This task was developed to reflect established rodent approach–avoidance conflict tests in a Pac-Man-style computer game. The current study used a shortened version with a reduced number of threat probability levels (two instead of three) and fewer trials per condition (20 instead of 40), and was presented using the MATLAB toolbox Cogent (www.vislab.ucl.ac.uk). The task included 80 epochs (and one bonus epoch; see below) (that is, time periods during which participants had the opportunity to accumulate monetary tokens). In each epoch, they collected tokens on a 24 × 16 grid while under threat of being chased by a predator. Being caught resulted in the loss of all tokens collected in that epoch. One corner of the grid was a location safe from predator attack. The safe place was either the player’s starting place or the opposite corner, randomly balanced over epochs. The 80 epochs were divided into five blocks of 16 epochs and approximately 5 min duration, with short self-paced breaks.

Tokens

At all times, ten tokens were uniformly distributed on the grid, and every 2 s one of the tokens changed its position randomly, to encourage uniform foraging across the grid. Collected tokens were replaced in a random position on the grid, and the number of collected tokens was displayed above the grid.

Predator

The predator was initially inactive in the corner diagonally opposite the safe place. Participants were instructed that the predator could become active and chase participants at any time. The colour of the frame around the grid indicated two distinct predator wake-up probabilities (0.25 or 0.75), which participants learned to distinguish between. Participants started either in the same place as the predator (active) or in the safe place (that is, opposite the predator (passive)). Notably, all epochs entailed going out onto the grid to collect tokens, and we have previously shown that over the course of an epoch behaviour becomes comparable for the two starting positions. As such, we averaged data over this factor, except for the single-trial analysis of performance, for which such averaging was not possible.

Movements on the grid

Participants coordinated their movements by pressing the four computer keyboard arrow keys. No diagonal movements were possible. Participants could move at a maximum speed of ten grid blocks per second if they held a key pressed. Both predators had the same speed of 40 grid blocks per second.

Epoch duration

The duration of the foraging phase was randomly drawn from 3, 6.5, 10 or 13.5 s. After the pre-determined foraging phase duration, the predator either woke up for a 5-s chase phase or the next epoch started. Only the foraging phase was analysed. Before each epoch started, there was a 3-s countdown with a preview of the grid layout, during which the player could not move, to facilitate orientation on the grid.

 For further information, please see the linked article: Predictors of risky foraging behaviour in healthy young people