The Difference Between Expert Radiologists And Novices In Medical Image Visual Searching

Modern medical photography provides structural and functional images of human tissues and organs in a noninvasive way and it plays an increasingly important role in medical diagnosis.According to the worldwide statistics,about 1 billion chest and breast X-ray examinations are taken per year,and averagely 120 medical images are produced per second.The rapid development of medical photography makes clinic diagnoses more precise and efficient.According to the researches on radio-logical examination,the average false-negative error rate is 20-30%.About 40 percent of radio-logical examinations are operated on chest with 26%false-negative errors.False negatives do harm to the health of the patients,lead to medical disputes and even causes significant medical negligence.Numerous studies have shown that accuracy and response speed of experts in medical image visual searching are better than novices.Clarifing the cognitive mechanism of visual searching of experts is helpful to promote diagnosis performance and to provide the expertise growth model of radiology.In this paper,psychological theories and methods,such as scene perception and visual search,are applied to research on visual search of medical image.X-ray is adopted to detect pulmonary nodule.Expert-novice paradigm is used to investigate the difference between expert radiologists and novices in medical image visual searching form the perspectives of visual complexity,tasks and clues.Three parts including 8 experiments were carried out by using visual searching paradigm.The first part aimed to find out the differences between experts and novices when they worked on the task of image visual searching by changing the visual complexity of materials,and to explore the effect of top-down and bottom-up processing on image visual searching tasks.This part includes 3 experiments.Experiment 1 was conducted to figure out the differences of visual searching between experts and novices at different levels of nodules.15 experts and 15 novices participated in the experiment to explore the decision making of experts and novices at different levels of significance(high,middle vs.low).The results showed that experts made fewer false-negatives errors and their scanning modes were more brief and efficient.Experts had more advantages when confronting with difficult experiment materials.Experts tend to make decision-making errors while novices were more likely to make scanning errors.The study indicated that the experience of the observers and the nodule salience together affected the searching performance and the allocation of fixation.Further analysis showed that they played a joint role in the visual attention on images at scanning stage,while they played independent roles at confirmation stage.Moreover,experience of conductors only worked at scanning stage.Experiment 2 was conducted to help experts and novices investigate the impact of nodule size and its position on visual searching.15 experts and 20 novices participated in the experiment to explore the decision making of experts and novices in different size(big or small)and location of nodules(concealed or non-concealed).The results showed that experts played better at searching performance and processing efficiency compared with novices,and experts' attention preference had high correlation with critical anatomical areas.The results also showed that the experience,along with size and position of nodules,jointly affected the observers' searching efficiency and allocation of their fixation at scanning stage,while they had separate impacts at confirmation stage.Meanwhile,experience of conductors only worked at scanning stage.Experiment 3 was conducted to help experts and novices to explore the impact of nodule size and density on visual searching.15 experts and 15 novices participated in the experiment to explore the decision making between experts and novices in different size(big or small)and density of nodule(high or low).The results showed that experts played better at searching performance and processing efficiency compared to novices.It was also found that experience and nodule density had joint impact on observers'searching performance and allocation of fixation.The further analysis indicated that the experience,along with density of nodules,jointly affected the visual fixation on images at scanning stage,while they had separate impacts on visual attention at confirmation stage,and knowledge and experience only worked at scanning stage.The second part aimed to explore the influence of tasks on medical image visual searching carried out by experts and novices and reveal the occurrence mechanism of false negatives by manipulating various timing pressure and target prevalence.Two experiments were included in this part.Experiment 4 was conducted to explore their differences of visual searching under different timing pressure.13 experts and 13 novices participated in the experiment to explore the decision making between experts and novices in different pressure of time(1-8)and size of nodules(big or small).The results showed that timing pressure had obvious impact on false negatives by both experts and novices.The performance of experts and novices were slightly different in each level of timing pressure with experts outdoing novices in sensibility:for big nodules,the false negative rate of experts and novices became steady after 10 seconds of scanning,while,for small nodules,the false negative rate of experts became steady after 25 seconds of scanning with the false negative rate of novices