Euclidean coordinates are the wrong prior for primate vision
The mapping from the visual field to V1 can be approximated by a log-polar transform. In this domain, scale is a left-right shift, and rotation is an up-down shift. When fed into a standard shift-invariant convolutional network, this provides scale and rotation invariance. However, translation invariance is lost. In our model, this is compensated for by multiple fixations on an object. Due to the high concentration of cones in the fovea with the dropoff of resolution in the periphery, fully 10 degrees of visual angle take up about half of V1, with the remaining 170 degrees (or so) taking up the other half. This layout provides the basis for the central and peripheral pathways. Simulations with this model closely match human performance in scene classification, and competition between the pathways leads to the peripheral pathway being used for this task. Remarkably, in spite of the property of rotation invariance, this model can explain the inverted face effect. We suggest that the standard method of using image coordinates is the wrong prior for models of primate vision.
Exploring fine detail: The interplay of attention, oculomotor behavior and visual perception in the fovea
Outside the foveola, visual acuity and other visual functions gradually deteriorate with increasing eccentricity. Humans compensate for these limitations by relying on a tight link between perception and action; rapid gaze shifts (saccades) occur 2-3 times every second, separating brief “fixation” intervals in which visual information is acquired and processed. During fixation, however, the eye is not immobile. Small eye movements incessantly shift the image on the retina even when the attended stimulus is already foveated, suggesting a much deeper coupling between visual functions and oculomotor activity. Thanks to a combination of techniques allowing for high-resolution recordings of eye position, retinal stabilization, and accurate gaze localization, we examined how attention and eye movements are controlled at this scale. We have shown that during fixation, visual exploration of fine spatial detail unfolds following visuomotor strategies similar to those occurring at a larger scale. This behavior compensates for non-homogenous visual capabilities within the foveola and is finely controlled by attention, which facilitates processing at selected foveal locations. Ultimately, the limits of high acuity vision are greatly influenced by the spatiotemporal modulations introduced by fixational eye movements. These findings reveal that, contrary to common intuition, placing a stimulus within the foveola is necessary but not sufficient for high visual acuity; fine spatial vision is the outcome of an orchestrated synergy of motor, cognitive, and attentional factors.