Ocular Saccades Influence Loudness Perception more than Button Presses: The Role of Prediction Error …

Overview & Synopsis

Voluntary actions, such as pressing a button, can affect the loudness of the sounds produced. To date, the role of intentional motor-sensory coupling and the involvement of more general prediction mechanisms remain unclear. Asking participants to make ocular saccades (which do not naturally produce sounds: weak coupling) instead of pressing a button (which frequently produces sounds: strong coupling) allowed us to investigate this question. Two independent groups of participants performed either a saccade task (N=42) or a keypress task (N=43). In a short movement-sound delay condition, a tone of variable intensity was presented 150 ms after movement onset. In a long delay condition, the tone was presented 1500 ms after movement onset, in order to dissociate it from possible motor-based effects. We also manipulated motor-sensory coupling within each task by presenting the tones after every movement in one subgroup, whereas in another subgroup, tones were delivered randomly after 50% of the movements. A reference tone was presented 800-1200 ms after the variable tone, and participants indicated which of the two tones was louder. The only significant effect we observed on the psychometric functions was a larger JND in the 150-ms delay condition of the saccade task compared to all other experimental conditions. We found no significant effects of the movement-tone contingency. A reinforcement learning model was then used to compute a prediction error regarding tone occurrence for each trial (in the 50% movement-tone contingency). Prediction error affected the judgment of saccade generated tones (GLMM analysis, p = .005), but not the judgment of keypress generated tones (p = .285). These results suggest that motor-based effects on the perception of self-generated tones depend critically on the strength of the previously learned association between a movement and the sound it produces. This may explain the inconsistent results found in the literature.