Objective Difficulty Research Articles

The new impact factor of World Psychiatry

The new impact factor of World Psychiatry

The Web as Information Source: a Case Study on the Impact of Internet Search Lessons

The use of the Web by students has increased more and more and it has become the most recurring way to find quick information for educational purposes. Given the lack, in Italy, of thorough programs for the integration of Information Literacy and Internet searches in schools and universities, the adults who are now using it are almost always self-taught. Consequently, many different approaches to the medium have spread, and with them an objective difficulty in planning Internet-research courses, since everyone has his/her own way to search and a unique perception of his/her search skills. That’s why delivering a course where every participant is forced to follow the same learning path may originate feelings of frustration, unease, or boredom, thus reducing the learning potential offered by the course. This research focuses on the Internet Search side of Information Literacy and analyzes the impact of short lessons on first and second year university students in Education at the University of Bolzano, Italy. The students are either native German-speakers or native Italian-speakers, and the research focuses, in an European perspective, on the differences in their Internet-research approaches as well. The first phase consists in interviews and test (the logs of the internet sessions are recorded by a software) to find out the perception of reliability of the Internet information and the way to find it by the students. The second phase is the course in itself, which focuses on Boolean operators, information retrieval theories and exercises, and evaluation of web pages. After the course the students are interviewed and tested again, to check if their approach to internet research has changed and in which way. The results can be used to plan courses on Information Literacy and Internet Search with individualized programs, or to propose methods to assess the learning in this field.

Disseminated Intravascular Coagulation in Burn Injury

Disseminated intravascular coagulation (DIC) is a complex and multifaceted disorder characterized by the activation of coagulation and fibrinolytic pathways, consumption of coagulation factors, and depletion of coagulation regulatory proteins. The introduction into the circulation of cellular debris characterized by strong thromboplastic activity due to tissue factor exposition or release (in or from burned tissues), which can thereby activate extrinsic pathway of coagulation system and trigger massive thrombin generation when present in sufficient concentration, represents the most plausible biological explanation to support the development of intravascular coagulation in patients with burn injury. Severe burns left untreated might also lead to an immunological and inflammatory response (activation of the complement cascade), which can amplify fibrinolysis and blood clotting. Overall, the real prevalence of DIC in patients with burns is as yet unclear. Postmortem, retrospective, and even longitudinal investigations are in fact biased by several factors, such as the objective difficulty to establish whether DIC might have occurred as a primary complication of burns or rather as a consequence of other superimposed pathologies (e.g., sepsis, multiple organ failure), the different diagnostic criteria for assessing DIC, and the heterogeneity of the patient samples studied. Nevertheless, the current scientific evidence is consistent with the hypothesis that biochemical changes suggestive for DIC (hypercoagulability, hypo- and hyperfibrinolysis) are commonplace in patients with burn trauma, and their severity increases exponentially with the severity of injury. Overt DIC seems to occur especially in critically ill burn patients or in those with severe burns (up to third degree) and large involvement of body surface area, in whom an appropriate therapy might be effective to prevent the otherwise fulminant course. Although early prophylaxis with antithrombin concentrates holds promises, especially in the acute phase of thermal injury, larger clinical trials are needed to confirm the benefit of this therapeutic approach.

Magnetic resonance (MR) pelvimetry as a predictor of difficulty in laparoscopic operations for rectal cancer

