Visual motion serves but is not under the purview of the dorsal pathway

Abstract

Visual motion processing is often attributed to the dorsal visual pathway despite visual motion's involvement in almost all visual functions. Furthermore, some visual motion tasks critically depend on the structural integrity of regions outside the dorsal pathway. Here, based on numerous studies, I propose that visual motion signals are swiftly transmitted via multiple non-hierarchical routes to primary motion-dedicated processing regions (MT/V5 and MST) that are not part of the dorsal pathway, and then propagated to a multiplicity of brain areas according to task demands, reaching these regions earlier than the dorsal/ventral hierarchical flow. This not only places MT/V5 at the same or even earlier visual processing stage as that of V1, but can also elucidate many findings with implications to visual awareness. While the integrity of the non-hierarchical motion pathway is necessary for all visual motion perception, it is insufficient on its own, and the transfer of visual motion signals to additional brain areas is crucial to allow the different motion perception tasks (e.g. optic flow, visuo-vestibular balance, movement observation, dynamic form detection and perception, and even reading). I argue that this lateral visual motion pathway can be distinguished from the dorsal pathway not only based on faster response latencies and distinct anatomical connections, but also based on its full field representation. I also distinguish between this primary lateral visual motion pathway sensitive to all motion in the visual field, and a much less investigated optic flow sensitive medial processing pathway (from V1 to V6 and V6A) that appears to be part of the dorsal pathway. Multiple additional predictions are provided that allow testing this proposal and distinguishing between the visual pathways.

Predictive coding with neural transmission delays: a real-time temporal alignment hypothesis

“…However, an influential body of literature has proposed that the human visual system is organized into two (partly) dissociable pathways: a ventral "what" pathway for object recognition and identification, and a dorsal "where" pathway for localization and motion perception [81][82][83][84] . Two decades later, the distinction is more nuanced 85,86 , but the question remains whether velocity signals are truly ubiquitous throughout the visual hierarchy. Consequently, whether real-time temporal alignment is restricted to the "where" pathway or is a general feature of cortical processing remains to be elucidated.…”

Investigating face and house discrimination at foveal to parafoveal locations reveals category-specific characteristics

“…in LOC, FFA, PPA) [8][9][10][11][12][13][14] . This high-level visual specialization is predominantly manifested in two anatomically distinct visual processing pathways, the ventral perception visual pathway processing aspects related to shape and form, and the dorsal spatial visual pathway processing aspects related to action preparation and location in space [15][16][17][18][19] .…”

Continuous theta burst TMS of area MT+ impairs attentive motion tracking

“…Area MT+ has a central role in this hypothesis because the vast majority of relevant studies assess dorsal stream function with global motion stimuli that are specifically designed to target MT+ (Braddick et al, 2001;Kaderali, Kim, Reynaud, & Mullen, 2015;Newsome & Pare, 1988;Newsome, Britten, & Movshon, 1989;Simoncelli & Heeger, 1998). This approach is based on the idea that area MT+ is a dorsal stream area, although it has been argued that the division of processing into dorsal and ventral streams takes place after MT+ (Gilaie-Dotan, 2016;Milner & Goodale, 1995;Schenk, Mai, Ditterich, & Zihl, 2000;Schenk & McIntosh, 2010). Impaired global motion perception linked to dorsal stream vulnerability has been reported in a range of neurodevelopmental disorders including William's syndrome (Atkinson et al, 1997Atkinson et al, 2006;Palomares & Shannon, 2013;Reiss, Hoffman, & Landau, 2005), preterm birth (Guzzetta et al, 2009;Taylor, Jakobson, Maurer, & Lewis, 2009), autism (Brieber et al, 2010;Spencer et al, 2000), dyslexia (Edwards et al, 2004;Talcott, Hansen, Assoku, & Stein, 2000), and fetal alcohol syndrome (Gummel, Ygge, Benassi, & Bolzani, 2012).…”