Development of head movement propensity in 4-15 year old children in response to visual step stimuli.
Head movement frequency of children in response to horizontal step stimulus is investigated. The aim is to determine if there is a correlation between the age of the child and the frequency of head movements made to visual step stimuli presented at a fixed distance. Also of importance is whether there is a period of rapid change in the frequency of head movements, and if so, what factors could be influencing this change. Seventy-three participants, between the ages of 4 and 15 years were requested to "look at a spot of light" in response to step stimuli which varied in size from 5 to 60 degrees. Eye and head movements were recorded with a video based eye tracker (EL-Mar 2020) equipped with a Flock of Birds head tracker. Frequency of head movements was calculated for each participant and averaged across participants for each age group. Average head movement frequency was then plotted as a function of age. The frequency and variability of head movements decreases as a function of age. This decrease is linear between the ages of 4 and 15 years (y = -1.465x + 22.58; R(2) = 0.4378; F = 26.48; P < 0.0001). More head movements are made in response to larger step sizes than to smaller ones for all ages. The gradual decrease in frequency of head movements in response to step stimuli suggests that a specific environmental event, such as reading, is not the cause of the decline. Improved efficiency of eye movements could be due to pre-programmed factors related to neurological development. Alternatively, cognitive factors may be involved. Children may actually learn that utilizing their head for gaze shifts is more energy and time consuming, than merely using the eyes alone.