Hierarchical processing of complex motion along the primate dorsal visual pathway

Abstract

Neurons in the medial superior temporal (MST) area of the primate visual cortex respond selectively to complex motion patterns defined by expansion, rotation, and deformation. Consequently they are often hypothesized to be involved in important behavioral functions, such as encoding the velocities of moving objects and surfaces relative to the observer. However, the computations underlying such selectivity are unknown. In this work we have developed a unique, naturalistic motion stimulus and used it to probe the complex selectivity of MST neurons. The resulting data were then used to estimate the properties of the feed-forward inputs to each neuron. This analysis yielded models that successfully accounted for much of the observed stimulus selectivity, provided that the inputs were combined via a nonlinear integration mechanism that approximates a multiplicative interaction among MST inputs. In simulations we found that this type of integration has the functional role of improving estimates of the 3D velocity of moving objects. As this computation is of general utility for detecting complex stimulus features, we suggest that it may represent a fundamental aspect of hierarchical sensory processing.receptive field | optic flow I n the early stages of the primate visual system the receptive fields of neurons can be readily estimated from the responses to simple stimuli such as spots, bars, and gratings or even by hand mapping (1-3). However, for neurons farther along the visual pathways, the relationship between stimulus input and neuronal output is often far from obvious, particularly in areas that respond to complex stimuli such as faces, objects, or optic flow patterns (4-7). Uncovering this relationship is crucial for understanding the computations that underlie important behavioral functions such as object recognition and navigation.One well-known example of complex cortical processing is the range of selectivities found in the medial superior temporal (MST) area of the primate visual cortex. Previous work has shown that MST neurons are highly selective for visual stimuli composed of combinations of motion patterns such as expansion, deformation, translation, and rotation (8-12). Although this selectivity has been documented many times over the last 25 y, very little is known about the computations by which it is derived. One prevalent hypothesis is that the selectivity of MST neurons is determined by specific strategies used by the brain to calculate one's direction of motion, or heading, through the world (13-15). In these models, heading is computed by combining the output of detectors tuned to specific motion patterns, and these patterns are reflected in the internal structure of an MST neuron's receptive field.Although this hierarchical account of MST selectivity is appealingly simple, it has been difficult to confirm experimentally. Indeed previous studies have concluded that MST responses to complex stimuli often cannot be predicted, even qualitatively, from their responses to simple ones (7-9, 16). For ...

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“…This functional form resembles a familiar rectified-linear function and additionally facilitates well behaved model optimization (Paninski, 2004;McFarland et al, 2013). To validate the use of this parametric form of F [⅐], we also measure the spiking nonlinearity using nonparametric histogram method (Chichilnisky, 2001, Paninski, 2004.…”

Coordinated Control of Three-Dimensional Components of Smooth Pursuit to Rotating and Translating Textures

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An integrated artificial vision framework for assisting visually impaired users

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