Vision Ret. Vol. 22 pp. 341 to 346. 1982 0042-6989/82/030341-!%$02.00/0 Prinwd in Great Britain Pergamon Press Lrd zyxwvut THE POSTNATAL DEVELOPMENT OF MONOCULAR OPTOKINETIC NYSTAGMUS IN INFANTS JANICE R. NAEGELE and RICHARD HELD Department of Psychology (ElO-139), Massachusetts Institute of Technology, Cambridge, MA 02139, U.S.A. (Received 9 January 1981; in zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJI revisedform 18 September 1981) Abstract-Monocular optokinetic nystagmus (OKN) was studied in 24 human infants aged 3-35 weeks using electro-oculography and moving vertical-gratings. At a constant velocity of 25deg/sec, infants display direction-dependent slow phase asymmetries until approximately 5 months after birth. A com- parison was made of the cumulative eye displacement during the slow phases of OKN for nasal and temporal movement. A preliminary report of these findings has appeared previously (Naegele J. R. and Held R.. 1980) ARVO Annual Meeting. Orlando, FL. INTRODUCTION Optokinetic nystagmus (OKN) is a reflexive pattern of eye movements, typically elicited by a moving surround while the head is held stationary. With horizontal movement, the slow phase component of OKN is in the direction of stimulus movement and is interrupted periodically by fast saccades in the oppo- site direction. OKN is identical in form to the eye movements generated by inertial stimulation of the semicircular canals induced by angular acceleration of the head. Both reflexes serve to stabilize images of the world on the retina. Recently, studies of monocular OKN in human infants and young animals have generated interest in the maturation of various structures that contribute to the production of OKN and the role of uncrossed versus crossed projections for this visuomotor reflex (Atkinson, 1979; Montarolo et al., 1981; Van Hof- Van Duin, 1976). Developmental studies of OKN in neonatal kittens, monkeys and young human infants indicate that under monocular conditions, elicitation of OKN is strongly biased for temporal-to-nasal (anteriorly di- rected) motion (Atkinson, 1979; Atkinson and French, 1979; Flandrin et al., 1979; Van Hof-Van Duin, 1978). With increasing age, OKN becomes bidirectional. In kittens, the appearance of the following or slow component of nystagmus in response to temporally moving stimuli lags behind the appearance of the slow component of nystagmus for nasally moving stimuli by an average of 10-15 days (Van Hof-Van Duin, 1978). A similar observation was made of the nystagmic responses of l-, 2- and 3-month-old human infants by timing the duration of nystagmic-like eye movements while the infants viewed horizontally moving patterns (Atkinson, 1979). Atkinson found that l- and 2-month-olds exhibited only brief periods of nystagmus when viewing temporally-moving pat- terns and longer periods of nystagmus when the pattern moved nasally. By 3 months, the duration of nystagmic-like eye movements in response to the two directions of moving patterns was equal. Unfortunately, the eye movements were not re- corded in Atkinson’s study and therefore the question of whether age-related, directional asymmetries in infant monocular OKN resulted from differential gains of the nasalward and temporalward slow phase component of nystagmus could not be answered. Conventionally, an analysis of gain (equals: eye velo- city/stimulus velocity) has been used to describe the match between the velocity of pursuit or slow phase nystagmus and the stimulus velocity. Consequently, we have used electro-oculography (EOG) to record infant nystagmus in order to compare the slow phase component of OKN for nasalward and temporalward directions from shortly after birth through five months. . Subjects METHODS Optokinetic responses to horizontally moving, ver- tical gratings were tested in 50 human infants between the ages of 3 and 35 weeks. Infants were recruited by mail, through birth records obtained at the Cam- bridge City Hall, Cambridge, Massachusetts. To account for gestational as well as postnatal age, a standard gestation period of 40 weeks was used and the postnatal age of an infant was adjusted if the preg- nancy term was longer or shorter than 40 weeks. Each infant was tested once. It has been shown that changes in the state of alertness in the human adult has a marked effect on optokinetic gain (Collins et (I/., 1975). For this reason, trials and sessions in which an infant showed signs of drowsiness or inattentiveness were discarded. Twenty-six out of 50 infants were excluded from the final analysis for this reason. Apparatus Electra-oculographic (EOG) recordings of eye movements were performed using plastic Ag-AgCl 341