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theoretical frameworks of human vision argue that object responses remain stable, or 'invariant', despite changes in viewing conditions that can alter object appearance but not identity. Here, in a major departure from previous approaches that have relied on two-dimensional (2-D) images to study object processing, we demonstrate that changes in an object's appearance, but not its identity, can lead to striking shifts in behavioral responses to objects. We used inverse multidimensional scaling (MDS) to measure the extent to which arrangements of objects in a sorting task were similar or different when the stimuli were displayed as scaled 2-D images, three-dimensional (3-D) augmented reality (AR) projections, or real-world solids. We were especially interested in whether sorting behavior in each display format was based on conceptual (e.g., typical location) versus physical object characteristics. We found that 2-D images of objects were arranged according to conceptual (typical location), but not physical, properties. AR projections, conversely, were arranged primarily according to physical properties such as real-world size, elongation and weight, but not conceptual properties. Real-world solid objects, unlike both 2-D and 3-D images, were arranged using multidimensional criteria that incorporated both conceptual and physical object characteristics. our results suggest that object responses can be strikingly malleable, rather than invariant, with changes in the visual characteristics of the stimulus. The findings raise important questions about limits of invariance in object processing, and underscore the importance of studying responses to richer stimuli that more closely resemble those we encounter in real-world environments.Understanding how naturalistic stimuli are processed and represented in the human brain remains a major challenge for psychology, neuroscience and computer vision. Current theoretical frameworks of object vision posit that effective recognition requires invariance -that mental representations remain stable despite changes in visual cues that can alter an object's appearance but not its identity 1-5 . Support for representational invariance has been derived from behavioral 6-8 and neuroimaging studies 3,9 (although with some limitations, for example, depending on the retinal location of the stimulus 10,11 and task demands 12 ). Two-dimensional (2-D) images of objects have been shown to elicit size-invariant responses during recognition 13 , priming 7,14 , perceptual learning 15 , and visual search 16 . Similarly, neuroimaging studies have shown that responses in shape-selective regions within ventral occipito-temporal (vOT) cortex remain relatively constant despite changes in image size 17,18 , as well as changes in position 19 , viewpoint 4,9,11,15 and depth cues 18,20 . Reliable adaptation in ventral object areas across changes in the size of object images is observed in children by 5 to 10 years of age 21 . FMRI responses in vOT have also been found to remain constant across changes in t...

Object interaction requires knowledge of the weight of an object, as well as its shape. The lateral occipital complex (LOC), an area within the ventral visual pathway, is well known to be critically involved in processing visual shape information. Recently, however, LOC has also been implicated in coding object weight before grasping-a result that is surprising because weight is a nonvisual object property that is more relevant for motor interaction than visual perception. Here, we examined the causal role of LOC in perceiving heaviness and in determining appropriate fingertip forces during object lifting. We studied perceptions of heaviness and lifting behavior in a neuropsychological patient (M.C.) who has large bilateral occipitotemporal lesions that include LOC. We compared the patient's performance to a group of 18 neurologically healthy age-matched controls. Participants were asked to lift and report the perceived heaviness of a set of equally weighted spherical objects of various sizes-stimuli which typically induce the size-weight illusion, in which the smaller objects feel heavier than the larger objects despite having identical mass. Despite her ventral stream lesions, M.C. experienced a robust size-weight illusion induced by visual cues to object volume, and the magnitude of the illusion in M.C. was comparable to age-matched controls. Similarly, M.C. evinced predictive fingertip force scaling to visual size cues during her initial lifts of the objects that were well within the normal range. These single-case neuropsychological findings suggest that LOC is unlikely to play a causal role in computing object weight.

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