Lecturing is commonly regarded as a teaching method that involves information transfer from a teacher to a group of learners (1). Traditional didactic lectures are often viewed as a “sage on the stage method” because they are teacher- centered, and students are passive recipients of information (2). As such, the traditional didactic lecture approach has long been criticized for its inability to stimulate deep learning and knowledge acquisition (3–6). Despite these criticisms, a review of the roles of lectures in higher education revealed that lectures are still an important and relevant teaching method, particularly because they offer meaningful benefits, including pedagogical (i.e., content framework of a subject), practical (i.e., listening and notetaking skills), and social (i.e., cost effective and shared communal understanding) in nature (7). In fact, modern lectures have evolved beyond the capacity of the traditional lecture and are commonly delivered in a more engaging and interactive way (8, 9). Several published guidelines on lecturing suggest that lectures can be more effective when practiced alongside other teaching modalities and when the delivery adopts educational principles (1, 10–12). With these innovations, the practice of lecturing has become more flexible in catering to diverse student learning styles and changes in the learning environment.

The SARS-CoV-2 (COVID-19) pandemic has changed our lecturing environment, causing a shift from face-to-face to online lectures (13). Prior to the COVID-19 pandemic, online lectures in higher education were mainly used in blended and online distance learning and were usually delivered asynchronously as homework or pre-class assignments (14, 15). In other words, online lectures were not comprehensively practiced by all faculty members. However, the COVID-19 pandemic has resulted in an abrupt suspension of face-to-face lectures and the exclusive adoption of online lectures by faculty members in many higher education institutions. In fact, recent descriptions of online lectures during COVID-19 suggest that lecture design and delivery have diversified beyond the routinely practiced approach (16). Online lectures are typically delivered synchronously through online platforms (i.e., Webex, Zoom, Google Classroom, and Microsoft Teams) that promote interactive conferences and live discussion as well as asynchronously through the university's learning management system in order to cater to the learning needs of students who have limited access to high-speed Internet connections (17). Nevertheless, this abrupt transition to online lectures has presented significant challenges for faculty members as they have had to rapidly develop their digital competency skills for adoption in their teaching (18). In addition, students have highlighted several barriers to online learning, even before the COVID-19 pandemic, as they often perceive online instruction and delivery practices to be less effective than blended learning and traditional face-to-face teaching (19). Likewise, a study that explored students' perceptions of online lectures amid COVID-19 through semi-structured interviews revealed that online lectures did not improve students' understanding of subject content due to the lack of interaction, sustained attention focus, and stimulated interest (20). Thus, the design and delivery of online lectures require proper planning to enable meaningful learning experiences. This may be achieved by incorporating instructional design theories that are not usually explicit in the context of online lectures (18).

Online lectures that adopt instructional design theories in their design approach may be necessary to ensure effectiveness in achieving intended learning outcomes. An effective lecture should be able to enhance the development of students' learning competencies, particularly in relation to cognitive, volitional, attitudinal, and behavioral goals (21). In addition, the design of an effective lecture should be more dynamic and should cater to two-way interactions between students and lecturers (22). Consequently, an effective online lecture should be able to stimulate students' cognitive engagement and motivation and reduce their cognitive burden through interaction and intra-lecture activities. This could be accomplished by adopting cognitive load theory (CLT) and cognitive theory of multimedia learning (CTML) principles into the design of online lectures (12, 23).

CLT and CTML are instructional design theories that describe optimal learning when instructional material is designed according to the architecture and function of human cognition (24, 25). The core of CLT and CTML principles is working memory, which processes raw information received from sensory memory into meaningful schema, eventually transferring this schema to long-term memory for permanent storage (26). Given that working memory has limited processing and storage capacity, the principles of CLT and CTML have been designed to manage all cognitive input imposed on the working memory system (27). This facilitates information processing and guards against overloading working memory with information. In the CLT context, cognitive input can be categorized into three types: (1) intrinsic load (IL, i.e., input that is relevant to learning) (28), (2) extraneous load (EL, i.e., input that is irrelevant to learning) (29); and (3) germane load (GL, i.e., mental effort used by learners to process relevant learning materials) (29). To achieve optimal learning, the summation of IL and EL—known as the total cognitive load—must not exceed the working memory capacity, and GL should be increased to process learning materials. Based on this paradigm, CLT and CTML outline several empirically proven principles that manage the IL, reduce the EL, and increase the GL of learners when learning complex instructions.

