| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
HOW WE TEACH
1 Department of Molecular Biophysics and Physiology, Rush Medical College, Chicago, Illinois 60612
2 Zoology Department, University of Washington, Seattle, Washington 98195
3 National Resource for Computers in Life Science Education, Seattle, Washington 98115
4 Department of Biology, Niagara University, Niagara University, New York 14109
5 Section of Neurobiology, Physiology and Behavior, University of California at Davis, Davis, California 95616
6 Department of Physiology, College of Medicine, University of Oklahoma Health Science Center, Oklahoma City, Oklahoma 73190
7 Department of Physiology, University of Kentucky, Lexington, Kentucky 40536
8 Section of Neurobiology, University of Texas, Austin, Texas 78712
9 Department of Biology, Glendale Community College, Glendale, Arizona 85302
10 Biological Science and Nursing, Lexington Community College, Lexington, Kentucky 40506
Abstract
Undergraduates students in 12 courses at 8 different institutions were surveyed to determine the prevalence of 13 different misconceptions (conceptual difficulties) about cardiovascular function. The prevalence of these misconceptions ranged from 20 to 81% and, for each misconception, was consistent across the different student populations. We also obtained explanations for the students’ answers either as free responses or with follow-up multiple-choice questions. These results suggest that students have a number of underlying conceptual difficulties about cardiovascular phenomena. One possible source of some misconceptions is the students’ inability to apply simple general models to specific cardiovascular phenomena. Some implications of these results for teachers of physiology are discussed.
Key words: misconceptions; conceptual difficulties; mental models
Students studying any science discipline come into the classroom with naive conceptions, preconceptions, or alternative conceptions about the subject matter that impact mastery of that discipline (5, 10, 11). These terms are not, of course, synonyms, since each of them carries a different set of assumptions. However, for teachers, the most important thing that they all have in common is the interference with learning that they are known to cause.
As teachers, we become aware of the existence of these preconceptions, alternative conceptions, or misconceptions when we ask a student a question, receive an answer, and then reflect on the possible implications of that answer. Such questions can diagnose the existence of conceptual or reasoning difficulties, and the student’s incorrect answers thus serve as diagnostic signs of those difficulties. That is, the student’s answers suggest that there is some conceptual difficulty causing the wrong answer. To determine what underlying conceptual difficulty is present, we ask additional questions to get the student to elaborate on his/her thinking. It is not uncommon to find that even a follow-up question to a correct answer reveals that the student has significant difficulty thinking about the issue at hand (i.e., the question was answered correctly, but for the wrong reason).
Misconceptions (conceptual difficulties) have been studied extensively in physics but less so in chemistry and biology (see Ref. 8 for a bibliography of studies of misconceptions in science). The biology topics that have been studied most frequently include photosynthesis, genetics, evolution, and the circulatory system. Mintzes and colleagues (1, 5) have examined the differences that are present in students’ understanding of the circulatory system at different educational levels (4th grade to college) and observed that some alternative conceptions are quite resistant to change, whereas others become much less prevalent in older students. However, they studied a relatively narrow range of concepts, and some of the questions they asked students seem directed more at factual knowledge than conceptual understanding.
Previously, we (2, 4) studied the prevalence of misconceptions that students have about concepts in respiratory physiology. In these studies, we gave the students a set of respiratory diagnostic questions and asked them to answer the question and then offer an explanation of that answer. In some studies, this was done in writing, whereas in other studies this was done with a follow-up multiple choice question. We used these explanations to attempt to determine the underlying conceptual or reasoning difficulty that led the students to the incorrect answer (diagnostic sign). We found that the prevalence of these respiratory misconceptions was quite consistent across a wide spectrum of undergraduate populations. We also found some significant patterns in the conceptual or reasoning difficulties that seemed to underlie some of the inability of students to answer respiratory questions correctly; one of these patterns has been pursued in the present study (see below).
In our present study, we determined the prevalence of misunderstandings about certain concepts related to the cardiovascular system (which shares certain similarities with the respiratory system but is nevertheless sufficiently different that there will be a quite different set of possible misconceptions present) in a large and diverse population of undergraduate students. We identified the underlying conceptual difficulties associated with these misunderstandings by collecting written explanations of their reasoning and through the use of multiple-choice follow-up questions. We also hypothesized that at least some conceptual difficulties in understanding cardiovascular physiology arise from the students’ inability to reason about simple physical and chemical systems, what Modell (6) has called general models, that are applicable to specific situations in the cardiovascular system. Our results offer some support for this hypothesis and suggest further experiments to explore this idea.
