Lap-dissolve slides. Multiple-use formats for pre-laboratory instruction

Abstract

The attainment of an effective level of laboratory instruction poses many interesting challenges to the instructor in that students need to be evaluated on such diverse matters as manipulative skills, data aquisition, and interpretive abilities. The most important characteristics of any laboratory exercise lie in the student's ability to successfully carry out the procedure while gaining a clear understanding of the theory on which the experimental procedure is based. To simplify the transition that the chemistry student must make-in putting classroom theory into laboratory practice-pre-laboratory instruction has become an important element of undergraduate chemistry.Pre-laboratory instructional programs tend to vary in their scheduling formats and content emphasis. The direct approach is the traditional short lecture presented a t the start of the laboratory period. Here, theory relevant to the experiment is reviewed-time nermittine. But eenerallv. the em--phaiis is placed on disa~ssim of laboratory proredures directly related to the en~eriment. Both time limitations and class size often preclude effective pre-lab demonstrations of the exneriment. A serious disadvantaee of this instructional format is its infringement on scheduled laboratory time. As an alternative, actual course lecture time can be set aside each week for laboratory orientation. However, if discussion of the laboratory exercise coincides with the first class meeting of the week, two or three days may elapse before students carry out the exoeriment in the laboratorv-a considerable disadvantage frim an instructional point of view.While all of these formats are nominally effective, they uniformly suffer from an old idea: in order for a laboratory exercise to become a meaningful educational experience, students must' be made to grope and stumble to a proper conclusion on their own. While there are important lessons to be learned in unaided discoverv. it is doubtful that facultv members can continue to indulge cn'these same tactics because of increasing demands for classroom efficiency and instructional accountability. We believe that the use of audiovisual technoloev nrovides an excellent means of workine toward -" .those goals in that a maximum of information can be made available to the student in a minimum of time.The pre-laboratory programs that we have developed during the past six years provide teacher-produced instructional materials for use by students and faculty in coniunction with a variety of media delivery systems. The focus bf the media component for these pre-laboratory programs are sets of highly registered 35mm slides for use with twin slide projectors, alternately activated by a dissolve control unit. This delivery technique, known asLap-Dissolve Projection, has nroven to be a remarkablv effective means of demonstrating chemical concepts through controlled motion for a erowing audience of chemistrv instructors (1-5).-We wish to describe the use of ~a~-~i s s o l v e materials to prepare self-pacing instructional programs that stud...

Reasserting the role of pre-laboratory activities in chemistry education: a proposed framework for their design

“…Description of a typical pre-laboratory was thus: "a short lecture presented at the start of the laboratory period… theory relevant to the experiment is reviewed -time permitting. But generally, the emphasis is placed on discussion of laboratory procedures directly related to the experiment" (underlined emphasis in original) (Fine, Harpp, Krakower, & Snyder, 1977). Changes in curriculum organisation because of larger class sizes meant that laboratory work began to be decoupled from lectures, and became more stand-alone in nature.…”

“…One way was to offer a version of the prelaboratory lecture. Indeed Fine's own work describes an innovative approach where lecture slides were prepared to explain the chemical concepts of a general chemistry laboratory; these could be used by the lecturer or by the student as "self-pacing instructional programs" at any time before the laboratory session (Fine et al, 1977). Because this approach aimed to mimic and replace the traditional prelaboratory lecture, these materials also included details on experimental protocols (see below).…”

Teaching Chemical Technique. A Review of the Literature

“…The pre-laboratory demonstration has undergone some changes over the years. Since the 1970s, references to demonstrations recorded on video (slides, short movies, videotape and videodisc recordings, CD-ROM) began to appear in the literature (38)(39)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49). Research by Kemper and Palmer showed that videotaped demonstrations are as effective as written instructions in promoting technical skills (38).…”

The introduction of crystallographic concepts using lap-dissolve slide techniques

“…The lap-dissolve technique uses two (or more) matched slide projectors focused on a single screen so that their images overlap and a dissolve unit which fades out the image from one projector as it fades in the image from the other (2)(3). By replacing the momentary blank between consecutive slides in a classical one-projector presentation with a controlled dissolve between visually related images, the lap-dissolve technique can provide a form of pseudo-animation which helps the viewer to maintain a correlation between the spatial relationships in one slide and the next.…”