Comparative evaluations of reward dimensions in honey bees: evidence from two-alternative forced choice proboscis-extension conditioning.

A major challenge in understanding choice behaviour is determining how subjects evaluate alternatives that differ along multiple dimensions. Of particular interest is whether similar dimensions are compared to each other or whether each alternative is assigned an absolute value (utility). We assumed that choice proportions would follow Weber's effect, according to which discrimination is proportional to relative difference (difference/mean). We tested honey bees in a two-alternative forced choice (2AFC) paradigm of proboscis-extension response (PER) conditioning. Subjects were conditioned over six trials to associate each of two odours with sucrose solution rewards and then tested in a choice trial between the two alternatives. Each group of subjects was tested in one treatment, and there were four treatments in each of six experiments. Rewards differed in delay, duration of feeding, and sucrose concentration. In each treatment, the high-profitability alternative was better than the low-profitability alternative along a single dimension, but between treatments of each experiment values in another dimension monotonically increased. Proboscis-response proportions during the conditioning phase tended to be greater for the high-profitability alternative, and choice proportions for it in the choice phase ranged between 0.72 and 0.89 in the 24 treatments. We show for the first time that harnessed bees are sensitive to reward delay. Preferences did not differ statistically between the different treatments of any of the experiments. The results support comparative evaluation of alternatives and are pertinent to multi-attribute choice, with implications for context-dependent preferences. We also discuss the potential advantages of the 2AFC PER simultaneous choice assay.