David N. Harpp McGill University Montreal. Quebec. Canada and James P. Snyder H. C. 0rsted Institute Universitetsparken 5 2100 Copenhagen 0. Denmark
Science instruction a t the university level has been almost exclusively confined to a weakly coupled combination of the lecture and the laboratory. Electronics has provided some new variations in recent years by offering delivery systems based on film, television, the computer, and the portable tape recorder. Along with the proliferation of devices, experimentation with modular instruction in a variety of forms has taken place. Accordingly, new directions have focussed on selfmotivated and individualized study. By inference as well as design, the lecture has begun to lose its position as the indispensable pedagogical practice. The diminished stature of the lecture in teaching can be justified on two closely related grounds. The first is derived frnm evidence of modern learning research ( I ) . - - - the ~ ~collective ~ I t is now generally recognized in principle, ifnot always in practice, that individuals learn a t different rates and in divergent ways. The current expansion of the teaching aid industry is, in part, a response to this new awareness. Provision of learning alternatives has been a boon for the student as well as a nowerful stimulant for the teacher.' he second reason for the decline of the lecture is perhaps as old as the University itself, arising precisely because ~
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DISSOLVE CONTROL
Vitalizing the Lecture Lap-dissolve projection teaching-learning options are growing. The situation is epitomized hv a New York Times descri~tionof a lecture course offered ik a single room simultan~ouslyto 1300 students (2).
... lecture notes and a course outline will (be) mimeographed. . . for students whoare unable to see the writing on the blackboard
Lectures are often large and crowded, almost always passive and im~ersonal.Inaddition, thestudent is frequently obliged to operite as an ineffective secretary for 3 4 hours a week for each class. By student count most lecturers are boring (3).All in all the lecturing technique has not progressed significantly in the past thousand years, advances in blackboard design and cnlor ~~~~-notwithstandine. -~~~ In this paper two assumptions are made. First, in spite of current trends, the lecture as a n ancient teaching form is likely to continue for the foreseeable future as the major method of universitv education. Second, there are unexploited means for vitalizing the lecture which do not demand exceptional talent on the part of the teacher. I t has been said that: "Science is essentially the monitoring and explanation of change." In the same spirit the corollary expression "The teaching of science . . ." ought to provide critical guidelines for the educator. Since teaching lectures are routinely delivered with chalk, to some extent by the overhead and slide projector, and occasionally with film, the principal dynamism of the subject must be provided by the lecturer. We have experimented with a tool, lap-dissolve projection (L-D),which allows the lecturer to simulate motion and change of all kinds entirely a t his or her discretion ( 4 ) . 2Unlike any previous lecture technique, lap-dissolve permits a forceful integration of the lecturer's individual stvle and the dvnamism of both developing concepts and actial physical change. A variety of other bekficial side effects both for the student and the teacher arises from use of the method.
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The Lap-Dissolve Effecl: Instrumentation Presently the lap-dissolveeffect is achieved by means of two 35mm slide projectors integrated with a dissolve control unit (Fig. 1). Slides numbered 1,3,5,. . .are placed in the carousel of projector 1and slides numbered 2 , 4 , 6 , . . . in projector 2. Both projectors are arranged so that their projected images fall onto the same area of the screen. The program begins with the disnlavof slide 1.Bv remote control the lecturer activates the dis'solGe box; the lamp in projector 1(slide 1) dims while that in nroiector 2 (slide 2) briehtens. The transition from slide 1 to slide-2 optimally takesufrom 1-2 s. The dissolve box mechanism assures that the total light intensity plaved on the screen is constant during this ~ e r i o dconsequently, . image 1 appears to melt gradually into image 2. Lap-dissolve projection derives its name from this visual event. During the brief
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Figure 1. Lapdissolve system. Portrayed are two Carousel Ektagraphic model pmjectors, dissolve control and remote control. Slide 1 (projector 1) is shown while slide 2 (projector 2) is fading in (Dashed scheme). At this moment, the sensation of motion occurs. 68 I Journal of Chemical Education
Unfortunately, the accompanyingside effects of frequent overstimulation and increased matCriel administration are not always considered minor. Wthers (5) have disclosed their preliminary findings in this ares. Current cinema and television make frequent use of the technique to achieve a range of dynamic and static effects.