Based on these principles, Hadie et al. (12) developed a lecturing guideline—the CLT-based lecture model—which was studied for its effectiveness in a multi-center randomized controlled trial in several medical anatomy lectures. CLT-based lectures have undergone face-to-face delivery and were found to effectively promote students' knowledge acquisition and retention, self-perceived learning, and cognitive engagement while also reducing medical students' cognitive loads (23). Nevertheless, the potential impact of the CLT-based lecture model on the design and delivery of online lectures has yet to be explored. Indeed, Andersen and Makransky (30) raised concerns over the potential increase in their students' EL, which could have been imposed from noises, media, and devices within the online environment. Research has proven that handling online devices during learning requires students to multitask, thus imposing higher EL (31). Likewise, noise generated from the online environment will cause distraction, thereby hampering learning (32, 33).

The unprecedented COVID-19 pandemic has paved the way to explore the effectiveness of CLT-based online lectures. As the effects of CLT are only observable when applied to complex instruction (26), this study explores the effect of CLT-based online lectures on medical, dental, and allied health professionals. Studies have indicated that topics relating to medical, dental, and allied health professional are among the most complex in higher education as the content is highly integrated with that of other disciplines, covers a wide range of diseases and management, and evolves rapidly over time with advancements in research and technology (34–36). This study explored the impact of CLT-based online lectures across different disciplines on students' learning achievement through comprehension, cognitive load level, cognitive engagement, and motivation. Specifically, we address these research questions—(1) Do CLT-based online lectures enhance comprehension of difficult health professional topics regardless of learning and lecture styles? (2) Do CLT-based applications work in an online setting? and (3) Does CLT-based online teaching provide an advantage to enhance motivation and reduce cognitive loads in learning compared to traditional lectures? We hypothesize that CLT-based online lectures will improve students' lecture comprehension, which is influenced by the improvement of students' engagement and motivation and a reduction in their intrinsic and extraneous load.

The CLT-based lecture model is a lecturing guideline developed by Hadie et al. (12) in an attempt to find solutions aimed at increasing the learning of complex anatomy lectures. The model adopts several CLT effects—modality, split-attention, isolated-interacting elements, redundancy, goal-free, guidance fading, worked example, and completion example effects (37)—and CTML principles such as signaling, contiguity, segmenting, coherence, pre-training, personalization, and voice (24). The model contains four phases of lecturing: (1) preparation, (2) initiation, (3) delivery, and (4) end phases, which underlie 27 lecturing strategies [for details, see (12)] (Figure 1).

Briefly, the preparation phase covers the lesson construction and aims to reduce IL and EL by aligning presentations based on clear taxonomy-based learning outcomes. The concept of information chunking is explicitly applied along with guides to manage visual presentation and information load. In the initiation phase, students' prior knowledge is stimulated in order to connect their readiness to learn the topic and focus attention (38), thus increasing their GL before the topic content is presented. During the delivery phase, the focus is to reduce EL by having lecturers revisit previous knowledge, use of proper lecture pacing and voice, and the avoidance of distracting verbal and non-verbal acts. The last phase or end phase aims to increase students' cognitive resources to process IL and allow them to assess how much they have learned during the lecture and plan their own self-study. This is ensured via summaries or short quizzes on lecture content.

In addition, rather than cognitive load, the CTML principles applied in this model emphasize three types of cognitive processing: essential, extraneous, and generative processing (24). Essential processing refers to the cognitive effort invested in processing relevant text and pictorial instruction from a multimedia presentation into sensory and working memory; thus, it involves selecting and organizing the processing task through the segmenting principle (i.e., words and pictures are presented in learner-paced segments) and pre-training principles (i.e., students are exposed to the key elements of instruction prior to class to enhance their understanding of the pictorial materials and text) (39). Extraneous processing—through its contiguity principle (i.e., diagrams and related text are presented together on the same screen and are explained verbally), coherence principle (i.e., extraneous materials are excluded from instructional design and delivery), and signaling principle (i.e., visual and auditory cues are added to highlight important information)—processes unrelated extraneous information, which usually results from poor instructional design (24, 39). Generative processing involves the cognitive effort invested in making sense of acoustic and iconic representations through the personalization (i.e., verbal narration is presented informally) and voice (i.e., narration is spoken by a friendly human voice as opposed to a machine voice) principles (24, 39). Thus, essential, extraneous, and cognitive processing are positively correlated with the manipulation of IL, EL, and GL, respectively (40).

This study provided significant evidence regarding the effectiveness of CLT-based online lectures across different disciplines within the medical and allied health sciences programs. In general, the study proved that CLT-based online lectures promotes students' understanding of the lecture content, self-perceived learning, engagement toward the learning material, and motivation to learn. It was also found to be effective at reducing students' mental burden through the reduction of intrinsic and extraneous loads. Despite these findings, the CLT- based online lecture did not influence the students' engagement and motivation in the medical and nutrition disciplines. However, a within-groups comparison revealed that the variations in the data regarding the improvement in the lecture comprehension scores were marginally explained by the individual variables measured in this study. These findings indicate that the variations in the data regarding the improvement in the lecture comprehension scores could not be explained by individual factors; rather, this required a combination of the outcome variables to be working together during the learning process.

