Visual Peripheral Stimulus Localization of Dynamic Stimuli by Young Infants.

Brittany M. Mallin & John E. Richards, Dept. of Psychology, University of South Carolina.

Currently, we are investigating the effect of the presence of a central stimulus on saccadic localization of a peripheral stimulus. Traditional studies in this area have used simple black and white geometric stimuli to show that attention to a focal stimulus attenuates localization of a peripheral stimulus. A prior study by Mallin & Richards (submitted) found that the nature of complex and dynamically-changing stimuli and attention affected the latency to localize peripheral stimuli. The goals of the present study were: 1) to control audio and visual components in construction of movement conditions using complex and dynamically-changing stimuli, 2) to implement a new addition condition, more similar to prior research using simple, black and white stimuli, made up of scenes in which a silent new character was added in a different location, 3) to examine heart rate changes and stimulus movement together, so peripheral stimulus localization could occur during attention or inattention. Infants at 14, 20 and 26 weeks of age were presented with scenes from a “Sesame Street” movie until fixation on a moving character occurred, and then presented with scenes in which the character movement occurred in a new location. The electrocardiogram (ECG) was recorded and heart rate changes were used to define attention phases. For 20-wk-old infants, localization of the peripheral stimulus was faster when infants were attentive than when inattentive for scenes in which the character moved from one location to another and for scenes in which movement and sound shifted from one character to another. For both age groups localization of the peripheral character was slower during attention when the first character disappeared and a new character appeared in a different location, as previously found. The new addition condition also elicited this result. Interestingly, for 20-wk-old infants, overall reaction times were faster in conditions where the initial character moved or was replaced, that is no character remained in the initial location. Upon examination of the main sequence relationship, we found that there was a decreased slope for 20-wk-olds and a larger slope for 26-wk-olds while engaged in attention. We also found a significantly larger main sequence slope for the new addition condition, characterized by an initial stimulus that continues to move when the peripheral stimulus is presented, compared to the shift condition, where movement of the first stimulus stops upon presentation of the peripheral stimulus. These results partially replicate prior findings showing that attention to a focal stimulus affects localization of peripheral stimuli, but suggest that the nature of the stimuli being localized modifies the role of attention in affecting eye movements to peripheral stimuli.

Our current studies in this area use this presentation procedure to examine the effect of changing auditory and visual information. Infants are presented with complex, dynamically changing, audio-visual, figures extracted from Sesame Street movies. The stimuli are presented in one location until the infant is looking. Then the audio and visual components of the stimulus are changed independently, and shown in the first or second location. With this procedure we can distinguish the separate effects of localizing a changing audio-visual stimulus, changing auditory stimulus, or changing visual stimulus. The effects of stimulus modality on the localization of peripheral stimuli may be independently examined.