METHODS
Members of the Physiology Educational Research Consortium (PERC) contributed lists of cardiovascular topics that, in their experience (class interactions with students, examination results), students found difficult. From this list, a set of multiple-choice diagnostic questions was written that probe for the existence of conceptual or reasoning difficulties. We specifically selected questions that were diagnostic for difficulties that can seriously interfere with students’ mastery of the topic at hand. Diagnostic questions were generally of the form: "If X increases, then will Y increase/ decrease/show no change?" In several of the early surveys, students were asked for brief written explanations of their answers. The written explanations were collected and analyzed to determine the students’ underlying conceptual and/or reasoning difficulty. These written explanations were also used to help generate multiple-choice follow-up explanations that were used in later surveys.
The list of possible diagnostic questions was circulated to all PERC members, and each was asked to identify a set of questions that would be appropriate for use with students in his/her classes. Because the courses to be surveyed spanned the range from introductory anatomy and physiology at community colleges to advanced physiology courses at research universities, it was essential that each site use only diagnostic questions that corresponded to the educational objectives of their course(s). It would not be useful, for example, to probe for a conceptual or reasoning difficulty about "inotropic state" from students who are not expected to know what this means. Thus, although some diagnostic questions appeared on all of the surveys administered, others were used at only two or three institutions. Table 1 contains the 13 diagnostic questions (DQs) used in this study. For each question, we have indicated some possible underlying difficulties for which the question might be diagnostic solely on the basis of an analysis of the physiology involved.
|
|
The cardiovascular diagnostic survey was administered either at the beginning of each course or just before the class began the topic of cardiovascular physiology.
Table 3 lists the eight institutions (and the 12 participating courses) at which the cardiovascular diagnostic survey was administered. A total of 1,076 students participated. Table 4 provides a basic description of the characteristics of the total population of students that we studied.
|
|
Prevalence of respiratory diagnostic sign.
Among the students surveyed in the present study (n = 1,052), 57.6% had some conceptual and/or reasoning difficulty about the determinants of minute ventilation. The prevalence of this difficulty in individual courses ranged from a low of 40.2% to a high of 70.6%. These results are very similar to our previously reported findings (2, 4).
Prevalence of cardiovascular diagnostic signs.
Table 5 shows for each diagnostic question: 1) the percentage of each student population studied that did not answer correctly, 2) the percentage of the total population (all institutions and courses) that had answered incorrectly or had conceptual difficulty with the question, and 3) the mean prevalence and standard deviation for all of the courses.
|
The prevalence of particular cardiovascular diagnostic signs varied considerably; the most prevalent difficulty (CVDQ4: CARDIAC OUTPUT AND RESISTANCE) was exhibited by 81% of the students studied, whereas the least common (CVDQ2: HEMORRHAGE AND VENOUS PRESSURE) was exhibited by only 20% of the subjects. The prevalence of any particular diagnostic sign tended to be consistent across the individual student populations; the largest standard deviation was 18.7% for CVDQ6.
What are the underlying difficulties that lead to the diagnostic signs we obtained?
In three of the earliest surveys (SU3a, SU4, SU5; Table 3) students were asked to provide written explanations for their answers to four of the diagnostic questions (CVDQ1, -4, -6, and -8). For each question, we looked for patterns in the explanations offered for both wrong answers (diagnostic signs) and correct answers. We examined 
300 written responses. Some typical explanations are presented in Table 6.
|
Explanations offered by students who correctly predicted that the downstream pressure would decrease commonly revealed incorrect thinking about hemodynamics. Despite their correct prediction, these students were often confused about the relationships among flow, flow velocity, resistance, and blood volume. Some explanations for the correct prediction presented ideas that were simply irrelevant (changes in fluid movement across the walls of the capillary).
