An anti-Hick's effect for exogenous, but not endogenous, saccadic eye movements

Previously, we have shown that the reaction times (RTs) of exogenously generated saccadic eye movements decrease with an increase in the number of response alternatives (Lawrence et al. in J Vis 8(26):1-7, 2008; Lawrence and Gardella in Exp Brain Res 195(3):413-418, 2009). Because this pattern of RTs is in the direction opposite that predicted by Hick (Q J Exp Psychol 4:11-26, 1952), we termed the effect an "anti-Hick's" effect. In the present study, we examined whether this effect characterizes saccades in general, or only those saccades that are exogenously generated. An anti-Hick's effect was found for exogenous, but not for endogenous, saccades. These results demonstrate a clear dissociation between exogenously and endogenously generated saccades and place an important constraint on the anti-Hick's effect.