Size constancy affects the perception and parietal neural representation of object size

Stephanie Kristensen,Alessio Fracasso,Serge O Dumoulin,Jorge Almeida,Ben M Harvey

doi:10.1016/j.neuroimage.2021.117909

Stephanie Kristensen, Alessio Fracasso + Show 3 more

Open Access

https://doi.org/10.1016/j.neuroimage.2021.117909

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Abstract

Humans and animals rely on accurate object size perception to guide behavior. Object size is judged from visual input, but the relationship between an object's retinal size and its real-world size varies with distance. Humans perceive object sizes to be relatively constant when retinal size changes. Such size constancy compensates for the variable relationship between retinal size and real-world size, using the context of recent retinal sizes of the same object to bias perception towards its likely real-world size. We therefore hypothesized that object size perception may be affected by the range of recently viewed object sizes, attracting perceived object sizes towards recently viewed sizes. We demonstrate two systematic biases: a central tendency attracting perceived size towards the average size across all trials, and a serial dependence attracting perceived size towards the size presented on the previous trial. We recently described topographic object size maps in the human parietal cortex. We therefore hypothesized that neural representations of object size here would be attracted towards recently viewed sizes. We used ultra-high-field (7T) functional MRI and population receptive field modeling to compare object size representations measured with small (0.05–1.4°diameter) and large objects sizes (0.1–2.8°). We found that parietal object size preferences and tuning widths follow this presented range, but change less than presented object sizes. Therefore, perception and neural representation of object size are attracted towards recently viewed sizes. This context-dependent object size representation reveals effects on neural response preferences that may underlie context dependence of object size perception.

Highlights

Object size perception guides human and animal behavior and decisions, for example when planning to grasp an object or choosing the larger of two fruits
Object size tuned neural response models were estimated from the fMRI data and stimulus time course, as previously described (Harvey et al, 2015). This approach is based on methods we developed to estimate visuo-spatial population receptive field properties in human visual cortex (Dumoulin and Wandell, 2008)
We focus on the area around the previously defined object size map in the posterior parietal cortex (Harvey et al, 2013)

Summary

Introduction

Object size perception guides human and animal behavior and decisions, for example when planning to grasp an object or choosing the larger of two fruits. An object appears larger when placed in part of a scene that appears further away, and the cortical activation the object produces is correspondingly larger, even with no binocular disparity cues to distance (Murray et al, 2006). This effect of spatial scene context is mirrored by a temporal size constancy effect: sequentially presented objects appeal closer in size than they are (Holway and Boring, 1941). Like considering the sizes of surrounding objects (spatial context), accounting for recently viewed object sizes (temporal context) could compensate for the variable relationship between retinal size and real-world size, when the object’s real-world size is unknown or ambiguous

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