Much work has been done to try to understand the physiological and the anatomical changes that accompany amblyopia. The ability to track might be compromised in amblyopic vision if the signals arriving at the cortex are compromised on account of losses in the retina or the lateral geniculate nucleus (LGN). However, most studies have found no amblyopic deficit in the retina or the LGN (DeLint, Berendschot, & van Norren,
1998; Hendrickson et al.,
1987; Movshon et al.,
1987; however, see Miki, Liu, Goldsmith, Liu, & Haselgrove,
2003, who found reduced fMRI activity in human LGN and V1 for motion stimuli presented to the amblyopic eye of an anisometropic observer). In contrast, a host of studies in cats, monkeys, and humans have reported amblyopic abnormalities in primary visual cortex. These reports include: reduced widths in the ocular dominance columns in the input layers of V1 that are controlled by the amblyopic eye (Crawford & Harwerth,
2004; Goodyear, Nicolle, & Menon,
2002; Löwel,
1994; but see Horton, Hocking, & Kiorpes,
1997; Murphy et al.,
1998; Schmidt, Singer, & Galuske,
2004; Tychsen & Brukhalter,
1997), reduced proportion of cells driven by the amblyopic eye (e.g., Kiorpes, Kiper, O'Keefe, Cavanaugh, & Movshon,
1998), reduced metabolic activity within amblyopic ocular dominance columns (Wong, Burkhalter, & Tychsen,
2005), reduced contrast sensitivity for neurons driven by the amblyopic eye (e.g., Movshon et al.,
1987), increased amblyopic suppression (e.g., Smith et al,
1997), reduced binocularity (e.g., Crawford, Harwerth, Chino, & Smith,
1996; Crawford, Harwerth, Smith, & von Noorden,
1996; Zhang et al.,
2003), abnormal horizontal connectivity (e.g., Löwel & Singer,
1992; Tychsen, Wong, & Burkhalter,
2004), reduced fMRI activity for stimuli presented to the amblyopic eye (Barnes, Hess, Dumoulin, Achtman, & Pike,
2001), and slower and attenuated MEG responses for the amblyopic eye (Anderson, Holliday, & Harding,
1999). The anomalous responses in V1 for stimuli presented to the amblyopic eye could compromise tracking performance for the following reasons.