ABOVE: © IKUMI KAYAMA, STUDIO KAYAMA
Psychologist Beatrice Gelber conducted experiments in the 1950s and 1960s to test for associative learning in Paramecium aurelia. In her main trials (top row, image below), she reported that, while the single-celled ciliates (green) ignored a bare wire dipped into their microscope slide, they swam over when she coated the wire in bacteria (red), which Paramecium eats. After several such sessions, she put bare wire back into the liquid, and reported that the protozoans still swam over, suggesting to her that they’d learned to associate the wire with food. Gelber ran controls to try to exclude other explanations: in one, she didn’t present the wire or any food during the training period (bottom row); in another, she presented bare wire instead of bacteria-covered wire (middle row). Neither of the control conditions resulted in learning, she concluded. Her critics said that she failed to control ...
