However, this offset between the fixation target and the fovea is not constant but has a strong dynamic component as our physical gaze is typically far less steady than our mental experience would indicate. When we fixate on a visual target, our eyes constantly drift and jump, by up to 0.5°, around the point we feel we are fixating (Ortero-Millan, Troncosco, Macknik, Serrano-Pedraza, & Martinez-Conde,
2008; for a review, see Rolfs,
2009). Movements of this magnitude are easily seen when they occur in the external world (Murakami,
2003), yet we do not generally sense the visual motion caused by our eye movements of fixation. Instead, it requires special techniques (Verheijen,
1961; Murakami & Cavanagh,
1998; Murakami,
2003), or highly controlled laboratory conditions (Haddad & Steinman,
1973) for us to perceive the movements in our fixations.Thus, while our eyes are often jittering around the fixation, our subjective experience is more that our gaze is locked onto the fixation point. This difference between the subjective feeling of unwavering fixation and the objective measurement of rapid, random jumps and drifts (Rolfs,
2009) indicates that the subjective feeling of where we are looking is not determined simply by what falls directly on, or even slightly offset from, the fovea. It has been suggested that the perception of the motion caused by the eye movements of fixation may be suppressed based on the retinal motion signals themselves (Murakami & Cavanagh,
1998; Poletti, Listorti & Rucci,
2010; Arathorn, Stevenson, Yang, Tiruveedhula, & Roorda,
2013). However, the suppression of motion signals is not sufficient—we see our fixation not only as lacking in motion energy, but also as having a clearly fixed position (i.e., not jumping from point to point or being smeared). So some additional mechanism may be steadying the perceived position of the fixation along with the mechanisms that are suppressing its motion.