Multivariate Patterns in the Human Object-Processing Pathway Reveal a Shift from Retinotopic to Shape Curvature Representations in Lateral Occipital Areas, LO-1 and LO-2

Abstract

Representations in early visual areas are organized on the basis of retinotopy, but this organizational principle appears to lose prominence in the extrastriate cortex. Nevertheless, an extrastriate region, such as the shape-selective lateral occipital cortex (LO), must still base its activation on the responses from earlier retinotopic visual areas, implying that a transition from retinotopic to "functional" organizations should exist. We hypothesized that such a transition may lie in LO-1 or LO-2, two visual areas lying between retinotopically defined V3d and functionally defined LO. Using a rapid event-related fMRI paradigm, we measured neural similarity in 12 human participants between pairs of stimuli differing along dimensions of shape exemplar and shape complexity within both retinotopically and functionally defined visual areas. These neural similarity measures were then compared with low-level and more abstract (curvaturebased) measures of stimulus similarity. We found that low-level, but not abstract, stimulus measures predicted V1-V3 responses, whereas the converse was true for LO, a double dissociation. Critically, abstract stimulus measures were most predictive of responses within LO-2, akin to LO, whereas both low-level and abstract measures were predictive for responses within LO-1, perhaps indicating a transitional point between those two organizational principles. Similar transitions to abstract representations were not observed in the more ventral stream passing through V4 and VO-1/2. The transition we observed in LO-1 and LO-2 demonstrates that a more "abstracted" representation, typically considered the preserve of "category-selective" extrastriate cortex, can nevertheless emerge in retinotopic regions.

Foreground-background segmentation revealed during natural image viewing

“…The observed behavior of V4 and LOC is consistent with several investigations on shape features selectivity in these regions, and in their homologues in monkey (Carlson ET et al 2011;Hung CC et al 2012;Lescroart MD and I Biederman 2013;Vernon RJ et al 2016). In fact, the extraction of shape properties requires segmentation (Lee TS et al 1998), and presumably occurs in brain regions where background is already suppressed.…”

Shape coding in occipito-temporal cortex relies on object silhouette, curvature and medial-axis

“…Finally, IT (Kayaert et al 2005b;Yue et al 2014), LO (Vernon et al 2016) and FusG (Caldara et al 2006) were bilaterally tuned to contour curvature (Figure 3, bottom in blue), in accordance with previous neuroimaging investigations. Actually, LO has a pivotal role in object processing (Grill-Spector et al 2001;Grill-Spector et al 1999;Kourtzi and Kanwisher 2001), as IT in monkeys (Brincat and Connor 2004;Desimone et al 1984;Kayaert et al 2005a;Op de Beeck et al 2001;Tanaka 2003;Zoccolan et al 2007).…”

White matter dissection and structural connectivity of the human vertical occipital fasciculus to link vision-associated brain cortex

“…We also found the cortical projections of VOF to the lateral occipital visual area (e.g., LO1, LO2, LO3, V4t) from the dorsal visual stream (e.g., V3CD, V3A, IP0, V7). LO1 preferentially activates in response to orientation-selective and boundary information, while LO2 shows preferential retinotopic activation to encode information about the shapes of stimuli 29,47,48 . LO3 is an important hub between the dorsal and ventral streams to integrate, encode, and process detail, motion, and shape information 29,49 .…”