Familiarization, Attention, and Recognition Memory in Infancy: An Event-Related Potential and Cortical Source Localization Study.

Abstract

This study investigated the effects of familiarization and attention on event-related potential (ERP) correlates of recognition memory in infants. Infants 4.5, 6, or 7.5 months of age were either familiarized with 2 stimuli that were used during later testing or presented 2 stimuli that were not used later. Then, infants were presented with a recording of Sesame Street to elicit attention or inattention and presented with familiar and novel stimuli. A negative ERP component over the frontal and central electrodes (Nc) was larger in the preexposure familiarization group for novel-than for familiar-stimulus presentations, whereas the Nc did not differ for the group not receiving a familiarization exposure. Spatial independent components analysis of the electroencephelogram and "equivalent current dipole" analysis were used to examine putative cortical sources of the ERP components. The cortical source of Nc was located in areas of prefrontal cortex and anterior cingulate cortex.Visual attention and recognition memory in infants are closely related. For example, infants demonstrate greater memory for events they were exposed to while in an attentive state than for events they were exposed to in an inattentive state (Frick & Richards, 2001;Richards, 1997). Events that have been partially encoded into memory or events that are novel elicit larger attention responses than those events that have been fully encoded (Bornstein, 1985;Fantz, 1961Fantz, ,1963. Infants show larger orienting responses to novel events than to those events that are familiar to them. Studies examining visual attention and recognition memory simultaneously can provide insight into the overall cognitive activity involved in an organism's adaptive responses to environmental information. The present study shows that attentionelicited event-related potential (ERP) responses differ as a function of the infant's familiarity with the stimuli and suggests that these effects are mediated by the prefrontal cortex of the brain.Several studies of infant recognition memory development have used the electroencephelogram (EEG) to measure ERPs related to recognition memory. ERPs are scalp voltage oscillations that are time locked with a specific physical or mental event (Fabiani, Gratton, & Coles, 2000;Picton et al., 2000). Courchesne, Ganz, and Norcia (1981) recorded ERP during an oddball procedure. They exposed 10 infants from 4 to 7 months of age to tachistoscopically presented slides of two unfamiliar female faces. One female face was presented on 88% of the trials (standard stimulus), and the other female face was presented on 12% of the trials (oddball stimulus). A negative component over the frontal and central electrodes with a latency of 700 ms, labeled Nc ("negative central"), was larger to the oddball stimulus than to the standard stimulus. A later occurring (latency = 1,360 ms) positive component followed both the infrequently and frequently presented stimuli. The authors concluded that the frequently presented stimulus was more familiar to t...

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“…In contrast, later attentional responses are greater to temporally asynchronous events. Greater Nc responses to asynchrony may reflect the fact that, after early sensory integration occurs, infants find the asynchronous condition more novel or interesting (Reynolds & Richards, 2005). Alternatively, one might interpret the smaller Nc Intersensory Perception 22 response to the synchronous condition as attenuation, similar to that seen in earlier sensory responses of adults but more temporally drawn out.…”

“…For example, Hyde and colleagues (2011) presented 5-month-olds with static images of face paired with a voice saying "hi" in perfect greater response (more negative) for the asynchronous condition compared to the synchronous condition on the later-going Nc component, known to index attentional orienting in infants (see Reynolds & Richards, 2005).…”

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“…A second component that reflects attention is the Nc, a large negative component that originates from the fronto-central cortex (Reynolds and Richards 2005). Like the P3b, the Nc is triggered by events that are important or salient to the individual.…”