Compare and Contrast Theories of Visual and Auditory Attention

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Opinion

TRENDS in Cognitive Sciences

Vol.7 No.6 June 2003

What is a visual object?
Jacob Feldman
Department of Psychology, Center for Cognitive Science, Rutgers University, New Brunswick, NJ 08903, USA

The concept of an ‘object’ plays a central role in cognitive science, particularly in vision, reasoning and conceptual development – but it has rarely been given a concrete formal definition. Here I argue that visual objects cannot be defined according to simple physical properties but can instead be understood in terms of the hierarchical organization of visual scene interpretations. Within the tree describing such a hierarchical description, certain nodes make natural candidates as the ‘joints’ between objects, representing division points between parts of the image that cohere internally but do not perceptually group with one another. Thus each subtree hanging from such a node corresponds to a single perceived ‘object’. This formal definition accords with several intuitions about the way objects behave. Objects are everywhere in cognitive science. Objects are thought to be the building blocks of children’s conception of the physical world [1,2]; to delineate the boundaries respected by visual attention [3 – 5]; and to influence neural processing even at the earliest stages of visual cortex [6,7]. But what exactly is an object? In a phrase due to the American jurist Potter Stewart, ‘we know one when we see one’ – but what does the word actually mean? How do we know where one object ends and the next begins? The premise of this article is that this is not (as it were) an ‘objective’ question, but rather one that relates to how we mentally divide the world up into coherent units. That is, it is less about physics and more about the mental assumptions lurking behind the word ‘coherent’. The division of the world into objects seems so intuitive and effortless, at least under everyday conditions, that we speak about this division as if the world

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