Laparoscopic surgery for rectal cancer is now well estab-lished. Recent studies have shown no difference in survivalor oncologic outcomes when laparoscopic surgery iscompared to open procedures [1, 2]. The laparoscopicapproach does, however, present the surgeon with inherentchallenges. Previous abdominal surgery, tumours closer tothe anal verge, high body mass index (BMI), and preop-erative radiotherapy have been shown to increase the dif-ficulty of laparoscopic procedures in the pelvis [3–6].It is often assumed that laparoscopic resections for rectalcancer are also complicated by a deep, narrow pelvis inwhich access and vision are both restricted by pelvicanatomy. Although a majority of patients undergo preop-erative pelvic magnetic resonance (MR) staging, radio-logical measurement of the bony pelvis––pelvimetry––hasnot been fully assessed as a predictor of difficult laparo-scopic operations.Male sex has been shown to correlate with surgeons’perceived difficulty of laparoscopic resections, althoughmore objective evidence of increased difficulty, in the formof longer operating times or more frequent involvement ofthe circumferential resection margin (CRM), is sparse [6].Indeed, while some authors have demonstrated significantdifferences in pelvic measurements between the sexes [7,8], others have shown considerable overlap [9], suggestingthat the measurements themselves may be a more usefulpredictor of difficulty than sex alone.MR pelvimetry has been evaluated for potential appli-cation in predicting the technical difficulty and outcomes ofopen rectal resection and prostatectomy [3, 4, 7, 10].Various dimensions of the bony pelvis thought to be ofimportance during surgery were studied; all studies used acombination of anteroposterior (AP) measurements in themid-sagittal plane and some form of transverse measure-ment to describe the breadth and depth of the pelvis. Someauthors measured angles and dimensions on the mid-sag-ittal slices to define the acuity of the sacral curve and theother boundaries of the pelvis [3, 7, 10]. One author wentfurther, developing a synthetic measurement designed tobetter describe the pelvic depth observed by the surgeonperforming open radical prostatectomy––the apical depthof the pelvis divided by the transverse interspinous distance[11]. None of these measurements were shown to signifi-cantly predict any objective or subjective measure ofoperative difficulty and pelvimetry seems to have beenabandoned as a predictor in open resections.It is reasonable to expect that pelvic anatomy may bemore important in laparoscopic resections. A prominentsacral promontory, an acutely curved sacrum, or a pelvisparticularly narrow in the transverse plane could conceiv-ably represent anatomical bottlenecks, impeding vision,access, and space in which instruments can be manipulated.Indeed, initial research has shown correlations betweenlonger operating times and a larger pelvic outlet [4] and asmaller lower pelvis diameter [5] and between CRMinvolvement and shorter transverse interspinous distances[12]. Further ascertainment of the influence of pelvic

Assessing Cognitive Load on Web Search Tasks

Assessing cognitive load on web search is useful for characterizing search system features and search tasks with respect to their demands on the searcher's mental effort. It is also helpful for examining how individual differences among searchers (e.g. cognitive abilities) affect the search process. We examined cognitive load from the perspective of primary and secondary task performance. A controlled web search study was conducted with 48 participants. The primary task performance components were found to be significantly related to both the objective and the subjective task difficulty. However, the relationship between objective and subjective task difficulty and the secondary task performance measures was weaker than expected. The results indicate that the dual-task approach needs to be used with caution.

Assessing Cognitive Load on Web Search Tasks

Assessing cognitive load on web search is useful for characterizing search system features and search tasks with respect to their demands on the searcher’s mental effort. It is also helpful for examining how individual differences among searchers (e.g. cognitive abilities) affect the search process. We examined cognitive load from the perspective of primary and secondary task performance. A controlled web search study was conducted with 48 participants. The primary task performance components were found to be significantly related to both the objective and the subjective task difficulty. However, the relationship between objective and subjective task difficulty and the secondary task performance measures was weaker than expected. The results indicate that the dual-task approach needs to be used with caution. INTRODUCTION AND BACKGROUND Web search behavior is affected by the task, system, and individual searcher characteristics. Search tasks and their characterization have been a subject of recent systematic studies [1-3]. In particular, researchers have focused on the effects of task complexity and difficulty on information search process [4-10]. One kind of difficulty encountered by searchers is related to mental, or cognitive, requirements imposed by the search system or the task itself. Understanding factors that contribute to user’s cognitive load on search tasks is crucial to identifying search system features and search tasks types that impose increased levels of load on users. As new interactive features are introduced into the information search systems we need to understand what determines their acceptance and why some evidently useful functions are not widely used. For example, user relevance feedback is a feature that has been reported to be avoided by users due to the heightened cognitive load [11]. Among other factors affecting search performance are the user’s cognitive characteristics (e.g., [12, 13]). Methods used to date in assessing cognitive load included searcher observation, self-reports (e.g., using questionnaires, think-aloud protocols, and post-search interviews), dual-task techniques [14, 16], and various approaches that employ external devices to collect additional data on users (e.g., eye-tracking, pressure-sensitive mouse and other physiological sensors [17]). The latter two groups of techniques have the advantage of enabling real-time, ontask data collection. However, the use of external devices can be expensive and impractical. Hence, the promise of dual-task (DT) method that allows for an indirect objective assessment of mental effort on the primary task. Only few studies employed this method to assess cognitive load in online search tasks (e.g., [14, 15, 18]). The article discusses the dual-task method as the technique for assessing cognitive load on web search tasks and presents research that *Address correspondence to this author at the Department of Library & Information Science, School of Communication and Information, Rutgers University, New Brunswick, NJ, USA; E-mail: WebCog@gwizdka.com contributes to better understanding of how objective task difficulty affects searchers’ behavior and their perception of task difficulty.

