VISUAL OFFSETS FACILITATE SACCADIC LATENCY - DOES PREDISENGAGEMENT OFVISUOSPATIAL ATTENTION MEDIATE THIS GAP EFFECT

Saccadic reaction time (RT) is reduced when a fixation stimulus is ext inguished 200 ms before a target appears. An attentional predisengagem ent theory (APT) may explain this gap effect: When covert attention is engaged (e.g., on fixation), the saccadic system is inhibited and RT is delayed; when the attended stimulus is extinguished, attention is d isengaged, the inhibition is removed, and RT is facilitated. In 3 expe riments covert attention was endogenously cued to an object on the ver tical meridian. Onset of a saccadic target on the horizontal meridian could be preceded by the offset of an attended or unattended object. C ontrary to APT, RTs were identical after attended and unattended offse ts. Results suggest that the gap effect has 2 components, and covert v isual attention plays no role. One component is motor system preparati on; the other is fixation offset effect specific to the oculomotor sys tem.