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moment of chanee from one nicture to the next. the imaees overlap and dissolue into one another. The resulting effect is precisely what distinguishes this method from that observed by using a single projector. With thesingle instrument each picture is static and separated from that before and after i t by a distracting and ah;upt black-out. Lap-dissolve, by contrast, provides for a gentle blending of each successive pair of projected slides. At no time during the presentation is the viewer faced with a forced pause; continuity is maintained during the entire program. Examples of the L-D Technique
The lap-dissolve projection technique is characterized in the broadest sense hv three kev features: chanee. - . continuitv. .. and control. In the ciassroom iituation the teacher possesses the means to effect with large visual images a continuous and uninterrupted display of virtually any set of relationships entirely at his or her discretion. The ultimate power of L-D is manifested when internally related and precisely registered slide sequences are at the lecturer's disposal. Under these conditions certain types of motion and sequential relationships can he strikingly demonstrated with a sinele stroke of the remote control button. " We have employed the lap-dissolve technique in our classrooms since earlv 1970. Over this neriod a wide varietv of sequences has been created specificky for teaching org&c and general chemistry. They have been prepared to cover a range of applications, including the manipulation of three-dimensional objects, molecular motion, experimental demonstrations, and the partitioning of relatively complex ideas.3 For instance, certain princinles are incapable of description without reference to ~ h & ~ i @ ~ o s i t i oinnthree-space. In these cases L-D permits the viewer to crasp and analvze the actual ic motion on a stepwise basis. ~onsi;derthe m i ~ r o s & ~situation in which an iodide ion (I-) attacks methyl bromide (CH3Br), a bimolecular nucleophilic substitution reaction. The reaction has been studied in great detail and is generally acknowledged to he one of the classic cornerstones in our understanding of mechanistic events at the molecular level. A variety of welldefined structural and bondine changes characterizes the reaction. These are depicted inkigure'i which begins by illustratine the I- advance on the backside of carbon. For simplicit;, individual atoms are symbolized by spheres. Upon close approach, hond formation is represented by the appearance of a long "dashed" (partial) bond between carbon and I-. Similarly, hond weakening involves the fading of the original C-Br hond into a similar hut shorter "dashed" bond. Inversion through the carbon pentavalent transition state proceeds with a smooth alteration of hond angles and lengths ( d ) . Finally, the inverted system expels Br- to produce methyl iodide (f).All pictures are in color, the three-dimensionality is evident and the sequence is projected with the reacting system in full view a t all times.4 It is necessary to emphasize that L-D is a lecture tool designed to complement the style and organization of the instructor. It is neither a replacement for a good teacher nor a panacea for a poor one. Thus a mere exnosition of seauence Hteps by itselfhas little of the impact ok the visual a"d oral parts operating as an integrated whole. If a random selection ;,I 1cctu.rers were induced iu use the above descrihed sequence, each wvuld undoubtedly differ in a significant wav as to the presentation of the detailed content add the choicebf context in which the material would be placed. T o a large measure, the unique power of the L-D technique lies here. Slides can he edited not only prior to class to suit the lecturer's general course goals, but also during the lecture by the appropriate choice of verbal emphasis. We have often used the same sequence of slides in the first year and graduate courses to discuss an idea a t two different levels of sophistication. One of two t w e s of slides mav he used for a eiven seauence. ~ 1 r a i ~ h f f o r w acolor ; i photography is suitahi; for moiecular modolr (Sa I ' laboratory tnitrurnenrs and mrthods, and certain
Figure 2. SNZ reaction (1ith)during sequential stages of development. Only one master drawing is made: simple overlays provide tne necessary animation. types of animation. The use of "litb" slides: however, is much more flexible. I t does not relv on the availahilitv. of nhoto. graphic props; the slides are easily and inexpensively prepared bs the non-ex~ert.5Hv takinr advantaee of the rudirnentsof f i m animation, lith m&erialspermit vkually any idea to he presented dramatically. Student Response