Perfil de professores de educação especial: dilemas e desafios na construção da educação básica inclusiva

Discussões acerca da necessidade de redimensionar a escola básica para torná-la um espaço inclusivo são realizadas e as pesquisas sobre formação de professores aptos a colaborar na (re)construção dessa escola tornam-se relevantes. O professor de Educação Especial poderia ser considerado o profissional que, devido a sua experiência e formação, desempenharia um importante papel na construção de espaços escolares inclusivos. Trata-se de reconhecer aspectos, tais como a competência técnica e o compromisso político dos professores, associados a condições mínimas de execução de um projeto de escola que dê conta das diversidades presentes na sociedade brasileira. Este artigo – resultado de uma pesquisa tipo survey – traçou um perfil dos professores que atuavam em escolas especiais na cidade de Fortaleza – CE, por meio de 15 entrevistas com esses atores. Os dados foram organizados com uso da Análise de Conteúdo (BARDIN, 1977). Os professores enfatizaram a inviabilidade objetiva da consecução de práticas inclusivas na escola básica, o que subliminarmente pode indicar uma negação das possibilidades de aprendizagem e desenvolvimento de alunos com necessidades educacionais especiais na escola regular. Estudos dessa natureza podem auxiliar nas alternativas de formação dos professores com vistas à construção da escola básica inclusiva.

EMULATION OF HUMAN FEELINGS AND BEHAVIORS IN AN ANIMATED ARTWORK

The behavior of an animated artwork, survivor — a classroom chair which walks, with a dynamics which some viewers find haunting — reflects an attempt to emulate (and suggest to viewers) some feelings and behaviors that are typical of survivors of landmine blasts, learning to use crutches. The artwork itself is intended for sensitizing viewers to the horror experienced by those who survive, and those who do not. The behavior of such a survivor is affected by several factors: some are due to the objective difficulty of using prosthetic legs, and some are due to emotional factors, e.g., fear, "shame" of being in such situation, and pain. The mechanical structure, strongly conditioned by artistic requirements, was combined with a control system that exhibits appropriate behaviors. Behavioral control, a technique developed for the control of mobile robots, was used in survivor, and implemented over a modified version of the traditional Brooks' subsumption architecture. This technique makes it possible to emulate normal locomotion behaviors such as the need of avoiding obstacles and typical animal feelings such as curiosity, hunger, fatigue and fear. We describe the mechanics and viewers' response, and formalize aesthetic response. We briefly survey computer modelling of emotions, robotic art, and biomimetic locomotion in robotics.

Comparison of video and direct observation methods for measuring oral behaviour in veal calves

