The time it takes for border-ownership signals to emerge constrains the type of intercortical network that can plausibly perform figure-ground segregation. Researchers have proposed that B cells access global information either
intra-areally, i.e., by lateral connections within a single visual cortical area, such as V2 (Zhaoping,
2005), or
interareally, i.e., where cells with larger receptive fields communicate contextual information about the scene via feedback projections to visual areas with small receptive field cells fewer synapses away from the retina (Angelucci et al.,
2002). Intra-areal and interareal axonal conduction velocities have been estimated to be 0.3 m/s (Nowak, Munk, Girard, & Bullier,
1995; Nowak & Bullier,
1997; Angelucci et al.,
2002) and 3.5 m/s (Girard, Hupe, & Bullier,
2001) in early visual areas, respectively (Bullier,
2001). Hence, interareal connections can be an order of magnitude faster than intra-areal connections for propagating information across the visual field. Sugihara, Qiu, and von der Heydt (
2003) showed that B cell responses to 3° squares did not differ in latency compared to those to an 8° square, which is consistent with the use of interareal connections, but not intra-areal connections, to propagate contextual figure-ground information. Although a variable amount of time is required to propagate information about a figure within a single cortical area, transmitting the information to another area with large receptive field cells could afford a roughly fixed delay irrespective of the figure size in the visual field. Using published neuroanatomical data (Gattass, Gross, & Sandell,
1981; Gattass, Sousa, Mishkin, & Ungerleider,
1997), we estimate the cortical distance along the horizontal meridian and spanning 0°–5° eccentricity within V2 as 22.25 mm, which agrees with prior estimates (Craft et al.,
2007). Traversing such a distance at 0.3 m/s would take approximately 75 ms which cannot account for border-ownership latency of 10–25 ms reported in neurophysiology (Zhou et al.,
2000). Hence, it appears that connections within a single cortical area alone could not plausibly account for the fast global scene integration that is observed in B cell border-ownership responses (but see Zhaoping,
2005, who argues otherwise as we describe in the
Discussion section).