We have examined the visuotopic organization of area V2 of
macaque monkeys in relation to its modular construction, comprising
repetitive cycles of stripes running perpendicular to the border
with area V1. Receptive fields were plotted in anesthetised
animals, mainly using long penetrations parallel to the V1 border
crossing several stripes in dorsal V2 within the representation
of paracentral, inferior visual field. We confirm that each
set of modules (thick, thin, and interstripes) mounts an unbroken
coverage of the visual field, since there is almost invariably
some overlap between the aggregate fields recorded in successive
stripes of the same class, at intervals of one cycle. Also as
expected, penetrations perpendicular to the stripes record changes
in eccentricity along an isopolar visual meridian. We measured
the size of the point image along such an isopolar meridian
in nine cases, and showed that on average it exceeds the length
of a typical cycle; again, this implies that no point in space
escapes analysis by any of the functional modules. The
representation of eccentricity across a cycle of stripes resembles
a “ratchet” model, in which the gradient of
eccentricity across a single stripe exceeds the gradient across
the full cycle, leading to discontinuities
(“switchbacks”) at the borders between stripes.
The shift in eccentricity across the width of a stripe is
sufficient to maintain a virtually continuous map across successive
stripes of the same class; when coupled to receptive field scatter
about the mean trend, this creates the overlap of aggregate fields.