Figure 1

Sequence of events in the ensemble coding tasks. (A) Example of one trial in Experiment 1. Stimuli were presented at the fovea with different degrees of dispersion (see “General methods” section). After the fixation cross, an ensemble of 25 disks was presented for 200 ms, followed by a blank interval. The task was to adjust the size (diameter) of a single central disk so that it reproduced the average size of the set of stimuli in the ensemble. (B) Example of one trial in Experiment 2, with the ensemble presented on the right side of the display. In this experiment, ensembles could randomly appear on the left, in the center or on the right side. (C) Example trial in Experiment 3. At the beginning of each trial, participants received a visual cue (here ‘IN’) indicating the region of the screen where the relevant ensemble was presented (here the internal region). After a fixation interval, two ensembles separated by colored frames were presented. Participants had to reproduce the average size of stimuli inside the relevant ensemble, indicated by a frame that matched the color of the initial cue. (D) Derivation of spatial weighting maps (SWMs). Local variations in the size of each disk across trials were used as multivariate regressors explaining the trial sequence of adjustment responses. Two-dimensional SWM were obtained by estimating the weight (regression coefficient) of each disk at each location on participants’ responses.