Neuroimaging Findings on Amodal Completion: A Review

Abstract

Amodal completion is the phenomenon of perceiving completed objects even though physically they are partially occluded. In this review, we provide an extensive overview of the results obtained from a variety of neuroimaging studies on the neural correlates of amodal completion. We discuss whether low-level and high-level cortical areas are implicated in amodal completion; provide an overview of how amodal completion unfolds over time while dissociating feedforward, recurrent, and feedback processes; and discuss how amodal completion is represented at the neuronal level. The involvement of low-level visual areas such as V1 and V2 is not yet clear, while several high-level structures such as the lateral occipital complex and fusiform face area seem invariant to occlusion of objects and faces, respectively, and several motor areas seem to code for object permanence. The variety of results on the timing of amodal completion hints to a mixture of feedforward, recurrent, and feedback processes. We discuss whether the invisible parts of the occluded object are represented as if they were visible, contrary to a high-level representation. While plenty of questions on amodal completion remain, this review presents an overview of the neuroimaging findings reported to date, summarizes several insights from computational models, and connects research of other perceptual completion processes such as modal completion. In all, it is suggested that amodal completion is the solution to deal with various types of incomplete retinal information, and highly depends on stimulus complexity and saliency, and therefore also give rise to a variety of observed neural patterns.

Defending subjective inflation: an inference to the best explanation

“…In amodal completion, on the other hand, the completed parts are not subjectively visualized—which is why it is amodal—but are still visually represented, giving rise to a visual sense of presence of occluded figures ( Fig. 1B; Michotte and Burke 1951 ; van Lier and Gerbino 2015 ; Thielen et al 2019 ).…”

Amodal Completion Revisited

“…The recent literature on AC includes, besides phenomenological and psychophysical studies (among others Ekroll et al, 2018;Øhrn et al, 2019;Peta et al, 2019;Scherzer & Ekroll, 2015;Scherzer & Faul, 2019; for a partial review, see van Lier & Gerbino, 2015), philosophical discussions that elucidate the theoretical impact of empirical research on amodal phenomena (Briscoe, 2018;Brown, 2018;Nanay, 2018;Orlandi, 2014), animal research on recognition of amodally completed shapes (Pepperberg, 2017;Pepperberg & Nakayama, 2016), as well as neural models of pattern completion (Tang & Kreiman, 2017). The fastgrowing neuroscientific evidence relevant to AC and related processes has been reviewed by Thielen et al (2019). As regards artificial vision, some computational models embody AC processes (Follman et al, 2018;Oliver et al, 2016;Zhu et al, 2017), while occasional references to AC are found in the broader literature on object recovery from images with missing regions, not necessarily due to occlusion (Ehsani et al, 2017;Guo et al, 2018;Han et al, 2017;Harary et al, 2014;Hueting et al, 2017;Li & Malik, 2016;Mavridis et al, 2015;Oliver et al, 2017;P erez et al, 2016;Shao et al, 2014).…”

“…The recent literature on AC includes, besides phenomenological and psychophysical studies (among others Ekroll et al., 2018; Øhrn et al., 2019; Peta et al., 2019; Scherzer & Ekroll, 2015; Scherzer & Faul, 2019; for a partial review, see van Lier & Gerbino, 2015), philosophical discussions that elucidate the theoretical impact of empirical research on amodal phenomena (Briscoe, 2018; Brown, 2018; Nanay, 2018; Orlandi, 2014), animal research on recognition of amodally completed shapes (Pepperberg, 2017; Pepperberg & Nakayama, 2016), as well as neural models of pattern completion (Tang & Kreiman, 2017). The fast-growing neuroscientific evidence relevant to AC and related processes has been reviewed by Thielen et al. (2019).…”

The Illusion of Absence in Magic Tricks

“…The illusion of absence is reminiscent of the well-known phenomenon of amodal completion ( Figure 1C and D ) because it also refers to a curiously compelling experience of occluded regions in a visual scene. Amodal completion refers to experiences of complete objects partially hidden behind an occluder, which are particularly compelling although only a few fragments of the object are directly visible ( Kanizsa, 1985 ; Michotte et al., 1964 ; Scherzer & Faul, 2019 ; Thielen et al., 2019 ; Van Lier & Gerbino, 2015 ). Figure 1D , for instance, evokes a very compelling experience of a single long finger, rather than the two separate fingers, which are aligned behind the cylinder ( Figure 1C ).…”