DEVELOPMENT OF MOTION-DEFINED FIGURE GROUND SEGREGATION IN PRESCHOOL AND OLDER CHILDREN, USING A LETTER-IDENTIFICATION TASK

Background. Three-month-old infants can discriminate motion-defined (M D) form, but we do not know the age at which this ability reaches adul t levels, Previous psychophysical evidence suggests that different neu ral mechanisms are involved in the processing of luminance-defined (LD ) and MD spatial form in adults. This difference may be reflected in t he development of LD versus MD form identification in children, Method s. We measured speed threshold for identifying MD letters, letter-char t (i.e., Snellen) acuity for high-contrast LD letters and single-lette r acuity for high- and low-contrast LD letters. Forty-seven children b etween 3 and 12 years of age and 20 adult subjects were tested, Result s. Development to the adult level was observed as follows: low-contras t single-letter acuity before 3 years; high-contrast single-letter acu ity by 5 to 6 years; the ability to identify MD letters by 7 to 8 year s; letter-chart acuity by 9 to 10 years. Conclusions. MD form identifi cation continues to mature in preschool children. LD form identificati on also matures in this age group but with a different time course, MD letters are not equivalent to low-contrast letters developmentally. O ur findings provide further support for the hypothesis that the spatia l aspects of MD and LD form are processed separately to some extent.