The effectiveness of the L-D technique has been highlighted by a number of classroom and laboratory indicators. Invariably the first class or two of an L-D-rich course leads tosome puzzled and pleased concern on the part of th9tudents as to the origins of the visual display. Howeve%ey rapidly accept the method as it becomes a routine component of each class. The qualitative results of exposing large numbers of students to the technique over extended time periods are described helow. We hasten to add that some of the findings are most W e have prepared several hundred sequences in many areas including molecular spectroscopy and electronic structure, reaction mechanisms stereochemiitry and synthesis. The philosophy and desien of idea- resenta at ion will be discussed in a forthcomine .. reoort: , . at that time.~omplrtrderails for producing L.Dvirualsu,ill hegwen. In the meantime a drscriprion ofmater~alscanbe ubtaiwd from the authors. 'The 5 ~ reaction 2 can he effectively portrayed either by means of "lith" animation (Fig. 2) or by photography of modified Dreiding-type models (e.g. Benjamin-Maruzen) suspended with no visible support in front of a neutral background. "Lith" slides derive their name from the use of a high contrast copy Ortha-Lith negative film. The white characters on a black background may be conveniently deleted or colored hy treating the film directly. "or example, at the end of a 1-2 day lap-dissolve workshop for college chemistry teachers (e.g. "Cooperative Project for Two-Year College Teachers," Rensselaer Polytechnic Institute, May 1973; sponsored by NSF), almaat all participants had prepared at least one sequence suitable for classroom use. Several individuals expressed up to five separate ideas in L-D. Volume 54. Number 2,February 1977 1 69
certainly due to the operation of the Hawthorne effect (6). Reeardless of the origin of the result, its consequences are unmistakable. The Viewer Has an Increased Capacity to Reteh Informatione
For static and dvnamic two- and three-dimensional concepts, comprehension levels are elevated and digestion time accentuated. The viewer is more frequently able to independently extend the ideas presented. For example, following certain demonstrations, students usually ask questions indicating greater perception and sophistication than those given control demonstrations in the absence of lap-dissolve. In addition, these students are often able to perform better on written examinations than control groups unexposed to L-D and tested with less challenging questions. Manipulative Skills are Exercised with Greater Confidence
For example, science students begin experiments and use complex instruments with less urging after a lap-dissolve demonstration. The work becomes more self-directed and individually initiated in contrast to the behavior of control groups. Laboratory assistants, uninformed of the mode of pre-laboratory instruction,7 have consistently and immediately noted the upgraded quality of these students' laboratory performance relative to that of the controls. Finally, the same students break somewhat less equipment, direct fewer questions to the instructor, and complete experiments in a shorter time period with generally better results. Barriers to Transmitting Structural and Three-Dimensional Ideas are Lowered Substantially
This is an area uf great cnnceptual difficulty for most heginning and intermediate university students. For example, i]ha use of molecular models as an aid in correlatine many molecular concepts is considered hy most tr) be a .sine quo non in chemical education. However. it i i often difficult to induce students to voluntarily purchase them. Our experience with two comnarable introductorv . oreanic classes offers strong evidence' that lap-dissolve presentations using molecul& models in demonstrations significantly increase students' willingness to buy and use models. l n o n e semester (-500 students) onlv sinele concept slides of models were used. For a parallel a & s e (also X O s t ~ d e n t sa) variet~of L-D sequences wereempluved in addltlon to the same static slides. The mw tion presentations involved ethane, butane, and cyclohexane dynamics as well as other stereochemical manipulations illustrating enantiomers, diastereomers, and R S D L conventions. In the first situation, about 25% of the class voluntarily purchased a commercially available set ($5). I n the second group over 80% purchased the same set. ~~~~
Viewer Enthusiasm is Easier to Stimulate and Sustain
