The Development of Audio-Visual Integration for Temporal Judgements

Adults combine information from different sensory modalities to estimate object properties such as size or location. This process is optimal in that (i) sensory information is weighted according to relative reliability: more reliable estimates have more influence on the combined estimate and (ii) the combined estimate is more reliable than the component uni-modal estimates. Previous studies suggest that optimal sensory integration does not emerge until around 10 years of age. Younger children rely on a single modality or combine information using inappropriate sensory weights. Children aged 4–11 and adults completed a simple audio-visual task in which they reported either the number of beeps or the number of flashes in uni-modal and bi-modal conditions. In bi-modal trials, beeps and flashes differed in number by 0, 1 or 2. Mutual interactions between the sensory signals were evident at all ages: the reported number of flashes was influenced by the number of simultaneously presented beeps and vice versa. Furthermore, for all ages, the relative strength of these interactions was predicted by the relative reliabilities of the two modalities, in other words, all observers weighted the signals appropriately. The degree of cross-modal interaction decreased with age: the youngest observers could not ignore the task-irrelevant modality—they fully combined vision and audition such that they perceived equal numbers of flashes and beeps for bi-modal stimuli. Older observers showed much smaller effects of the task-irrelevant modality. Do these interactions reflect optimal integration? Full or partial cross-modal integration predicts improved reliability in bi-modal conditions. In contrast, switching between modalities reduces reliability. Model comparison suggests that older observers employed partial integration, whereas younger observers (up to around 8 years) did not integrate, but followed a sub-optimal switching strategy, responding according to either visual or auditory information on each trial.Author Summary: To complete everyday activities, such as judging where or when something occurred, we combine information from multiple senses such as vision and audition. In adults, this merging of information is optimal: more reliable sensory estimates have more influence (higher weight) in the combined, multisensory estimate. Multisensory integration can result in illusions: if a single visual flash (e.g. a bright disk appearing briefly on a screen) occurs at the same time as two beeps, we sometimes perceive two flashes. This is because auditory information is generally more reliable than vision for judging when things happen; it dominates our audio-visual percept for temporal tasks. Previous work suggests that children don’t combine information from different senses in this adult-like way until around 10 years. To investigate this further, we asked children and adults to report the number of visual flashes or auditory beeps when these were presented simultaneously. Surprisingly, all children used appropriate sensory weights: audition—the more reliable signal—tended to dominate perception, with less weight given to vision. However, children didn’t show the adult-like reduction in uncertainty until around 8–10 years. Before that age, they switched between using only auditory or only visual information on each trial.