Causal inference and the evolution of opposite neurons.

A pesky mosquito continues to annoy you and you are poised to swat it. You see it hovering above your arm, and feel a gentle tickle, but in a slightly different spot (Fig. 1 A ). Where should you strike? The mathematically optimal solution is to average the locations indicated by vision and touch, with greater weight given to the more reliable signal, the one that typically leads to smaller errors. A substantial literature indicates that for most modality pairings and perceptual tasks humans behave in accordance with this optimal prescription for sensory integration (1⇓⇓–4). However, if vision and touch indicate very different locations, the tickle might be due to another cause such as an old mosquito bite (Fig. 1 B ). In this case, it makes sense to segregate the sensory signals, ignore touch, and swat at the location indicated by vision. This decision requires making a “causal inference,” that is, an inference as to whether two sensory signals derive from a common source or separate sources. Humans (5, 6) and monkeys (7, 8) behave as if they perform causal inference; they do not integrate signals unlikely to come from the same source. The challenging question is, how are sensory cue integration and causal inference implemented in the brain? Fig. 1. Multisensory integration and causal inference. ( A ) When a common cause is inferred, sensory signals are integrated; ( B ) when separate sources are inferred, the segregated visual signal is used. ( C ) Congruent neurons have similar tuning for heading direction across modalities; ( D ) opposite neurons’ preferred directions differ across modalities. Both types of neurons contribute to ( E ) self- and ( F ) world-motion estimation as well as ( G ) causal-inference judgments, but to different degrees. ( H ) In Bayesian estimation, the integrated and segregated estimates are combined with weights equal to the probabilities of each … [↵][1]1To whom correspondence may be addressed. Email: landy{at}nyu.edu. [1]: #xref-corresp-1-1