Visual grouping in human parietal cortex

Abstract

To efficiently extract visual information from complex visual scenes to guide behavior and thought, visual input needs to be organized into discrete units that can be selectively attended and processed. One important such selection unit is visual objects. A crucial factor determining object-based selection is the grouping between visual elements. Although human lesion data have pointed to the importance of the parietal cortex in object-based representations, our understanding of these parietal mechanisms in normal human observers remains largely incomplete. Here we show that grouped shapes elicited lower functional MRI (fMRI) responses than ungrouped shapes in inferior intraparietal sulcus (IPS) even when grouping was task-irrelevant. This relative ease of representing grouped shapes allowed more shape information to be passed onto later stages of visual processing, such as information storage in superior IPS, and may explain why grouped visual elements are easier to perceive than ungrouped ones after parietal brain lesions. These results are discussed within a neural object file framework, which argues for distinctive neural mechanisms supporting object individuation and identification in visual perception.brain imaging ͉ object processing ͉ visual attention ͉ working memory ͉ fMRI T o comprehend the continuous influx of visual information in everyday life, visual input needs to be organized into discrete units that can be selectively attended and processed. One important selection unit is visual objects, whose formation has been shown to profoundly impact subsequent visual processing (1). An important factor determining object-based selection is the grouping between visual elements by various gestalt principles (2, 3), such as connectedness and closure (4-7). Such grouping cues shape conscious visual perception. For example, after unilateral parietal lesions, observers' ability to perceive the presence of two objects, one on each side of the space, was greatly improved by connecting the two objects with a bar forming one big object with two parts instead of two separated objects (8-10). Likewise, after bilateral parietal lesions that result in Balint's syndrome (11), patients could still perceive a single complex object, but their ability to perceive the presence of multiple visual objects is severely impaired (11-13). Such lesion data point to the importance of the parietal cortex in object-based representations, but our understanding of these parietal object grouping and selection mechanisms in normal observers remains largely incomplete. Parietal brain responses have been associated with the number of visual objects actively represented in the mind, including those from the inferior intraparietal sulcus (IPS), which participates in attention-related processing (14-16), and the superior IPS, whose response correlates with the number of objects successfully stored in visual short-term memory (VSTM) (17-20, †). For example, when observers retain variable numbers of object shapes in VSTM, inferior IPS functiona...

Repetition blindness: The survival of the grouped

“…Some recent neurological evidence is consistent with this object file framework: Xu and Chun (2007) distinguished the roles in visual working memory of two brain areas. They found that grouped shapes produced less activation than ungrouped shapes in the inferior intraparietal sulcus (IPS), but not in the superior IPS.…”

Gestalt Effects in Visual Working Memory

“…These data support and largely extend the existing evidence (e.g., Jiang et al, 2000;Kemps, 2001;Peterson & Berryhill, 2013;Woodman et al, 2003;Xu & Chun, 2007) showing that Gestalt principles of perceptual organization, like the tendency to perceive and interpret environment in the simple, orderly, and regular way (Law of Pragnanz), and the influence of such attributes of perceptual objects as proximity, similarity, closure, and continuity for their grouping into coherent wholes, which are well-known to organize visual perception, influence also the active maintenance and access of information in VWM during the absence of perceptual stimulation. These results have crucial significance for our understanding of the mechanisms and function of one of the crucial elements of human mind architecture -working memory (i.e., its visual component).…”

“…Some studies have demonstrated that satisfying such principles by the group of objects not only helps in perceiving them in a particular way, but also facilitates their retrieval from VWM (that is, Gestalt principles "work" even when objects are not accessible perceptually). For instance, objects displayed in proximity to an object that had been cued were more likely reported than distant objects (Woodman, Vecera, & Luck, 2003), and the overall number of reported objects was larger if they were grouped in preceding display than when they were not grouped (Xu & Chun, 2007; for an analogous result pertaining to grouping by similarity see Peterson & Berryhill, 2013).…”

Real-world spatial regularities affect visual working memory for objects

“…However, this effect could partly reflect low-level Gestalt grouping, which is known to enhance VWM (Anderson et al, 2013;Peterson & Berryhill, 2013;Woodman et al, 2003;Xu, 2006;Xu & Chun, 2007). Although we carefully selected our stimuli to avoid the regular and irregular object pairs differing along low-level dimensions, in Experiment2 we included a control condition to directly rule out any influence of such putative low-level differences.…”

“…For example, VWM is enhanced when individual stimuli can be grouped by Gestalt principles or by forming illusory contours (Anderson, Vogel, & Awh, 2013;Peterson & Berryhill, 2013;Woodman, Vecera, & Luck, 2003;Xu, 2006;Xu & Chun, 2007). Similarly, VWM is enhanced when participants learn to associate stimuli through arbitrary spatial contingencies (Brady, Konkle, & Alvarez, 2009;Olson, Jiang, & Moore, 2005).…”