David S. Wooding

Eye movements of large populations: II. Deriving regions of interest, coverage, and similarity using fixation maps.

The analysis of eye movement traces (i.e., the patterns of fixations in a search) is more complex than that of such parameters as mean fixation duration, and as a result, previous attempts have focused on a qualitative appraisal of the form of an eye movement trace. In this paper, the concept of thefixation map is introduced. Its application to the quantification of similarity of traces and the degree of coverage by fixations of a visual stimulus is discussed. The ability of fixation maps to aid in the understanding and communication of large numbers of eye movement traces is examined.

Eye movements of large populations: I. Implementation and performance of an autonomous public eye tracker.

This paper details the design and construction of an autonomous public eye tracker exhibit, which was installed at the National Gallery, London, in 2000/2001. For over 3 months, it functioned both as an informative exhibit and as a controlled eye movement experiment, gathering data from over 5,000 participants. The issues associated with automatic unattended recording of the eye movements of members of the public are discussed. The performance of the exhibit is examined, and its successes and problem areas are highlighted with regard to potential applications and future exhibits. The success of the project proves the viability of autonomous public eye trackers as both data-gatherers and public exhibits.

Breast screening technologists: Does real-life case volume affect performance?

In the UK fewer radiologists are now specialising in breast cancer screening. Consequently, a number of technologists have been specially trained to read mammograms so as to double-read with existing radiologists. Each year the majority of these film-readers examine a set of difficult cases as a means of self-assessing their skills. We investigated whether the technologists performed as well as breast-screening radiologists on this difficult test set. We also investigated technologists’ performance over a number of years to compare the performance of those technologists who have read a greater number of breast screening films and those who have had less experience. Finally, we investigated real-life experience and performance on the scheme by comparing; volume of cases read, experience, and technologists’ performance over time versus radiologists’ performance. Data for approximately 250 breast screening Radiologists and 80 specially trained technologists over three years for six sets of 60 difficult recent screening cases were examined. Overall, those technologists who have not read the same volume of cases as radiologists did not perform as well on this particular task. Although when the group was fractionated by volume of cases read in real-life and the number of years reading cases, then the technologists performed at a level similar to the radiologists.

Differences in coverage patterns in cervical cytology screening

The visual screening of cervical smears is a complex process requiring appropriate slide coverage to detect any unusual appearances without making any omission errors. In examining a smear the observer has both to move the microscope stage appropriately to bring different slide areas into view, plus visually search the information presented within the binocular visual field. This study examined the patterns of slide coverage by different individuals when they inspected liquid based cervical smears. A binocular microscope was first adapted in order to record both the physical movement of the stage by the observer and also to access the microscope’s visual field. An image of the area of the smear under the microscope was displayed on a PC monitor and observers’ eye movements were recorded as they searched this. By manually adjusting the microscope controls they also moved the stage and all stage movements and focussing were also recorded. The behaviour was examined of both novices and an expert screener as they searched a number of test cervical smears. It was found that novices adopted a regular examination pattern, which maximized slide coverage, albeit slowly. In contrast, the experienced screener covered the slides faster and more effectively ensuring more overlap between microscope fields.

Are there demographic differences in film reading skill

Since 1991, the majority of UK breast screening radiologists have annually taken part in the Personal Performance in Mammographic Screening (PERFORMS) self-assessment scheme. In addition to reporting a set of difficult mammographic cases, they have also completed a questionnaire where they indicated their normal screening practices (e.g. number of cases read per week, mammographic views used and the time of day they usually read screening cases) and demographic details (e.g. age, gender and experience). The purpose of this study was to determine whether there were any correlations between these questionnaire data and the various performance measures provided by the self-assessment film sets. Additionally, any change in response to the questionnaire over time was examined. All data presented are anonymous. There were no significant differences for gender, but significant correlations were found for some of the questionnaire responses and performance. For example, experience and the number of cases read per week were positively correlated with some performance measures. In conclusion, different screening practices and some demographic differences can have an effect on an individuals performance in interpreting a self-assessment film set. This finding may also be applicable to actual breast screening performance.

European breast screening performance: does case volume matter?

U.K. breast screening radiologists typically read over 5,000 screening cases per annum, whereas in Europe this figure may be lower as in some countries national breast screening programs are in development. The PERFORMS scheme in the UK permits radiologists annual self-assessment of their film-reader skills. As part of a Bavarian breast-screening training scheme a number of German radiologists have now also read the current PERFORMS case set. We investigated whether real-life case volume affects reading performance by the comparison of matched groups reading these screening cases. For each case, individuals identified which key mammographic features were present, whether the case was abnormal and should be recalled or not. For this analysis the participants were matched on volume of cases read and years of experience. Assessment of case volume was elicited by questionnaire data. The radiologists were compared on several key performance measures; cancers detected, correct recall and correct return to screen, signal detection performance statistics and real-life screening practice. It was found that whilst the performance of the Bavarian radiologists on the current test sets was extremely good, on average they performed less well than their UK counterparts. Reasons for this are considered.