Error in localising a target that is flashed near the time of an isolated saccade is not identical to the error found near the time of the last of a sequence of saccades

Abstract

Flashes presented around the time of a saccade are often mislocalized. The precise pattern of mislocalization is influenced by many factors. Here we study one such factor. In daily life we make saccades in various directions in rapid succession in response to the content of the scene and in accordance with our intentions. In contrast, most studies of peri-saccadic mislocalization impose a very simple pattern of saccades in order to reduce the variability between trials. Participants are instructed to fixate a dot at a fixed position on the screen. When the dot disappears the participant has to make a horizontal saccade towards a second dot: the saccade target. Here, we compare mislocalization near the time of saccades in this commonly used design with mislocalization when the participant more or less automatically follows a randomly jumping dot with his or her eyes. Saccade amplitude and most other details were the same in both conditions. A black dot was flashed at various locations in the vicinity of the saccade target. By estimating the saccade latency we were able to present the flash near the time of saccade onset. The participants were asked to localize the flash by touching the appropriate location on the screen. Our results show that there is a difference between the peri-saccadic mislocalization under the two conditions, especially when the flash is presented more eccentrically.