Figure 4. Motion priming between modalities with congruent directions. (A) Auditory motion primes visual motion (AV). Data for judging visual speed were binned into ‘previous slower’ [20, 40, 50 °/s] and ‘previous faster’ [70, 80, 100 °/s] groups and psychometric functions fitted to each group. There was a significant AV priming effect: the PSE was significantly lower after ‘previous fast’ trials (p < .0001). (B) Visual motion primes auditory motion (VA). Same format as panel A, except auditory motion preceded visual motion and produced a significant priming effect (p < .0001). (C) Motion priming for all levels of previous velocity. PSEs decline (more “perceived faster” responses) as preceding velocity increases for both AV and VA conditions. A bootstrap sign-test indicated the slopes of the best fitting lines differed significantly between the conditions, with VA having a steeper slope than AV (p = .0009). (D) Columns on the right show the mean crossmodal priming effect from panel C. For comparison, the means of the unimodal priming functions from Figure 3b are shown. Error bars in all panels are 95% confidence intervals based on 10,000 bootstraps.
Finally, we averaged the PSEs in the AV and VA priming functions in panel C into a single value (Figure 4d, right) and compared them with the average of the unimodal priming functions plotted in Figure 3c (see Figure 4d, left). This shows whether the PSE (i.e., mean perceived speed) for a given modality differs depending on whether it was primed by the same or different modality. The biggest difference occurs for the visual PSE (Figure 4d, red columns): when primed by visual motion (VV), the mean PSE was 46.843°/s and rose to 52.715 (+5.872°/s, p < .0001) when primed by auditory motion (AV). A smaller and opposite effect occurred for the auditory PSEs (blue columns): when primed by auditory motion (AA), the mean PSE was 54.717°/s and fell slightly to 54.091 (-0.626°/s, p = .8656) when primed by visual motion (VA).