacturing, aligning with the ongoing progression of medical requirements, and elevating the potential for advancing patient care.In the development of the 3D video laryngoscope, Londoño et al.  employedIn the initial design process, the model must possess certain features, as identified by Huysamen : it shouOther characteristics relevant to the device design were described, including a hyper-angulated blade similar to those of the Airtraq and Pentax WS , as well as increased blade thickness for patients with limited mouth opening .Although sparsely discussed, several considerations regarding the resistance and force exerted on a video laryngoscope can be inferred from the literature references. Generally, two types of forces are assessed in studies: the force required to open the oral cavity and the equipment's resistance force, associated with a minimum usage force. This latter force is relevant due to the potential for deformities and fractures in the device.3, suggesting the viability of using PETG filament for the video laryngoscope blade. Other researchers, as in [References  and 21]21] repors, as in , studiedRegarding the maximum force necessary for opening the oral cavity, a technical document  comparedThe Macintosh blade design is the most prevalent among the examined studies, primarily due to its capacity to ameliorate minor intubation difficulties and optimize neck mobility angle. Beyond these factors, further advantages have been underscored with the utilization of this blade, including ease of attachment, illumination, field of view, clinical applicability, applied force, and intubation duration, all of which were significantly influenced by the blade type . RegardiRegarding the cleansing of metal blades, it was demonstrated that standardized disinfection techniques did not effectively neutralize proteinaceous materials present in secretions such as blood, which come into contact with the blade and handle. In a study evaluating the disinfection process of 100 conventional laryngoscopes, a notable 38% contamination rate of the handle was observed, with the presence of Streptococcus viridians in the culture, thereby questioning the efficacy of the process and suggesting the use of disposable blades . The recFor devices manufactured through additive manufacturing, no specific sterilization and cleansing protocol has been indicated. Instead, standardized hospital protocols for reusable devices and ethylene oxide disinfection are suggested . As of nIn our study, comparative data were obtained using metal laryngoscopes, video laryngoscopes with Macintosh blades, and 3D-printed video laryngoscopes on simulation mannequins with experienced physicians using the devices. Team training, resistance tests, and comparisons with commercial video laryngoscopes were conducted using SimMan3G simulation mannequins with ease and difficult airway, involving a fully inflated tongue and stiff neck, to assess the efficacy of the 3D-printed video laryngoscope. A total of 266 professionals experienced in intubation procedures participated in the studies , 21, 24.Five experimental studies examined the performance of the 3D-printed video laryngoscope on mannequins , 21, 24.The intubation time was significantly shorter when using the 3D-printed video laryngoscope developed by De Villiers et al.   when compared to other 3D-printed prototypes and commercial devices , 9, 10.4.1% whenWhile experimental tests have been conducted on mannequins, further studies need to be undertaken to evaluate the suitability of this equipment for human use. Limitations such as fog or anatomical features must be taken into account, as they cannot be properly assessed in mannequins .However, a systematic review  of five In the same study, it was identified that the highest rates of intubation success and intubation times, along with the lowest rates of complications, were achieved when inexperienced physicians utilized the Gladescope brand’s Macintosh-bladed video laryngoscope. On the other hand, no significant differences were observed between devices when used by experienced anesthesiologists , 9, 10.Two documents, PCT WO2019075588A1  and PCT The objective of conducting this scoping and technological review is to present a holistic exploration of contemporary advancements. Encompassing the timeframe from 2007 to 2022, this review delves into the manufacturing processes, attributes, and validation protocols of video laryngoscopes crafted through additive manufacturing methods.In the realm of additive manufacturing, the availability of materials accessible for widespread use in 3D printers has led to notable choices such as ABS and PLA filaments. These materials have found applications in prototyping, validation, and airway access training on mannequins , 17. NevThe design methodology has proven to be relevant, although it is not extensively described in the studies and patents. It should be noted that blade characteristics are crucial in optimizing laryngeal access in the device design . RegardiRegarding the force magnitudes, experimental investigations involving 24 patients and commercial devices unveiled notable findings. The application of force at the lingual base was studied using both a comparative Macintosh laryngoscope