Monkeys naturally integrate auditory-visual looming signals

Looming signals (signals that indicate the rapid approach of objects) are behaviourally relevant for primates. We investigated whether rhesus monkeys can integrate the auditory and visual signals of a simulated looming object using the preferential-looking method. Monkeys were presented with two black discs, each on a separate LCD monitor. One disk symmetrically expanded (‘visual looming’), while the other disk symmetrically contracted (‘receding’ stimulus). An auditory signal synchronized with both visual stimuli but either increasing (‘auditory looming’) or decreasing (‘receding’) in intensity was played through a centrally-located speaker (see Ghazanfar et al. (2003) PNAS 99:15755-15757). Viewing behaviour was video-taped, digitized and looking times measured. Our preliminary results reveal that all subjects looked longer at the visual looming stimulus when presented simultaneously with an auditory looming stimulus. Conversely, the effect of the receding sound had little or no influence on their viewing behaviour. Monkeys thus appear to naturally integrate auditory-visual looming signals without any explicit training. The integration of looming, but not receding stimuli, may be because of the strong behavioural relevance of approaching objects. Since many neurons in the superior temporal sulcus are polysensory and selective for looming visual stimuli, we are currently investigating whether such neurons integrate auditory-visual looming signals