Disentangling Representations of Object and Grasp Properties in the Human Brain

Abstract

The properties of objects, such as shape, influence the way we grasp them. To quantify the role of different brain regions during grasping, it is necessary to disentangle the processing of visual dimensions related to object properties from the motor aspects related to the specific hand configuration. We orthogonally varied object properties (shape, size, and elongation) and task (passive viewing, precision grip with two or five digits, or coarse grip with five digits) and used representational similarity analysis of functional magnetic resonance imaging data to infer the representation of object properties and hand configuration in the human brain. We found that object elongation is the most strongly represented object feature during grasping and is coded preferentially in the primary visual cortex as well as the anterior and posterior superior-parieto-occipital cortex. By contrast, primary somatosensory, motor, and ventral premotor cortices coded preferentially the number of digits while ventral-stream and dorsal-stream regions coded a mix of visual and motor dimensions. The representation of object features varied with task modality, as object elongation was less relevant during passive viewing than grasping. To summarize, this study shows that elongation is a particularly relevant property of the object to grasp, which along with the number of digits used, is represented within both ventral-stream and parietal regions, suggesting that communication between the two streams about these specific visual and motor dimensions might be relevant to the execution of efficient grasping actions.

Enhancing Gesture Decoding Performance Using Signals from Posterior Parietal Cortex: A Stereo-Electroencephalograhy (SEEG) Study

“…First, the hand shape selective area may indeed occupy a small area of PPC, most likely AIP. Although several fMRI studies indicate the hand shape selective area includes beyond AIP such as SMG, the whole IPS, and SPL (Fabbri et al, 2016;Króliczak et al, 2016;Ariani et al, 2015), AIP is consistently found to take part in the special encoding of hand shape Binkofski et al, 1998;Klaes et al, 2015), which has been demonstrated in this work as well ( figure 3). Therefore, since SEEG electrodes are randomly distributed within the whole PPC, it is reasonable that only a small percentage of them presented gesture selective.…”

“…Intracortical electrical stimulation to lateral region of monkey's area 5 within PPC elicits finger and wrist movements (Rathelot et al, 2017). Functional magnetic resonance imaging (fMRI) studies reveal that grip type (power vs precision grasp) is encoded in several subareas of PPC (Fabbri et al, 2016;Di Bono et al, 2015). In addition to objectrelated grasp, other intransitive hand gestures like scissor-rock-paper can also be decoded from PPC, as demonstrated by another fMRI study (Dinstein et al, 2008).…”

“…Therefore, SEEG recordings across subjects allows an exhaustive investigation on a wide human PPC area about its involvement in hand motor task. Beyond wide coverage, SEEG electrodes can reach both the gyri and sulci of PPC (e.g., the intraparietal sulcus (IPS), which is important for hand movement Fabbri et al, 2016)). Using the SEEG recordings, we first investigate whether and how much the neural activities, recorded from electrodes that distributed in PPC and primary sensorimotor cortex (PRC and POC), contain activation information relating to the task and selective information with respect to specific gestures.…”

Towards a unified perspective of object shape and motion processing in human dorsal cortex

“…Rather, dorsal object-representations are unique from those in ventral cortex in several fundamental respects. First, object processing in dorsal cortex follows an overarching posterior-to-anterior visual-to-motor gradient, with more posterior areas (such as CIP) dedicated predominantly to analysis of visual properties such as 3-D curvature, while anterior areas (such as AIP) are increasingly concerned with computations related to potential motor interactions with the stimulus, such as encoding the object’s absolute object location in egocentric space, reaching trajectory, and hand preshaping (Culham and Valyear, 2006; Fabbri, Stubbs, Cusack, & Culham, 2016; Shmuelof and Zohary, 2005; Stark & Zohary, 2008). In fact, this visual-to-motor gradient may not be limited to the rostro-caudal axis, but may also extend along a medio-lateral axis as well, reflecting the underlying connectivity patterns with the visual and motor cortices (Freud et al, 2016; Kravitz et al, 2011).…”

Sociality and Interaction Envelope Organize Visual Action Representations

“…A related consideration is how best to depict these actions in order to probe underlying neural responses at a meaningful level of abstraction. Historically, researchers have relied on highly-controlled action stimuli (Jastorff et al, 2010;, often sampling primarily from hand actions such as reaching or hammering (Watson & Buxbaum, 2014;Fabbri et al, 2016;Wurm et al, 2017). However, these welldesigned and controlled stimuli are fundamentally limited in the range of actions they depict, which in turn constrains researchers' ability to discover joints in the broader domain of action perception.…”