What Can Object Indexes Explain

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What Can Object Indexes Explain

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There is a wide range of evidence that four- and five-month-olds can track briefly occluded objects. Such evidence comes from infants’ reactions to a range of different scenarios. Some scenrios involve a comparision between the number of objects (Spelke, Kestenbaum, Simons, & Wein, 1995, p. e.g.][), others involve infants’ abilities to track the causal effects of unperceived objects (Baillargeon, 1987, p. e.g][), while others require infants to track properties such as the shape and size of unperceived objects (Wang, Baillargeon, & Brueckner, 2004, p. e.g.][), or to remember the location of a hidden object (Wilcox, Nadel, & Rosser, 1996, p. e.g.][).

The evidence also comes from studies using a variety of different methods including habituation (Spelke et al., 1995, p. e.g.][), violation-of-expectations (Wang et al., 2004, p. e.g.][), and anticipatory looking (Rosander & Hofsten, 2004, p. e.g.][); (Bertenthal, Gredebäck, & Boyer, 2013, p. e.g.][).

4- to 6-month-olds can track briefly occluded objects

scenario method source
1 vs 2 objects habituation Spelke et al 1995
one unperceived object constrains another’s movement habituation Baillargeon 1987
where did I hide it? violation-of-expectations Wilcox et al 1996
wide objects can’t disappear behind a narrow occluder violation-of-expectations Wang et al 2004
when and where will it reappear? anticipatory looking Rosander et al 2004
marker of object maintenanc EEG Kaufman et al 2005

scenario	method	source
1 vs 2 objects	habituation	Spelke et al 1995
one unperceived object constrains another’s movement	habituation	Baillargeon 1987
where did I hide it?	violation-of-expectations	Wilcox et al 1996
wide objects can’t disappear behind a narrow occluder	violation-of-expectations	Wang et al 2004
when and where will it reappear?	anticipatory looking	Rosander et al 2004
marker of object maintenanc	EEG	Kaufman et al 2005

I have described these findings as supporting a conclusion about tracking rather than about representing.

For a process to _track_ the path of an occluded object is for it to nonaccidentally depend in some way on the occluded object’s path: in an interesting but limited range of situations, changes to the object’s path will cause corresponding changes to how the process unfolds. Relatedly, to say that someone can track occluded objects is to say that there are processes in her (or otherwise appropriately involving her) which track the paths of some occluded objects.

How?

The fact that four- and five-month-olds can track briefly occluded objects raises a question. How do they do this?

	occlusion	endarkening
violation-of-expectations	✔	✘
manual search	✘	✔

Charles & Rivera (2009)

\emph{The CLSTX conjecture} Five-month-olds’ abilities to track occluded objects are not grounded on belief or knowledge: instead they are consequences of the operations of object indexes. \citep{Leslie:1998zk,Scholl:1999mi,Carey:2001ue,scholl:2007_objecta}.

The CLSTX conjecture:

Five-month-olds’ abilities to track briefly unperceived objects

are not grounded on belief or knowledge:

instead

they are consequences of the operations of

a system of object indexes.

Leslie et al (1989); Scholl and Leslie (1999); Carey and Xu (2001)

(‘CLSTX’ stands for Carey-Leslie-Scholl-Tremoulet-Xu \citep[see][]{Leslie:1998zk,Scholl:1999mi,Carey:2001ue,scholl:2007_objecta})

... and of a further, independent capacity to track physical objects which involves motor representations and processes.

This generates lots of predictions. For example, should be able to modulate object tracking of endarkened objects by interfering with, or boosting, motor cognition. But the same manipulations should not affect occlusion.

A Question:

What can object indexes explain?

[Q WILL BE: How does a difference in operations involving object indexes result in a difference in looking times?]

	occlusion	endarkening
violation-of-expectations	✔	✘
manual search	✘	✔

Charles & Rivera (2009)

How does help us with the puzzles?

Object indexes can survive occlusion but ...

Functions of object indexes:

✔ influence how attention is allocated

✔ guide ongoing actions (e.g. visual tracking, reaching)

✘ initiate purposive actions

The primary functions of object indexes include influencing the allocation of attention and perhaps guiding ongoing action. If this is right, it may be possible to explain anticipatory looking directly by appeal to the operations of object indexes. But the operations of object indexes cannot directly explain differences in how novel things are to an infant. And nor can the operations of object indexes directly explain why infants look longer at stimuli involving discrepancies in the physical behaviour of objects.

Wynn 1992, fig 1 (part)

We know that infants are likely to maintain object indexes for the two mice while they are occluded. Accordingly, when the screen drops in the condition labelled ‘impossible outcome’, there is an interruption to the normal operation of object indexes: infants have assigned two object indexes but there is only one object. But why does this cause infants to look longer at in the ‘impossible outcome’ condition than in the ‘possible outcome’ condition? How does a difference in operations involving object indexes result in a difference in looking times?

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What Can Object Indexes Explain

What Can Object Indexes Explain

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