Segmentation and the Principles of Object Perception

Lecturer: Stephen A. Butterfill

Humans, adult and infant, segment objects in accordance with four principles: cohension, boundedness, rigidity and no action at a distance (Spelke 1990).

Slides

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Notes

Infants can use featural information such as shape and texture to segment objects from around 4.5 months of age (Needham, 1998). But they are not limited to featural information: they can also exploit movement cues:

`infants perceive the boundaries of a partly hidden object by analyzing the movements of its surfaces: infants perceived a connected object when its ends moved in a common translation behind the occluder. Infants do not appear to perceive a connected object by analyzing the colors and forms of surfaces: they did not perceive a connected object when its visible parts were stationary, its color was homogeneous, its edges were aligned, and its shape was simple and regular’ (Kellman & Spelke, 1983; see also Spelke, Hofsten, & Kestenbaum, 1989).

How is it that infants can exploit a range of movement cues to segment objects? Spelke (1990) suggests that infants rely on a set of principles to segment objects.

The Principles of Object Perception

cohesion—‘two surface points lie on the same object only if the points are linked by a path of connected surface points’

boundedness—‘two surface points lie on distinct objects only if no path of connected surface points links them’

rigidity—‘objects are interpreted as moving rigidly if such an interpretation exists’

no action at a distance—‘separated objects are interpreted as moving independently of one another if such an interpretation exists’ (Spelke, 1990)

Later we will also consider continuity—An object traces exactly one connected path over space and time (Spelke, Kestenbaum, Simons, & Wein, 1995, p. \ 113).

Three Questions about the Principles of Object Perception

To say that infants track objects in accordance with the Principles of Object Perception is not, of course, to say that they know, or represent, these Principles. We can distinguish three questions.

1. How do four-month-old infants model physical objects?

2. What is the relation between the model and the infants?

3. What is the relation between the model and the things modeled (physical objects)?

On Question 3, we will take for granted that the Principles of Object Perception provide a model that is accurate enough to explain the evidence of infants’ tracking abilities in the first six months of life. (This may require some revisions and extensions to the Principles.)

On Question 1, we will see more and more evidence in support of the idea that the Principles of Object Perception provide a model of the physical that is useful for understanding infants’ perspective in the first six months of life.

But what about the Question 2?

The Simple View (An Answer to Question 2)

As background, consider Fodor’s observation about an influential trend in cognitive science in the 1970s and 80s:

‘Chomsky’s nativism is primarily a thesis about knowledge and belief; it aligns problems in the theory of language with those in the theory of knowledge. Indeed, as often as not, the vocabulary in which Chomsky frames linguistic issues is explicitly epistemological. Thus, the grammar of a language specifies what its speaker/hearers have to know qua speakers and hearers; and the goal of the child’s language acquisition process is to construct a theory of the language that correctly expresses this grammatical knowledge’ (Fodor, 2000, p. \ 11).

Spelke (like many others following her) has used ‘explicitly epistemological’ vocabulary:

‘objects are conceived: Humans come to know about an object’s unity, boundaries, and persistence in ways like those by which we come to know about its material composition or its market value’ (Spelke, 1988, p. \ 198).

I interpret this as an endorsement of the the Simple View, which provides a neat answer to Question 2 above (What is the relation between the model and the infants?):

The Principles of Object Perception are things that we know or believe, and we generate expectations from these principles by a process of inference.

Glossary

References