Abstract
The visual system is known to extract summary representations of visually similar objects which bias the perception of individual objects toward the ensemble average. Although vision plays a large role in guiding action, less is known about whether ensemble representation is informative for action. Motor behavior is tuned to the veridical dimensions of objects and generally considered resistant to perceptual biases. However, when the relevant grasp dimension is not available or is unconstrained, ensemble perception may be informative to behavior by providing gist information about surrounding objects. In the present study, we examined if summary representations of a surrounding ensemble display influenced grip aperture and orientation when participants reached-to-grasp a central circular target which had an explicit size but importantly no explicit orientation that the visuomotor system could selectively attend to. Maximum grip aperture and grip orientation were not biased by ensemble statistics during grasping, although participants were able to perceive and provide manual estimations of the average size and orientation of the ensemble display. Support vector machine classification of ensemble statistics achieved above-chance classification accuracy when trained on kinematic and electromyography data of the perceptual but not grasping conditions, supporting our univariate findings. These results suggest that even along unconstrained grasping dimensions, visually-guided behaviors toward real-world objects are not biased by ensemble processing.
Highlights
Ensemble perception refers to the ability of the visual system to extract summary representations of groups of similar objects across various visual domains
The results indicated that grip orientation (GO) was larger in the small average size display (M = 46.3, SE = 3.04, 95% CI = [39.7, 52.8]) than in the large average size display (M = 43.2, SE = 3.03, 95% CI = [36.7, 49.8], and it was larger in the CCW average orientation display (M = 45.9, SE = 3.04, 95% CI = [39.4, 52.5]) compared with the CW orientation display (M = 43.6, SE = 3.03, 95% CI = [37.0, 50.1]; see Figure 3B)
Using traditional univariate techniques and more powerful support vector machine (SVM) multivariate statistical models, we found that both grip orientation and maximum grip aperture were not influenced by ensemble perception
Summary
Ensemble perception refers to the ability of the visual system to extract summary representations of groups of similar objects (ensembles) across various visual domains. Observers can accurately report the mean size of an array of different-sized circles, while, paradoxically, providing poor estimates of the size of the individual circles that are biased toward the mean size of the set (Ariely, 2001) This observation has been replicated (Chong and Treisman, 2003; Brady and Alvarez, 2011) and extended to other domains such as spatial position (Alvarez and Oliva, 2008) and orientation (Dakin and Watt, 1997; Parkes et al, 2001), and can be extracted across multiple visual domains in parallel (Emmanouil and Treisman, 2008; Attarha and Moore, 2015; Yörük and Boduroglu, 2020). While there is an abundance of research investigating the nature of ensemble processing in the perceptual domain, very little research has focused on understanding how and if ensemble processing informs objectdirected action
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