Measuring behaviour, especially oral behaviour, has always been a debated issue: therefore the aim of this paper is to closely examine the study of oral behaviour in calves and the approaching methodology. Behavioural observations were conducted by two media (direct observations by check sheets and indirect observations by videotapes recorded by cameras connected to a digital field switcher and a time-lapse video recorder) in order to compare data and assess the reliability and validity of the two methods in identifying some oral behavioural patterns in calves.The study was carried out on 54 Polish Friesian calves housed in group pens and in individual crates. The behaviour of the calves was investigated during the fattening period on the 2nd, 7th, 13th, 18th and 23rd week, one hour before and one hour after each of the two meals. Two experienced observers checked the behaviour of the calves, including oral behaviours on structures and buckets and oral stereotypies, by direct observations using a scan sampling every 2 minutes. The calves' behaviour was also video recorded on the same days in which the direct observations were carried out and analysed by the same two observers. Percentages of time spent on each type of behaviour were calculated and analysed by Chi-square test. Regardless of the housing system, the comparison between direct and indirect observations revealed significant differences in almost every behavioural category. Licking, biting and nibbling structures, nibbling and sucking the bucket, playing with the bucket and the teat, chewing and oral stereotypies were significantly higher in direct observations compared to indirect (P < 0.001), while inactivity was higher in video recorded observations (P < 0.001). In conclusion, regardless of the type of housing, our results revealed an objective difficulty in analysing videotapes with very detailed behavioural categories, like oral behaviours. Although video recording can certainly represent a useful and practical alternative to direct observations in many situations, the video recording system used in this study for investigating calves’ oral behaviour, in spite of the use of multiple cameras, could not replace direct observations, probably due to the restricted field of view, the low depth of focus, the black and white vision, the lack of audio and the time-lapse feature.

Duplex polymerase chain reaction assay to screen for feline herpesvirus-1 and Chlamydophila spp. in mucosal swabs from cats.

Respiratory infections are widespread in the cat population and they are often associated with several pathogens such as FHV-1, FCV and Chlamydophila spp. (Gaskell and Dawson, 1998). The definitive diagnosis of feline herpesvirosis and feline chlamydophilosis requires the isolation of their aetiological agents, since serology alone does not allow us to distinguish infected animals from vaccinated ones. FHV-1 isolation using cell cultures is easily performed, even if some cats can show negative results because of (i) inadequate amount of virus present in the ocular and/or pharyngeal swabs, (ii) presence of antibodies in the extra-cellular liquids able to inhibit viral replication in vitro, (iii) contemporaneous presence in the swabs of FCV that could disguise the cytopathic effect induced by FHV-1. As regards Chlamydophila felis these problems are increased by the objective difficulty of the isolation that can be performed through inoculation of embryonate eggs of chicken. To remove these disadvantages it is useful to utilize the techniques of molecular biology, such as the polymerase chain reaction, which is able to detect specific sequences of DNA. Furthermore, it is possible to proceed from the amplicons to the identification of the chlamydofiles after treatment with restriction enzymes. The aims of the current research are (i) to report the results of a study performed by duplex-PCR specific for FHV-1 and Chlamydophila spp. in a population of 40 cats with U.R.T.D.-related symptoms in order to appraise the prevalence of two of the most common agents associated with respiratory infections, and (ii) to identify Chlamydophila felis using restriction enzymes.

A new perspective in identifying the precursory patterns of eruptions

The complexity of the processes responsible for volcanic eruptions makes a theoretical approach to forecasting the evolution of volcanic unrest rather difficult. A feasible strategy for this purpose appears to be the identification of possible repetitive schemes (patterns) in the pre-eruptive unrest of volcanoes. Nevertheless, the limited availability and the heterogeneity of pre-eruptive data, and the objective difficulty in quantitatively recognizing complex pre-eruptive patterns, make this task very difficult. In this work we address this issue by using a pattern recognition approach applied to the seismicity recorded during 217 volcanic episodes of unrest around the world. In particular, we use two non-parametric algorithms that have proven to give satisfactory results in dealing with a small amount of data, even if not normally distributed and/or characterized by discrete or categorical values. The results show evidence of a longer period of instability in the unrest preceding an eruption, compared to isolated unrest. This might indicate, even if not necessarily, a difference in the energy of processes responsible for the two types of unrest. However, if the unrest is followed by an eruption, it seems that the seismic energy released during the unrest (parameterized by the duration of the swarm and the maximum magnitude recorded) is not indicative of the magnitude of the impending eruption. We also found that, in general, unrest followed by the largest explosive eruptions have a longer repose time than those related to moderate eruptions. This evidence supports the fact that the occurrence of a large eruption needs a sufficient amount of time after the last event in order to re-charge the feeding system and to achieve a closed-conduit regime so that a sufficiently large amount of gas can be accumulated.

