Development of selective attention in young infants: Enhancement and attenuation of startle reflex by attention

This study examined the effect of level of attention engagement on the modification of the blink reflex in young infants. Infants at 8, 14, 20, or 26 weeks of age were presented with interesting visual or auditory stimuli. At delays defined by changes in heart rate known to be associated with sustained attention or attention disengagement, blink reflexes were elicited by visual or auditory blink reflex stimuli. Blink amplitude varied according to the level of attention, and the match between the foreground and blink reflex stimulus. If the infant was attending to the foreground stimulus, a blink reflex stimulus in the same modality resulted in enhanced blink reflex magnitude. A blink reflex stimulus in the other modality resulted in an attenuated blink reflex magnitude. If attention was not engaged with the foreground stimulus, this modulation of the blink reflex did not occur. This ‘selective modality effect’ showed an increasing tendency to occur between 8 and 26 weeks of age. These results show that selective attention to modalities increases over this age range. © Blackwell Publishers Ltd. 1998, 108 Cowley Road, Oxford OX4 1JF, UK and 350 Main Street, Malden, MA 02148, USA Developmental Science 1:1 pp 45–51 Address for correspondence: John E. Richards, Department of Psychology, University of South Carolina, Columbia, SC 29208, USA. email: [email protected] relatively mature patterns of sustained attention to the foreground stimulus. This should lead to attenuation and/or facilitation of the blink reflex at that age in a pattern similar to that found in adult subjects. Infants at younger ages, whose attentional system is not as mature, should not have the system that affects the CNS control of the blink reflex, and should show less modulation. This study used two strategies to study selective attention. First, I manipulated the match between the foreground stimulus and the blink reflex stimulus. This study used the same modality match-mismatch as the Anthony and Graham (1983) study: visual foreground and visual blink stimulus (match), visual foreground and auditory blink stimulus (mismatch), auditory foreground and visual blink stimulus (mismatch) and auditory foreground and auditory blink stimulus (match). The match/mismatch conditions show modality-based selective attention when the blink reflex is enhanced when the modality of the blink stimulus and the foreground stimulus are the same, and the blink reflex is attenuated when the modalities are different. Second, attention was manipulated using heart rate changes elicited by the foreground stimuli. Heart rate changes have been used in young infants to distinguish attention phases labeled stimulus orienting, sustained attention, and attention termination (Berg and Richards, 1997; Graham, 1979; Graham, Anthony, and Zeigler, 1983; Richards and Casey, 1992; Richards and Hunter, 1998). Heart rate deceleration in the young infant is elicited by interesting visual or auditory stimuli and indicates stimulus orienting, and a sustained lowered heart rate indicates that attention is still engaged (sustained attention). Alternatively, after attention engagement, infants will often keep fixation on a stimulus, but heart rate will return to its prestimulus level. At this point the infant is not actively attending to the stimulus (attention termination). Thus, rather than presenting the blink stimulus delayed at a fixed point in time for ‘interesting’ or ‘dull’ stimuli, only ‘interesting’ stimuli were used on each trial and the blink stimulus was presented following delays in which heart rate indicated sustained attention was occurring (heart rate deceleration) or attention was unengaged (return of heart rate to prestimulus level following sustained attention; Richards, 1987, 1997). These heart-ratedefined attention phases should result in blink reflex modification consistent with the experimental manipulations of attention used in adult studies (Hackley and Graham, 1983; Haerich, 1994) or the use of different stimuli to elicit attention/inattention (Anthony and Graham, 1983). The selective attention effects elicited by the match-mismatch manipulation should depend on attention engagement. Selective attention should occur when attention is engaged (stimulus orienting, sustained attention) but not when attention is unengaged (prestimulus, attention termination).