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Nicole C. Rust, James J. DiCarlo; Balanced increases in selectivity and invariance produce constant sparseness across the ventral visual pathway. Journal of Vision 2009;9(8):738. doi: 10.1167/9.8.738.
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© ARVO (1962-2015); The Authors (2016-present)
While several studies report neurons in inferotemporal cortex (IT) that are highly selective for particular objects or images, other studies report that neurons in IT tend to be broadly tuned. To investigate how selectivity changes across the ventral visual pathway, we compared the responses of neurons in a mid-level visual area (V4) and a high-level visual area (IT). We first assessed the selectivity of neurons in each area by determining how well each population could discriminate between natural images and “scrambled” versions of those images that have the same low-level structure but configured randomly. We found that the V4 population discriminated between members of the two image sets with similar fidelity whereas discrimination by the IT population was considerably degraded for the scrambled images. These results suggest that IT neurons are in fact more selective than V4 neurons in terms of the image features that drive these cells. As a second estimate of selectivity, we measured the tuning bandwidth of neurons for natural images (“sparseness”). Surprisingly, we found that distributions of sparseness values were indistinguishable between V4 and IT. How can the selectivity for natural image features increase while the tuning bandwidth for natural images remains constant? One possibility is that increases in selectivity for particular image features are offset by increases in tolerance for the (e.g.) position and scale of those features. We found that indeed, measures of tolerance were higher in IT than V4. These results confirm that neurons increase both their selectivity for image features and their tolerance to changes in the position and scale of those features as signals propagate through the ventral pathway. Remarkably, the rates of increase of these two parameters appear to be set such that the tuning bandwidth for natural images is maintained across each stage of cortical processing.
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