and a commercial Glidescope VLP. Data acquired through sensors, encompassing metrics such as peak, average, and impulse forces, revealed a substantial reduction exceeding 50% in the peak force (25 N) when utilizing the Glidescope video laryngoscope, as compared to the average force of 41 N exerted with the Macintosh laryngoscope metal during laryngoscopy .In a comparative manner, the study conducted by Rassam in 2005  entailedComparative evaluation of 20 different disposable and non-disposable blade materials, excluding polymer filament material, indicated that laryngoscopy duration exhibited a direct correlation with increased force. Consequently, lighter devices facilitate visualization and reduce intubation time. Moreover, the utilization of polycarbonate blades could be repeated for up to 100 intubations without damage or fracture—a figure analogous to predictions for polymer filament blades , 23.With regard to blade angulation, the video laryngoscope models produced demonstrated a faithful replication of the conventional Macintosh laryngoscope model, specifically utilizing the number 3 blade pattern that attaches to the handle. The interrelation between the blade's angulation and its attachment to the handle emerged as a pivotal factor in diminishing the risk of equipment fracture and enhancing oral cavity accessibility. These enhancements were particularly pronounced in the context of the Macintosh model, where blade angulation was meticulously optimized to ensure optimal laryngeal visualization , 8. CertIn contrast, an investigation comparing Glidescope blades with varying angulations in 162 patients indicated that a 70° angle yielded reduced intubation time and higher success rates, rendering it more preferable than the 90° angle . These rSeveral device attributes contribute to ease of use and glottic visualization. An optimal distance of 5.5 cm from the blade’s tip was identified as ideal for microcamera positioning, enabling effective laryngeal visualization . The incThe validation of the video laryngoscope prototype encompassed assessments conducted on simulation mannequins and experienced professionals, underscoring the preliminary testing phase of the equipment. The utilization of mannequins was recommended to ascertain the basic functionality of the device. However, the new blades must undergo patient-based testing before reaching the consumer market. Comparative tests with conventional equipment, such as metal and plastic blades, are imperative to identify the optimal performance of the device , 32.During simulations involving mannequins, a standardized scale consistently informed the studies. Key evaluation parameters encompassed intubation time, laryngeal visualization time, and intubation success rates within the context of 3D-printed models. Primary parameters, particularly intubation time and success rate, were deemed essential for evaluation. Intubation failure was defined as instances requiring 120 s or more for intubation within a maximum of 3 attempts . IntubatThe video laryngoscope is considered a semi-critical medical device, as it comes into contact with non-intact skin or intact mucous membranes, making it susceptible to contamination by microorganisms such as bacteria, fungi, viruses, or prions. As a result, these devices require a level of disinfection that can be achieved with the use of chemical disinfectants when dealing with stainless steel or smooth plastic devices. Medical devices classified as semi-critical should undergo at least medium to high-level disinfection after cleaning. The Centers for Disease Control and Prevention (CDC) and the American Society of Anesthesiologists recommend cleaning and disinfection with chemical agents, and the FDA recommends a minimum of 10 min contact time, although autoclaving for disinfection is considered the ideal method. A strong recommendation is that both the blade and the handle be thoroughly cleaned and disinfected to reduce the risk of infection , 34.In a study conducted in Spain, 38% of laryngoscope devices were cleaned and disinfected, with no national protocol in place. Esler et al.  describeThe disinfection process with disinfectant products or physical thermos disinfection should comply with the health regulations of each country. To enable patient testing, the disinfection methodology is one of the key considerations when seeking approval from hospital ethics committees, as it is essential to prevent contamination of the medical equipment and reduce the risk of infections among patients. This underscores and justifies the need for elucidating the best and most efficient disinfection methodology for the 3D video laryngoscope , 34In this study, limitations may be present in the selection phase and complete reading of the articles, leading to selection bias. In addition, comparisons are limited owing to the heterogeneity between studies.The paramount feature of the video laryngoscope is its hyper-angled blade, ideally positioned within the range of 70° to 90° , 8. The Additional file 1: Table S1. Studies encountered according to the type of publication/study, authorship, title, journal/institution, country of study, and year of publication.Additional file 2: Table S2. Description of technological documents.