Normative Representation of Objects: Evidence for an Ecological Bias in Object Perception and Memory

Normative Representation of Objects: Evidence for an Ecological Bias in Object Perception and Memory Talia Konkle (tkonkle@mit.edu) Aude Oliva (oliva@mit.edu) Department of Brain and Cognitive Sciences Massachusetts Institute of Technology Cambridge, MA 02139 Abstract 1998; Palmer, Rosch, & Chase, 1981), which has shown that the ¾ view is preferred in object identification. However, the role of visual angle in object representation has largely been ignored, as much research has suggested that object representation is size-invariant (e.g. Biederman & Cooper, 1992). Here, we explore the possibility that each object has a perceptually privileged visual size, which we term the normative size. Our hypothesis that there is a normative size has two motivations. First, resolution limits across the visual field might enforce this: something too big or too small in your visual field will be hard to see. Second, our experience with an object is statistically constrained: a fork is typically interacted with in a particular range of distances which exposes the visual system to a particular distribution of visual angles for forks (Figure 1). An apple can be held in your hand if you are eating it, or be perceived in a fruit bowl from a few meters away. While the apple’s real-world size is constant, the visual angle it subtends in your visual field varies based on your distance to the apple. Given the range of visual angles that an object can subtend in the visual field, is there a visual angle that is preferred? The current experiments show evidence supporting the idea of a privileged visual size for object representation, termed the normative size. In Experiment 1, observers adjusted the visual size of objects on a monitor, selecting the subjectively ‘right’ size to see the object. Inter-observer selections were strikingly consistent, and showed a correlation between the size selected on the screen and the actual physical size of the objects in the real world. These size selections were taken as estimates of the normative size for each object. In Experiments 2 and 3, using a size memory task and a change detection task, we found evidence that both long-term and short-term memory for the visual size of objects is biased towards the normative size. Altogether the results support the claims that perception of objects is sensitive to a normative size and that object memory is biased toward this perceptual norm. Keywords: Object representation; perception; memory; size. Introduction Figure 1: Hypothetical distribution of visual experience with sample real-world objects. “For each object, as for each picture in an art gallery, there is an optimum distance from which it requires to be seen, a direction viewed from which it vouchsafes most of itself: at a shorter or greater distance we have merely a perception blurred through excess or deficiency. ” - Merleau-Ponty In the current studies, we examined the role of visual angle by varying the presented size on a monitor, as a way to simulate viewing distance. Specifically, observers could simulate moving closer or farther from objects by making them larger or smaller on the screen. In Experiment 1, observers were presented with a picture of an isolated object and adjusted the visual angle of the object until the object was the “right size” on the screen. Despite the subjectivity of the task, the selected size for each object was remarkably consistent across observers. Additionally, we explored the possibility that, if perception is sensitive to a normative size, then memory for that object might also be biased toward a normative size. In Experiment 2, observers were presented with pictures of objects subtending a range of visual angles. Afterwards, participants adjusted the visual angle of the object to match the presented size. The remembered objects showed systematic errors biased towards the normative sizes from We see each object in the world from a variety of viewing distances, and this distance changes as we move or as the objects move. Consequently, objects can appear at almost any size in the visual field depending on how close or far you stand in relation to them. For example, when crossing the road, a car in the distance will initially appear quite small in your visual field, but as the car approaches it will fill increasingly more of the visual field. In general, the physical size of an object and your viewing distance to that object determine the angle it subtends in your visual field. Given the range of visual angles that an object can subtend in our visual field, is there a visual angle that is preferred? Research on perceptually privileged or canonical object views has traditionally looked at viewpoint (Tarr,