CVDQ4 asked students to predict the immediate and direct (not via a reflex) effect on arteriolar resistance of an increase in cardiac output. There is essentially no change in resistance. Arteriolar compliance is relatively low, and the change in volume that occurs is small. Thus there is an insignificant change in the radius of the vessel (which is more importantly determined by sympathetic inputs and the concentration of local tissue metabolites). Students who predicted either increases or decreases in resistance commonly explained their predictions either by asserting that flow and/or pressure are direct determinants of vessel resistance, or they invoked some sort of regulatory response (i.e., reflex) to the change in cardiac output, even though the question explicitly stated that reflexes were NOT involved in the response to be thought about.
Although many students who predicted no immediate, direct change in resistance correctly identified the determinants of resistance (length, viscosity, radius), others were unable to generate a coherent explanation.
CVDQ6 asked students to compare the volume pumped by the right and left ventricles with each beat. The volumes pumped by the two sides of the heart are the same; the output of the right ventricle fills the left ventricle and the output of the left ventricle ultimately fills the right ventricle. If the outputs are not identical, a change in filling will result that will make the two outputs equal. Of the 34 students who predicted that the output of the left ventricle was greater than the output of the right ventricle, 16 explained this by noting that the left ventricle is bigger than the right ventricle. In some cases, the students indicated that they had seen this in a laboratory dissection experiment. Fourteen of the 34 students explained their prediction by noting that the left heart output has to supply blood to the whole body (thus requiring a larger output), whereas the right ventricle output supplies blood only to the lungs. Other students actually offered both arguments for this answer. Interestingly, students who answered that the right ventricle output was greater than the left ventricle output offered the same explanations (size and destination) but had apparently confused the right and left sides of the heart when they inspected it in the lab.
Not a single student who correctly said that the right and left ventricles pump the same volume per beat offered a fully correct explanation for that phenomenon. Several observed that the volumes are the same even though the pressures developed by the two ventricles are different. Although this statement is correct, and perhaps an appropriate observation to make about this general phenomenon, it does not constitute an explanation for their prediction. Many more students seemed to understand that if the volumes were not the same there would be a change in volume in different parts of the closed circulatory system and that this would possibly result in a change in pressure. Again, this is correct, but at best this is a teleological explanation for their prediction. However, most students simply argued that the input (what goes into the ventricles) and the output (what is pumped out of the ventricles) had to be the same and therefore the two sides must pump the same volumes (as an explanation this is more or less circular).
Finally, CVDG8 asked students to predict whether denervating the heart would cause the heart to stop beating, continue at the same rate, or continue beating at a different rate. The heart would beat at a different, faster rate. The spontaneous firing rate of the SA node is higher than the resting heart rate, which is normally slowed by parasympathetic inputs. Those students who said that the heart would stop beating quite commonly explained this by stating that the heart is like skeletal muscle and requires a neural input for contraction to occur. Among those who predicted that the rate would stay the same, most invoked the autorhythmicity of the heart (which is, of course, present) and claimed that its beat was therefore independent of the nervous system (not true).
Those students who knew that the rate would change generally had quite spurious arguments to explain this. Many commented on "pacemakers," and several indicated that the nervous system modulated the spontaneous (autorhythmic) heart rate. However, none of the respondents knew that the spontaneous rate of the SA node was higher than the resting heart rate in a normal individual, even if they did know that denervating the heart somehow changes it rate.
Five hundred twenty students provided us with explanations for their answers to four of the diagnostic questions (CVDQ1–4) by selecting items from follow-up multiple-choice questions. These students were enrolled in four different courses: SU1, SU2, SU3d, and SU4 (Table 3). Tables 7, 8, 9, and 10 contain the distribution of explanations that were selected.
|
|
|
|
Individual student performance on each question in each of the three pairs of questions was determined. We could, therefore, determine whether students answering the general-model question correctly were more or less likely to answer the matched physiology question correctly. From these numbers, we calculated the percentage of students who answered both the general model and the physiology question correctly. Table 11 contains the results of this analysis. A 
2 test with computed expected values (9) was performed on these data, and the results are reported below.
|
46% of the students who answered the general model question correctly answered the cardiovascular diagnostic question correctly, whereas only 26% of the students who missed the general model question could correctly answer the physiology question. The difference in performance on the follow-up CVDQ as a function of being able to correctly apply the general model was significant (P < 0.001). For the elastic structure questions (GMDQ2 and CVDQ2), the percentage of students answering CVDQ2 correctly was the same for those answering GMDQ2 correctly or incorrectly (75.3% vs. 71.3%); this difference is not significant (P > 0.10).
