Task Context Overrules Object- and Category-Related Representational Content in the Human Parietal Cortex

Abstract

The dorsal, parietal visual stream is activated when seeing objects, but the exact nature of parietal object representations is still under discussion. Here we test 2 specific hypotheses. First, parietal cortex is biased to host some representations more than others, with a different bias compared with ventral areas. A prime example would be object action representations. Second, parietal cortex forms a general multiple-demand network with frontal areas, showing similar task effects and representational content compared with frontal areas. To differentiate between these hypotheses, we implemented a human neuroimaging study with a stimulus set that dissociates associated object action from object category while manipulating task context to be either action- or category-related. Representations in parietal as well as prefrontal areas represented task-relevant object properties (action representations in the action task), with no sign of the irrelevant object property (category representations in the action task). In contrast, irrelevant object properties were represented in ventral areas. These findings emphasize that human parietal cortex does not preferentially represent particular object properties irrespective of task, but together with frontal areas is part of a multiple-demand and content-rich cortical network representing task-relevant object properties.

Goal-Directed Visual Processing Differentially Impacts Human Ventral and Dorsal Visual Representations

“…By examining responses in an action and an object category task, using fMRI MVPA, Bracci et al (2017) reported greater task modulation of visual representation in parietal than in occipitotemporal region, with no representation found in parietal region for the task-irrelevant information. Although their overall conclusion is consistent with ours, the use of an event-related design likely weakened the effect and prevented them from observing the representation of the task-irrelevant information in the dorsal region.…”

“…However, both monkey and human studies over the last two decades have reported robust representations of a variety of "what" information in the dorsal pathway (Sereno and Maunsell, 1998;Sawamura et al, 2005;Janssen et al, 2008;Konen and Kastner, 2008;Liu et al, 2011;Christophel et al, 2012;Hou and Liu, 2012;Ester et al, 2015;Xu and Jeong, 2015;Bettencourt and Xu, 2016;Bracci et al, 2016;Freud et al, 2016;Jeong and Xu, 2016). These findings challenge the two-pathway view and argue for a convergence between the two pathways.…”

“…The existence of top-down attentional control signals in parietal cortex (Corbetta and Shulman, 2002; Yantis and Serences, 2003) and task modulation of parietal visual responses (e.g., Toth and Assad, 2002;Todd and Marois, 2004;Freedman and Assad, 2006;Xu and Chun, 2006;Gottlieb and Synder, 2010;Xu, 2010;Liu et al, 2011;Jeong and Xu 2013;Xu and Jeong, 2015;Shomstein and Gottlieb, 2016;Bracci et al, 2017) suggest that task may exert a stronger impact on visual representations in the dorsal than ventral pathway. However, some studies have failed to find such an effect (Konen and Kastner, 2008;Harel et al, 2014).…”

“…Attention can also modulate visual responses in human early visual areas (Gandhi et al, 1999;Martínez et al, 1999;Somers et al, 1999) and ventral object-processing areas (O'Craven et al, 1999;Murray and Wojciulik, 2004;Reddy et al, 2009;see also Ç ukur et al, 2013;Harel et al, 2014). Nevertheless, the impact of task is not always found in these regions either (e.g., Kourtzi and Kanwisher, 2000;Yi et al, 2004;Peelen et al, 2009;Bracci et al, 2017). There are thus conflicting reports within each visual pathway regarding the impact of task on visual representation and the degree to which the two pathways differ in this regard.…”

“…This suggests that the stronger the conjunction between the task-relevant and -irrelevant features, the weaker the task effect. Yet, existing studies have not taken this into account when comparing dorsal and ventral regions and have instead either focused on a single manipulation (Xu and Jeong, 2015;Bracci et al, 2017) or averaged results from a number of different manipulations (Harel et al, 2014). Consequently, a variety of results have been obtained.…”