Contributions of magno- and parvocellular channels to conscious and non-conscious vision

Abstract

The dorsal and ventral cortical pathways, driven predominantly by magnocellular (M) and parvocellular (P) inputs, respectively, assume leading roles in models of visual information processing. Although in prior proposals, the dorsal and ventral pathways support non-conscious and conscious vision, respectively, recent modelling and empirical developments indicate that each pathway plays important roles in both non-conscious and conscious vision. In these models, the ventral P-pathway consists of one subpathway processing an object's contour features, e.g. curvature, the other processing its surface attributes, e.g. colour. Masked priming studies have shown that feed-forward activity in the ventral P-pathway on its own supports non-conscious processing of contour and surface features. The dorsal M-pathway activity contributes directly to conscious vision of motion and indirectly to object vision by projecting to prefrontal cortex, which in turn injects top-down neural activity into the ventral P-pathway and there ‘ignites’ feed-forward–re-entrant loops deemed necessary for conscious vision. Moreover, an object's shape or contour remains invisible without the prior conscious registration of its surface properties, which for that reason are taken to comprise fundamental visual qualia. Besides suggesting avenues for future research, these developments bear on several recent and past philosophical issues.

Sharpening of hierarchical visual feature representations of blurred images

“…Previous studies have proposed that the brain makes an initial processing step using low spatial frequency information. This step generates predictions of the content of the image in the orbitofrontal cortex; these predictions are then used to drive the top-down modulation effect (Bar and Aminoff, 2003;Bar et al, 2006;Kveraga et al, 2007;Breitmeyer, 2014 (Bar et al, 2006;Chiou and Lambon Ralph, 2016). As we demonstrate here, the DNN representations could offer a plausible proxy for representing brain activity and for attaining a pure-feedforward baseline that can be used for measuring top-down effects.…”

Center-surround velocity-based segmentation: Speed, eccentricity, and timing of visual stimuli interact to determine interocular dominance

“…This is because it posits that some features, such as eccentricity, color, and spatial and temporal frequencies, are processed by two different channels and are, thus, bound within those channels, such as with parvocellular and magnocellular pathways. The two pathways originate in the retina, go through lateral geniculate nucleus (LGN) and extrastriate areas, and subsequently predominantly fuse into ventral and dorsal pathways, respectively (Breitmeyer, 2014;Livingstone & Hubel, 1987;Nassi & Callaway, 2009;Tapia & Breitmeyer, 2011). Parvocellular pathway is known to be biased toward higher spatial and lower temporal frequencies and is color-opponent; magnocellular pathway, on the other hand, is associated with lower spatial and higher temporal frequencies and is colorblind.…”

The perceived present: What is it, and what is it there for?

“…According to Goodale and Milner (1992) and Goodale (2014), the dorsal pathway is specialized for the guidance of interactions with objects and the ventral pathway is specialized for constructing a visual model of the world. Action can be guided by perceptual information processed through the dorsal pathway that seems not to enter the perceived present (Goodale, Milner, Jakobson, & Carey, 1991), and indeed reactive actions can occur on a shorter time scale than that needed to construct relevant content in the perceived present (Brenner & Smeets, 1997;Castiello, Paulignon, & Jeannerod, 1991;Prablanc & Martin, 1992). There is, therefore, a functional dissociation between the perceived present, at least in vision, and the control and visual guidance of actions.…”

“…There is, therefore, a functional dissociation between the perceived present, at least in vision, and the control and visual guidance of actions. Goodale and Milner (1992) argued that the two pathways are not completely separate, and indeed it would make sense for some degree of functional integration between the two kinds of visual processing to occur (Breitmeyer, 2014). However, evidence shows that patients who have no apparent impairment in perceiving and recognizing a certain kind of object may be considerably impaired in their ability to act on it, even when it is stationary (e.g., Jakobson, Archibald, Carey, & Goodale, 1991).…”