A Fresh Look at the Two Visual Streams: Or How to Stop Worrying about Zombies

Abstract: According to the "Two Visual Systems Account" (Two-Systems), the visual system is divided into two independent sub-systems, a ventral system implementing "vision for perception," and a dorsal system implementing "vision for action" (Milner and Goodale, 2006). Two-Systems is widely discussed in philosophy because it implies that our actions are controlled by an independent, unconscious system. It's been argued that this 'zombie action hypothesis' has crucial implications for our understanding of perception and of its role in the active mind (Clark 2001, 2007, 2009). However, recent evidence undermines Two-System's core tenets: it no longer appears that the ventral and dorsal streams constitute isolated processing systems, and there is now evidence for the involvement of both streams in both conscious experience and online motor control. (e.g. Schenk and McIntosh 2015). Since Two-Systems fails, so too, apparently, does the zombie action hypothesis and its corresponding implications. Against this backdrop, I make two central claims. First, I develop my "Direct Dorsal Control Account" (Dorsal-Control) and show that it's immune to the three empirical challenges facing Two-Systems. Second, I show that, regardless of the truth or falsity of zombie action, Dorsal-Control has the same central philosophical implications of Two-Systems. Thus, I suggest a reorientation of the two streams debate away from zombie action and toward more precise, functional distinctions.