Visual control of action directed toward two-dimensional objects relies on holistic processing of object shape

Abstract

Visual perception relies on holistic processing of object shape. In contrast to perception, previous studies demonstrated that vision-for-action operates in a fundamentally different manner based on an analytical representation of objects. This notion was mainly supported by the absence of Garner interference for visually guided actions, compared to robust interference effects for perceptual estimations of the same objects. This study examines the nature of the representations that subserve visually guided actions toward twodimensional (2D) stimuli. Based on recent results suggesting that actions directed toward 2D objects are mediated by different underlying processes compared to normal actions, we predicted that visually guided actions toward 2D stimuli would rely on perceptually driven holistic representations of object shape. To test this idea, we asked participants to grasp 2D rectangular objects presented on a computer monitor along their width while the values of the irrelevant dimension of length were either kept constant (baseline condition) or varied between trials (filtering condition). Worse performance in the filtering blocks is labeled Garner interference, which indicates holistic processing of object shape. Unlike in previous studies that used real objects, the results showed that grasping toward 2D objects produced a significant Garner interference effect, with more variable within-subject performance in the filtering compared to the baseline blocks. This finding suggests that visually guided actions directed toward 2D targets are mediated by different computations compared to visually guided actions directed toward real objects.

Dissociable effects of irrelevant context on 2D and 3D grasping

“…In addition, the current findings converge to those of a recent study to suggest that the RSE can be used as reliable measure for probing the representations that mediate visual perception and action. These results are consistent with the results of previous studies that showed that 2D grasping is subjected to the effects of relative processing of size (Holmes & Heath, 2013;Hosang et al, 2016) and shape (Freud & Ganel, 2015). Freud and Ganel used the Garner speeded-classification task to show that unlike as for 3D grasping (Ganel & Goodale, 2003, Ganel & Goodale, 2014, Schum, Franz, Jovanovic, & Schwarzer, 2012; but see Eloka, Feuerhake, Janczyk, & Franz, 2015;Hesse & Schenk, 2013), 2D grasping relies on holistic shape representation in which one dimension of an object cannot be processed independently from other dimensions belonging to the same object.…”

“…Interestingly, however, DF's normal sensitivity to size during 3D grasping extends to situations in which line drawings of 2D objects are presented as targets (Westwood, Danckert, Servos, & Goodale, 2002). Although these findings seem to be at odds with the findings of the current study, and with other behavioral evidence of differences between 2D and 3D grasping (Freud & Ganel, 2015;Holmes & Heath, 2013;Ozana & Ganel, 2017), it is important to note that that perceptual processing in visual form agnosia may be different from that of neurologically intact individuals. The fact that perceptual processing is severly impaired in Patient DF could account for why relative and contextual perceptual information does not affect her 2D grasping performance.…”

“…Unlike for perceptual judgments, JNDs for the common standard were unaffected by the context range in which it was embedded, indicating the operation of a selective processing style, typical to visuomotor control toward real objects (Goodale & Ganel, 2015). The results of the current study provide further evidence for the idea that such selective, analytic processing style does not characterize 2D grasping (Freud & Ganel, 2015;Holmes & Heath, 2013). The resolving power to detect changes along the size of a common 2D target was modulated by contextual information.…”

“…This pattern of results suggests that the visuomotor system, which in other cases was found to be immune to task-irrelevant contextual information, is intruded by this information when 2D objects are presented for grasp. It can be argued therefore, that similarly to other perceptual attributes that affect 2D grasping but not affect 3D grasping (Freud & Ganel 2015;Holmes & Heath, 2013), context has similar effects via perceptual processing that intrudes into action.…”

“…Based on these findings, it has been suggested that, unlike as for actions directed to real objects, actions directed to 2D objects are intruded by irrelevant perceptual information about relative size and shape (Freud & Ganel, 2015;Ozana & Ganel, 2017). It is still unclear, however, whether 2D grasping can be characterized as strictly perceptual and relative in nature along all aspects of visual processing (Freud & Ganel, 2015). Specifically, it is unclear whether contextual processing-a hallmark of relative perception-extends to grasping movements directed toward 2D objects.…”