The L-D technique stimulates significantly greater subject interest than traditional lecture methods. Even for topics illustrated by a series of single concept slides, hut shown in the dissolve format, the continuous visual association of the viewer with the flow of ideas appears to result in a stronger focus on the develodng . - material. This effect cannot he achieved hy conventional, single projector slide viewing where the transition between each slide involves a momentary disappearance of the image. After extended exposure to L-D lectures, many students have volunteered that such a professional and detailed approach to the visual aspects of a course commands their attention in a way that has no close parallel in other academic situations. One of the most impressive indications of the motivational power of L-D is found in the willingness of students to ask other staff to use the technique in their courses, and (in the face of staff inertia) to actually construct sequences for these courses on their own i n i t i a t i ~ eIt . ~is interesting to note the diversity of topics that students have undertaken both for 70 / Journal of Chemical Education
coune use as well as for special projects. These include aspects of mathematics, eenetics, anatomy, drug function, molecular biology, zoology,~alcoholism,flu&oc&ons, cancer, metallurgy, and ecology. We have remlarlv monitored student attitudes towards lap-dissolve byrquesiionnaire at the end of earh course.* Responses from over 3000 class memben in 13 different g r o u ~ s ' ~ over a five-year period yielded the following evaluation.Specifically concerning the use of dissolve sequences (motion concept slides),you feel as a teachine aid they are: (1) indispensable (2) very helpful
38% 45
(3) helpful
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(4) o.k. sometimes (5) generally not needed
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Lap-Dissolve and Other Visual Aids
It should be pointed out that L-D does not in any way ohviate the use of standard 35mm slides, the overhead projector, or the blackboard. In fact. in our courses a large number of single concept slides (pict&es of individuals, $aces, and illustrative objects) are regularly included along with the various dissolve sequences. On average, one-third to one-half of a class Deriod is devoted to slides of all types, with the remainde; of the lecturer's time being used for blackboard, overhead. discussion. or an occasional film. Durine the L-D presentation student note-taking is not inhibited" Room lights need onlv be set a t sliehtlv lower levels than normal daylight; projeitions can be s~enclearlybecause of the high light intensity produced by 35mm projectors, I t is safe to-siy that amhire suitable materials are a\,ailable the lap-dissolve m e t h d renders most dassrwm film viewings unnecessary. One of the major advantages of the 35mm overlap format is that the instructor is in complete control of the visualnresentation to the class and can cbanee -Dace with great ease. Traditional film demonstrations of almost any tonic reduce the active role of the lecturer to that of a ~ a s s i v e observer. This is especially true if the film piece is accompanied by narration. However, even in the absence of narration, films usually isolate the teacher. Response to spontaneous remarks or questions is often prevented for two quite practical reasons. First, movie projectors are not commonly equipped with remote. stoo-and-go controls. Second. when films are arrested, light intensity is almost always significantly reduced hv a nrotecrive filter which prevents heat damage t o t h e film r 1 2 ) . ' ~ h e ncumparing the E~assroornadvantag& of film and I.-n, it is u s e t ~ ~ tol rememher that films run until ,r,u stop them; L-D is stopped until you run it.'" Wn tests have been conducted to determine whether significant retention extends for long periods of time. Qualitative effectivenessfar pre-laboratory instruction seems to descend from lap-dissolvein the order: single concept 35mm slides, overheadihlackhoard, films: Harpp, D. N., and Heyge, E., IUPAC Conference on Lab Instruction, Rensselaer Polytechnic Institute, Troy, N.Y., June 1974; Fine, L., Harpp, D. N., Krakower, E., and Snyder,J. P., J. CHEM. EDUC., 54,72 (1972). Ta their credit, our colleagues have generously either tolerated or collaborated with this spin-off. Two or three questions on L-D are included in an extensive questionnaire of 3 U 0 items covering all aspects of the course. Most students feel strongly that the technique assists their grasp of the material. No other analogous teaching aid we have used (blackboard, overhead, static slides, films, TV) has elicited student enthusiasm which remotely compares with that for the L-D technique. '"Classes in which we have employed lap-dissolve with regularity range in size from 25-600 attendees. " In our experience more satisfying classes result when students are provided with teacher-prepared notes. Class-timenote-taking is accordingly minimized and concentration an the visual-verbal presentntion maximized " l'racurill nnd rrlati\.el\ mrrprnjive super-Rmm iwtrum~nrs which a\oiu lhls prnhlmm arc fhe Koduk MF5-h and rne I ' I P prolPcrrws T h e dmuhark, ufohtnmi~~y auitalh Amm materials, image resolution in large classrooms (8mm versus 35mm), and the nearly complete lack of editing convenience remain, however. ~~
