Instrumental conditioning or sensitization?

Even the "simplest" flatworms (planaria) are capable of learning to respond more quickly to an aversive stimulus, as described by Abramson:

For instrumental conditioning the turning response consists of a contraction followed by an extension of the animal. Following several contractions and extensions the animal begins to turn away from the direction of the airpuff and swims in the opposite direction. For example, if the animal is swimming in a clockwise direction repeated presentations of an airpuff elicits a number of contractions and extensions. These behaviors are followed by the animal turning and swimming in a counterclockwise direction. In our demonstration the dependent variable of interest is the number of airpuffs required to make the animal swim in the opposite direction. As training progresses the number of airpuffs required to produce a turning response steadily declines (Abramson, Kirkpatrick, Bollinger, Odde and Lambert, 2001).

These observations could be interpreted in various ways. Is the animal learning to associate its behaviour (swimming direction) with a punishment (the air puff) - i.e. undergoing instrumental conditioning - or is it simply becoming sensitized to the air puff (non-associative learning, as distinct from "true" learning)? Is the animal really "trying out" different directions of swimming, or is it simply avoiding an aversive stimulus to which it has become sensitized?

Instrumental conditioning or classical conditioning?

Classical conditioning may also be confused with instrumental or operant conditioning. Even the study which showed that C. elegans worms could be conditioned to alter their food perferences, can be interpreted as operant conditioning, as the study's author acknowledged (Nuttley, personal email, 27 August 2003):

I've had people comment that what I am looking at is actually operant, and they make a good point. In my PNAS paper I show that the animals either approach or avoid benzaldehyde depending on whether it was previously paired with food (reward) or starvation (punishment). On the test, it is their chemotactic behaviour in response to the (trained) CS that is scored. Although the behaviour does not produce reward (food), we assume that they are acting appropriately to that 'expectation'.