For the mass balance questions (GMDQ3 and CVDQ3), a correct answer on the general model question was associated with a greater likelihood that the answer to CVDQ3 was correct (56.6% vs. 43.2%, P < 0.001).
DISCUSSION
Prevalence of the respiratory diagnostic sign.
The mean prevalence of the respiratory misconception (diagnostic sign) was essentially identical to that previously seen (2, 4). Individual course prevalence ranged from 40.2% to a high of 70.6%. In the previous study, the prevalences ranged from 31.1 to 69.4%. This suggests that the student population tested here was essentially the same as the population previously studied and that the manner of surveying students had not skewed the present results in some way.
Prevalence of cardiovascular diagnostic signs.
The prevalence of the cardiovascular misunderstandings surveyed varied from 20 to 81%, a range that is only slightly greater than the range of prevalence of the four respiratory misconceptions (diagnostic signs) previously reported (4). The least prevalent cardiovascular diagnostic sign (HEMORRHAGE AND VENOUS PRESSURE) deals with a phenomenon about which knowledge is quite widespread regardless of formal studies in physiology (see below). On the other hand, the most prevalent misunderstanding about cardiovascular physiology (CARDIAC OUTPUT AND RESISTANCE) deals with concepts from hemodynamics, a subject that students at all educational levels find particularly challenging.
What are the difficulties that impact students’ understanding of cardiovascular physiology?
The responses to pairs of matched questions suggest that students who can apply general models to their understanding of cardiovascular phenomena are more likely to be able to correctly answer a related cardiovascular question. For two of the three pairs of questions, answering the general model diagnostic questions correctly was associated with a greater likelihood that the cardiovascular diagnostic questions would be answered correctly. Upon examination of the one exception, the elastic structures questions, it appears likely that students have available to them knowledge about the effects of hemorrhage (the fall in blood pressure) that is independent of their understanding of the behavior of elastic structures (which would be required to explain why pressure falls, but not the fact that it does fall) and independent of what they learn in the classroom.
These results offer support for our hypothesis that some conceptual difficulties in cardiovascular physiology arise from the students’ inability to apply certain general models to specific physiological situations. We will be pursuing this idea in our next survey, which will examine the prevalence of conceptual and reasoning difficulties about renal physiology. If, as we suspect, a significant number of physiology misconceptions are the product of an inability to transfer and apply general models, it will strengthen the argument that improving students’ understanding of and ability to use these models can have widespread positive effects on learning this material (6).
There is another source of difficulty that affects our students’ understanding of important concepts in cardiovascular physiology. Some of the misconception questions (Table 1) appear to be nothing more than statements of facts about the cardiovascular system. For example, CVDQ9 deals with the "fact" that the right and left ventricle contract at essentially the same time. One might argue that a wrong answer to this question merely tells us that students do not know this fact. Even if this is the case, it is both surprising and troubling for both the students and teachers. One can feel the beat of ones’s heart or one’s own pulse and immediately know that the two sides of the heart beat so closely together in time as to be indistinguishable. In addition, every student whom we surveyed studied something about the cardiovascular system in elementary or high school biology. Finally, some of the students surveyed were in upper-level courses and quite likely had had a lower-level introductory physiology course. So the failure of so many students (70% of those surveyed on this question; Table 5) to "know" that the right and left heart beat at the same time remains puzzling.
We might expect that textbooks would address this topic in a way that would help our students understand this phenomenon. However, an examination of four popular undergraduate and advanced physiology textbooks (not necessarily the textbooks recommended in any of the courses surveyed) reveals that three of them never state that the right and left ventricles contract at the same time, and the fourth textbook states it, but in a way that could easily be overlooked by the reader. How then would we expect students to eventually understand that the right and left heart contract together? It would be possible for students to infer or deduce this from an understanding of the structure and function of the cardiac conduction systems (topics that are extensively covered in all the textbooks), but it seems likely that most students will be unable to make this inference. The result is a misunderstanding of a significant phenomenon based on a model that is quite different from the appropriate mental model—a cardiovascular misconception is present.
What are the implications of these results for teachers of physiology?
