Learning improves the contribution of auditory distance cues to size constancy in perception and grasping when vision is limited

When vision is restricted, proprioceptive distance cues fully restore size constancy for scaling grip aperture when grasping objects, despite only limited improvement in perceptual judgments of object size. This suggests that specific task demands and associated neural mechanisms determine the relative weighting of cues during multisensory integration. Is this specific to proprioceptive cues? Here, we examined the contribution of auditory information to perception and action systems under restricted viewing conditions. Surprisingly, in contrast to proprioception, providing auditory distance information had no impact whatsoever on size constancy in grasping but did improve perceptual judgments of size. After participants received extensive training in discriminating distance from auditory cues, there was a modest improvement in grip scaling. Taken together, we suggest that the neural mechanisms mediating grasping cannot incorporate distance information from audition as easily as they can from proprioception when computing real-world object size but this ability can be improved with training.