Fig. 1.

Overview of the experimental approach. (A) Schematic illustration of the sound categories. Each alien was paired with four sound exemplars. Each exemplar was composed of an invariant low-frequency spectral peak (P1; dashed line) and one of the four possible higher-frequency spectral peaks (P2; either a gray or black solid line). (A, Upper) The four categories learned by the experimental group. (A, Lower) The categories learned by the control group. Each group experienced an identical pair of offset sound categories, defined by a single acoustic dimension (i.e., decreasing vs. increasing in frequency across time). Only the onset-sweep categories differed across groups. For the experimental group, onset categories were organized into two categories potentially linearly separable in a higher-dimensional perceptual space defined by the integration of multiple acoustic dimensions [i.e., steady-state (SS) frequency and P2 onset-frequency locus]. For the control group, onset-category exemplars were randomly drawn from this space (Methods). The scatterplots show the higher-dimensional relationships of the onset-sweep categories for each group, with color indicating the categories. (B) Illustration of the videogame. (B, Left) A game screenshot. Each alien creature appears from a consistent quadrant. (B, Right) A schematic depiction of a game trial structure with multiple events. On each trial, one alien appears and a single exemplar from the associated sound category is presented repeatedly. Participants must navigate the videogame to center the alien and take the correct gaming action (23). The trial length (appearance of each alien) depends upon how well participants play the game; thus, it is highly variable within and across participants.