Reaction-time differences between the left and right hemispheres for face and letter discrimination in children and adults.

Twenty boys at each age level 7, 10, and 13 years and 20 adult males were tested for choice manual reaction times to photographs of faces or letter pairs tachistoscopically presented 3 1/2 degree to the left or 3 1/2 degree to the right of a central fixation point, in the left visual field (LVF) or the right visual field (RVF) respectively. All subjects were right-handed. Subjects were tested monocularly. They used a different hand and a different eye in the first and second half of trials. Eye order and hand order were randomized across subjects. Seven- and 10-year-olds were intermittently rewarded with a poker chip following fast correct responses. Analysis of correct reaction time scores indicated an overall LVF superiority for the speed of response to faces, but no significant field differences for responses to letter pairs. The interaction of these field-stimulus effects with age was not significant, suggesting that the obtained field effects with faces and letter pairs were consistent across the range of ages tested. The results of comparisons of field differences within individual subjects suggested a "switchover" from a left-field advantage with letter pairs at age 7 to a right-field advantage at the adult level; this tendency, however, was not significant. None of these results was influenced by the use of different hands or eyes or to frequencies of commission of errors. The results suggested that a left-field advantage in speed of response to familiarized faces is found as early as 7 years of age and does not change appreciably thereafter. The finding of a significant left-field advantage for faces in the 7-year-old group represented an earlier age of left-field, right hemisphere lateralization for face stimuli than that previously obtained by other investigators. The failure to find over field differences with letter pairs was attributed to a possible tendency among subjects to process to letters visually (i.e., graphemically), a tendency which may have been more marked in the 7-year-old group due to the relative inexperience of children of this age with alphabetical material.