This thesis reports significant differences in visual attention demonstrated by infants at 6 and at 12 months of age who were exposed in utero to deficient thyroid hormone (TH). Four clinical groups with different profiles of TH deficiency present different behavioural phenotypes. Each that belies the timing in neurodevelopment of that TH deficit.Significant deficits are described in all four groups at both ages with regards to engagement latency, disengagement latency, fixation duration, and percentage of anticipations, percentage of valid looks, anticipatory latency, and reaction time for non-anticipations.The Visual Expectation Paradigm (VExP) is used. A Neuroconstructivist perspective is described allowing for this expansion of the VExP and also for more meaningful interpretation of low level deficits in visual attention in other at-risk populations of infants. Deficits (and lack of deficits) are observed not only in anticipatory and reactive saccades but also disengagement, duration, and sustained attention.