Label-based expectations affect incentive contrast effects in bumblebees

Abstract

While classic models of animal decision-making assume that individuals assess the absolute value of options, decades of research have shown that rewards are often evaluated relative to recent experience, creating incentive contrast effects. Contrast effects are often assumed to be purely sensory, yet consumer and experimental psychology tell us that label-based expectations can affect value perception in humans and rodents. However, this has rarely been tested in non-model systems. Bumblebees forage on a variety of flowers that vary in their signals and rewards and show contrast when rewards are lowered. We manipulated bees' expectations of stimulus quality, before downshifting the reward to induce incentive contrast. We found that contrast effects were not solely driven by experience with a better reward, but also influenced by experience with associated stimuli. While bees' initial response did not differ between treatments, individuals were faster to accept the lower-quality reward when it was paired with a novel stimulus. We explored the boundaries of these label-based expectations by testing bees along a stimulus gradient and found that expectations generalized to similar stimuli. Such reference-dependent evaluations may play an important role in bees' foraging choices, with the potential to impact floral evolution and plant community dynamics.

Judgement bias may be explained by shifts in stimulus response curves

“…Receiving a high-quality food reward, either in the colony, or in this case, on the outside of the colony, may give individuals information that there is higher-quality food in their environment [ 42 , 43 ]. We would expect this to lead to greater search on ‘novel’ flowers that were not previously associated with a particular reward value, since bees form specific expectations of reward quality based on the associated stimuli [ 44 , 45 ]. However, this would not explain our results either: bees that experienced the higher-quality sucrose reward did not visit novel stimuli A and B more in Experiment 1, nor any novel stimuli more in Experiments 2 and 3.…”

Bundling and segregation affect pheromone deposition, but not choice, in an ant

“…The finding that bundling and segregation affect ant value perception adds this behavioural economic effect to several others which have also been shown to affect perceived value in insects, including decoy effects (Sasaki and Pratt, 2011;Shafir et al, 2002;Tan et al, 2015), invested effort increasing perceived value (Czaczkes et al, 2018a), relative value perception (Bitterman, 1976;Couvillon and Bitterman, 1984;Wendt et al, 2019), and labelling effects (Hemingway and Muth, 2022;. It is becoming clear that the underlying patterns driving value perception in insects are in many ways parallel those of humans.…”

Motivational modulation of flight speed in foraging bumblebees

“…In addition to corroborating the significance of the effect observed in trial 7 (by making it unlikely to result from simple effects of trial repetition), this pattern suggests that the inertia for change in reward valuation is asymmetric with regards to the direction of change (46,80). This asymmetry is partly caused by the non-independence of consecutive trials due to incentive contrasts (60,81), such that previously highly valued options become less preferred after the bees experience higher quality rewards. Importantly, the experiment does not allow to determine whether bees would maintain the elevated speed seen at trial 7 after several presentations of the highly valued reward, or return to the initial speed due to the costs associated with faster movements (30,82) (but see (83) for evidence of long lasting effects of high-value rewards on vigour).…”

“…Here, neither the increase in sugar concentration nor the two consecutive trials with the highest concentration led to a change in behavioural vigour. This is despite the fact that bees have been shown to form expectations about potential rewards (59,60), and alter their search behaviour based on their pattern of variation (46,61,62). This suggests that a reduction of uncertainty is required before the expectation of a reward alters flight speed in bees.…”