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Preoaration Time While the production time is initially fairly high for any individual class (2-4 hours ner I s 1 5 slide seauence for an idea of moderate c ~ m p l e x i t y ) the , ~ ~same slides can usually he reused the following year without change. A modest beginning inevitably leads to agood library of sequences over two cycles of a course. Each slide showingrequires some set-up time15: 3-5 min, if a projection booth is used and the equipment is present; 5-15 min, if the projectors are organized ab initio. Channeling the Vlewer's Attention One final point concerns the channeling of the student's attention. Necessarily, a slide used under normal circumstances contains far more information than one prepared for a lap-dissolve presentation. For a 15-min discussion of the same material one might use 9-12 slides with a single projector, but 40-60 slides under L-D conditions. Consider a single slide showing a full mechanistic picture of the S N reaction. ~ The student must face 5-10 separate pieces of information and several different concepts simultaneously?Wonetheless, the lecturer is ohliged to move stepwise through the entire story while material pertaining to aspects not under discussion a t the moment are in full view. Furthermore, the student experiences no visual change, save perhaps for the movement of the teacher's pointer. With L-D only a manageable hit of information appears a t any one time, changing a t the direction of the instructor (Fig. 2). In this context, the dissolve system can be likened to a highly sophisticated electronic chalkboard. The story develops stepwise; the conclusion arrives on cue. Throughout, the student has little choice hut to focus on the item under discussion. His attention is concentrated and encouraged to remain so by the frequent small changes. Viewer attention to projected materials is a function hoth of complexity and the length of time the material is shown. I t has been estimated that the viewer's mind begins to wander from a newly projected image after about 15 s. The L-D technique generally solves hoth problems by revealing only small changes in a comparable time. Conclusion We believe that lau-dissolve oroiection adds a sienificant new dimension to thebldest k n o b teaching form, th;? lecture. Tested on several thousand students in Canada. Denmark. and the United States, it appears capahle of effecting a rang; of desirable pedagogical results. We have mentioned its effi-
cacy for information retention, concept com~rehension. confidence-huilding in laboratory situations, and generation of enrhusiasm. The manifestations of the technique are not limited, however, to the student. For us. a srrong interest in teaching has been translated into a powerful pro/~saronal commitment (8). At the same time the rnutine employment of 1.-1) has forced upon us a degree and qualiry of organizati~~n not easily anticipated at the outset of our experiments. That is largely a consequence of the fact that optimum use of lapdissolve reuuires forceful inweration of verbalization and well-prepared sequences. In view of recent develo~mentsin the technoloev of educational aids, lap-dissolve can play an important complementary role as well. Under traditional lecture conditions, the best that can he achieved is usually a visually static, personal interpretation of textual materials which students can often obtain elsewhere. Now the dynamism of micro- and macroscopic events can be portrayed under conditions of mutual interaction between student and teacher. Subsequent selfstudy with written material, film strips, tape recorder, TV, super-8lpulsed audioI7 and computer is thus strongly reinforcing. Although our experience has been primarily confined to chemically related t o p i q 3 L-D is by no means limited to this field of knowledge. Colleagues of ours in such diverse fields as mathematics, molecular biology, dentistry, medicine, genetics, metallurgy, and the history of science, have found themselves persuaded to develop L-D sequences. It is our conviction that any situation which calls for verbal presentation to groups of any size can he enormously vitalized by the lap-dissolve method.
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Acknowledgment Some early stagesof the work wereconducted at the Belfer Graduate School uf Science. Yeshiva Universitv. New York City. We also thank the ~ d u c a t i o n a l~ e v e l o i m e n tBoard (McGill University) and the Camille and Henry Dreyfus Foundation; we appreciate helpful discussions and assistance from Professor John S. Daniel (Universith du Quhhec, Sainte-Foy), and E. Heyge (McGill University). It is our pleasure to acknowledge continuing feedback about the L-D technique from some ofour colleag
