| The present study sought to determine whether the shift in retinal local signs that accompanies a saccade is entirely pre-saccadic, very abrupt--or both. The methodology involved an illusion of visual direction known as the phantom array. Specifically, if one saccades in the dark across a point-light source blinking 120 times per second, the perceived location of the light does not remain constant. Rather, one sees an array of flashes, the first of which discretely materializes near the intended endpoint of the saccade. Subsequent flashes materialize closer and closer to the actual location of the blinking light. Once a flash within the array materializes, its perceived location does not change, indicating that the spatial coordinates (local signs) of the retina are not changing during the saccade. Further, the discrete displacement of the first flash in the array indicates that the shift in retinal local signs is entirely pre-saccadic, very abrupt--or both.;M was seen as being coincident with the right end of the array when M flashed from 80 to 0 ms before the onset of the saccade. Marker flashes presented from 215 to 80 ms prior to the onset of the saccade were seen at either the left or the right end of the array. These two results indicate that the shift in retinal local signs that accompanies a saccade is both entirely pre-saccadic as well as very abrupt.;To determine which of these is the case, four trained observers made judgments about the perceived location of a 1 ms flash of light generated by two LEDs (light-emitting diodes). The two LEDs vertically bracketed a third LED that flashed 200 times per second as the observer saccaded to the right, in the dark, from a fixation point (F) to a saccadic target (T). The flashing light, which was positioned between F and T, served to generate the phantom array. The perceived location of the 1 ms marker flash (M) was judged relative to the phantom array on a scale of 1 to 5, with 1 indicating the left and 5 indicating the right end of the array respectively. |