Online lectures are not a new concept in higher education. They were in pervasive use even before the outbreak of the COVID-19. The effectiveness of online lectures has been widely explored; however, the findings are inconsistent across different studies (15, 58, 59). A scoping review of online lectures in undergraduate medical programs reported improvements in students' learning outcomes when online lectures were used as an adjunct to normal face-to-face classes. However, the review identified cultural lag in adopting educational theories—particularly the multimedia learning theory—in online lecture design, which the authors believed could optimize students' learning achievements (60). Therefore, the present study makes several noteworthy contributions to the effectiveness of online lectures. First, this study adopted the empirically proven strategies of CLT and CTML into the design of online lectures. Second, it applied a synchronous approach to online lectures, which was comparable to the face-to-face live lecture.

The higher improvement in the post-lecture test scores after attending the CLT-based online lectures indicates that the students gained a better understanding of the lecture contents, which could have been influenced by the CLT effects. This result is in line with that of previous CLT research documenting improvements in students' performance from the pre- to post-intervention test scores following exposure to CLT-based instruction (61–63). Although it could be argued that students are often overloaded with information during a lecture, this study proved that a well-designed lecture can be easily intelligible to students, especially when it is designed to fit the human cognitive function. This finding supports the fact that CLT-based online instruction freed some of the students' working memory resources, which were then utilized to process the relevant subject content (64). Consequently, the processed information (i.e., schema) were transferred to the long-term memory for permanent storage, thereby indicating actual learning (65). When actual learning occurs, students are better able to understand the content of the instruction that they are learning (66).

Similarly, in this study, the improvement in the students' tests scores could indirectly indicate a reduction in the students' total cognitive load during the CLT-based online lecture. This was confirmed by the significant reduction in the students' IL and EL after they attended the CLT-based online lectures. These two types of cognitive loads contributed to the total cognitive load (26), and thus, managing these loads during instructional design and delivery was pertinent to the prevention of cognitive overload (i.e., total cognitive load exceeded the working memory resources) (67, 68). These findings are similar to those of a previous study by Hadie et al. (12) on the effectiveness of CLT-based lectures delivered face-to-face. Likewise, a study by Andrade et al. (69), revealed negative correlations between post-test scores and ECL scores in all students who were exposed to different multimedia instructions that were designed according to the CTML theory. When the teaching strategies and learning materials are designed effectively, it will increase the students' concentration and reduce the amounts of mental effort used to process the EL. Hence, more mental effort—which represent the GL—were directed for processing IL Andrade et al. (70). In light of the replicability of the results, the impact of CLT-based online lectures on students' cognitive load can be considered valid and reliable, at least in the context of various disciplines in the medical and allied health sciences.

Two possible postulations of successful IL reduction were the stimulation of prior knowledge and the systematic introduction of information during the lecture. At the beginning of each CLT-based online lecture, the students were given a pre-lecture task in the form of a quiz or video to stimulate or instill prior knowledge. It was reported that stimulation of prior knowledge would prevent unnecessary use of working memory resources in an attempt to retrieve prior knowledge (i.e., previously stored schema) from long-term memory (71). By helping the students retrieve their prior knowledge, their working memory resources were reserved and would suffice for information procession (71). Likewise, introducing information in a systematic manner could also reduce the intrinsic load, as explained by the isolated interacting element effects of CLT (72). In this research context, the lecturers were trained on how to apply the “chunking mechanism” concept, allowing them to gradually introduce information and combine this isolated information at a later stage of the lecture once the students had gained some understanding of the isolated components (73).

In this study, the reduction in EL could have been due to successful eliminations of redundant and irrelevant input during the lecture. This condition could have been reached through several lecturing strategies utilizing certain CLT effects related to EL (i.e., modality, split-attention, redundancy, and expertise reversal effects). For instance, the lecturers were guided on how to stimulate students' visual and auditory sensory modalities during the lecture through the application of slide preparation techniques and diagram management. Giving the facts that human working memory has both visual and auditory centers (i.e., a visuospatial sketchpad and phonological loop, respectively) (74), verbal explanations using one's own words and visual stimulus through systematic illustration were enforced during the CLT-based online lecture. This strategy ensured that the students optimize the use of their working memory capacity for information processing by utilizing both auditory and visual centers. Likewise, the use of other strategies (e.g., proper font size and color coding, appropriate animations and cues, and removal of redundant information) were aligned with other cognitive load effects aimed at preventing the unnecessary use of working memory resources in processing information that is irrelevant to learning (75, 76).

