Table 1.
Brief descriptions of proposed eye-movement control mechanisms, arranged along two dimensions that determine when saccadic programming is initiated. The type of control mechanism can be direct or indirect, and the type of information mediating control can be lexical or non-lexical.
| Control type |
Information type |
Examples |
|---|---|---|
| Direct | Lexical | • Completion of some stage of lexical processing initiates saccade (e.g., Just & Carpenter, 1980; Morrison, 1984; Rayner & Pollatsek, 1989; Reichle et al., 1998; Reilly, 1993; Salvucci, 2001) |
| • Lexical processing difficulty inhibits saccade initiation (e.g., Engbert et al., 2005; Reilly & Radach, 2006; Yang, 2006) | ||
| Non-lexical | • Completion of pre-lexical visual word encoding initiates saccade (e.g., McDonald et al., 2005) | |
| • Visual encoding difficulty inhibits saccade initiation (e.g., Engbert et al., 2005; Reilly & Radach, 2006) | ||
| • An autonomous and automatic low-level visual routine that was acquired based on reading experience influences saccade initiation (Vitu et al., 2001, 2007) | ||
| • Efference copy of a saccade program initiates rapid “corrective” saccade (e.g., Engbert et al., 2005; McDonald et al., 2005; Reichle et al., 2009) | ||
| Indirect | Lexical | • Saccades are initiated to maintain overall rate of lexical processing (e.g., Bouma & DeVoogd, 1974; O’Regan, 1990; Yang, 2006) |
| Non-lexical | • Random timer initiates saccade (e.g., Engbert et al., 2005) | |
| • Low activity of “maintain fixation” mechanism initiates saccade (Reilly & Radach, 2006; Yang, 2006) | ||
| • Saccade initiated if fixation duration exceeds deadline (e.g., Henderson & Ferreira, 1990; Reilly & Radach, 2006) | ||
| • Successive fixation durations are correlated (McDonald et al., 2005) |
Note The above descriptions are meant to illustrate our classification scheme, but do not provide a complete description of the cited models or an exhaustive list of all proposed control mechanisms. Furthermore, this scheme refers to the mechanisms of control, not the models per se, as indicated by the fact that most of the models include two or more mechanisms (e.g., SWIFT includes both direct lexical and indirect non-lexical mechanisms).