Dissociating higher-order visual processing in typical and atypical development

Abstract

Background: Research with adults has established that higher-order visual information is processed along two functionally specialized pathways: a ventral stream and a dorsal stream. Surprisingly, however, less is known about how this dissociation emerges and matures during development. The present study (1) investigated typical development of higher-order visual processes and (2) determined whether the developmental trajectories of these visual processes differed for atypically developing individuals. Methods: In Experiment 1, 30 typically developing adolescents (age 10-16 years) completed four computerized experimental paradigms designed to differentially draw on dorsal or ventral processing resources. These tasks required participants to (a) either decide if two abstract shapes match (ventral task) or fit together (dorsal task) or (b) either pay attention to the identity (ventral) or the location (dorsal) of drawings of buildings, upright faces, and inverted faces. Results show no association between age and accuracy, but reaction times were negatively correlated with age. These relationships held for both dorsal and ventral tasks. Data are compared with accuracy and reaction time results from young adults (age 18-25 years). In Experiment 2, the same computer tasks were completed by a group of atypically developing children with congenital hypothyroidism (CH), a paediatric endocrine disorder caused by lack of thyroid hormone (TH) that is present at birth. TH is a critical endocrine modulator of normal brain development known to affect development of the visual system. CH had significantly poorer accuracy scores on both ventral and dorsal tasks, but were also significantly slower to judge identity than controls. Conclusions: First, our findings suggest that there is very little development in the dorsal and ventral pathways after ten years of age in typically developing individuals, although processing speed does increase with age. Secondly, TH insufficiency during gestation is associated with impairments in higher-order visual processing in adolescence.