Hennessey et. al.’s example of Classical conditioning in paramecia (1979) is a “willy-nilly” approach to conditioning that actually exemplifies operant conditioning (see Rescorla, 1988). However, it is typical of misrepresentations where explicitly unpaired stimuli are used, but cause and effect is still reported.
This willy-nilly approach to cause and effect is also the approach commonly used by animal trainers and behaviorists who have bastardized the concept of Pavlovian (aka classical) conditioning. However, receptor-mediated events are required to demonstrate classical conditioning. Since there was no evidence of a receptor-mediated event in the paramecia, the authors rightfully commented on the likelihood that a forthcoming invertebrate model might best differentiate classical conditioning from the willy-nilly operant conditioning, like tone and shock pairing (Rescorla, 1988). The problem with discussion of conditioning in paramecia is that the observed behavioral change cannot be attributed to synaptic interactions.
That problem established the basis for my use of the honeybee model organism as an invertebrate species that links receptor-mediated cause and effect to behaviors in species from microbes to man (Kohl, 2012). In the classical conditioning of honeybees and people, sensory stimuli from the environment must epigenetically alter intracellular signaling and stochastic gene expression. These epigenetic effects occur due to nutrient chemicals and pheromones in microbes. But in the honeybee model organism and in other models of brain-directed classically conditioned behavior, the epigenetic effects of nutrient chemicals and pheromones occur via receptor-mediated events in hormone-secreting nerve cells of brain tissue. These receptor-mediated events are required to link sensory stimuli directly to classically conditioned hormone-driven behavioral affects (i.e., via the effects of the sensory stimuli on hormones).
People who are not familiar with the basic principles of biology and levels of biological organization may continue to assert that classical conditioning was demonstrated in paramecia despite the willy-nilly tone (i.e., a vibratory tone) and shock pairing that characterizes operant conditioning, and that also distinguishes it (e.g., as training) from receptor-mediated classical conditioning. Others, like me, who have learned how to model behavioral development using the molecular biology that is common to all species, will continue to laugh at any assertions that willy-nilly tone and shock pairing is classical conditioning.
The willy-nilly approach is also silly in the context of any attempt to demonstrate more than a correlate of animal training. Those who are interested in learning about cause and effect may therefore want to differentiate classical conditioning from operant conditioning. We can do so by referring to classical conditioning as Pavlovian conditioning, which it is, and referring to operant conditioning as willy-nilly silly conditioning, which it is.