First, undergraduate students find many cardiovascular concepts difficult to understand, and the prevalence of these difficulties is surprisingly uniform across diverse student populations. It is possible that this prevalence is independent of how advanced the students are in their academic careers.
As teachers, it is essential that we know what our students find hard to understand if we are to succeed in helping them learn. This study and others like it represent the beginning of an attempt to undercover these difficulties in a systemic, broad-based way. In the classroom, we must be aware of these conceptual difficulties and find ways to probe our students’ understanding of these concepts.
Second, undergraduate students may "understand" less than they appear to "know." Even when they are able to answer a question correctly, their ability to explain their answer may be so limited as to suggest that they have guessed or memorized a fact about the phenomenon in question, but have not developed a robust understanding of that phenomenon.
As teachers, we need to probe our students’ understanding of important physiological phenomena below the superficial level to determine whether our students truly understand what we think they understand. This can best be accomplished in a learning environment in which students are constantly testing their mental models through interactions with one another and with the teacher (7). We also need to use formal assessment tools (multiple choice, short answer, or essay questions, etc.), that measure conceptual understanding, not just memorized information.
Third, one source of conceptual difficulty about many phenomena is the students’ lack of understanding of simple general models (6) or the inability to recognize that these models apply to the topic under consideration.
We, as teachers, need to think about general models and organize our teaching to take advantage of the power that this approach provides. This is not something to be done in a single lecture, but something that must be revisited as each new topic arises. Furthermore, we must provide students with the necessary opportunities to practice recognizing and applying these ideas.
Fourth, another source of conceptual difficulty for students is our failure as teachers and textbook writers to appreciate the difficulty that students have integrating knowledge drawn from many disciplines (physics, chemistry, biology) and many levels of organization (molecular, cellular, organ, organismal, etc.) into a robust understanding of a physiology concept. Students need help with such integration. If that help is not provided in the textbooks students read or in the classroom, then their understanding may stay at the level of memorized information "bites" and never achieve the meaningful learning that we say we value (3).
If you have comments or questions about the studies that are reported here, you can post them on the PERC web forum, which can be found at www.physiologyeducation.org/forum.
Acknowledgments
This research was supported by National Science Foundation Grant REC-9909411. The opinions expressed are those of the authors and not necessarily those of the Foundation.
Address for reprint requests and other correspondence: J. Michael, Dept. of Physiology, Rush Medical College, 1750 W. Harrison St., Chicago, IL 60612 (e-Mail: jmichael{at}rush.edu).
Received for publication January 14, 2002. Accepted for publication March 1, 2002.
References
This article has been cited by other articles:
|
|
 |
|
  A. Fyrenius, C. Silen, and S. Wirell Students' conceptions of underlying principles in medical physiology: an interview study of medical students' understanding in a PBL curriculum Advan Physiol Educ, December 1, 2007; 31(4): 364 - 369. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. Michael Conceptual Assessment in the Biological Sciences: a National Science Foundation-sponsored workshop Advan Physiol Educ, December 1, 2007; 31(4): 389 - 391. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. I. Modell Helping students make sense of physiological mechanisms: the "view from the inside" Advan Physiol Educ, June 1, 2007; 31(2): 186 - 192. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. Michael What makes physiology hard for students to learn? Results of a faculty survey Advan Physiol Educ, March 1, 2007; 31(1): 34 - 40. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. Michael Where's the evidence that active learning works? Advan Physiol Educ, December 1, 2006; 30(4): 159 - 167. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. U. Silverthorn, P. M. Thorn, and M. D. Svinicki It's difficult to change the way we teach: lessons from the Integrative Themes in Physiology curriculum module project Advan Physiol Educ, December 1, 2006; 30(4): 204 - 214. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
W. H. Cliff Case study analysis and the remediation of misconceptions about respiratory physiology Advan Physiol Educ, December 1, 2006; 30(4): 215 - 223. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
N. J. Pelaez, D. D. Boyd, J. B. Rojas, and M. A. Hoover Prevalence of blood circulation misconceptions among prospective elementary teachers Advan Physiol Educ, September 1, 2005; 29(3): 172 - 181. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. Richardson and D. Speck Addressing students' misconceptions of renal clearance Advan Physiol Educ, December 1, 2004; 28(4): 210 - 212. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Visit Other APS Journals Online |
