Competition between exogenous and endogenous signals revealed by saccade latency and saccade curvature in the monkey

Abstract

Natural visual environments contain multiple stimuli competing for our attention, only one of which is selected at a given moment. The processes underlying this competition may be reflected in the time required to generate a saccade to the goal stimulus (Walker et al., 1997), and the nature of the saccade trajectory (McPeek et al. 2003). We trained two monkeys on an oculomotor capture paradigm (Theeuwes et al. 1999) in which one of six homogenous stimuli becomes a target singleton through a color change in the other five items. The monkeys had to make a saccade to the odd colored target. Simultaneously on half the trials an additional distractor suddenly appeared either near or far from the saccade goal. We found that correctly directed saccades showed longer latencies when the distractor was present versus absent. In contrast, latencies were shorter when the eyes were overtly captured by the distractor. In addition, the proportion of capture was always greatest when the distractor appeared near the goal of the saccade. On correct trials, saccades were often curved in the direction of the near distractor. Furthermore, the eyes were also captured by other items more often when the distractor was near the saccade goal suggesting that efforts to avoid the sudden onset occurred at a cost of capture by other non-targets. The results are consistent with the idea that the activity associated with exogenous and endogenous signals combine locally (Trappenberg et al. 2001).

Footnotes

 Supported by HFSP grant.