The Reform of the Italian Local Government Accounting System. A Critical Analysis

In 1995 the Italian Parliament passed a measure that introduced some significant innovations in the accounting system of Italian local governments. According to their promoters, these innovations should have improved the overall quality of decisions and increased public efficiency, thanks to the availability of targeted and reliable economic information. At the same time, Municipalities and Provinces should have implemented - in accordance with the trends currently emerging in the leading Western countries - an accrual-based accounting system, that should have led to assessing with fuller knowledge of the facts whether local governments are managed by considering intergenerational equity. Today, six years after the introduction of the decree many expectations have been disappointed, while there is no proof of significant improvement - i) neither in the quality of economic information, ii) nor in the quality of the decisions taken by local governments. This paper aims at documenting a series of elements of objective difficulty in the implementation of the 1995 reform, thereby discussing their possible causes and feasible solutions. To this end, the paper provides some data about the framework of Italian local governments and then briefly examines the reasons behind the 1995 reform. The paper then moves on to illustrate the contents of the reform, thereby chiefly dwelling upon the introduction of accrual-based financial reporting. It finally focuses on a sample of 23 local governments that produced these reports for the first time in 1998, and highlights a series of problems that emerged with regard to both communicational efficacy and fair presentation. The conclusions summarize the major gaps between the reform's objectives and actual effects, and tries to grasp the reasons for these gaps and formulate some suggestions in order to re-design the system.

Comparison of performance in successive CASP experiments.

As the number of completed CASP (Critical Assessment of Protein Structure Prediction) experiments grows, so does the need for stable, standard methods for comparing performance in successive experiments. It is critical to develop methods for determining the areas in which there is progress and in which areas are static. We have added an analysis of the CASP4 results to that previously published for CASPs 1, 2, and 3. We again use a unified difficulty scale to permit comparison of performance as a function of target difficulty in the different CASPs. The scale is used to compare performance in aligning target sequences to a structural template. There was a clear improvement in alignment quality between CASP1 (1994) and CASP2 (1996). No change is apparent between CASP2 and CASP3 (1998). There is a small barely detectable improvement between CASP3 and the latest experiment (CASP4, 2000). Alignment remains the major source of error in all models based on less than about 30% sequence identity. Comparison of performance in the new fold modeling regime is complicated by issues in devising an objective target difficulty scale. We have found limited numerical support for significant progress between CASP3 and CASP4 in this area. More subjectively, most observers are convinced that there has been substantial progress. Progress is dominated by a single group.

COUPLING THEORETICAL DATA AND TRANSLATIONAL FRFS TO PERFORM DISTRIBUTED STRUCTURAL MODIFICATION

Predicting the effect of distributed structural modifications, such as rib or plate stiffeners, on structures for which a theoretical model is not available, is not practically considered in the technical literature: this is due to the objective difficulty of coupling continuous modifications with an original structure known through its frequency response function. While this is not the case when lumped modifications are accounted for, the possibility of describing distributed modifications requires non-trivial operations involving the use of different models for the structure and the modification, an appropriate use of a condensation procedure and a careful consideration of non-local effects introduced by the above condensation. The basic requirements for a consistent modelling are here considered and some results are presented.

Differential allocation of study time: Incomplete compensation for the difficulty of the materials

The results of many experiments have shown that although people distribute their study time depending on the perceived difficulty of the materials, they do not succeed in compensating for this difficulty (e.g., Mazzoni & Cornoldi, 1993). The purpose of this paper was to explore possible ways to induce compensation. The objective difficulty of the items was varied by manipulating their concreteness. In Experiment 1, we explored whether compensation could be increased through practice. In Experiment 2, predictive memory judgements were obtained to determine to what extent participants were sensitive to the characteristics of the material that made it difficult. Finally, in Experiment 3, participants were given instructions designed to achieve complete compensation. Results showed that although participants' judgements of learning and their allocation of time were sensitive to the objective difficulty of the materials, this knowledge was not spontaneously used to compensate. Thus, even with practice participants recalled more easy items than difficult ones. Only instructions that induced greater awareness of the nature of the material were able to produce complete compensation.

