THE ECCENTRICITY EFFECT - TARGET ECCENTRICITY AFFECTS PERFORMANCE ON CONJUNCTION SEARCHES

The serial pattern found for conjunction visual-search tasks has been attributed to covert attentional shifts, even though the possible cont ributions of target location have not been considered. To investigate the effect of target location on orientation X color conjunction searc hes, the target's duration and its position in the display were manipu lated. The display was present either until observers responded (Exper iment 1), for 104 msec (Experiment 2), or for 62 msec (Experiment 3). Target eccentricity critically affected performance: A pronounced ecce ntricity effect was very similar for all three experiments; as eccentr icity increased, reaction times and errors increased gradually. Furthe rmore, the set-size effect became more pronounced as target eccentrici ty increased, and the extent of the eccentricity effect increased for larger set sizes. In addition, according to stepwise regressions, targ et eccentricity as well as its interaction with set size were good pre dictors of performance. We suggest that these findings could be explai ned by spatial-resolution and lateral-inhibition factors. The serial s elf-terminating hypothesis for orientation X color conjunction searche s was evaluated and rejected. We compared the eccentricity effect as w ell as the extent of the orientation asymmetry in these three conjunct ion experiments with those found in feature experiments (Carrasco & Ka tz, 1992). The roles of eye movements, spatial resolution, and covert attention in the eccentricity effect, as well as their implications, a re discussed.