In addition, this study revealed significant increments of germane load, as represented by the increase in the self-perceived learning measure after the students had attended the CLT-based online lecture. These findings correspond with those of previous studies documenting increases in GL measures when students were exposed to CLT-based instructions (77–79). This finding supports the fact the reduction in EL is often accompanied by increases in GL load as more working memory resources were reserved for processing IL rather than EL (80). Although it may be argued that GL is not an independent construct—as it is assumed to be indistinguishable from IL (81, 82)—this study contributes to the body of evidence showing that GL moderates IL levels, as reported in several previous studies (83–85). Thus, GL is a reflection of students' efforts toward devoting their cognitive resources toward better comprehension of the lecture content and, thus, could be represented by the self-perceived learning measure.

GL requires a conscious mental effort or effortful strategies invested in learning. Previous studies have documented a direct association between GL and motivation, engagement, and the metacognition construct (86, 87). Similarly, this study found a significant increase in the motivation and engagement levels of the overall cohort of students who attended the CLT-based online lecture. These findings strengthen the indication that students possess a greater ability to invest their cognitive resources in information processing when they are motivated to learn or engage in learning materials and processes (83). In fact, the CLT-based lecturing strategies used in this study reinforced elements that can stimulate students' motivation and engagement (e.g., segmenting principle through the “pause and ask” strategy; personalization and voice principles through the provision of forethought, learning purpose, and reassurance; and self-explanation principle through clinical applied and mind-blowing quizzes). Moreover, it has been reported that the self-perceived learning construct is an important determinant for self-appraisals of academic competence as it influences actual learning capability, motivation, academic resiliency, persistence, and performance (88). Thus, we postulate that CLT-based online lectures successfully instill higher self-perceived learning through continuous encouragement and feedback from the lecturer as well as engaging learning experiences through the application of CLT and CTML principles.

In addition, this study demonstrated an intriguing and elusive relationship between improvements in the lecture comprehension scores in each of the variables measured: IL, EL, self-perceived learning, motivation, and engagement. Given the fact that each variable contributed marginally to the improvement in the lecture comprehension score, it could be argued that these variables could have interacted with each other during the learning process, thereby explaining the improvement in the test scores. For instance, EL might have been inextricably bound to GL elements (i.e., self-perceived learning, motivation, and engagement), as reported in a previous study (89). Furthermore, studies have shown that overall mental workload measures are modulated by attention, focus, alertness, prior learning experience, familiarity with learning tools, and the learning atmosphere (80, 90). Therefore, the current study makes an important contribution to the literature on online lectures by highlighting the importance of the optimal design and delivery of online lecture material that concurrently addresses all three components of cognitive load.

Taken together, the findings of this research contribute in several ways to our understanding of the effectiveness of CLT-based lectures. First, the CLT-based lecture is applicable and feasible across different lecture delivery approaches, including face-to-face and online approaches. Second, CLT-based lectures are effective at promoting students' learning across different disciplines and at a high difficulty comprehension level, in the context of medical and allied health sciences. Third, the results of previous studies were replicated in this present study, thereby contributing to the validity and reliability of the CLT lecturing guideline. Indeed, this study has proven the continued relevance of the lecturing method for students' learning. The study also provided a resolution to the perceived limitations of the lecturing method, which is based on a solid empirically proven instructional design theory.

Nevertheless, this study was limited in several ways. The most important limitation lay in its study design—the pre-post quasi experimental design. The unprecedented COVID-19 pandemic and the implementation of the national lockdown in Malaysia hindered the accomplishment of the planned crossover design as face-to-face lectures were prohibited during the pandemic period. The disruption was integrated into the study to reflect the reality of student comprehension as it occurred in real life and we saw the possible benefits of CLT-based online lectures. To increase robustness, further studies are encouraged to have similar lesson settings as controls, e.g., online lesson with and without (controls) CLT-based applications. Furthermore, the generalizability of these findings are limited to the context of medical and allied health sciences programs. Thus, further research is needed to investigate the applicability and impact of CLT-based online lectures in non-medical disciplines. To achieve a better comparison of the results with minimal confounding factors, it is also recommended that future studies adopt randomized trials with a crossover design.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving human participants were reviewed and approved by Human Research Ethics Committee, Universiti Sains Malaysia (USM/JEPeM/19070414). The patients/participants provided their written informed consent to participate in this study.

SH had a major role initiating the idea, constructing the conceptual framework of the study, managing the data collection session, and involved in manuscript writing. VS was involved in data analysis and manuscript writing. NO and NN were involved in data collection and manuscript writing. HL and KK were involved in verification of the results and manuscript writing. All authors contributed to the article and approved the submitted version.

This work was supported by the Geran Penyelidikan Akademik Universiti Sains Malaysia (Grant Number: 1001.PPSP.8080007).

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.