A Reconsideration of Parallel Processing in Vision: Importance of Lower Spatial Frequencies to Form Vision

The appreciation of parallel visual pathways from retina to cortex in mammalian vision has greatly advanced our understanding of sensory processing. While these anatomical pathways are well-characterized, their specific functional roles remain incompletely understood, particularly in terms of parsing natural scenes. Here, we start with a re-evaluation of the functional contributions of parallel X and Y pathways in the cat, emphasizing the underappreciated role of Y cells in spatial vision. Contrary to the traditional view that prioritizes the importance of high acuity for visual function and thus the role of X cells, because they support high acuity vision, we argue that lower spatial frequencies are more important for visual function. For instance, these lower frequencies dominate natural visual scenes, and Y cells are much more responsive to these than X cells are. We provide further anatomical and behavioral evidence that the Y pathway plays the dominant role in basic spatial vision, particularly during active vision. These findings challenge the adequacy of visual acuity and the X pathway as a proxy for visual function and underscore the need to consider functioning in response to natural scenes in models of visual processing. Implications for primate and rodent vision are discussed, including the need for comparative and integrative research and the importance of understanding similarities and differences across species.