Effects of stimulus-response uncertainty on saccades to near-threshold targets.

Kveraga et al. (2002, Exp Brain Res 146(3):307-14) reported that saccade latencies are immune to the effects of stimulus-response uncertainty and constitute one of the few response systems that violate Hick's law. Similar effects have been reported for keypresses triggered by vibrations of the fingertips, but robust uncertainty effects were subsequently revealed using weak, low-frequency vibrations (Ten Hoopen et al. 1982, Acta Psychol 50:143-157). We wondered whether immunity of saccadic responses would demonstrate a similar intensity-dependency and therefore re-examined the effects of response entropy on saccade latencies using near-threshold visual stimuli. Saccadic latencies remained independent of stimulus-response uncertainty, indicating that saccadic motor programming is unaffected by the duration of the target detection process.