Flashes are localised as if they were moving with the eyes

Abstract

Targets that are flashed during smooth pursuit are mislocalised in the direction of the pursuit. It has been suggested that a similar mislocalisation of moving targets could help to overcome processing delays when hitting moving objects. But are moving targets really mislocalised in the way that flashed ones are? To find out we asked people to indicate where targets that were visible for different periods of time had appeared. The targets appeared while the subjects' eyes were moving, and were either moving with the eyes or static. For flashed targets we found the usual systematic mislocalisation. For targets that moved with the eyes the mislocalisation was at least as large, irrespective of the presentation time. For static targets the mislocalisation decreased with increasing presentation time, so that by the time the presentations reached about 200 ms the targets were not mislocalised at all. A simple model that combines smooth retinal motion with information about the velocity of smooth pursuit could account for the measured tapping errors. These findings support the notion that the systematic mislocalisation of flashed targets is related to the way in which people intercept moving objects.

Local motion inside an object affects pointing less than smooth pursuit

“…Figure 3 shows that pursuit gain decreased about 100 ms after target onset. This is highly consistent with previous reports (Mitrani et al 1979;Rotman et al 2004Rotman et al , 2005. Because the pursuit target continued to move for another 500 ms, the decrease shows that observers voluntarily stopped pursuing the target.…”

“…Long Xashes produce more retinal motion opposite to pursuit than short Xashes. According to Rotman et al (2005), retinal motion signals opposite to pursuit cancel out extra-retinal eye movement signals. Therefore, the localization error should be reduced with long Xashes.…”

“…Therefore, correlations were calculated separately for each presentation time and direction of sine-wave motion. Variations in eye velocity after Xash presentation (referred to as late interval) determine the strength of the eye signal during the integration period (Rotman et al 2005). The relative size of the correlations in the early and late intervals will indicate whether smooth pursuit after the Xash has an eVect independently of retinal motion.…”

“…An alternative to latency-based explanations was put forth by Rotman et al (2005). Rotman et al noted the apparent discrepancy between accurate combination of retinal and extraretinal signals in everyday life, and the blatant errors observed in the lab.…”

“…In support of this idea, the forward error for targets moving with the pursuit target (i.e., no retinal motion) was of the same magnitude as for Xashed targets. Further, the error decreased as the presentation time of static stimuli was increased from 1 to 193 ms. Rotman et al (2005) state that "the perceived position depends on the sum of the pursuit signal and the retinal motion, integrated over some time. " (p. 361).…”