Statistics of Visual Responses to Object Stimuli from Primate AIT Neurons to DNN Neurons

Cadieu et al. (Cadieu,2014) reported that deep neural networks(DNNs) could rival the representation of primate inferotemporal cortex for object recognition. Lehky et al. (Lehky,2011) provided a statistical analysis on neural responses to object stimuli in primate AIT cortex. They found the intrinsic dimensionality of object representations in AIT cortex is around 100 (Lehky,2014). Considering the outstanding performance of DNNs in object recognition, it is worthwhile investigating whether the responses of DNN neurons have similar response statistics to those of AIT neurons. Following Lehky et al.'s works, we analyze the response statistics to image stimuli and the intrinsic dimensionality of object representations of DNN neurons. Our findings show in terms of kurtosis and Pareto tail index, the response statistics on single-neuron selectivity and population sparseness of DNN neurons are fundamentally different from those of IT neurons except some special cases. By increasing the number of neurons and stimuli, the conclusions could alter substantially. In addition, with the ascendancy of the convolutional layers of DNNs, the single-neuron selectivity and population sparseness of DNN neurons increase, indicating the last convolutional layer is to learn features for object representations, while the following fully-connected layers are to learn categorization features. It is also found that a sufficiently large number of stimuli and neurons are necessary for obtaining a stable dimensionality. To our knowledge, this is the first work to analyze the response statistics of DNN neurons comparing with AIT neurons, and our results provide not only some insights into the discrepancy of DNN neurons with respect to IT neurons in object representation, but also shed some light on possible outcomes of IT neurons when the number of recorded neurons and stimuli is beyond the level in (Lehky,2011,2014).