Neural markers of subordinate-level categorization in 6- to 7-month-old infants.

Subordinate-level category-learning processes in infants were investigated with ERP and looking-time measures. ERPs were recorded while 6- to 7-month-olds were presented with Saint Bernard images during familiarization, followed by novel Saint Bernards interspersed with Beagles during test. In addition, infant looking times were measured during a paired-preference test (novel Saint Bernard vs. novel Beagle) conducted at the conclusion of ERP recording. Slow wave activity corresponded with learning a familiarized category at the subordinate and basic levels, whereas Negative central (Nc) and P400 components were linked with novel category preference. The results provide the first evidence identifying the neural markers of subordinate-level categorization observed in looking-time tasks conducted with infants. Moreover, when considered in conjunction with prior research investigating the neural markers of basic-level categorization in infants, the findings indicate that (1) slow wave and Nc components of infant ERP waveforms are general markers for processes of category learning on the one hand and novel category preference on the other, (2) novel category preference for a contrast category at the basic and subordinate levels have the Nc component in common, but novel category preference at the subordinate level is accompanied by an additional P400 component, a finding in keeping with the notion that subordinate-level categorization is governed by mechanisms supplementary to those underlying basic-level categorization, and (3) slow wave activity associated with subordinate-level learning followed that associated with basic-level learning by approximately 200 ms, a result in accord with a coarse-to-fine scheme for the emergence of category partitioning.