The 48-Pictures Test: A two-alternative forced-choice recognition test for the detection of malingering

We tested the validity of the 48-Pictures Test, a 2-alternative forced-choice recognition test, in detecting exaggerated memory impairments. This test maximizes subjective difficulty, through a large number of stimuli and shows minimal objective difficulty. We compared 17 suspected malingerers to 39 patients with memory impairments (6 amnesic, 15 frontal lobe dysfunctions, 18 other etiologies), and 17 normal adults instructed to simulate malingering on three memory tests: the 48-Pictures Test, the Rey Auditory Verbal Learning Test (RAVLT), and the Rey Complex Figure Test (RCFT). On the 48-Pictures Test, the clinical groups showed good recognition performance (amnesics: 85%; frontal dysfunction: 94%; other memory impairments: 97%), whereas the two simulator groups showed a poor performance (suspected malingerers: 62% correct; volunteer simulators 68% correct). The two other tests did not show a high degree of discrimination between the clinical groups and the simulator groups, except in 2 measures: the 2 simulator groups tended to show a performance decrement from the last recall trial to immediate recognition of the RAVLT and also performed better than the clinical groups on the immediate recall of the RCFT. A discriminant analysis with the latter 2 measures and the 48-Pictures Test correctly classified 96% of the participants. These results suggest that the 48-Pictures Test is a useful tool for the detection of possible simulated memory impairment and that when combined to the RAVLT recall-recognition difference score and to the immediate recall score on the RCFT can provide strong evidence of exaggerated memory impairment.

Diagnosis of Multiple Faults in Systems: Effects of Fault Difficulty, Expectancy, and Prior Exposure

It has often been noted that today's human operators of complex industrial systems must occasionally deal with multiple component failures, but that they are trained instead to think in terms of single faults. This can lead to the minor inconvenience of simply taking longer to troubleshoot, or to the major hazards of a fundamental misunderstanding of system state. In two studies we examined these influences on subjects' ability to diagnose a multiple fault in a simulated electronic circuit: (1) objective multiple fault difficulty, (2) prior practice with multiple faults, and (3) expectancy or mental set for multiple faults. Previous research had confounded the latter two variables. Experiment 1 showed that the difficulty of multiple faults varied as our model predicted, but that the difficulty of certain faults interacted with verbalization. Experiment 2 showed that both prior practice and expectancy influence how effectively subjects deal with a difficult multiple fault, but not quite as expected. We conclude that the ability to diagnose multiple faults is multiply determined, depending on degree of practice, mental set, and the difficulty of the multiple fault itself. These results will help us define the requirements for decision support tools and they have also led us to perform investigations in the field, as reported in Reising and Sanderson (1995).

Mapping the Domain of Electronic Repair Shops: A Field Study in Fault Diagnosis

Recent experimental research has indicated that different multiple faults impose differing levels of objective and subjective difficulty on human troubleshooters. Technological advances suggest that systems are becoming more complex and integrated, in which case multiple components will fail. Operators will have to be able to deal with these more complex failures. In this paper we report field work conducted in order to build and substantiate a model of the factors influencing fault diagnosis in the field. By conducting field observations and by constructing concept maps, we investigated how expert troubleshooters handle the difficulty associated with diagnosing multiple faults. The troubleshooters were expert electronic technicians in departmental repair shops on a large university campus. The end product of the research is a model of fault diagnosis that is grounded in field data. Our results suggest that diagnostic difficulty arises from several factors: (1) organizational structure, (2) technicians' strategies for fault diagnosis, and (3) equipment design. The field observations and concept maps indicate that technicians approach the diagnostic task with standard, ritualistic methods that they have developed over years of experience. They generally go through two phases of troubleshooting: (1) the problem definition phase and (2) what we call the At-the-Equipment-TroubleShooting (AETS) phase. Technicians also reason about multiple failures in series, considering one simple explanation at a time. Our principal conclusion is that in real-world settings the three previously mentioned factors have evolved to avoid situations in which technicians must engage in prolonged functional reasoning. These findings will be used (1) to develop further the model of fault diagnosis, and (2) to guide future experimental investigations studying the influences of fault diagnosis.

