Reynolds, G.D. & Richards, J.E. (2004). The convergence of electroencephalographic and heart reat measures of attention in infancy. International Society for Infancy Studies, Chicago, IL.
In two recent studies conducted in our laboratory, we have utilized heart rate (HR) and electroencephalographic (EEG/ERP) measures simultaneously with infant participants. These studies examined the effects of attention (measured with visual fixation and HR) on electrophysiological correlates of attention and recognition memory. In both studies, infants at ages 4.5, 6, and 7.5 months were presented with a “Sesame Street” movie that elicited periods of attention and inattention, and computer-generated stimuli were presented overlaid on the movie for 500 ms. Infants were familiarized with two stimuli that were used during testing. Following familiarization, infants were exposed to a modified oddball paradigm with presentations of three types of memory stimuli: frequent familiar (FF), infrequent familiar (IF), and infrequent novel (IN). ERP averages were made from -50 ms to 2000 ms around stimulus onset, and the heart rate data was parsed into HR-defined attention phases. This design resulted in three experimental conditions: age (4.5, 6, and 7.5 months), stimulus type (FF, IF, and IN), and attention (stimulus orienting, sustained attention, and attention termination).
In the first study, the EEG was recorded from twenty locations. Topographical ERP scalp potential maps were calculated. An ERP component labeled the “Nc” (Negative Central, about 450 - 550 ms after stimulus onset) was larger during attention than inattention and increased in magnitude over the three testing ages during attention. Late slow waves in the ERP (from 1000 to 2000 ms post-stimulus onset) consisted of a positive slow wave in response to the infrequent familiar stimulus at all three testing ages. The late slow wave in response to the infrequent novel stimulus during attention was a positive slow wave for the 4.5 month old infants, to a positive-negative slow wave for the 6 month old infants, and a negative slow wave for the 7.5 month old infants. These results show attention facilitates the brain response during infant recognition memory and show that developmental changes in recognition memory are closely related to changes in attention.
In the second study, two familiarization groups were utilized: familiarization and familiarization control. Infants in the familiarization group were familiarized with two stimuli that were used during testing, infants in the familiarization control group were familiarized with two stimuli that were not used in subsequent testing. EEG recordings were made with a 124-channel system. The ERP were quantified with spatial independent component analysis, and "equivalent current dipoles" were estimated to locate cortical sources of the ERP components. A negative component (Nc) was found to occur about 500 ms after stimulus onset. The cortical source of this component was located in the anterior cingulate gyrus. Differences in amplitude of Nc were found across groups during attentive states but not during periods of inattention. Late slow wave components were demonstrated that varied in temporal and spatial morphology with stimulus type. These findings suggest that familiarization, attention, and stimulus type impact ERPs associated with recognition memory in infants. Furthermore, the use of HR as a means of controlling for attentiveness in infants during stimulus presentation may serve to increase effect sizes found in studies utilizing EEG recordings.