steady after 20 seconds of scanning.The judgments of experts and novices tend to be more prudent with the increase of timing pressure level.Experiment 5 was conducted to explore their differences of visual searching at different target prevalence.15 experts and 15 novices participated in the experiment to explore the decision making between experts and novices in different target prevalence(50%or 10%)and size of' nodules(big or small).The research indicated that false negative errors for both big and small nodule low target prevalence,with the influence of low prevalence much smaller than that of novices.Under low target prevalence,scanning error might be the main reason for both experts'and novices' false negatives.The third part aimed to investigate the impact of clues on medical image visual searching carried out by experts and novices by manipulating different types of clues.3 experiments were included in this part.Experiment 6 was conducted to explore the impact on visual searching carried out by experts and novices if there were no clues.15 experts and 20 novices participated in the experiment to explore the decision making between experts and novices in different cue categories(yes or no),different size(big or small)and location(concealed or non-concealed)of nodules.The results showed that,for experts,the false negatives rate of small nodule in concealed position with clues was lower than without clues,while,for novices,the false negatives rate of all sizes of nodule with clues was lower than that without clues.Experts were less affected by clues than novices.With the help of clues,both times of fixation and total fixation time increased.The times of re-fixation indicated that novices spare more cognitive resources on processing of clue words.Experiment 7 was conducted to investigate the impact of the authoritative degree of clue on experts and novices in visual searching.15 experts and 19 novices participated in the experiment to explore the decision making between experts and novices in different authority level of clue(high,low vs.no-clue).The results showed that,for novices,the false negatives rate under the help of both highly and lowly authoritative clues was lower than that without clues,while,for experts,the false negatives rate under the help of highly authoritative clues was lower than without any clues.But novices were more influenced by highly authoritative clues than experts.For novices under the help of both highly and lowly authoritative clues,both times of fixation and total fixation time were higher than that without any clues.For experts under the help of both highly authoritative clues,both times of fixation and total fixation time were higher than that without clues.Experiment 8 was conducted to explore the impact of the consistency of clues on visual searching carried out by experts and novices.16 experts and 20 novices participated in the experiment to explore the decision making between experts and novices in different consistancy of clue(consistent,inconsistent vs.no-clue).The results showed that,for experts,the marginal false negative rate under consistent clues was higher than that under inconsistent clues.But,for both experts and novices,there was no obvious difference for false negative rate under no clues.For novices,the false negative rate with consistent clues was lower than that without clues,but the false negative rate with inconsistent clues was higher than that without clues.Conclusions was made as follow based on the finding of the three parts:(1)Visual searching of medical images boasts the effect of perception coding advantage of expertise.Experts make fewer false negatives and find objects faster,have the ability of using stored long-term practical experience to selectively process image information.Their scanning mode tends to be more efficient,and has broader perception span.(2)Experts' advantages lie in the visual searching of more difficult medical image.(3)The medical images identify objects by the integration way of 2 processes namely top-down and bottom-up.Differences of the interacted impact of experience and knowledge and features of objects vary at different stages.At scanning stage,both of them have joint role in visual fixation on images,while they have independent roles in visual fixation on images on confirmation stage.Expertise works only on scanning stage.(4)The false negative rates for both experts and novices are influenced by timing pressure,but their tending to make errors are slightly different under different level of timing pressure.The searching time for medical image takes at least 25 seconds.(5)Low target prevalence effect exists in visual searching of medical image.For novices,,low prevalence effect exists in both big and small nodules,while low prevalence effect exists only in small nodule cases for experts,but the influence of low prevalence effect for experts is much smaller than that for novices.Under low target prevalence,scanning error might be the main reason for both experts' and novices' false negatives.(6)Experience and others impacts play a joint role in radiologists' decision-makings,while others impacts on novices play a bigger role in the decision-making process.(7)Experience has impact on the judgments of experts.Under low nodule salience,experts tend to make decision errors,while novices tend to make scanning errors.(8)The research on false negatives error of visual searching of medical image finds that high visual complexity,high timing pressure,low target prevalence,and wrong clues will significantly increase the false negative error of visual searching of medical image.