Foraging under threat of predation is a paradigmatic scenario involving the interplay between approach and avoidance motivation across species.  Previous foraging paradigms in humans have revealed aspects of approach-avoidance behavior and its neural underpinnings, but have generally involved simple choices such as a binary decision to stay or flee.  Here, we present results from 40 adult participants who completed the Weighing Opportunity and Loss in Foraging (WOLF) task, a novel two-dimensional foraging context with threat of predation in which participants choose from five possible actions at each turn.  We fit computational models in which choices depend on the subjective utility of each option, which itself depends on approach motivation (resource richness) and avoidance motivation (predator distance).  Model comparison revealed that an inverse power law model, in which the marginal subjective utility of additional distance from the wolf diminished with wolf distance, outperformed a linear model.  Model parameters explained more than 75% of the variance in task performance, mediated by the average resource richness of choices (for the approach-related parameter) and the number of deaths on the task (for the avoidance-related parameters).  An exploratory analysis found that self-reported anxious arousal was associated with a more linear relationship between wolf distance and avoidance motivation.  The results demonstrate that a behaviorally rich foraging paradigm in which participants select from multiple options at each turn can enable explicit modeling of subjective utilities in the interplay between approach and avoidance motivation.  Future work can examine neural underpinnings of complex approach-avoidance behavior and their alteration in mental health disorders.

Participants

Forty participants (n = 19 women) from the San Diego area completed the WOLF task (Mean age = 27.9, SD = 10.69; range = 18-58; 37.5% Asian, 45% White, 2.5% multiracial, 15% prefer not to say/other; 25% Hispanic, 75% not Hispanic; Mean years of education = 15.725, SD = 2.85).  In addition to performing the experimental task (described below), participants completed the Mood and Anxiety Symptom Questionnaire (MASQ), an assessment of affect with anxiety-specific, depression specific, and shared symptom factors.  Informed consent was obtained from all participants prior to participating and participants were monetarily compensated for their time.  The institutional review board of the University of California San Diego approved all study procedures.

WOLF Task

The interactive task was displayed using PsychoPy on a desktop PC where participants controlled a farmer icon within a 5×5 grid of resource fields with the arrow keys on a keyboard.  Each field was represented by a circle that varied in color from green to yellow, indicating the resource availability at that location.  The objective of the task was to maximize harvested resources while avoiding a wolf, represented by a separate icon that moved concurrently with the farmer. 

At the start of each game, the farmer started at the middle of the screen.  Each turn lasted one second, during which the participant selected one of five possible actions: remain stationary or move up, down, left, or right.  The fields were harvested automatically at the end of each decision. Harvesting was denoted in real-time by a change in field color at the end of each decision (i.e., change from green to yellow), decreasing in value by 30% per decision until depletion.  The initial configuration of the field varied across 18 games, each comprising up to 25 turns.  Some games began with all fields in a fully green, high-resource state, while others presented spatially structured distributions, with one region of the grid containing higher-value fields and another region containing lower-value fields in a gradient reduction (see Fig. 1). 

A wolf was also present in each game placed at a random corner.  The wolf moved simultaneously with the farmer according to one of three predetermined behavioral patterns.  In random movement games (8 games), the wolf selected a movement direction at equal probability from the four cardinal directions.  In stationary trials (2 games), the wolf remained in its starting location throughout the game.  In high-predation trials (8 games), the wolf exhibited behavior biased toward the farmer’s location.  This was achieved using a weighted probability mechanism, wherein movement options that reduced the distance between the wolf and the farmer were included in the selection pool 50 times, while all other movement options were included only once.  A movement direction was then selected randomly from this weighted distribution, increasing the likelihood that the wolf would approach the farmer. 

Participants accumulated points based on the total value of harvested resources.  However, if the farmer and the wolf occupied the same field at any time, the game resulted in farmer’s “death” and terminated immediately, and the participant forfeited all points accrued during that game.  The next game then began with a new field configuration.  This task structure required participants to balance resource maximization with predator avoidance.