Visual areas and spatial summation in human visual cortex

Abstract

Functional MRI measurements can securely partition the human posterior occipital lobe into retinotopically organized visual areas (V1, V2 and V3) with experiments that last only 30 min. Methods for identifying functional areas in the dorsal and ventral aspect of the human occipital cortex, however, have not achieved this level of precision; in fact, different laboratories have produced inconsistent reports concerning the visual areas in dorsal and ventral occipital lobe. We report four findings concerning the visual representation in dorsal regions of occipital cortex. First, cortex near area V3A contains a central field representation that is distinct from the foveal representation at the confluence of areas V1, V2 and V3. Second, adjacent to V3A there is a second visual area, V3B, which represents both the upper and lower quadrants. The central representation in V3B appears to merge with that of V3A, much as the central representations of V1/2/3 come together on the lateral margin of the posterior pole. Third, there is yet another dorsal representation of the central visual field. This representation falls in area V7, which includes a representation of both the upper and lower quadrants of the visual field. Fourth, based on visual field and spatial summation measurements, it appears that the receptive field properties of neurons in area V7 differ from those in areas V3A and V3B.

Automatic volumetric segmentation of human visual retinotopic cortex

“…These areas are at the limit of the current methodology and therefore may be only partially identified, if at all, as evidenced by inconsistent descriptions of several studies (Press et al, 2001;Smith et al, 1998;Tootell et al, 1998a,b). Press et al (2001) found an upper and lower visual field representation for both V3B and V7. Smith et al (1998) could determine only a lower field representation for area V3B, while Tootell et al (1998a,b) could only measure a lower field representation for area V7.…”

“…These results were replicated by DeYoe et al (1996) and Engel et al (1997), also utilizing a cortical surface-based analysis but manually distinguishing the borders based on polar-angle information. Further phase-encoded mapping studies with modifications of the stimulus revealed visual areas V3A (DeYoe et al, 1996;Tootell et al, 1997Tootell et al, , 1998c, V3B (Press et al, 2001;Smith et al, 1998), V7 (Mendola et al, 1999;Press et al, 2001;Tootell et al, 1998a,c;Tootell and Hadjikhani, 2001), V8 , a putative homologue of the lateral intraparietal area (LIP) (Sereno et al, 2001), and retinotopic organization in human MT/V5 (Huk et al, 2002).…”

Reproducibility of BOLD, perfusion, and CMRO2 measurements with calibrated-BOLD fMRI

“…In a preliminary scan session on a different day, subjects were presented with standard stimuli for retinotopic mapping (Engel et al 1997;Press et al 2001). The flickering rate and the visual field eccentricity of these stimuli were identical to the stimulus presented during calibrated-BOLD experiments.…”

“…Linear trends were removed from the datasets. Activation was assessed by correlating detrended data with the first harmonic of the stimulus variation frequency (Press et al 2001). Representations of the primary visual area V1 of each subject was delineated on the computationally flattened visual cortex to define the retinotopic ROI for each subject.…”

Occipital network for figure/ground organization

“…The boundaries of the retinotopic areas V1, V2d, V2v, V3d, V3v, and hV4 were established as described in Sereno et al (1995) and Engel et al (1997). Retinotopic areas V3A, V3B and V7 were speciWed in accordance with Press et al (2001) and Tyler et al (2005). Locations of the projections of the stimulus borders in retinotopic regions used the procedures described in Tyler et al (2005) and Schira et al (2007).…”