Diagnosing Multiple Simultaneous Faults

Most recent studies of human diagnostic reasoning, or “troubleshooting,” have concentrated on the human's ability to diagnose single faults in a system. Little attention has been paid to human diagnosis of multiple simultaneous faults. Multiple faults are usually functionally unrelated, but sometimes they interact with each other, resulting in potentially confusing symptoms. An experiment was conducted to test the relative difficulty of diagnosing multiple faults whose symptoms interacted to a lesser or greater degree. The experimental test-bed was a simulated binary adder (logic circuit) into which one or more faults could be inserted by the experimenter. Four levels of objective multiple fault difficulty were identified based on the type of evidence available and the type of reasoning required to successfully diagnose the fault. Subjective mental workload and the number of tests required for each diagnosis increased as objective multiple fault difficulty rose from level 1 to 4. The time taken for a diagnosis increased as difficulty rose from level 2 to 4, but level 1 was higher than expected, suggesting difficulties that were not captured in the initial classification. Further analysis has explored these finding through performance measures and verbal protocols. Overall, this research indicates that multiple faults differ in how readily they can be diagnosed. However performance and subjective mental workload depend upon a number of factors that are now just starting to be understood, including the ease and speed of extracting the sufficient evidence for diagnosis, prior exposure to the constituent faults, and the testing strategy used by troubleshooters.

Perception de la difficulté, entropie et performance

De nombreux modèles psychologiques du comportement utilisent le concept de difficulté perçue, sans pour autant en étudier la nature, ni les modalités d'élaboration. L'expérience présentée vise à éclairer, dans une perspective psychophysique, les processus à l'œuvre dans la perception de la difficulté. Certains travaux réalisés dans les années 70 sur ce sujet n'ont pu donner de résultats consistants (Borg et al, 1971). Cela peut être expliqué par un manque de rigueur dans l'utilisation des méthodes psychophysiques et de leurs propriétés mathématiques. L'expérience présentée utilise les tâches de pointage de Fitts (1954), avec cinq niveaux de difficulté. Les sujets (n = 27), après réalisation de chaque tâche, en évaluent la difficulté selon la méthode d'estimation des grandeurs. Une relation exponentielle est mise en évidence entre difficulté objective et difficulté perçue. La relation difficulté objective-performance est également de type exponentiel. En revanche, la relation performance-difficulté perçue est de type puissance, mais ce type de fonction n'est mis en évidence qu'en ce qui concerne les données moyennées. Ces résultats suggèrent que la perception de la difficulté ne se base ni sur les caractéristiques objectives de la tâche, ni sur une évaluation de la performance, mais sur une variable intermédiaire dont la nature demeure à déterminer. Many psychological theories use the concept of perceived difficulty as a mediator of emotion, motivation and behavior. Nevertheless, these models do not give any explanation about its nature and its elaboration. The aim of this experiment is to investigate, according to a psychophysical point of view, how difficulty is perceived in perceptivo-motor tasks. Earlier research, conducted in the seventies by Borg et al on the problems of perceived difficulty, did not give any consistent results 1971. This could be explained in part by a lack of rigour in the use of the psychophysical methods and of their mathematical properties. The present experiment uses the Fitts (1954) tapping tasks with five levels of difficulty. The entropy of each task is calculated according to the formula proposed by Fitts. Subjects (n = 27) perform each task and rate its difficulty according to the magnitude estimation method. The easiest tasks serve as a modulus. Performance is recorded as movement time. An exponential function is evidenced between objective and perceived difficulty, for averaged data as well as for individual data. It is concluded that objective difficulty cannot represent the stimulus taken in to account, as the magnitude estimation method generally yields to power functions between stimuli and responses. However, it could be predicted that the true stimulus is an exponential transformation of objective difficulty. The relationship between objective difficulty and performance appears to be exponential, for averaged data as well as for individual data. Many authors have previously emphasized the linearity of the relation entropy-performance (Hick, 1952; Fitts (1954)). However, a re-examination of the original data of Fitts (1954) confirms the exponentiality of the relation. This issue is briefly discussed. On the other hand, the relationship performance-perceived difficulty can be fitted by a power function. Nevertheless, the last result is obtained for averaged data only. The relationship between performance and perceived difficulty, for individuals, is largely inconsistent. This indicates that performance equally cannot represente the stimulus taken into account. It is concluded that this stimulus should be an intermediate variable, of which performance could represent a probabilistic indicator.