Investigating category- and shape-selective neural processing in ventral and dorsal visual stream under interocular suppression

Abstract

Recent behavioral and neuroimaging studies using continuous flash suppression (CFS) have suggested that action-related processing in the dorsal visual stream might be independent of perceptual awareness, in line with the "vision-for-perception" versus "vision-for-action" distinction of the influential dual-stream theory. It remains controversial if evidence suggesting exclusive dorsal stream processing of tool stimuli under CFS can be explained by their elongated shape alone or by action-relevant category representations in dorsal visual cortex. To approach this question, we investigated category- and shape-selective functional magnetic resonance imaging-blood-oxygen level-dependent responses in both visual streams using images of faces and tools. Multivariate pattern analysis showed enhanced decoding of elongated relative to non-elongated tools, both in the ventral and dorsal visual stream. The second aim of our study was to investigate whether the depth of interocular suppression might differentially affect processing in dorsal and ventral areas. However, parametric modulation of suppression depth by varying the CFS mask contrast did not yield any evidence for differential modulation of category-selective activity. Together, our data provide evidence for shape-selective processing under CFS in both dorsal and ventral stream areas and, therefore, do not support the notion that dorsal "vision-for-action" processing is exclusively preserved under interocular suppression.

Weighing the evidence for a dorsal processing bias under continuous flash suppression

“…As opposed to Fang and He (2005), they found a ''stream-invariant'' reduction of neural activity for the invisible stimuli; a similar result was found in a second study (Hesselmann, Hebart, & Malach, 2011). Fang and He's findings are contrasted with results from Ludwig, Kathmann, Sterzer, and Hesselmann (2015) in Fig. 2 to exemplarily illustrate the difference in the pattern of results.…”

“…Other studies, however, do not support this dissociation (e.g., Franz, Gegenfurtner, Bülthoff, & Fahle, 2000; for reviews see: Franz & Gegenfurtner, 2008;Westwood & Goodale, 2011). Ludwig et al (2015), image provided by the authors. Different presentation techniques are used to achieve dichoptic stimulation: (1) mirror stereoscope, (2) anaglyph glasses ⁄ , (3) cardboard divider (+prism glasses), (4) linear polarizing filters ⁄ , (5) digital binocular presentation goggles.…”

“…For example, some studies use no masks in the visible condition (Fang & He, 2005), other studies use ineffective CFS masks . With respect to the control of stimulus awareness, Fang and He (2005) used offline assessment of objective visibility, while most of the other studies included an online (i.e., trial-by-trial) objective measure of visibility (Fogelson et al, 2014;Ludwig et al, 2015). Furthermore, different analyses of the neuronal data were employed (univariate and/or multivariate).…”

No evidence for surface organization in Kanizsa configurations during continuous flash suppression

“…Given that the construction of a Kanizsa surface percept not only requires grouping, but also figure-ground assignment, it is logical to predict that it should not manifest under CFS. This is furthermore reinforced by the studies reporting on neural activity associated with stimuli suppressed during CFS (Fogelson, Kohler, Miller, Granger, & Tse, 2014;Hesselmann & Malach, 2011;Ludwig, Kathmann, Sterzer, & Hesselmann, 2014;Sterzer, Stein, Ludwig, Rothkirch, & Hesselmann, 2014;YuvalGreenberg & Heeger, 2013). Invariably, these studies show that activity related to the suppressed stimulus is limited to early visual areas such as V1 and V2.…”

Exploring the boundary conditions of unconscious numerical priming effects with continuous flash suppression

“…Based on the functional overlap of visuospatial and numerical processing in human parietal cortex, Bahrami et al (2010) hypothesized that numerosity judgments should exhibit unconscious priming during interocular suppression by CFS. However, the results by Fang and He (2005) have so far not been confirmed in other CFS studies (Fogelson et al, 2014;Hesselmann & Malach, 2011;Ludwig, Kathmann, Sterzer, & Hesselmann, 2014). It still remains unclear what differences in study design and analysis might explain the divergent results.…”