2.2.1. Frisby Stereotest (Near)
The Frisby Stereotest (Near) (FSN; Frisby, Davis, & McMorrow, 1996) was used to assess stereopsis. Stereoacuity can be measured between 600″ (expected in TD six month olds) up to just 5″ (expected in TD children aged beyond six years old). The task measures stereoacuity in terms of the smallest visual angle that participants can reliably detect. The FSN has good test-retest reliability (e.g. Adams, Leske, Hatt, & Holmes, 2009). This task was selected as true depth in this test is not derived from stereograms or illusory depth cues. Additionally participants are not required to wear polarised glasses or coloured lenses as in the Titmus Stereo test (Stereo Optical Co.) or TNO (Alfred Poll Inc.). Therefore the task was administered under normal vision, making the task well-tolerated by the WS and TD groups.