Converging Neuronal Activity in Inferior Temporal Cortex during the Classification of Morphed Stimuli

How does the brain dynamically convert incoming sensory data into a representation useful for classification? Neurons in inferior temporal (IT) cortex are selective for complex visual stimuli, but their response dynamics during perceptual classification is not well understood. We studied IT dynamics in monkeys performing a classification task. The monkeys were shown visual stimuli that were morphed (interpolated) between pairs of familiar images. Their ability to classify the morphed images depended systematically on the degree of morph. IT neurons were selected that responded more strongly to one of the 2 familiar images (the effective image). The responses tended to peak ∼120 ms following stimulus onset with an amplitude that depended almost linearly on the degree of morph. The responses then declined, but remained above baseline for several hundred ms. This sustained component remained linearly dependent on morph level for stimuli more similar to the ineffective image but progressively converged to a single response profile, independent of morph level, for stimuli more similar to the effective image. Thus, these neurons represented the dynamic conversion of graded sensory information into a task-relevant classification. Computational models suggest that these dynamics could be produced by attractor states and firing rate adaptation within the population of IT neurons

Using artificial evolution and selection to model insect navigation

AbstractBackground: An animal's behavioral strategies are often constrained by its evolutionary history and the resources available to it. Artificial evolution allows one to manipulate such constraints and explore how they influence evolved strategies. Here we compare the navigational strategies of flying insects with those of artificially evolved “animats” endowed with various motor architectures. Using evolutionary algorithms, we generated artificial neural networks that controlled a virtual animat's navigation within a 2D, simulated world. Like a flying insect, the animat possessed motors that generated thrust and torque, a compass, and visual sensors. Some animats were limited to forward motion, while others could also move sideways. Animats were selected for the precision with which they reached a target specified by a visual landmark.Results: Animats given sideways motors could alter flight direction without changing body orientation and evolved strategies similar to those of flying bees or wasps performing the same task. Both animats and insects first aimed at the landmark. In the last phase, both adopted a fixed body orientation and adjusted their position to keep the landmark at a fixed retinal location. Animats unable to uncouple flight direction and body orientation evolved subtly different strategies and performed less robustly.Conclusions: This convergence between the navigational strategies of animals and animats suggests that the insect's strategies are primarily an adaptation to the demands of using visual information and compass direction to reach a position in space and that they are not significantly compromised by the insect's evolutionary history