Does Vergence Affect Perceived Size?

Abstract

Vergence (the angular rotation of the eyes) is thought to provide essential distance information for size constancy (perceiving an object as having a constant physical size). Evidence for this comes from the fact that a target with a constant retinal size appears to shrink as the rotation of the eyes increases (indicating that the target has reduced in distance). This reduction in perceived size is supposed to maintain a constant perception of physical size in natural viewing conditions by cancelling out the increasing size of the retinal image as an object moves closer. Whilst this hypothesis has been extensively tested over the last 200 years, it has always been tested in the presence of confounding cues such as a changing retinal image or cognitive cues to distance.Testing members of the public with normal vision, we control for these confounding cues and find no evidence of vergence size constancy. Statement of RelevanceThis work has important implications for the neural basis of size constancy and for multisensory integration. First, leading work on the neural basis of size constancy cannot differentiate between recurrent processes in V1 (based on triangulation cues, such as vergence) and top-down processing (based on pictorial cues). Since our work challenges the existence of vergence size constancy, and therefore much of the basis of the recurrent processing account, our work indicates that top-down processing is likely to have a much more important role in size constancy than previously thought.Second, vergence size constancy is thought to be largely responsible for the apparent integration of the retinal image with proprioceptive distance information from the hand in the Taylor illusion (an afterimage of the hand viewed in darkness appears to shrink as the observer's hand is moved closer). This explanation for the Taylor illusion is challenged, and a cognitive account proposed instead.

V1 as an egocentric cognitive map

“…These results are complemented by our results in Linton (2021b) on size perception (discussed below). Together they pose a real challenge to the suggestion that eye movements affect our visual experience.…”

“…By contrast, we used a 3° target to ensure that any retinal slip from the target moving in depth was undetectable. We found no evidence that vergence affects perceived size once subjective knowledge about the changing gaze position has been controlled for (Linton 2021b) . We therefore conclude that the vergence size constancy effects reported in the literature are merely cognitive rather than perceptual.…”

“…Consequently, the Taylor illusion is thought to provide evidence for the suggestion that vision ‘relies on multimodal signals’ ( Sperandio et al 2013 ; Chen et al 2018 ) and that ‘visual consciousness is shaped by the body’ ( Faivre et al 2015 , 2017a , b ). But if, as we argue in Linton (2021b) , the integration of the retinal image with the proprioceptive sensation of our own vergence eye movements is purely cognitive (and this is the major driver of the Taylor illusion), then it becomes very likely that the integration of the retinal image with the proprioceptive sensation of our own hand movements is also purely cognitive when this is a minor driver of the Taylor illusion. This cognitive interpretation of the influence of hand movements on visual perception also suggests a cognitive interpretation of variants of the Taylor illusion that show multisensory integration with the rubber-hand illusion (Faivre et al 2017a) and tool use ( Grove et al 2019 ).…”

“…The account of visual perception I develop in Linton (2017) (reviewed by Erkelens 2018 , and elaborated in Linton 2018f , 2021a ; the Brains Blog : Linton, 2018a ; 2018b , 2018c , 2018d , 2018e and two experimental papers: Linton 2020 , 2021b ) argues that many of the supposedly basic aspects of visual perception are better understood as post-perceptual cognitive influences. This includes (i) visual scale (the size and distance of objects; see Linton 2017 , pp.134–136, 2018f ), (ii) visual shape from multiple depth cues (depth cue integration; see Linton 2017 , chapter 2), (iii) pictorial cues and pictorial perception ( Linton 2017 , chapter 3), and (iv) multisensory integration ( Linton 2017 , pp.65–66).…”

V1 as an Egocentric Cognitive Map

“…The account of visual perception I develop in Linton (2017) (reviewed by Erkelens 2018, and elaborated in Linton 2018f, 2021athe Brains Blog: Linton, 2018a;2018b, 2018c, 2018d, 2018e and two experimental papers: Linton 2020, 2021b argues that many of the supposedly basic aspects of visual perception are better understood as post-perceptual cognitive influences. This includes (i) visual scale (the size and distance of objects; see Linton 2017, (ii) visual shape from multiple depth cues (depth cue integration; see Linton 2017, chapter 2), (iii) pictorial cues and pictorial perception (Linton 2017, chapter 3), and (iv) multisensory integration (Linton 2017, pp.65-66).…”