The effect of target scarcity on visual foraging

Abstract

Previous studies have investigated the effect of target prevalence in combination with the effect of explicit target value on human visual foraging strategies, though the conclusions have been mixed. Some find that individuals have a bias towards high-value targets even when these targets are scarcer, while other studies find that this bias disappears when those targets are scarcer. In this study, we tested for a bias for scarce targets using standard feature versus conjunction visual foraging tasks, without an explicit value being given. Based on the idea of commodity theory and implicit value, we hypothesized that participants would show a scarcity bias. The bias was investigated using a Bayesian statistical model which has been developed for predicting target-by-target foraging behaviours. However, we found no evidence of a scarcity bias in our experiment, suggesting that participants did not inherently find rarer targets more rewarding.

Keywords: cognitive modelling; foraging; visual search.

Figure 1.

Example stimuli. (a) Stimuli for the feature search, (b) conjunction search. For feature, from left to right; is scarce green target condition, equal target condition, and scarce red target condition. For conjunction search, from left to right; scarce green circle condition, equal targets condition and scarce red squares condition.

Figure 2.

Posterior probabilities after fitting the model to the simulated data. The yellow-shaded background areas represent the prior distribution ($53\%$ and $97\%$ Highest Posterior Density Intervals). Red lines indicate the parameter values used in the simulation.

Figure 3.

Posterior probabilities after fitting the model to the pilot data. The orange-shaded background areas represent the prior distribution ($53\%$ and $97\%$ HPDIs). (a) Posterior distribution for $p_A$. (b) Posterior distributions for the difference between the scare and equal conditions. (c,d) Posterior distributions for the other model parameters.

Figure 4.

Posterior probabilities after fitting the model to the real data. The grey-shaded background areas represent the prior distribution ($53\%$ and $97\%$ HPDIs). (a) Posterior distribution for $p_A$. (b) Posterior distributions for the stick probability $p_S$. (c) Posterior distributions for the proximity tuning parameter ${\sigma }_{\rho }$. (d) Posterior distributions for the direction tuning parameter.

Figure 5.

The random effects $u_A$ for each participant, for all scarcity and difficulty ((a) conjunction versus (b) feature) conditions.