Exposure-duration effects in localization judgments

The effects on localization accuracy of increasing exposure duration beyond 100 msec are explored for a wide range of object separations. Previous reports that localization accuracy for objects separated by a few minutes of arc increases for exposures up to at least 400 msec are confirmed. I report here that localization of larger objects at larger separations does not improve when the exposure duration is increased beyond 100 msec. This difference between the small- and large-scale results can be explained by the difference in the spatial-frequency content of the objects being localized: When high-frequency objects are substituted for spectrally broadband objects in the large-scale case, the exposure-duration effects for widely separated objects become similar to those obtained in the small-scale case. These results suggest that the exposure-duration effect previously reported in hyperacuity studies is not specific to the localization task per se but rather is a suprathreshold version of the familiar form of spatiotemporal interaction seen in contrast-threshold results. They also suggest that a single type of mechanism underlies small- and large-scale localization.