The Time Course of Perceptual Grouping in Natural Scenes

Abstract

Visual perception starts with localized filters that subdivide the image into fragments that undergo separate analyses. The visual system has to reconstruct objects by grouping image fragments that belong to the same object. A widely held view is that perceptual grouping occurs in parallel across the visual scene and without attention. To test this idea, we measured the speed of grouping in pictures of animals and vehicles. In a classification task, these pictures were categorized efficiently. In an image-parsing task, participants reported whether two cues fell on the same or different objects, and we measured reaction times. Despite the participants' fast object classification, perceptual grouping required more time if the distance between cues was larger, and we observed an additional delay when the cues fell on different parts of a single object. Parsing was also slower for inverted than for upright objects. These results imply that perception starts with rapid object classification and that rapid classification is followed by a serial perceptual grouping phase, which is more efficient for objects in a familiar orientation than for objects in an unfamiliar orientation.

The use of higher-order statistics in rapid object categorization in natural scenes

“…Animals were detected with uninterrupted processing within several tens of milliseconds (Bacon-Macé et al, 2005;Rieger et al, 2005). Moreover, such categorization could be followed by a perceptual grouping phase (Korjoukov et al, 2012). The hierarchical approach for object recognition, which supposes grouping and contour integration, is vulnerable with respect to the analysis of complex scenes.…”

“…Although these processes can be achieved, in theory, without recurrent processing (May & Hess, 2008;Rosenholtz, Twarog, SchinkelBielefeld, & Wattenberg, 2009;Supèr, Romeo, & Keil, 2010), neurophysiological studies support its involvement (Hupé et al, 1998;Scholte, Jolij, Fahrenfort, & Lamme, 2008;Supèr & Lamme, 2007). The fact that image parsing based on perceptual grouping in natural scenes is actually slower than animal/vehicle categorization (Korjoukov et al, 2012) also challenges the involvement of hierarchical processing.…”

Reading as functional coordination: not recycling but a novel synthesis

“…When finding an object, or a path, is difficult, we shift from holistic to analytical strategies and scan parts of the scene or display serially, one by one, in small fragments. As soon as we start doing so, we automatically become oblivious to global symmetries of objects that normally play an implicit role in their identification (Hogeboom and van Leeuwen, 1997; Roelfsema and Houtkamp, 2011; Korjoukov et al, 2012). …”

The “side” matters: How configurality is reflected in completion

“…Research with simple figures (e.g., Peterson, Harvey, & Weidenbacher, 1991) and natural images (Korjoukov et al, 2012) has shown that object recognition, which depends on feedforward processing and the selectivity of neurons in higher visual cortex, is a fast process that can precede image parsing (see also Thorpe, Fize, & Marlot, 1996). Knowledge about object identity can thereby facilitate the image parsing process by feedback projections from higher, object-selective visual cortex to lower visual cortex.…”