In this study, we aimed to evaluate the influence of the length of a PS, the learning load, and the format by analyzing the retained knowledge rate after standardized presentations. Our main findings are that in longer-term memory up to 14 days, the retained knowledge rate of PS is very weak, corresponding to less than 20% of the content that was originally presented and classified as a learning goal by a trainer. Furthermore, case-based presentations showed no improvement in retaining information. Surprisingly, learning load had no influence on the rate of retained knowledge, and there was no inverse correlation with respect to the length of the presentation.
Current ultrasound teaching almost always incorporates lectures and hands-on training. Presentations are widely used in ultrasound classroom teaching, but there are many critics pointing out that many connections are not displayed correctly due to widely used abbreviations and bulleted lists on the slides [10]. The phenomenon that presentations seem tedious and dull due to an overload of information and bad layout often has been called ‘death by PowerPoint’ [11, 12]. There is contradicting evidence about the use of multimedia presentations in education. Some studies comparing multimedia to overhead slides showed no difference in students' test results [13, 14]. Other studies were able to show that students performed better in multiple-choice test if they had listened to lectures using multimedia slides [15]. Lowry et al. were able to show that the amount of information presented on the slides had no influence on students' test performances [16].
To our knowledge, we present the first study analyzing the use of standardized PS in teaching ultrasound. All PS used during this study were developed according to the cognitive load theory of Sweller [17, 18]. This theory implies that there are two channels processing information: the visual and the auditory channel. Both lead the information into the working memory, which only has a limited capacity (cognitive load) to process information. According to Sweller's theory, cognitive load can be divided into three forms: (1) The extraneous load, which represents the unnecessary information not absolutely needed, such as visual animations for better visualization, should be reduced to a minimum so as not to burden the working memory. (2) The intrinsic load represents information that consists of the complexity of the learning content such as diagrams and flowcharts. (3) The germane load denominates the capacity that the trainee needs to process the information into new schemes. The germane load can be reduced by a conclusive presentation. The most important information was denominated as such by the lecturers and repeated at the end of the presentation. Although all the aforementioned aspects were incorporated in the PS, the retained knowledge rate in our study was low.
We analyzed the effect of the teaching intervention by measuring the RKR that was defined as the score of the participant divided by the possible maximum score of the presentation as defined by the lecturer (%). The RKR immediately after the presentations in both groups was low and showed the typical decline as presented by the forgetting curve of Ebbinghaus [3] for the group of students. The initial RKR of the postgraduate group was lower, which could be explained by a lower motivation to participate in the study. Another explanation is that students are trained to listen to and process information presented in the form of multimedia frontal presentations on a daily basis. As the study was performed during the introductory period of emergency ultrasound courses in Germany and a fee was charged for participation, we may assume that all participants were highly motivated. In a different study, participants were asked about their pre-course learning strategies. Participants stated that they would start preparation about 4 weeks prior to the course. Both may be interpreted as a high motivation.
The effect of case-based presentations has not been studied in ultrasound education so far. In our study, the use of case-based PS showed an increase of RKR in the short-term but obviously not reaching the long-term memory. We speculate that incorporation of cases into hands-on sessions might have a more profound effect.
In our study, there was an inverse relation between the length of a presentation and the RKR, meaning that the shorter the PS, the higher the RKR. This corresponds well to a study of Hofer et al. concluding that medical students preferred short PS and that a duration of 20 min should not be exceeded for ultrasound lectures.
We defined the learning load as learning content divided by duration (number/min). In our study we, unexpectedly could not find a significant difference between presentations with higher and lower LL. That corresponds to a study of Lowry et al. that showed no correlation of the amount of information on a slide and the students' achievement in a multiple-choice test [15]. However, further study is needed to analyze if an even higher LL of more than two items per minute remains without influence on the RKR.
Key messages were defined as content that was most important to the trainer. When comparing the RKR for overall learning content and key messages, the RKR for key messages was significantly higher at all time points in the postgraduate group. In the student group, the slope according to the forgetting curve of Ebbinghaus was seen again. The difference could be explained by the lack of clinical experience in the student group making it more difficult to recognize key messages. The students would then more likely be prone to direct their attention at to more detailed information not crucial to the general concept. Therefore, a PS can be improved by highlighting and repeating key messages at the end of every presentation.
With respect to the results of our study, our suggestion for future ultrasound courses would be to incorporate shorter presentations of less than 20 min with up to five key messages. Theoretical and hands-on sessions should either alternate or be divided into a theoretical morning session and a hands-on session in the afternoon. Alternating between theory and hands-on session might prevent fatigue and enhance retention of knowledge [19]. However, an alternating program has a higher staff expense as all trainers are required to be available all day and be able to teach every topic. Pre- and post-course training should be incorporated, for example, in the form of webcasts to define a learning pathway and repeat important learning targets using a blended learning concept.
Special courses for lecturers in ultrasound education have recently been established [20]. We believe that special courses for ultrasound trainers in addition to short sessions during ultrasound courses have the potential to better promote learning.
Limitations
Our study is limited as only theoretical knowledge was tested and no evaluation of practical skills was performed. Due to the number of participants of the courses, the number of study participants is not equal between the student and the postgraduate groups. We did not assess motivation of the participants before the study. Although all teachers were highly trained and experienced and presentations were designed in a standardized fashion, we did not assess the influence the individual teacher had on the learning effect.
