Long-term memory for pictures under conditions of thematically related foils

Memory for pictures was investigated under conditions of difficult foil discriminability and lengthy retention intervals. The foils preserved the theme of the studied stimulus, but differed in the number and quality of nonessential physical details. In each experiment, subjects viewed colored photographs, black-and-white photographs, elaborated line drawings, and unelaborated line drawings, followed by an old/new (Experiment 1) or a four-alternative forced-choice (Experiment 2) test given either immediately, 1 day, 1 week, or 4 weeks following study; Experiment 3 replicated Experiment 1 but with a 12-week delay. For the old/new procedure, performance was best on colored photographs, with performance differences among the four stimulus types still significant after 4 weeks. For the forced-choice test, performance on colored photographs and unelaborated line drawings was best, with performance differences among stimulus types also still significant after 4 weeks. A confusion analysis indicated that errors were based on physical similarity, even after 12 weeks. These results refute the hypothesis that the memorial representations for pictorial variations converge to a common, thematic code after lengthy delays; instead, non-thematic, analogue information is encoded and preserved for lengthy time periods.