The purpose of this study was to investigate the difference in effectiveness of four unmanned interpretive devices, which were: 1) a visual shock display, 2) a written brochure, 3) written signs, and 4) an automated audiovisual presentation. These technique types have only been sparsely studied in the past with regard to their comparative efficacy. Examination of the differences in relative effectiveness was warranted to help establish guidelines for future interpretive technique design and utilization.The four techniques, along with a control, were compared two at a time using aluminum can litter/recycling as the concept being interpreted. The number of aluminum cans recovered from park trash containers during each treatment period was used to evaluate the techniques. The comparison between each set of techniques was made using a z-statistic for a large sample, normal population. The number of cans purchased prior to park visitation was also analyzed with this same statistic to determine if this outside factor had any influence on the data.Of the four unmanned interpretive techniques tested, the written sign and the visual shock display were significantly more effective at interpreting the concept than were the written brochure, automated audiovisual program or the control. The written sign and the visual shock display were equally effective, while the automated audiovisual program and the written brochure were not significantly more effective than a control. Cans purchased prior to park visitation had no detectable effect on these results. Also, rainfall and temperature patterns showed no correlation with the data.