Table 1 contains measurements of the surface area of the visual field representations from 2–12 deg. Right and left hemispheres, (left and right visual field) as well as dorsal and ventral aspects (lower and upper visual field) are listed separately for each subject.
Table 1 also contains surface area measurements of the large central representation (0–2 deg). This cortical region falls at the confluence of areas V1, V2, V3 and hV4. The surface area of the central representation is shown as a single measurement because we did not separate the visual areas within this region.
Left hemisphere V1 surface area (mean = 1578 mm2) tended to be larger than right hemisphere V1 area (mean 1362 mm2). This difference was significant (pairwise t = 2.39, p = 0.033, df = 13). There were no significant differences between left and right V2 (means 1187 mm2 and 1044 mm2, respectively) or between left and right V3 (means 831 mm2 and 808 mm2, respectively).
The surface areas of corresponding visual areas in the two hemispheres of the same subject are correlated. This correlation was quite strong for V1 (r = 0.744, p = 0.001, df = 11) and the foveal confluence (r = 0.863, p = 0.009, df = 4). However, it was weaker for V2 (r = 0.455, p = 0.104, df = 11) and V3 (r = 0.349, p = 0.227, df = 11). The strong correlation between the two hemispheres for V1 agrees with the post-mortem data of Andrews et al. (
1997).
Across all the visual areas, dorsal regions (799 mm2, 597 mm2, 435 mm2 for V1, V2 and V3) tended to be larger than ventral regions (671 mm2, 518 mm2, 384 mm2 for V1, V2 and V3). This difference was significant in V1 (pairwise t = 3.24, p < 0.01, df=13), but not in V2 or V3.
A scatter plot comparing the surface areas of V1 and V2 (
Figure 2) shows a relatively high correlation (r = 0.621, p < 0.001, df = 25). The V2 surface area in the 2–12 deg representation is roughly 75% that of V1, and this size difference is statistically significant (pairwise t = 3.74, p < 0.001, df = 27). As reviewed by Sincich and Horton (
2002), V2 receives significant input from both V1 and the pulvinar. Hence, the reduced size of V2 suggests that it may only receive a portion of the V1 output or that it has a more efficient representation of this output.
No significant correlation was found between the surface area of V1 and V3 (r = 0.03, p = 0.879, df = 25). However, V3 was on average 56% the size of V1, and this difference was significant (pairwise t = 6.76 (p<0.001, df=27).
Despite the lack of a correlation between V1 and V3, the surface area of V2 was correlated with the area of V3 (r = 0.513, p = 0.006, df = 25).