Fig. 10. Development of emergent behaviors in the trained SC neurons as a function of the cross-modal input statistics.

Panels show the behaviors of the SC neurons in different phases of their maturation, in case of three trainings performed with different cross-modal input statistics. x-axis reports the training phases. y-axis shows the percentage of SC neurons showing a particular emergent behavior. Figure A) presents the sensory abilities of SC neurons in different development phases when the network is trained with just 40% of cross-modal stimuli. The network does not start its maturation since it has been stimulated by 150.000 inputs. Then the AES synapses become effective and the SC neurons begin to present cross-modal integrative capabilities. After about 200.000 training stimuli, immature, multisensory integrative, and unisensory SC neurons coexist in the network. As the training proceeds the multisensory integrative neurons evolve to unisensory, until a mature steady state is reached (at 240.000 stimuli) in which more than the 95% of the SC neurons are modality-specific, and just a few are multisensory. Figure B) presents the behaviors acquired by the SC neurons after a training with 60% of cross-modal inputs: here the network starts its maturation after 100.000 stimuli. As in figure A) in a first phase the network develops multisensory integrative (60%), unisensory (with and without integrative capabilities, 28% and 10% respectively) and still immature (2%) neurons. After 170.000 training stimuli, the network reaches a mature steady state in which there are only unisensory neurons (58% purely unisensory and 42% with integrative capabilities). Finally, Figure C) presents the abilities acquired if the SC is trained with 70% of cross-modal inputs: here the network reaches its maturation final state after about 150.000 stimuli. In this phase 96% of SC neurons are multisensory, while just 4% are unisensory. All of them show integrative capabilities.